Basic Cable Types
This is a guide on basic cable types.
Ethernet
In this presentation, we'll take a look at some of the specifications of Category 5 and 6 cables. Now this is typically what we tend to think of as Ethernet cabling. But the reason the categories exist is because this physical type of cabling has been in use for quite some time, but different categories define different implementations. And, in fact, you can go all the way back to Category 1, which was phone cable. But the internal structure of the cabling itself has been fairly consistent. In other words, Category 1 which was again just phone cable, still used twisted pair cabling. Now we'll talk about the nature of twisting in the very next presentation, but it refers to the fact that the internal wires were twisted around each other in pairs. Now Category 1, or phone cable, only had two twisted pairs or four wires. By the time you get to Ethernet, then it used eight wires in four twisted pairs. So each category defined new specifications because, of course, like any technology, it's continually improving.
So as the category increased, the capabilities of the cable increased as well. So Category 5, in fact, comes in what we call Cat5. Cat just being short for category, and Cat5e and the e stands for enhanced. But these defined Ethernet standards of 100BASE-TX, or just 100BASE-T, and 1000BASE-T. Now to break that down, the first number, in this case, the 100 or the 1000, refers to the speed in megabits per second. So 100 is 100 megabits per second. 1,000 is a gigabit per second. But it's fine to say 1,000 megabits. Then the BASE refers to baseband transmission. And this simply means that 100% of the available bandwidth of the cabling is used up. And you can think of it quite literally as kind of a clock cycle where the upswing goes all the way up to 100% and then the down swing goes all the way down to 0%. And if you imagine this being 1s and 0s, the 1 would be at the top, at the 100%, 0 would be at the bottom, 0%. In other words, there's no variance, you don't see any point where it's at 64%. It's all or nothing and that's how you get the 1s and the 0s from those signals, that's Baseband.
And the T or the TX simply indicates that it is Twisted Pair. But the X typically stands for extended and that refers to the distance. In most cases, you should be able to get 100 meters out of an Ethernet cable, or a Category 5 cable. But if it was just T, they really couldn't guarantee that distance. The TX implemented some extensions, if you will, some improvements so that they could actually guarantee that value before it became unreliable. So the TX, really just a little more reliable over that distance. So then Category 6 is still a twisted pair cable, nothing has changed there. But with Category 6 we see again, two varieties, Cat6 and 6A. And the A in this case stands for augmented but it addressed a similar issue. Cat6 all by itself, was really only reliable over 55 meters. 6A implemented some improvements and got a reliable distance of 100 meters. Now this does still remain compatible with the prior category, so it's backward compatible. You can quite simply remove Category 5 cable and drop it in a Category 6, or vice versa. But, of course, you're only going to get the specifications of the cable in terms of performance. But Category 6 implemented stricter specifications and defined an Ethernet standard of 10 gigabits per second.
Still Baseband transmission, still Twisted Pair. So this is much faster of course. So if you do take out a Cat6A cable, for example, and replace it with a Category 5, you certainly will not get the speed but it will still work. Now another feature to note with these cables is the internal wiring scheme or the color pattern. And you can see there are two implementations here, T-568 or B. [Video description begins] A diagram of two wiring standards displays: T-568A and T-568B. Both standards contain eight wires, each of which is numbered, labeled and color coded. In the T-568A standard, the wires are ordered as follows: g, G, o, B, b, O, br, and BR. In the T-568B standard, the wires are ordered as follows: o, O, g, B, b, G, br, and BR. [Video description ends] And ultimately at the end of the day, all that really matters is that you are consistent. So in other words, if you are crimping your own cables, as long as both ends match and they follow that pattern, it will work. But these are industry standard specifications so that everyone adheres to them and ensures that everyone is always consistent.
Now as long as it's either A or B, it will work in any scenario. But, again, it's just to ensure that everyone follows these specs so that we do have consistent cables. But, ultimately, as long as you follow either one, then you should be okay in terms of, again, making your own cables. But the only difference between the two is in fact the placement of the orange and the green. And if you look at the labeling, by the way, I should mention that the uppercase letter indicates a solid color, then the lower case indicates that it's always a white with stripes of that color. So lowercase g is green stripes, uppercase g is solid green. And, again, it's really just to ensure that everyone follows the same pattern so that each end of the cable has the same color wire in the same slot, if you will. And finally, one other consideration is what's known as Plenum Cabling and this is used in what's called the plenum space. And that refers to a space between the actual ceiling and a drop ceiling. So when you have those ceiling tiles, this typically is where cables are run, but the other thing that tends to run through plenum space is the air ventilation system.
So this comes down to a fire safety standard that was defined by the National Fire Protection Association in specification 90A. But it just means that if you are going to run cabling in the plenum space that it actually has to be made of a fire-retardant plastic. Because if a fire does happen, standard plastics produce a lot of toxic smoke and with the air ventilation system being in the same place, now you're circulating a lot of toxic smoke throughout the building. So plenum cabling uses a low smoke polyvinyl chloride, or PVC, and/or fluorinated ethylene polymer, or FEP, so that it's less prone to catch fire in the first place, but if it does, it produces less smoke. Now the cabling itself is also a little less flexible, but that's not necessarily a bad thing. The plenum space is usually a very tight space. There's not a lot of room to move if you are working up in there. So if you have to run a cable sometimes it's easier to push it into place and a less flexible cable is a little easier to push sometimes. But, ultimately, it can be a little more difficult to work with but it's because of those different materials that it is a little less flexible. But either way if you need to adhere to fire codes, then running cables through the plenum space requires it to be plenum-specific cabling.
STP vs. UTP
Now in this presentation, we'll talk about the nature of twisted pair cabling, as well as shielded versus unshielded. But to begin with the twisted pair aspect, this uses what's known as a balanced pair operation. And what that means is that there's differential signaling and that means that there are equal but opposite signals travelling on each pair member. And then examining the difference between each member allows for the receiver to determine what is noise and cancel it. Now backing up a little bit, again, this is a solid copper core. So as such, it is susceptible to electromagnetic interference. So if you were to imagine two perfectly straight copper core wires running side by side. Then imagine that there is some kind of source of interference, and let's imagine it's coming in from the right. Then in that case, the wire on the right is closer to the source of interference. The one in the left is farther away, so you would always get a better signal on the wire that is a little bit farther away from the interference.
So quite simply, twisting them around each other always ensures that a part of each wire is closer to the interference at some point, but then farther away at some point. So it really just evens things out, if you will. But again, examining the difference between those signals at the receiver, allows the receiver to say, well, I expected to see this on this wire, and that on the other wire, and here is where I see something that's different between them. Therefore, that's interference. That's noise and it can literally just be ignored. Now the other problem, if you will, that can happen within the cable is what's called cross talk, whereby the signal traveling down any one wire is actually being picked up a little bit by another wire, and twisting the pairs of wires around each other. Again, make them less susceptible to overall interference and cross talk, because you are quite literally insulating one wire with the other wire. Now you can improve this even further by enhancing or increasing the twist rate. In other words, the more tightly you twist them, the better the overall insulation. But at the same time, you're shortening the distance that can be covered by that wire the more you twist it.
So you need to essentially come up with a happy medium with respect to the twist rate. Now another aspect of twisted pair cabling is unshielded versus shielded. And unshielded means that there really is nothing else to protect the copper core other than the plastic sheaths or insulation. [Video description begins] A cross section of an Unshielded Twisted Pair cable displays. It contains eight wires divided into four twisted pairs. Each wire has a copper core or Conductor, and color coded insulation. A Sheath encases all eight insulated wires. [Video description ends] So there's an exterior casing, if you will, that encompasses all eight internal wires, and then each one of those wires does have an insulation surrounding it. So we do see each pair, again, wrapped around each other to provide a little bit of natural shielding, if you will, but there's nothing else. But, that does still leave it a little bit susceptible to interference.
So if you are in an environment where there quite simply is a lot of interference, then you might want to consider shielded twisted pair. This has a jacket and then some kind of shield braid that's usually made out of metal or some kind of a foil. [Video description begins] A cross section of a Shielded Twisted Pair cable displays. It contains eight insulated wires divided into four twisted pairs. Each pair is encased in Shield-foil, and all four pairs are encased in Shield-braid and a Jacket. A Drain wire runs through the center of the STP cable. [Video description ends] And you may see that around each pair and all four pairs, or one or the other. It's sort of a combination of both depending on the cabling itself. But quite simply, this provides extra shielding against interference. Now because that shielding is metal, you may also see a ground wire that's sometimes referred to as a drain wire, simply to ensure that no electrical current finds its way into the copper core.
But essentially, you still have the twisted pair then further wrapped up in more shielding to protect it against electromagnetic interference. So if you're running cable, let's say, right next to a very strong power source, then that could cause enough interference to degrade the signal to the point where it becomes problematic. Now shielded twisted pair will provide that extra shielding, but it's also a little more expensive. So you generally don't see shielded twisted pair run throughout an entire network in an entire building. It's usually only implemented in those specific areas where the interference is high and we do need that little bit of extra protection.
Fiber
In this presentation, we'll take a look at the basics of fiber optic cabling, which is a completely different medium than any kind of copper cabling, because it literally transmits data by using pulses of light. Now this also results in the primary benefit of being able to cover very large distances. Now we'll talk about that in greater detail in a moment, but because it is just a pulse of light, it essentially does not experience any kind of resistance on a copper cable. As an electromagnetic pulse goes down that cable there is quite simply friction. So ultimately, it can't travel that far before it degrades. But a pulse of light can go much farther. Now it also results in a highly secure data transmission from the perspective of physical access to the cable. With copper cabling it is entirely possible, if you have access to the cable itself, that you can tap into it and pick up on the signals. That really isn't possible with fiber optic cabling.
If you tap into the cable you quite literally break the cable. So it just doesn't work anymore. And again, it's just not affected by any kind of electrical or radio interference, because it is just a beam of light. So again, with copper cabling, if you're running it very close to strong power sources or other radio transmissions, then this can quite literally interfere. That can get on to the copper cabling. But with fiber optic that doesn't happen at all. And the cables themselves are actually quite robust. Now they really have to be, because you do need a hollow core through which the light can travel. And it's usually made of some kind of plastic or glass that essentially can't break. So the cabling is very robustly made to ensure that this simply does not happen. But as such, it is more expensive.
So looking at the cable design, we'll start with the interior. [Video description begins] A Fiber Cable Design diagram displays. The cable contains a core encased in four layers. Starting at the core, the layers are: Cladding, Coating, Strength member, and Outer jacket. [Video description ends] You can see the core there and it is very thin. Again, this needs to only carry pulses of light, so it's quite thin. You know, this is highly magnified. And then there's a cladding around that. Now the core and the cladding actually work together in terms of how the light travels through the core and again, we'll come to that in a moment as well. But then the coating is essentially just to act as a barrier so that no light can escape. Then the strength member is purely to strengthen the cable. And the outer jacket, of course, just surrounds everything. So there's several layers at work here. But again, really it comes down to the cladding and the core. And that's where we get into what's known as the Single-mode versus Multi-mode.
Now these are just graphics to illustrate what happens and they're not to be taken entirely literally. [Video description begins] A diagram of three fiber modes displays: Multi-mode - Step index, Multi-mode - Graded index, and Single-mode - Step index. In all three modes, a Source transmits light rays through a fiber cable. [Video description ends] But for starters, it is just a ray of light. So we have a source that is transmitting these light rays. And with the Multi-mode - Step index and graded index you do see a bit of a difference here. But for starters usually with the multi-mode, the source is something like an LED. [Video description begins] In both the Multi-mode - Step index and Multi-mode - Graded index, the light rays refract off the internal cladding as they travel along the cable. [Video description ends] Just a regular light, if you will, that pulses on and off. So that's not going to produce a particularly focused beam of light.
So you can see that what happens with the multi-mode, you get refraction. So as the light rays travel down in the core, they encounter the cladding and the cladding is what refracts it back toward the core. So with step index, what you get is a fairly sharp refraction. [Video description begins] In the Multi-mode - Step index, the cable cladding is thin and the light rays refract at various sharp angles. [Video description ends] So again this is the cladding that's doing the refraction. This is what I meant by, they work together. So the light rays, again, very sharply refract with multi-mode-step index. With multi-mode-graded index, it looks, in the graphic, as though we're seeing curved lines here. And of course, a beam of light is not going to travel in a curved line. [Video description begins] In the Multi-mode - Graded index, the cladding is thicker and the light rays refract in curves or waves. [Video description ends]
This is just to represent that there's a little more of the cladding in multi-mode. And what it's designed to do is smooth out the refraction. So that's what's meant by the curved lines there. It's just trying to not be as sharp as the step index. That's kind of the idea between step and graded. Graded is gradual, step is very sharp. So there's just less refraction, a little smoother, if you will, with multi-mode. And then single-mode typically uses a laser, for starters, as its source. So we get a much more tightly focused beam. [Video description begins] In the Single-mode - Step index, the cladding is very thick and the light travels through the cable in a straight line without refracting. [Video description ends] Now again, the line is just to indicate that there's as minimal refraction as possible. Clearly it's not going to go perfectly straight if the cable itself is bent.
So the idea here is just to indicate that there's as little refraction as possible. But that's also due to the nature of a laser versus an LED. A laser is much more tightly focused and if it does refract, it will be as minimal as possible so you see more cladding in the single-mode. So what happens with respect to the transmission? Well, with multi-mode typically this is a little cheaper for starters and this is true for multi-mode-step index or graded index. But what you get is less distance, okay? Single-mode can travel farther, because there's less refraction and it's much more tightly focused. So that's really the main concern in most cases, when it comes to which one should you choose. It's the distance that you need to cover. So overall considerations, you certainly can get possible surface flaws and this would be due to handling the cable a lot. And even right out of the factory there's always going to be microscopic flaws. It's never going to be perfect but you basically want to insure that you handle it as gently as possible, if you will, so that you aren't making sharp bends in the cable, you know, that will produce more internal surface flaws.
So overall handling and installation stresses should be at a minimum. You want to try to run it as straight as possible and just work with it as little as possible, so the interior core stays in as good a shape as possible. And again, there are environmental conditions to still consider and this might be the reason why you choose fiber. Again, if you have a lot of power and a lot of electromagnetic interference, then copper might not be the best option. Fiber is less susceptible to that interference, but fiber can still suffer from certain conditions. Maybe excessive heat, if it’s very, very hot, you may start to damage the cable itself. But in any installation you always have to consider where the cables are running. But certainly the cost versus the performance.
These days standard ethernet networks over copper cabling easily get into the gigabit range, so they perform quite well. And fiber is still much more expensive, so you certainly have to weigh those two out. But again, as mentioned, distance really is the main consideration when it comes to fiber. And in general, it's multi-mode for shorter distances, so that would be the cabling that has a fair amount of refraction and it's cheaper. So we would use this essentially in the data center. Then if we have to connect data centers that are fairly far apart, many miles, then we look at the single mode. But again, that certainly is more expensive. So you try to find a balance and try to find, of course, the best cable type for each implementation. But in general, multi-mode for short, single-mode for long.
Coaxial
In this presentation, we'll take a look at the basic characteristics of coaxial cable. While you typically won't find this in an Ethernet LAN environment, it is still fairly commonly used, particularly if you have cable Internet service or just standard cable TV. But you might also find it in specific scenarios such as a closed circuit TV system. And a lot of industry specific instrumentation will often still use coaxial cable as well. So looking at the physical structure, if we begin in the center, there is a solid copper core as the conductor. [Video description begins] A diagram of a Coaxial Cable displays. It contains a Center Conductor at the core and four layers. Starting at the core, the layers are: Dielectric, Foil shield, Braided shield, and Outer jacket. [Video description ends] And it is just that single conductor. So if you contrast this, for example, with unshielded twisted pair, of course, we have multiple pairs of wires, each one containing a copper core.
But with coaxial, just the single solid copper core. And it's much more robust than any one of the unshielded twisted pair wires. Then it's surrounded by a dielectric, which is just really a plastic type of insulating material so that any kind of conductivity does not get outside of the core. Then, we have a foil shield and a braided shield and the braid is also made up of copper wires but they're very fine and, again, braided together. And this is for enhanced protection against electromagnetic interference, although it can cause some issues that we'll talk about in a moment. And then everything is surrounded by the outer jacket. Now there are two main types in use today. RG-6 and RG stand for radio grade. And this is commonly used by the cable companies, again, for your Internet service or your TV, your cable TV service. And it's suitable for longer distances and higher bandwidth because it has a slightly larger core than its counterpart, which is RG-59.
Now I'm not sure if six is meant to really be 6.0, which, of course, is just slightly above 59. But this is more suitable for shorter distances and lower bandwidth. It's more commonly used as patch cables between devices. So again, maybe those industry specific instruments, for example, connecting to a monitoring device. Something like that, and it has a smaller core, so you generally don't see this, again, for Internet service or cable TV. Now looking at some of the key benefits of coaxial, it does offer multiple channel support. Now this is also referred to as broadband and we did mention baseband earlier. And that, again, is where the transmission uses 100% of the available bandwidth. And again, the 100%, if you will, represents the one and the 0%, if you think of it as a cycle, represents a zero. But with coaxial, it has multiple channels, meaning you can divide it up into frequency ranges. And this why you can get many channels on your TV over the same single cable. So coax offers that ability to divide it. And that's what broadband means in comparison to baseband. It also has lower error rates than twisted cable because there are eight individual wires in twisted pair.
You can sometimes end up with timing errors or synchronization problems with signals not arriving at their destination at exactly the same time. Since there's only a single core in coax, this doesn't really happen. It does have high capacity in terms of its bandwidth and also a rigid design, which makes it pretty robust. It's not very prone to breaks, for example. But there are still limitations to coaxial cable and the first one is known as signal leakage. And, in fact, this comes back to the braided shield. Ultimately that is designed to protect against interference but that's from the outside in. Leakage is a little bit of signal that's running on the core being picked up by the braided shield. It still is a collection of copper wires running through the same cable. So if, for example, there was a bit of a break in the insulator, then the signal could leak from the core to the shield. Noise from external fields is, in fact, the exact opposite direction. Now again, this is what the braided shield is there for, to protect against that but if it's too strong, then there's an awful lot of shielding in the cable. So any kind of electromagnetic field that does reach the shield, of course, will produce a bit of an electric charge. That's what happens when a copper wire is exposed to a magnetic field.
So it can actually get a little bit charged and that can cause noise. And that can also result in what's known as ground loops. Now this might only happen when you have a significant source of power reaching the braided shield. But if flat out is causing some kind of power signal to run down the shielding itself. And that can be picked up at the other end as a signal and quite literally cause interference. Or for those of you who may be remember TV going back many years, if this was being picked up by a television, it affected what we called your vertical hold. You would see a line right across the screen. And in some cases, it literally looped and you might have an adjustment on the TV where you could correct it. But what that was doing was adjusting the ground so we could eliminate the signal coming down the wire. So those kinds of problems typically only resulted in incorrect installations or physical damage to the cable itself. But they can still present problems in terms of getting a good, clean signal.
Speed and Transmission Limitations
Now in this video we'll take a look at some of the key features of category or Cat5 cables, and Cat6 in a moment as well, because these are by far the most common cable types implemented in ethernet LANs. Now beginning with Cat5, this is typically an unshielded cable that offers speeds of 10 or 100 megabits per second, and operated at a frequency of about 100 megahertz. Now in terms of the megahertz value, that didn't really have much of an effect on the performance, per se, but it was more so just to know about when it came to any other kind of frequency that might be present in the same area.
So if there was something else that operated at a similar frequency, then it would be most likely to cause interference. So typically, Cat5 by today's standards is considered to be rather slow. You would probably want to see at least a gigabit per second as your standard, and that is where Cat5e comes into play. Now it's still unshielded, but we do see that it offered the 1000 megabits per second, or a gigabit per second, and operated at more or less the same frequency range. So again, with both of them being unshielded, it was really just a matter of knowing, is there something maybe close by that's operating at a similar frequency, because that might cause problems. Now really, the only difference between 5 and 5e was essentially quality control. There were more stringent regulations around the testing and the manufacturing of 5e. Hence it was able to carry those greater speeds, but essentially the cables themselves look identical.
So you just want to make sure that you determine that it is 5e if you want to be assured of getting that faster speed. But there are some limitations, of course. Cat5 original only went as high as 100 megabits per second, so this is not ideal for large corporate environments these days. It's prone to electromagnetic interference from other devices and crosstalk, which is quite literally, the signal of one wire being picked up by another wire. So again, it was simply due to the fact that it was unshielded that it was a little more prone to interference. But that always depends on where it's being installed. 5e was a little less prone to cross-talk, not because of any shielding, but again, just those more stringent manufacturing specifications. But as such, it was more expensive than Cat5, and it still has lower performance characteristics than newer generation cables.
And this, of course, is where Cat6 comes into play. So for Cat6, it's shielded or unshielded, so you can generally get either. And we have a base speed of a gigabit per second, and it operated up around 250 megahertz or higher. So it was a little less prone to interference, because there aren't as many devices or other types of source of transmission that are operating up in that range. Then 6a, in this case the a stands for augmented, which was traditionally shielded by default. This offers up to 10 gigabits per second, and operates at 500 megahertz. So that, in combination with the shielding, generally meant that you were much more protected against interference and you could get much better speeds. But there are still limitations to Cat6. And with the original Cat6, the length in fact is limited only 55 meters in normal conditions, and maybe only 33, you might consider to be adverse conditions.
But 6 and 6a also had some installation caveats if the shielding was there. Now 6a almost always had shielding, but if you had shielding at all, that makes it a little less flexible, which results in susceptibility to damage from kinks or bends. So you needed to be a little extra careful when running your lines and the shielding also introduced the possibility of ground loops. So the same kind of scenario that we talked about with coaxial cable. If there's any kind of damage or just any kind of connectivity between a contact point and the shielding, then that can cause ground loops and just generate an actual current running down the shielding. So that could also cause problems. But in general, 6 or 6a was preferred, simply because of the better transmission rates. And, of course, the shielding which made it less susceptible to interference.
Video Cables
Now in the presentation, we'll take a look at several different video interfaces beginning with VGA or Video Graphics Array. Now this is actually a very old interface. It has been around since the late 1980s, but still remains fairly common, even in today's environments, because as improvements to the VGA specifications came along, it did allow us to support enhanced resolutions right up to what we would consider to be high definition today. Now what you're looking at is the physical connector face on, and you can always identify a VGA connection by the pin configuration. [Video description begins] A 15 pin VGA connector displays. [Video description ends] It's always 15 pins total in three rows of five with the middle row slightly off set. And, most of the time, the physical connector itself is blue. Now I wouldn't be surprised to see some black connectors, but most recent ones are blue.
And if you were to look at the back of your computer where the video output is, let's say, on the video card, oftentimes that's blue as well, so it just makes it easy to color code in terms of making the connection. Now the primary aspect of VGA is the fact that it's an analog signal. So it uses variances in electrical impulses to represent variances in colors, primarily red, green, and blue. So you may hear some people refer to this as an RGB connection for red, green, and blue. But because it is an analogue signal, there is a consideration and that is the distance you have to go with the cable. Now that's almost never an issue in terms of the distance between your computer and your monitor. But the longer the cable is, the more degraded the signal will become. So that could be an issue if you are trying to run a cable from your computer, let's say to a projector that was mounted on the ceiling in a large auditorium. That could be quite a distance. So by the time you reached the projector, the signal is not very bright or maybe it's a little distorted. So you might need some kind of amplifying unit which they do have, but ultimately distance is a concern when dealing with VGA connections.
Now the next interface is known as DVI, or Digital Visual Interface, and as its name indicates, this is a digital interface. Although it does work with analogue and I'll come back to that in a moment. And it might seem like there's a lot of different variances here, at least with respect to the physical connectors. And there are, but they are to a degree compatible. Now I'll come to the single link versus the dual link in a moment, [Video description begins] Five Digital Visual Interfaces display: DVI-I (Single link), DVI-D (Single link), DVI-I (Dual link), DVI-D (Dual link), and DVI-A. Each interface has one horizontal slot and a unique number of holes. [Video description ends] as well as the I versus the D versus the A. But looking at the physical connections, it might seem like they're quite different, but let's just look at that middle row.
DVI-I, dual link versus DVI-D dual link. The only difference are the four extra holes around that horizontal slot. So it depends on the pin configuration that you have. [Video description begins] The DVI-I (Dual link) interface has 28 holes, four of which are positioned above and below the horizontal slot. The DVI-D (Dual link) interface has 24 holes and a horizontal slot. [Video description ends] In other words, if you had a DVI-D dual link pin configuration, you would not have those four pins. You could still put that into the DVI-I and those holes simply would not be filled, but it would still work but only as DVI-D, okay? So some of them are compatible, and essentially, what it will come down to is that if it fits, it will work. But it will work at the specifications of whatever the pin configuration is, okay? [Video description begins] The DVI-I (Single link) has 22 holes, the DVI-D (Single link) has 18 holes, and the DVI-A has 16 holes. [Video description ends]
So with respect to the duel versus single and I versus D versus A, the dual versus single refers to the link, and if you will, that is the channel over which data flows. So a single link operates at 3.7 gigabits per second at 60 frames per second. A dual link doubles that to 7.4 gigabits per second and in fact can even operate at a higher frames per second value up to 85. Now single link would be more than adequate for most corporate environments, again, just using Office type of applications. But if you were, let's say a 3D animator or if you were doing a lot of gaming, you would definitely want the dual link. Then we have the A versus the D versus the I and A supports analog signals. So your output might be analog but you have to go to a digital device or vice versa. So in this case, you need the DVI-A which does actually support analog signals. So essentially, it's backward compatible. DVI-D is digital only, so clearly, no analog anywhere with D. And then DVI-I, the I stands for integrated, meaning it can support both. So that, again, just comes down to the physical connections that you have with respect to which type of interface you want to use.
Now DisplayPort is a fairly new connector. But this, of course, allows you to connect video sources to your display [Video description begins] A DisplayPort displays. It has 20 holes: 10 along the top and 10 along the bottom. The bottom right corner has an angle of 45 degrees. [Video description ends] and it should also be mentioned that DisplayPort does carry audio as well. But this was a specification that was defined by the Video Electronics Standards Association or VESA. And that's actually an association that has been around for quite sometime. But what this means is that it is not proprietary. So manufactures like this because they don't have to pay any kind of licensing fee to put a display port on their device. And, it’s also interesting because it uses packitized data transmission. So very much like an ethernet network, it breaks the data down into packets and transmits them as such. And that can sometimes help to just even out the flow of transmissions. And DisplayPort is also compatible with DVI and HDMI just by using simple adapters.
And finally, our last interface is High Definition Multimedia Interface or HDMI which is another digital video and audio interface, but what's important to take note of here is that it is digital only. So this replaces all analog standards and HDMI is not compatible with any kind of analog interface. [Video description begins] An HDMI port and connector displays. The port has 19 holes: 10 along the top and 9 along the bottom. The bottom left and right corners have an angle of 45 degrees. [Video description ends] Now there are generally two types of connectors, a type A and a type C. Both have 19 pins and both have the same specifications in terms of the signal. It's really just the physical size.
The type C is known as a mini-HDMI and it's quite simply for smaller devices where there's just limited space. The type A would be what we might call the standard connector that you would likely find these days in the back of your TV, if it's a newer TV or of course, even your computer monitor. And, looking at it top down, it can kind of look a little bit like USB. It's similar in size and shape but if you look at it face on the bottom corners are kind of knocked off. They're actually a little bit circular but like I said, it can kind of look like USB, but it certainly will not fit into a USB slot. So just be mindful of the physical connection when you go to insert it. The orientation, of course, does matter.
Lightning Cables
In this presentation, we'll take a look at the basics of lightning cables. Now these are proprietary to Apple products and in fact, Apple has trademarked that name. So if you hear lightning cable, it specifically means an Apple product. Now it's both a computer bus and a power connector, meaning that it can carry both data and power. So not only does it synchronize data, usually with the computer, it charges the device as well. And it uses a very simple 8 pin connector, which replaced the 30 pin connector of its predecessor, but it's used to connect iPhones, iPads, and iPods to other devices. Most notably your computer for synchronization or your wall port to charge it. In terms of its physical design, it's very simple. [Video description begins] A diagram of a lightning cable receptacle and connector displays. The receptacle has eight pins on the top side, which are numbered from eight to one. And the connector has a tab with eight matching contacts. [Video description ends]
Again, the receptacle is only eight pins, and of course the end itself has the eight contacts that match. But those same eight contacts are on the other side of the cable itself, so it doesn't matter in terms of upside down or downside up. You can put it in either way and you will still get your connectivity and your charge. And it's a very small connector, the image on the right, in fact, would be larger than actual size. So nice and small, and doesn't take up much space in any kind of device. And it is adaptable to various other types of connectors, so in other words, you can go from lightning to Micro USB, to HDMI for any kind of video output. You can adapt it to SD card readers, the previous 30 pin adapter, or even lightning to VGA. So a number of other types of devices can interact with lightning cables, you just need to make sure you get the appropriate adapter for whichever purpose you want to implement.
Thunderbolt Cables
In this presentation we'll take a look at Thunderbolt cables. Now this is a proprietary cable type that was developed by Intel in conjunction with Apple and it can be used to transmit both data and power. And it uses a combination of PCI Express and DisplayPort over two separate serial channels to allow for peripheral device connections in configurations that can in fact be daisy chained for up to six devices. So you can literally just go from device, to device, to device over a single port.
Now the cable length is limited to 3 meters if it's a copper cable, but you can extend that as far as 60 meters if you use optical cabling. And the physical connector itself is actually a mini display port connector. It might look a little bit similar to a lightning cable but, if you will, it's the opposite. A lightning cable has a tab whereas this has a slot. As for the specifications, there are three versions. Thunderbolt version 1 has a 20 pin configuration and uses that mini display port connector. And it offers a throughput of 10 gigabits per second per channel, times two channels for a total of 20 gigabytes per second.
Then Thunderbolt version 2 didn't change a whole lot. It's still 20 pins and it's still a mini display port connector, but it's 20 gigabytes per second total throughput aggregated, meaning that it can actually exceed 10 on one channel as long as you aren't exceeding 20 in total. And Thunderbolt version 3 uses a 24 pin configuration that actually uses the USB-C type connector. And this offers a total throughput of 40 gigabytes per second. So very high transfer rates and again, it can also handle power for your devices as well.
USB Cables
In this presentation, we'll take a look at the specifications of the Universal Serial Bus, or USB. And this was introduced in 1996 as version 1.0. And at that time, there were actually two variations. A slow speed, which operated at only 1.5 megabits per second over a distance of three meters, and the full speed, which operated at 12 megabits per second over a distance of five meters. And the physical connectors had pretty much just these two types. The Type-A would be what you would see connected to your actual computer, and then Type-B was typically connected to the device itself. And that was a very common connection for printers. [Video description begins] A diagram of the Type-A and Type-B connectors displays. The Type-A connector has four pins along the bottom, which are numbered from one to four. The Type-B connector also has four pins: two at the top and two at the bottom. These are numbered counterclockwise, starting in the top right corner. The top left and right corners have an angle of 45 degrees. [Video description ends]
Then USB 2.0 was released in 2000, and this introduced several modifications to the USB package. But most notably, the speed. It was increased to 480 megabits per second, so significantly faster, still over a distance of five meters. The Type-A and Type-B connectors were still available and they were also backward compatible to USB 1.0, but we did start to see new connectors emerge. And this really was dependent on the device and perhaps more specifically stated, the type of device in terms of which connector you would actually see. But as their names indicate, mini and micro, they were significantly smaller than the Type-A connections, or even the Type-B. [Video description begins] Two additional pairs of connectors display: Mini A and Mini B, and Micro A and Micro B. All four connectors have five pins. In the Mini A and Mini B connectors, the pins are positioned along the top and numbered from one to five. In the Micro A and Micro B connectors, the pins are positioned along the bottom and numbered from five to one. [Video description ends]
And you would commonly see these on devices where space was a concern. So a lot of digital cameras, for example, started using the mini or micro connectors. Then USB 3.0 was released in 2008, and this operated at what was also known as SuperSpeed, which again, implemented a tremendous increase, up to five gigabits per second over a distance of three meters. And this also implemented full duplex communication. Now duplex simply means both directions, so from computer to device, and from device to computer. But half duplex communication, which was the way that USB worked in all previous implementations, means that you have to take turns, essentially. If you imagine a phone conversation, one person speaks, the other person listens. Then you reverse, that's half duplex. Full duplex is both ways at the same time. So this helped to improve that overall transfer speed. And the connectors were still the Type-A and Type-B, but you can see that they did change a little bit. [Video description begins] Three connectors display: Type-A, Type-B, and Micro B. [Video description ends]
The Type-A implemented five additional pins. [Video description begins] The Type-A connector has nine pins. Pins one to four are positioned along the bottom and pins nine to five are positioned along the top. [Video description ends] Now the original four pins kept it backward compatible with USB 2.0. But if you had those extra pins for a USB 3.0 connection, then you could get the enhanced speed. The Type-B was similar but slightly different configuration, and then we also see a Micro-B SuperSpeed. [Video description begins] The Type-B connector also has nine pins. Pins one to four are positioned around the bottom portion and pins nine to five are positioned along the top portion. The Micro B connector has ten pins. Pins one to five are positioned along the bottom of the left portion and pins six to ten are positioned along the bottom of the right portion. There is a notch between the two portions. [Video description ends]
And, again, that really just depended on what the device was. Now shortly after the release of USB 3.0, we also saw the introduction of the new Type-C connector. [Video description begins] A USB Type-C connector displays. [Video description ends] And this uses a 24 pin configuration, but notice that it's 12 along the top and 12 along the bottom. So this, combined with its oval shape, meant that orientation no longer mattered with the Type-C connector. There is no upside down or downside up, it would work either way. This was the first USB connector to offer that functionality. And this was typically also implemented with some revisions to USB 3.1 maintained SuperSpeed transfer mode at 5 gigabits per second, but then also introduced SuperSpeed+ transfer mode, which was 10 gigabits per second. And then USB 3.2 came along and introduced two new SuperSpeed+ transfer rates relative to USB 3.0. So SuperSpeed+ original was still 10, but then we also now have 20 gigabits per second throughput when using USB 3.2.
Peripheral Cables
In this presentation, we'll take a look at serial peripheral cables, which is the transfer of data between devices using serial communication protocol. And that means that it literally transmits the data one bit at a time, that's serial, one after the other. Now this is a relatively simple communication protocol and it was primarily used for lower bandwidth devices but over longer distances. And this is because its counterpart, parallel communications, transferred multiple bits at one time. And you might immediately think well, isn’t that going to be faster? In general, it probably was but there was an issue with parallel communication, whereby the longer the distance you had to cover, the more likely it was that you would receive a bit over one wire before or after a bit on another wire.
And you were effectively supposed to receive them all at the same time. So there were timing and synchronization issues with parallel transmissions, particularly over longer distances. So the communication standards for serial, being a little simpler, really allowed you to overcome some of those problems. But there was no specific standard in terms of the distance. It really depended on the device, it depended on the cable specifications. So you would end up with varying transmission distances but in general, serial communications could travel further, more reliably. Now an example of serial communication is RS-232. This defines communication between a data terminal equipment or DTE, which is essentially your computer terminal and a data circuit terminating equipment or DCE, which really is just the end device, such as an external modem, and that’s only one example. But this is still a serial communication so one bit at a time.
And the RS-232 standard essentially defines the signal characteristics from an electrical standpoint, so the timing and the meaning of the signals, as well as the physical characteristics such as the pin out configuration of the cables. So many computers going back several years generally would have an RS-232 serial port as part of the computer, but really that was simply the location where you would attach some kind of peripheral device. So in terms of some of the common connections that might use an RS-232, they included a mouse, keyboard, an external modem, external storage, and often an uninterruptable power supply, not for transferring power but for configuring the device. So the idea here is that most of these are fairly simple devices. They really just don't need parallel communications, it's just not that much data. But something like a UPS, for example, or maybe even an external modem could be fairly far away from the computer.
So this is where the distance of serial communications became a little more advantageous than the speed. And the common physical connectors included, what was known as a DB-25 and a DB-9. And the DB stood for D-sub and if you turned it on its side and looked at it, it actually kind of looked like the letter D and then the 25 means 25 pins, and 9 means 9 pins. So it depended again on the device but those were just some common connections on the device end. But on the computer, it would typically be a 9 pin that you would use to connect to that device. Now it should be noted that this type of connection is quite out of date. I don't think you would find on any modern system because this has been largely replaced by interfaces such as USB.
Hard Drive Cables
Now in this presentation, we'll take a look at some of the connections used for storage devices, beginning with Integrated Drive Electronics or IDE. Now as mentioned, this is used for storage, but that did include hard drives, CD-ROMs, or even floppy disk drives. And the connection was made directly to your motherboard, with IDE, meaning this is for internal storage only, not any kind of external device. The cable itself was known as ribbon cable, because it quite literally looks like a ribbon. And there were three connection points, but again, one of them was connected to the motherboard. That was also known as the controller. Then you could have two devices attached to the same cable. So you could two hard drives, two CD-ROMs. Or one of each, that was fine. And there were also two different sizes for IDE, there was a 34 pin which was for your floppy disk and a 40 pin for hard drives or CD-ROMs. And of course, you could easily tell the difference because they were physically wider or narrower depending on the pin count.
Now IDE has been almost entirely superseded by Serial AT Attachment or Serial ATA, or SATA for short. The AT stands for advanced technology. And SATA came out with much faster speeds than IDE ever supported. And it was also easier to get multiple drives installed. Most IDE computers did have two controllers. So that meant you could have four devices total because you could, recall, put two devices on one cable. But that was pretty much it, a maximum of four. Serial ATA doesn't have an implementation where you share a cable. There's a dedicated connection to the motherboard but it was a much smaller physical connector. So it was a lot easier to just put multiple Serial ATA connections on the motherboard, maybe even six or eight, so that you could much more easily have multiple drives. Now in terms of the revisions, you see there are three different implementations, 1, 2, and 3. And each one just increased the speed, but 1.5 gigabits per second even in the first revision was much faster than what IDE could support.
Now this was only over 1 meter length, so a little better than 3 feet, but recall, this is still for internal storage, so that length usually did not represent any kind of restriction. Revision 2 doubled the speed up to 3 gigabits per second, and revision 3 doubled it again, up to 6. So again, much faster speeds than IDE could ever handle. Now eSATA is meant for external connectivity, so you can use the exact same interface for an external drive. Now with this because it is external, they anticipated that you might have the device a little farther away. So in fact, you can go up to 2 meters with eSATA, because it uses a shielded cable that has a little more stringent requirements, specified by the FCC and CE requirements, so that you can in fact increase the distance. Now those more stringent specifications on the cable are still backward compatible. So you can have both internal and external serial ATA connections. [Video description begins] A SATA and eSATA connector displays. Both connectors have seven pins. The pins are positioned along the bottom of the SATA connector and along the top of the eSATA connector. [Video description ends]
And it looks a little bit different in terms of the physical connector itself but it adheres to the same revision specifications as SATA. So revisions 1, 2, and 3 are exactly the same for eSATA as they are for SATA. Then finally, the Small Computer System Interface which was typically pronounced as SCSI, was implemented as a parallel interface. Which essentially meant that you could have multiple devices supported per cable. Now we did see that with IDE, but what you have to do with IDE is designate one device as a master and another one as a slave. That wasn't necessary with SCSI. In its original implementation, you could have eight in total, but one of them had to be for the motherboard. So it was the motherboard connection plus seven more devices. Then that was increased to 16 in later revisions, again still including the motherboard. Or I should also say, what was known as the controller card in many cases. But, one way or another, one of them was for the controller, then all remaining could be for all other devices.
So again, it was increased up to 16 in total, in later revisions. For the internal cables, they had 50, 68, and 80 pin versions, and for external, 50 and 68. Now the external typically was not so much for storage, but other peripheral devices that maybe used a lot of data such as scanners. And back in some of the original implementations of SCSI, it was fairly common to see those devices that carried a lot of data also using SCSI interfaces. So it wasn't just for storage, and they also came in shielded and unshielded versions. Again depending on the device that you are using, but SCSI was never dedicated to just storage. Now SCSI, in and of itself, is really just the protocol, the rules for transferring data back and forth. So it's actually gone through several revisions and several different implementations. Two of them including serial attached SCSI and Fiber Channel Protocol for SCSI.
Now serial attached still uses the SCSI protocol but it switches it from a parallel interface to a serial interface, meaning that you have much more control in terms of device to device when they're in a parallel interface. So let's just go with the original release where there was one controller connection and then seven more hard drives, let's say. It was treated much more so as a single storage unit. So there wasn't a lot of control at the device level. But with serial attached SCSI, each device is much more controllable on its own. And, in fact, the interface supports up to 128 individual devices, so again much easier to get more storage. Fiber Channel Protocol for SCSI is the ability to issue SCSI commands over a Fiber Channel Network. And this is the basis for a storage Area Network where you have the storage just as a huge rack of nothing but hard drives. And it's entirely external to the computer.
The computer simply accesses the storage using standard SCSI commands, but over a fiber network. And this allowed for very high capacity and very fast access to the storage. Now all told, SCSI was not particularly common in desktop systems. It was more expensive and it was more difficult to implement, but it did perform better at least compared to something like IDE. But at the desktop level, we didn't really need such robust storage or interfaces, so IDE was much more common in desktops. SCSI was much more common in servers. And that remains the same today. Many server systems will still implement SCSI interfaces because they do need that much more robust configuration and ability to implement the storage in these varying configurations such as serial attached and Fiber Channel.
Adapters
In any situation where you are looking to connect a device to your computer or possibly even a device to another device, you need to use some kind of cable or perhaps more specifically stated, some kind of interface. And, as we've seen already, there are a tremendous number of interfaces and sometimes you just don't have the correct cable or the two interfaces that you want to connect just don't match. So in this presentation, we'll take a look at some simple examples of adapters. And it should be noted that there are a tremendous number of adapters available. It depends what you have compared to what you need to connect to, of course in terms of what type of adapter, but many of them are compatible. So our first example is DVI to HDMI, and this is Digital Visual Interface to High Definition Multimedia Interface, but most commonly this is used for digital video. [Video description begins] A DVI to HDMI adapter displays. It has an HDMI male connector at one end and a DVI female connector at the other. [Video description ends]
So since both of them handle digital video, they in fact are compatible. And in general, you can just use what's known as a passive adapter, meaning, you don't need any kind of power supply or any kind of bulky transition type of unit in between. It literally can just be the two different ends on the single cable. So maybe your video card has a DVI output but the monitor you just bought only has a HDMI input. Well, you should be able to find a cable with the correct ends to still use those two devices without any kind of additional equipment necessary. Another very common adapter is USB to Ethernet. [Video description begins] A USB to Ethernet adapter displays. It has a USB male connector at one end and an Ethernet female connector at the other. [Video description ends] And you would most likely find this in newer laptops, ones with solid state drives and very thin profiles, very light weight units. Just including that physical RJ-45 connector would require the unit to be significantly thicker. So to keep things small and lightweight, they just go with USB and then you can simply insert the adapter and that will work perfectly fine.
And I would say USB is perhaps one of the most common adapter types. USB can carry just about any kind of data, so there are numerous adapters that would adapt from something to USB. And also, when working with video, you can adapt between DVI and VGA. This does actually maintain backward compatibility, because DVI does still support analog VGA signals. So again, maybe your video card output is only DVI, [Video description begins] A DVI to VGA adapter displays. It has a DVI female connector at one end and a VGA female connector at the other. [Video description ends] but the monitor you have maybe is a little bit older and it has VGA. So once again, you can adapt between the two and usually, you can just use a passive adapter. Again, no kind of separate power or no bulky transition type of unit that handles it. It's simply built in to the specifications of the connector to be able to translate from one to the other. So ultimately, you just need to make sure what you have in terms of the physical connections on your devices to see if it's going to be supported with a native cable or if you do need to obtain some kind of adapter.
Working with Network Cables
Now for our exercise this time we'll ask you to differentiate between Ethernet cable types such as Cat5, 5e, 6, and 6A. Then to differentiate between multi-mode and single mode fiber optic cabling. Then to differentiate between USB versions 1, 2, and 3. And finally, to differentiate between IDE and Serial ATA hard drive cables. So as always what we'd like you to do is to take a few minutes, pause the recording, jot down some responses, then we'll come back to review and we'll see how you made out. So we'll see you in a few minutes.
Okay, our first task was to differentiate between the categories of Ethernet cables beginning with 5 and 5e. Cat5 is typically unshielded and only carries speeds of 10 or 100 megabits per second over a frequency of 100 megahertz. 5e is essentially enhanced or sometimes extended, which is also unshielded but offered speeds of up to 1 gigabit per second or 1,000 megabits per second, still over a frequency of 100 megahertz. Cat6 however, comes in shielded or unshielded and offers a speed of 1 gigabits per second at 250 megahertz or higher. And for 6a, the a stands for augmented, and this is almost always shielded and offer speeds of up to 10 gigabits per second over a frequency of 500 megahertz. So it all depends on what you need for bandwidth and the conditions where the cables themselves are being installed. Again, shielding helps to prevent against electromagnetic interference. But if you don't expect there to be much interference, you may not need shielding.
Then we ask to differentiate between single mode and multi-mode fiber and this effectively comes down to the amount of refraction. [Video description begins] A diagram of three fiber modes displays: Multi-mode - Step index, Multi-mode - Graded index, and Single-mode - Step index. In all three modes, a Source transmits light rays through a fiber cable. [Video description ends] In both multi-mode cables, the light source is typically just an LED, a light emitting diode, which isn't particularly focused, so the light will refract. [Video description begins] In both the Multi-mode - Step index and Multi-mode - Graded index, the light rays refract off the internal cladding as they travel along the cable. [Video description ends]
So in step index you get very sharp refractions, and this can essentially cause the signals to take a little bit more time to get there. They are bouncing around a lot more. [Video description begins] In the Multi-mode - Step index, the cable cladding is thin and the light rays refract at various sharp angles. [Video description ends] With graded index, again, the actual path the light travels is certainly not curved, but this is just to indicate that it tries to smooth out the refraction a little bit. It interacts a bit more with the cladding for less refraction and then for single mode, the light source is typically a laser, so that's much more tightly focused. [Video description begins] In the Multi-mode - Graded index, the cladding is thicker and the light rays refract in curves or waves. [Video description ends]
And again, it's probably not going to be perfectly straight. [Video description begins] In the Single-mode - Step index, the cladding is very thick and the light travels through the cable in a straight line without refracting. [Video description ends] But it does its best, for lack of a better word, to eliminate refraction as much as possible. In the end, what the result is the distance that you can achieve when using the multi-mode implementations, it's typically fine over shorter distances. But the more it refracts, the longer that run goes, essentially the more difficulty you'll have in receiving all of the light rays at the same time. Single-mode being much more focused can travel much farther.
Then we asked about the specifications of USB versions 1, 2, and 3. So beginning with 1, this was released in 1996, had two implementations, a slow speed that only offered 1.5 megabits per second over 3 meters and a full speed that offered 12 megabits per second over 5. And there were two physical connector types, a Type-A and a Type-B. [Video description begins] A diagram of the Type-A and Type-B connectors displays. The Type-A connector has four pins along the bottom, which are numbered from one to four. The Type-B connector also has four pins: two at the top and two at the bottom. These are numbered counterclockwise, starting in the top right hand corner. The top left and right corners have an angle of 45 degrees. [Video description ends] The Type-A pretty much is what you'll find on the computer itself, the Type-B more commonly for the device such as a printer.
USB 2 was released in 2000. Many more connectors were introduced as you can see. [Video description begins] Two additional pairs of connectors display: Mini A and Mini B, and Micro A and Micro B. All four connectors have five pins. In the Mini A and Mini B connectors, the pins are positioned along the top and numbered from one to five. In the Micro A and Micro B connectors, the pins are positioned along the bottom and numbered from five to one. [Video description ends] And this also had several modifications to the speed, most notably up to 480 megabits per second over a distance of 5 meters. Now the mini and the micro connectors were typically found on devices that were physically small, such as digital cameras.
Then, USB 3 was released in 2008, again a few modification to the connectors, a few different types depending on the device. [Video description begins] Three connectors display: Type-A, Type-B, and Micro B. The Type-A connector has nine pins. Pins one to four are positioned along the bottom and pins nine to five are positioned along the top. The Type-B connector also has nine pins. Pins one to four are positioned around the bottom portion and pins nine to five are positioned along the top portion. The Micro B connector has ten pins. Pins one to five are positioned along the bottom of the left portion and pins six to ten are positioned along the bottom of the right portion . There is a notch between the two portions. [Video description ends] But this offered what we call SuperSpeed, which was up to 5 gigabits per second over a distance of three meters. And also implemented full duplex communication, meaning that communication between devices can occur at the same time, bidirectionally. So it's not just a half duplex where one device communicates, then the other.
And then finally, we asked about the differences between the IDE cable and Serial ATA. An IDE is Integrated Drive Electronics used primarily for storage devices such as hard drives, CD ROMs, and floppy disks. And the connections was made directly to your motherboard and that was known as the controller connection. Then we had what we typically called a ribbon cable, and again, they're worth three connection points but one of them was to the motherboard. The other two could then be for your devices. Most IDE systems tended to have two IDE connections, meaning you could have a total of four devices, but there were also two types. There was a 34 pin which was typically used for floppy disks and then a 40 pin which was typically used for hard drives or for CD ROMs.
Now the Serial ATA attachment is much faster than IDE and it's a single point to point connection, so you can't share devices on a single cable with Serial ATA. But it was a very small connection, so it was very easy to have multiple connections on the motherboard. In many cases at least four would be present and you could also get expansion cards that might have as many as eight or ten. So the only real distinction with respect to Serial ATA itself were these revisions 1, 2, and 3 and essentially it just comes down to the speed. So the first revision offers 1.5 gigabits per second over a 1 meter length. Revision 2 doubles that to 3 gigabits per second over the same length. And revision 3 doubles it again up to 6, again over the same length. So hopefully, you made it out all right with those questions, and if so, we're ready to move on to our next course.