Join Mike Meyers for an in-depth discussion in this video RAM features, part of CompTIA A+ (220-1001): Cert Prep 2 Microprocessing and RAM.
- RAM has a lot of features that I've kind of dumped all into one little episode that I'm going to call, cleverly, RAM features. So the first thing I want to talk about is a unique feature of RAM known as Parity vs ECC, so what I want you to do is take a look at these three stick right here in front of me. Count the actual chips, you see, one, two, three, four, five, six, seven, eight, one, two, three, four, eh, let's flip if over this way you can see it a little better, one, two, three, four, five, six, seven, eight, you see that? What you're looking at is, remember, when we talk about RAM we always say bytes, I have 16 gigabytes, I have one gigabyte, I always said 32 gigabytes, we never say gigabits or anything like that because when we measure RAM, it's always in bytes. And there are eight bits to a byte, each one of those chips handles a bit and that's why you pretty much always see eight little chips on a stick of RAM. There's a few exceptions but they're rare. So let's look down here one more time though, on this one we have one, two, three, four, five, six, seven, eight, nine. Hey, Mike, what's happening? Well, what we're looking at right here is what we call a Parity or, arguably, an Error Correction Code, or ECC RAM. It's still good old DRAM, it could be DDR2, DDR3, DDR4, that doesn't change anything, but these very special types of RAM add an extra chip known as a Parity chip. RAM very rarely dies, usually the only time RAM dies is when people grab it and electrocute it. If you leave RAM alone in systems it tends to run for a long, long time, however, sometimes it's really, really important to make sure that whatever the RAM is doing is right, and this is where we start using Parity or ECC RAM. Parity's a little bit older, we don't see it quite as much, pretty much today if you're going to be buying a motherboard that needs this type of Parity, we just call it ECC or Error Correction Code, if you want to be technical the difference is; is that with Parity RAM I can have one of the other eight, one chip of the other eight be bad, with ECC I can have two of the other eight be bad. That's about the only real difference. ECC is great, it's extremely expensive, and you can only put it on motherboards that are designed to use it, you can't sit there and go hey, I'm going to upgrade my motherboard and put some ECC, nope, it has to be designed from the ground up to be able to accept ECC or you're simply not going to be able to do it. Also, keep in mind though, most of the motherboards that require ECC, well, they have to have it. We tend to see it more in servers than anything else. Now the other thing I want to show you are what we call Small Outline, SO-DIMMs. What we have here are some examples of this. SO-DIMMs are designed in places where big long sticks don't really work the way we want them to. So, laptops are probably the best example, you tend to see these all the time. Now just because they're SO, that doesn't mean that they don't have the same different types of technologies, and I've got 'em right here. So here at the top I've got a DDR4, DDR4 SO-DIMMs use a 260 pin package, here's DDR3, DDR3 uses a 204 pin package, and then when it comes to anything before DDR3 it gets kind of fuzzy. So what I have here is a 200 and a 144 pin, but there is no perfect correlation of DDR2 will only use this, or DDR will only use that, so it's really only for the DDR3 and DDR4 where you can absolutely predict the package. Just because they're SO-DIMMs, nothing that we've talked in other RAM episodes changes. They will often use dual channel, or even possibly triple channel, you have to use the exact same types, they come in pairs, nothing changes other than the fact they're a little bit smaller. So be comfortable with SO's, and if you've got a laptop you're probably going to be seeing these guys. Alright, so the last thing I want to talk about, it's actually something kind of fascinating, I don't know why I took these sticks away. Built in to every RAM stick on Earth is a little bit of brains known as Serial Presence Detect, or SPD. Now if you take a look at these three sticks in front of you, there is a little teeny tiny chip on every single one of these, on this one it's right about here, on this guy it's right about here, on this guy it's way over in the corner. The SPD chip is an absolutely wonderful chip which allows your system to actually query the RAM chip and say what's your capacity, how fast are you, what technology are you, heck, it'll even tell you who made it and what's your model number based on the manufacturer. The trick with SPD is you need a tool to be able to actually query that chip and luckily for us, the wonderful CPU ID's CPU-Z program does all this for us. Let me show ya. So I've got CPU-Z already up and running, now if you've watched other episodes you've seen some of the CPU stuff, but what I want to do in this case is go right over to SPD. Now when I click on this, this tool gives me all kinds of incredible information. First of all it tells me that there's four slots on this particular motherboard, and I can click through on each one of these, so here in slot number one I've got DDR4, it's an eight gigabyte stick, 1000 megabytes is a gig, it's DDR4, it's made by Kingston, I even see what my DDR speed is here, it gives me everything that I want to know, it even tells me what week and year it was made, it's absolutely amazing. Now you might be tempted to look at all this stuff down here, please stay away from this, this is used by overclockers to actually overclock their RAM and unless you're overclocking, this is not an area you need to worry about. So while we're in here there's a couple other things I like to make mention. So we'll see that in the other bank, there's a different kind of memory, it's still DDR4, it's still the same speed, it's just a different brand. Now one of the things that would be nice, if I clicked on this, and say I clicked on slot three, and it was empty, that might be a really handy tool for me to be able to say hmm, could I snap more RAM into this system? And while we're here, there's also this generic memory that just basically gives you a quick overview, I've got DDR4 in here, I've got 32 gigabytes of DDR4, it's dual channel, and it's running at 3.2 gigahertz. So we've seen a number of RAM features in this episode, but I got to tell ya, I love SO's, they're absolutely fantastic, when it comes to Parity and ECC, unless I'm working on a server you're probably never going to see it, but man, oh man, serial presence detect. I can't tell you how many times it's saved me from crawling under a system, opening it up just to see if I've got some RAM slots, in case I wanted to add more RAM.