Memory Technologies – CompTIA A+ 220-1101 – 3.2

Our system RAM can provide a number of different features. In this video, you’ll learn about virtual memory, multi-channel memory, parity memory, and error correcting code (ECC) memory.

Let’s start our conversation about memory technologies with what we do when we run out of memory. There are ways to help when you run low on random access memory. And one of the things you can do is take information you’re not currently using in RAM and swap it out to a hard drive or SSD.

We sometimes refer to this as virtual memory, although we can also refer to it as virtual RAM or a swap file. In Windows in the Performance Options, there’s an Advanced tab that allows you to configure a virtual memory section. This is an area of your hard drive or SSD that Windows can use as if it was actual memory. Obviously, a hard drive or SSD is slower than actual random access memory so this is really an area where we’re temporarily storing things until we find more room within our normal random access memory.

Many operating systems will manage this process automatically. In Windows, there’s a checkbox that says “Automatically manage paging file size for all drives.” But you can manage this yourself. If you uncheck that option, you can specify exactly how much virtual memory you’d like to allocate on your storage drive.

Another memory technology that can greatly increase the throughput in your system is multichannel memory. Sometimes you’ll see this as dual channel, triple channel, or quad channel memory. This takes the throughput that normally would be sent to one single memory module and spreads that load across multiple memory modules. Ideally, you would have exactly the same memory module types in each of these multichannel slots. If your motherboard supports multichannel memory, then you might want to look at the memory modules and see if they have different colors. This is often done so that you know exactly which slots to use for the multichannel memory.

One thing you might have to consider is what might happen to your system if there happens to be an error with the memory that you’re using. In some environments, you’re able to have memory check itself. And if a memory does occur, then we can choose to perform some other functions. This is the type of memory that you might have in a system that’s running virtual machines. It may be very large database servers or anything where you want to maintain the uptime and availability of those services.

One type of memory you might use is parity memory. This adds an additional parity bit to the information that you’re storing in RAM. This isn’t a perfect way to identify problems because parity memory can’t always identify when an error has occurred. And parity memory has no method to be able to correct any problems that it happens to find.

If you would like to use memory that can make corrections to any problems, then you want to use a motherboard that can support error correcting code memory or ECC memory. This will not only identify when an error has occurred but it will make a change to the memory to correct any of those problems. It’s this parity bit that allows us to identify when an error may have occurred with the data. Many memory modules use even parity, which means adding the parity bit means that there will be an even number of ones in that data.

Let’s see how this parity bit is calculated and added to the existing data. Let’s look at this first line of data. And we want to count the number of ones. So in this particular data that’s 1, 1, 1, 0, 0, 1, 1, 1, we have one, two, three, four, five, six ones within that data. That six is already an even number so we don’t need any additional ones to make this even. Therefore, the parity bit will be zero.

Let’s take the next bit of data. This data is 0, 0, 0, 0, 0, 0, 1, 0. If we count the number of ones, there is a single one which means there are an odd number of ones. To be able to make this even parity, we need to add one more one into this mix so that we have an even number of ones in this data.

And lastly, we have 1, 0, 0, 1, 1, 0, 0, 0.. We count the number of ones. There are one, two, three, ones. That’s an odd number. So to get even parity, we’re going to add a one. And now we have an even number of ones in that data.

So with the existing parity bit, we can run some tests of some data that may already be existing to see if the data appears to be correct. So let’s evaluate the parity bit, assuming that we’re using even parity. We’ll take this first bit of data and count the number of ones. We have 0, 0, 0, 0, 0, 1, 1, 1, 1 with a one as the parity bit. And if we count the number of ones, we have four ones. That is an even number. Therefore that data has been validated.

Let’s do the next bit of data, which is 0, 0,0 0, 0, 0, 0, 1, 0, with a 0 on the end. We count the number of ones. That one is an odd number, which means something has gone wrong with that data and it does not validate. And then lastly, we have 0, 1, 1, 0, 0, 1, 0, 0 with a one parity bit. If we count the number of ones, there’s one, two, three, four ones, which means it is even parity. That validates and that data appears to be correct.