An Overview of Memory – CompTIA A+ 220-1101 – 3.2

Memory is a critical resource for our computing devices. In this video, you’ll learn about DIMM sizes, SDRAM, DDR data transfers, and DDR3, DDR4, and DDR5 RAM.

If you’ve ever installed an application or an operating system, you’ll notice there’s a specification that requires you have a certain amount of memory inside of your system. This memory is referring to random access memory or RAM. It’s the type of memory we commonly use inside of our personal computers.

This is very specifically talking about the memory modules or sticks of memory that are inside of your computer. This is not referring to an SSD or a hard drive storage space. This is specifically referring to the high speed temporary storage area that’s commonly used when you load an application or document. You’re only able to use these applications and documents when all of that information is loaded into memory.

If you go back in time and look at much older videos for A+, you’ll notice there are a number of different memory slots that were mentioned. But these days, practically everyone uses exactly the same type of memory slots in their computers. These are designed to transfer data very quickly between the information that’s in the memory modules and the CPU of your system. The faster you can transfer information between those two components, the faster your overall system will be.

However, the specific type of memory in your system can vary widely so make sure you look at your motherboard documentation to know exactly what type of memory needs to be installed in those memory slots. What fits into those memory slots is a dual in-line memory module or what we commonly refer to as a DIMM. This is a dual in-line memory module because the connectors that are on one side of the memory module are different than the connectors that are on the other side of the memory module.

Another common specification for these DIMMs is information is transferred in and out of the DIMM in 64-bit data widths. So we’re able to transfer these blocks of information to the CPU or the storage devices that are on our system. Here’s the installation of a DIMM onto these memory slots on a motherboard. To install the memory, you would push it very lightly into that slot, and there are clips on the end that will hold that memory in place so that it can’t accidentally be removed.

If you’re using a laptop, then you’re probably not using the full sized DIMM. Instead, you’re using a SO-DIMM. The SO stands for small outline dual in-line memory module, and it’s about half the width of a normal dual in-line memory module. These are very common on laptops and other mobile devices, where space is at a premium because these modules are so much smaller than the full sized DIMMs.

Here’s a view of the installation of a SO-DIMM. You can see that these are a lot smaller than the full size DIMMs, and they, just like the other DIMMs, will fit into a slot and then push down and lock in place. Here’s a picture of a DIMM and a SO-DIMM next to each other. This is to scale. So this is exactly the sizes that you would see, and you can see that a SO-DIMM really is about half the width of a standard size DIMM.

On the memory module itself, you’ll notice that there are these black components. That is the random access memory or RAM that is located on those modules. This is the memory itself, and we often refer to this as dynamic random access memory or D-RAM because this constantly needs to be refreshed so that the data does not disappear. This is one of the requirements for this type of memory is that there’s always a power source providing that refreshing of the information that’s in these memory modules.

And the random part of the random access memory means that we can access any data that’s on any part of this module by simply asking for it. We don’t have to fast forward or rewind through this module. We can simply request a particular area of memory and have that information provided to us directly from the dynamic random access memory. On our personal computers, this memory is not only dynamic and random, it is also synchronous.

There’s a clock on our system that regulates the flow of data in and out of these memory modules, and every clock cycle, there will be some data that is transferred either in or out of this system. This provides a standard time frame for sending or receiving data from your memory. This also allows all the other components of your motherboard to know exactly when this data will be transferred.

You may have noticed in these images of the DIMMs or the SO-DIMMs that there are notches on the bottom of the module, and depending on the type of memory you’re using, the notches may be in a different place. These notches prevent us from using the wrong type of memory in our system. So if you try to install a DDR2 module into a system with a DDR3 slot, you’ll notice that particular notch will not allow that memory to be installed. As I mentioned earlier, there’s a clock inside of our computer that keeps track like a metronome, so we know exactly when data will be transferred in and out of memory.

If you’re using a much older computer that has single data rate memory, then one clock cycle is able to transfer one bit of data. So you can see what the single clock cycle, we have data one, data two, data three and so on. Our modern systems use double data rate memory or DDR. This double data rate can transfer twice in a single clock cycle, which means we can effectively transfer twice as much than a single data rate.

As our systems have evolved through the years, we’ve also updated our memory modules. Version 3 of this memory type is double data rate three or DDR3. These were an improvement over the older DDR2 memory and allowed you to increase the data rates to be twice as fast as those older DDR2 systems. We’re also able to have memory modules that have a maximum amount of RAM of 16 gigabytes per module. And remember, there’s no backwards compatibility with these memory modules, so this notch at the bottom ensures that this will only be installed on a system that can support DDR3.

On newer systems, you may find DDR4, which increases the speed over DDR3, but perhaps even more importantly, increases the maximum amount of storage on a single module to 64 gigabytes. Again, this is not backwards compatible with previous versions, so if you want to use DDR4 memory, you’ll need a motherboard that can support this memory type. And you may find some systems that can support faster memory in the form of DDR5.

This still has a maximum total size per module of 64 gigabytes, but it is a faster throughput than the older DDR4. And of course, this notch or key that’s on the memory has moved so you can only use DDR5 memory on a motherboard specifically designed for DDR5.