Motherboard RAM Slots – CompTIA A+ 220-901 – 1.2

Your computer system uses a particular size and package of memory, and the size of the RAM slot usually depends on the overall size of the system. In this video, you’ll learn about DIMM, SO-DIMM, and Micro-DIMM RAM slots.

<< Previous: Motherboard Expansion Slots and Bus SpeedsNext: CPU Sockets >>

RAM, or random access memory, has changed a lot through the years. We’ve had different kinds of connections on our motherboard. There are many different kinds of memory types and different kinds of memory connections. Memory is one of the most important components on your computer. When you’re using an application, when you’re browsing the internet, when you’ve got a spreadsheet open and you’re working with those numbers, all of that information is being stored and executed in the memory of your computer. So there’s a lot of communication between this memory and the CPU and back again, and speed is very, very important when it comes to the memory.

Every motherboard is a little bit different as to the memory that it uses. It uses different speeds and different technologies in the memory, so you want to be sure if you’re ever adding or replacing memory on your motherboard that you always look at the motherboard documentation. One common memory type, especially on desktop computers, is a DIMM. That stands for Dual Inline Memory Module. This is obviously a single module that would be plugged into the system. All of the memory is in line. These are not separate chips that we would be adding to the computer. Everything is in one single long chipset here.

And you can see that it is a dual inline memory module, because the electrical contacts on this side are different than the electoral contacts that are on the other side. If we were to flip this over, it looks identical on the other side. And you may think that these contacts are connected to each other, but on a DIMM, they are dual inline, which means that each side of this is effectively a different set of contacts to the memory. These DIMMs have a 64-bit data width.

We talk about the memory bus of the computer, that is the size of the communication path that’s going to be used between the memory and the CPU. There’s different kinds of DIMMs and we’ll look in a later video about the DDR SDRAM that has 184 pins. There’s also DDR2 and DDR3 memory that has 240 pins. So it depends on the DDR memory that you’re using on this DIMM memory module type as to the number of pins that it will use to connect to the motherboard.

If you’re working with a laptop computer, you may need something like a SO-DIMM. When you get into these mobile devices, we need a smaller form factor. And so we’ve taken the idea of a DIMM and we’ve collapsed it into a Small Outline Dual Inline Memory Module. These are relatively small because they’ll fit in our mobile devices. And these will have for DDR and DDR2 200 pins in the total size across the bottom. If this is a DDR3 SDRAM it’ll have 204 pins. And it fits into those very small form factors that are about 68 millimeters wide for your mobile and laptop devices.

One thing that’s interesting, whether we’re looking at a DIMM, SO-DIMM or other memory types, you’ll see there’s a little notch in the memory right here at the bottom. The notch is designating the type of memory that it is. If you have a laptop that needs DDR memory, it’s only going to fit this kind of memory module because there’s a slot there that will prevent a DDR2 or a DDR3 from fitting into the same slot. That way when you’re plugging in memory, you know you’re plugging in exactly the right type for that motherboard.

And a bit smaller than the SO-DIMM is the Micro-DIMM. This is really designed for even smaller mobile devices, about 54 millimeters in width. And we can even fit even more memory onto the smaller devices, amazingly enough. If this is DDR memory, then it’s 172 pin memory module. If this is using DDR2 or DDR3 memory, there are 214 pins connecting to the memory interface in that device.

Here’s a view of this memory to scale. I put a DIMM, a SO-DIMM and a Micro-DIMM all next to each other and took this picture so that you can really get an idea of the size of the DIMM you might have in a traditional desktop computer, a SO-DIMM that you might fit inside of a laptop, or now the much smaller Micro-DIMM that goes into these even smaller mobile devices.