Overview of Memory – CompTIA A+ 220-1001 – 3.3

Our RAM modules are some of the most important components on our motherboard. In this video, you’ll learn about memory modules, DDR data rates, and comparisons between DDR2, DDR3, and DDR4.

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If you’re looking at the specifications of your computer and you notice a section that describes memory, or somebody asks you how much memory is inside of your computer, they’re referring to the amount of random access memory, or RAM. We’re not describing the size of an SSD or the capacity of a hard drive. We’re referring to the components inside of your computer where all of the transactions are taking place.

When you’re using the programs and the data on your computer, they’re moved off of your SSD or your hard drive and they’re put into RAM so that you can perform calculations on that information And then store that information back on the SSD or the hard drive when you’re finished.

Your desktop computer or your laptop will have slots where you can install the random access memory modules. The different motherboards may have different types of slots, but it makes it very easy to add, remove, or upgrade the memory that’s in your system. The process of moving information in and out of memory is happening all the time inside of your computer. So the faster memory you have, the faster the overall performance will be of your computer. Every motherboard will be a bit different on how fast these transfers can occur in and out of memory. So check the documentation of your computer to see exactly how fast you can expect your memory to run.

The type of physical package that installs into those slots on your motherboard is a DIMM. This is a dual inline memory module. It’s called a dual inline memory module because this memory module has a series of contacts on one side of this module. It has another set of contacts on the other side of the module. And those two contacts are different on each side of that memory module.

These dual inline memory modules have a 64-bit data width, so we’re able to transfer data from these memory modules in chunks of 64 bits at a time. The memory that’s inside of a laptop is probably a smaller version of the DIMM. This is the small outline dual inline memory module, and it’s about half the width of a standard DIM that you would find in a desktop computer. You can find the DIMMs and the SO-DIMMs available in DDR2, DDR3, and DDR4 flavors of SDRAM. We’ll explain what all of those are later on in this video.

If you’re using a SO-DIMM, it’s probably inside of a laptop or a mobile device because of the size. You’re able to fit a lot more information into a smaller area, which is important for those mobile devices.

Here’s a good size comparison of these two. The DIMM is the larger memory module that you would find in a desktop computer. And the SO-DIMM, you can see, is about half the size, and you would find that in laptops and other mobile devices.

The type of random access memory that is on these DIMMs is called a dynamic random access memory. It’s called dynamic because it constantly needs to be refreshed. This is very different than the type of memory you might have in a flash drive, where you would store information and then unplug it to move it to another computer. That flash drive doesn’t need to be constantly refreshed to maintain that information. But the memory that we use inside of our computers is a much faster memory and it requires this constant refreshing to be able to maintain the data that’s on those DIMMs.

If you were to power off your computer, and no longer able to refresh that memory, everything that was inside of those DIMMs modules would soon disappear.

The use of the word “random” inside dynamic random access memory is because we can access anything in that memory at any place at any time. This is very different than how we used to access information on a magnetic tape, where you’d have to wind through the tape to get to the section that you’d need to read. With dynamic RAM, you can simply specify an address, grab that information, and then be able to access that data

The type of dynamic random access memory that you would find on today’s computers is a type called synchronous dynamic random access memory. It’s synchronous because it is synchronized with the common system clock of your computer. The standard flow of communication based on these clock cycles allows the system to cue things up at a very standard format. This is different than earlier types of dynamic random access memory where there was no synchronization. But in today’s desktops and laptop computers, all of the memory that we’re going to be using will be synchronous DRAM.

Here’s the way that we’re able to use these clock cycles to be able to pull information off of this memory. In a single data rate memory, or SDR, we have a single clock cycle. You can see the up and down wave of the clock cycle. And there’s a number of clock cycles listed on this diagram. And through each single clock cycle with the single data rate memory, we can pull one bit of data, which means if we have one, two, three, four, five, and six different clock cycles then we can pull six different pieces of data.

With dual data rate memory, we still have the same clock cycle. Things haven’t changed as far as the clock going up and down, and having those six different clock cycles. The difference with double data rate memory is that we’re able to pull information on the upside of the clock cycle and the downside of the clock cycle, meaning that there’s two different bits of data that we can gather in the same clock cycle. That’s where the double in the double data rate comes from.

In older computer systems, you might even find double data rate generation 2, or DDR2 SDRAM. These are memory modules that were faster than the original double data rate memory modules, and they’re not backwards compatible with those. In fact, they’re not forward compatible either. If you have a computer system that requires DDR2, then you must use a DDR2 module in that system. You’re not able to replace it with a DDR, a DDR3, or a DDR4.

The generation of memory after DDR2 is DDR3, or double data rate 3. DDR3 ram has twice the data rates of DDR2, so greatly improved performance for those systems that could support DDR3. It also improved the maximum size on a single DIMM to 16 gigabytes of memory. And, again, if you have a motherboard that requires DDR3 memory, then you must use a DDR3 memory module. You can’t take the DDR2 modules from an older system and move them into a DDR3 system. They won’t fit into the module slots at all.

One of the newer generations of DDR memory is DDR4. This fourth generation of memory has speed improvements over the third generation, and it increases the maximum size of a single DIMM up to 64 gigabytes per memory module. And, as you might expect, the changes with DDR4 also mean there’s no backwards compatibility to earlier versions of modules either.

Not only did we change the technology between these different generations of DDR memory, but we also physically changed the package. So when we say that it’s not backwards compatible, it’s not even an option. You can see there is a key, or a small slot, that’s inside the memory module, and the slot is in a different place in each generation of memory type. This means that if you have a motherboard that expects DDR4 memory modules, this is the only type of memory module that will physically fit into the memory slot.

If you’re trying to install a memory module in a computer and you notice that it’s not fitting perfectly, it may be because you have the wrong type of DDR memory.