Memory Channel
In a computer, there is a bus that transfers data from the memory modules to the CPU. In the 2000s, memory speed and CPU speed increased and transferring memory to the CPU started to become a bottleneck. With computers, a bottleneck is where one component limits the performance of the rest of the computer. In this case, the memory bus could not transfer data quickly enough to the CPU.
To understand how this problem was solved, let’s consider the simplest example of how the memory bus works. This information applies to memory modules before DDR5, as DDR5 changes things slightly. At the end of this video, I will have a look at how DDR5 has changed things compared to earlier memory modules.
In its most simple form, the memory bus is a single 64-bit channel. In the old days this was causing a bottleneck, so something needed to be done. Modern CPUs have cache which puts a lot less load on the CPU, thus this is not such a problem as it used to be. It also depends whether you are running a memory intensive application.
To get better performance, in the 2000s a second channel was added. This channel allowed data to be transferred over a second 64-bit bus. Each of these buses is called a channel. When two channels are being used this is called “dual channel”.
Although in this example I have used a single memory module, it is possible for two memory modules to be installed on the same channel. Later in the video I will look at how that is implemented.
Dual channel is still used today, and a lot of computers only support dual channel. However, there are some computers that support triple channel. Triple channel is when there are three 64-bit buses. Lastly, there is quad channel which, of course, is four 64-bit buses.
If you are planning to use multiple channels, you next need to look at compatibility problems.
Compatibility
When using memory modules in a computer, when possible, it is best to use memory modules that are the same. In some cases, this may not be possible. Mismatched memory modules will reduce their speed to that of the lowest speed memory module.
In some cases, mismatched memory modules may cause random crashes and other instabilities. In some cases, it will work and at other times it won’t. You can always give it a try and run a memory tester to see if your computer is stable.
When installing memory modules, you should use memory modules of the same capacity. Multi-channel can only work with memory modules that are of the same size. In some cases, your motherboard may support “Flex” mode. Flex mode allows different memory modules of different sizes to be used together. The capacity that matches is run as multi-channel while the remainder runs as single channel.
When purchasing memory modules, they are often sold in kits. Thus, you can guarantee they will work together. If you are using different memory modules, check the specifications to see if they are the same. If they are different, you can always give it a try.
Installing Memory Modules
Now, let’s have a look at how to install some memory modules. For this demonstration, I will use this motherboard. I will be installing this memory module kit. These kits have identical memory modules, thus making it easy to install dual channel.
You can also get these kits in triple and four packs, if you want to use triple or quad channel. On this motherboard there are four memory slots. They are divided up into two channels, these being channel A and Channel B. Each channel can transfer 64-bits at once. If you use two channels, then each channel can transfer 64 bits, making a total of 128 bits at the same time.
On this motherboard, there are two channels and each channel has two slots attached to it. The CPU has a direct connection to one of the slots in each channel. This slot is connected to the slot below it. When installing memory modules, the motherboard manufacturer will generally recommend installing the memory modules in certain slots. This is for two reasons: the first reason is to avoid the signal going through a memory module that is empty and the second is to take advantage of multiple channels.
For this motherboard, you can see the recommendation is to install the first memory module in the second slot of channel A, otherwise known as A2. The next memory module is slot 2 of channel B, otherwise known as B2. The motherboard may also have printed on it which memory slots should be used first. If it does not have that, at least it should have the channel and slot number.
Although a lot of motherboards are designed to use the second slot from the CPU first, you cannot guarantee this will be the case. It is generally a good idea to check your motherboard manual to ensure that you are plugging the memory into the correct slot. On some motherboards, the computer won’t work if you don’t plug the memory module into a certain slot. Thus, if your computer won’t start or memory is not being detected, check to see if the memory module is in the correct slot.
I will now install two memory modules into the motherboard. To start with, the two latches on either side of the memory slots need to be pushed down to put them in the unlocked position. On some motherboards, there may only be a latch on one side. Generally, memory modules that only have one latch are found close to expansion cards. If the latches were on both sides,and a large expansion card was in the computer, it would make it hard to get to the latch, which is why these motherboards have only one.
The memory modules have a notch in the middle. This is off center to prevent it going in the wrong way. You will also notice that the edge of the connector is not straight across. The connector is wider in the middle than on the outside. The curved connector is made this way to make it easier to install the memory module and reduce stress on the connector. Since the connector is curved, the memory module needs to be installed flush with the connector rather than at an angle.
To start with, I will install the memory module the wrong way. Because it is the wrong way, the notch in the memory modules won’t line up with the keying. For different versions of DDR, the notch will be in different places. It is important that if you get the memory module in the wrong way or use the wrong memory modules, that you don’t force it, as it will damage the memory module.
I will now flip the memory module so it is the correct way. Once the memory module is orientated the correct way, you will notice that the notch will line up with the slot.
The last part is to push down on either side of the memory module until you hear it click into place. Since the edge of the memory module is curved, it should not be too hard to push it into place. If you are having trouble, you can wiggle it a little bit, but not too much. With the older straight-edged memory modules, you could wiggle them more to get them to go into place, but these memory modules are designed for you to push down on them. Only give them a slight wiggle if you are having problems getting the memory module to go in. Sometimes the motherboard slot may be a bit stiff and the memory module may be a little difficult to get in. If you are having problems, pull the memory module out, check it is the correct type and orientated correctly. If you force it in, you risk damaging the slot and the memory module.
I will now install the next memory module. This will be installed in channel B. Thus, I am using the full 64-bit bandwidth from channel A and the full 64-bit bandwidth from channel B. If I were to put the memory module in channel A, the two memory modules would be sharing channel A’s 64-bit bandwidth and channel B’s bandwidth would not be being used at all.
As before, I will unlock both sides of the memory module slot. I will then put the memory module into the slot and push down on both sides until I hear it click into place.
That’s it for installing memory modules; however, there is a small change in how DDR5 memory modules operate which does not affect how you install them.
DDR5 BUS
DDR5 has two separate 32-bit buses to the memory module. DDR4 has one 64-bit bus. This effectively means that DDR5 has two independent channels to send data whereas DDR4 has one. This, however, does not affect how you would install the memory modules or how multi-channel works.
So, install DDR5 the same way you would install any other DDR memory. Don’t let the fact that the channel is effectively divided into two confuse you, the process is the same.
End Screen
That concludes this video on installing memory modules. I hope you have found this video informative. Until the next video from us, I would like to thank you for watching.
References
“The Official CompTIA A+ Core Study Guide (Exam 220-1101)” pages 69 to 70
“Multi-channel memory architecture” https://en.wikipedia.org/wiki/Multi-channel_memory_architecture
“Picture: DDR memory modules” https://commons.wikimedia.org/wiki/File:Desktop_DDR_Memory_Comparison.svg
Credits
Trainer: Austin Mason http://ITFreeTraining.com
Voice Talent: HP Lewis http://hplewis.com
Quality Assurance: Brett Batson http://www.pbb-proofreading.uk
