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Memory Timings

In this video from ITFreeTraining I will look at memory timings. When you purchase a memory module, it will most likely have a whole heap of numbers on it. After watching this video, you will understand what these numbers mean and this will allow you to determine what memory modules you should be buying to meet your needs. Download PowerPoint: https://itfreetraining.com/handouts/a... Memory Timings To understand how timing works, let’s jump right in and have a look at a memory module. This is a DDR4 eight gigabyte memory module. On the memory module there should be a sticker that will tell you more information about the memory module. The information on the sticker includes information like the memory type, the size, serial number and timing information. The information we are interested in is the timing information. On the sticker there is the type of memory and the speed. In this case, the memory is DDR4 and runs at 3200MHz. The clock speed of the memory module gives you an idea of how fast it will run, but as we will see, there are other factors that will determine how fast the memory will be able to transfer data to and from the memory controller. Also, on the sticker will be what is referred to as the memory timings. These timings determine how long it takes to complete certain functions on the memory module. On the memory module you will generally have a group of four, maybe five numbers. I will go into more detail what these numbers mean in just a moment. For the exam, it is unlikely that you will get a question asking directly about memory timings, but in a troubleshooting scenario you may get a question that relates to adjusting the memory timings. So, having a basic understanding of these will help you in the exam. The last value that I am interested in is the voltage. The voltage itself has nothing to do with the timings, however if you start playing around with the timings you may also need to adjust the voltage. Before I have a look at the timings in more detail, I will first have a look at how the BIOS gets these timings from the memory module. Serial Presence Detect (SPD) Modern memory modules contain a small chip on them called the Serial Presence Detect or SPD chip. This chip contains the basic timing settings for the memory module. Manufacturers tend to be conservative with their timings to ensure the memory module works correctly in all computer systems. The SPD chip may also contain enhanced performance profiles. These are a different set of memory timings which will give you better performance. The risk of course in using these profiles, is that it may reduce the stability of your computer system. Before I look at the timing settings, I will first have a look at how memory is laid out. Memory Layout The memory in the memory modules is essentially laid out into rows and columns. If you consider memory to be similar to a warehouse, where each shelf in the warehouse is at a different location and contains a fixed amount of storage. In this example, we will consider that each individual shelve contains four bits. In order to get to the shelf, we have a scissor lift. To reach a row, we first need to move the scissor lift up to the required row. Once this is done, we next need to move the scissor lift across until we get to the shelf. Once at the shelf, we can access everything on the shelf, which in this case is four bits of data. So, essentially there are two movements of the scissor lift required to access one shelf. One to raise the scissor lift to the correct height and a second to move it to the required row. You may be asking yourself, why could we not combine the movements into one? If you think of electrical circuits, you are essentially activating a circuit. In the first case this is the row and until the row is activated you cannot access any column. When accessing any location in memory, two steps are required. One to select the row and once this is done, the second step is to access the column. Both take time to complete, so you have probably guessed by now, the time taken to select a row and column is found on the sticker of the memory module. Timing Settings Before I look at the timing settings, a quick reminder that it is very unlikely CompTIA will ask you a question on a specific timing. The question may give you a scenario where a computer is unstable and the answer may be related to changing the timing settings. Description too long for YouTube. Please see the following link for the rest of the description. https://itfreetraining.com/ap/3a45 References “3D Model: Rigged - Scissors Lift” https://www.blendswap.com/blend/16656 Credits Trainer: Austin Mason http://ITFreeTraining.com Voice Talent: HP Lewis http://hplewis.com Quality Assurance: Brett Batson http://www.pbb-proofreading.uk