PC System Memory Basics
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Memory (referred to as RAM) is essentially the computer's workspace – the place where the computer temporarily stores data and programs. How well memory works is an important factor that influences the overall performance of your PC. Memory speed allows more data to be transferred in a given time for greater system response and performance in demanding applications and games.
PC system memory is a means to temporarily store data and instructions for use by the central processing unit (CPU). System memory is typically referred to as RAM, which stands for Random Access Memory. Modern system memory can store different data in different areas, which can be accessed randomly for processing. Previous versions of system memory were accessed sequentially. To better understand this concept, compare finding a song on a cassette tape with finding a song on a CD.
System memory is typically attached to the motherboard in the form of a chip or module called a DIMM (Dual Inline Memory Module), which is a circuit board that holds the memory chips and plugs into specific slots on the motherboard.
Supplemental Information: DRAM vs. SRAM
There are also several subcategories of RAM. The type of RAM that most people work with is DRAM or Dynamic RAM, which means that the memory must continually be refreshed or recharged upwards several thousands of times a second. If it is not refreshed, the RAM will lose its stored content. The opposite of DRAM is SRAM or Static RAM, which does not have to be refreshed and is therefore faster than DRAM. SRAM is also much more expensive to manufacture, so is typically only found in small amounts as CPU cache.
All data and instructions are processed by the CPU. In order to load the data into its registers, the CPU must find the information from the different places where the data might be stored. The process follows a fast to slow hierarchy, meaning the CPU will look for the information in the place that can deliver the data quickest. Typically this means that the CPU first looks in its on-die cache – usually L1 and L2 cache – which are forms of SRAM. If the data is not in the cache, the CPU looks in the next fastest place, which is the RAM. If the information is not in the RAM, the CPU looks for it on the hard disk drive.
As an example, you may notice that when you exit a program and load a different program that your computer may take a little longer to load the second program. That’s because none of the information the CPU is looking for is in the cache or the memory, so it has to call the hard drive. You may have also noticed that when you exit the second program and reload it later, the program comes up much quicker. That’s because the cache and memory are already holding information the CPU needs to load that program, since you used it last.