Random Access Memory (RAM)
RAM stands for Random Access Memory, which simply means that it' memory where any individual byte can be accessed (read from or written to) randomly (i.e without affecting the preceding and following bytes). As explained in the previous section, it's used as a cache, to store information that's likely to be needed repeatedly. Since data in RAM can be accessed much faster than data on disk, this speeds up your computer.
RAM is contained in standalone memory modules which plug into slots inside your computer. This means that it's relatively easy to upgrade the amount of RAM after you've purchased your computer if you find that you don't have enough.
When you look at the specification for the RAM in a computer, you'll often see lots of technical terms thrown in, as in the examples below.
- 1024MB 667MHz Dual Channel DDR2 SDRAM [2x512]
- 2048MB 667MHz Dual Channel DDR2 SDRAM [2x1024]
- 2048MB 800MHz Dual Channel DDR2 SDRAM [2x1024]
- 4096MB 800MHz Dual Channel DDR2 SDRAM [4x1024]
The format of each of these specifications is: Amount of RAM, clock speed, RAM types, number and size of RAM modules. While a specification may be worded in a different way, it usually contains the same basic pieces of information. These pieces are explained in the following sections.
Generally though you can ignore most of the details, and really only focus on how much RAM you want. Unless you're selecting individual components to build your own computer from scratch, you don't need to worry about the rest of the specification. what you'll get is a list of options for RAM configurations which are compatible with your chosen computer, and the main factor in deciding which option to take is how much RAM you think you'll need.
Amount of RAM
This is the amount of RAM, measured in megabytes or gigabytes (a gigabyte is 1025 megabytes). The more you have the better, since your computer will be able to cache more data in RAM, and reduce the number of times it needs to access the disk.
Clock Speed
This is the clock speed of the RAM, which determines how quickly data in the RAM can be accessed. Obviously faster speeds are better, but the speed at which the RAM will operate is also limited by other components in your system, so you can't choose faster RAM unless it's compatible with the rest of your computer.
RAM Type
In these examples, the following terminology is used:
- Dual Channel:
Dual channel refers to an architecture that uses two channels to communicate between the RAM and memory controller. This means that 2 RAM modules can communicate with the memory controller simultaneously, which improves speed and efficiency. - DDR2:
Double Data Rate (DDR) refers to a method of transferring data twice during each each clock cycle, which makes data transfer twice as fast as before. As the name implies, DDR2 transfers twice as much data during each clock cycle as DDR. - SDRAM:
Dynamic RAM (DRAM) uses individual capacitors within an integrated circuit to store each bit of data. The charge placed on these capacitors degrades over time, so they need to be periodically refreshed, which is what makes the memory dynamic. While this seems inefficient compared to Static RAM (SRAM), the design of a DRAM chip is much simpler so that more data can be accommodated in each chip.
Synchronous Dynamic RAM (SDRAM) means that access to the memory is synchronized with a clock signal. Again, this allows for more efficient design.
Number and Size of RAM Modules
This part specifies the number of memory modules and the size of each of them (so 2x1024 is 2 modules of 1024MB each). A desktop computer will typically have 4 slots for RAM, while a laptop will typically have 2. On the one hand, it may seem desirable to put more memory into fewer slots, so as to leave open ones available for future expansion. The problem with this though is that it reduces the benefit of dual channel access - the ability for the memory controller to interface to two RAM modules simultaneously. For this reason it is generally recommended that memory is installed in matching pairs of modules.
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