Component Lessons
Lesson 3: Computer memory.
Male Speaker: Your computer's memory also called RAM or Random Access Memory is used to hold the information that the computer is working on. When you power the computer on, it reads all the information it needs to start Windows from the hard drive into memory. Once Windows is loaded, the computer loads any programs or files you open from the hard drive into memory. The reason for this is the computers memory or RAM is hundreds of times faster than the computer's hard drive. This allows the computer to form faster. The more memory your computer has the more programs and files can be opened at once. For most computers one gigabyte is more then enough.
If you plan to do a lot of picture or video adding, you should consider getting two gigabytes or more RAM since these types of applications take up more memory in typical programs. The speed of the RAM is also important. The speed of the memory is measured in megahertz or MHz and ranges from 400 megahertz to 1000 megahertz or one gigahertz and up. Generally you should get the fastest RAM the motherboard you choose can handle. Another measurement of RAM speed is called CAS, it's measured in nano seconds or NS and comes in speeds of 3 to 5. Three is faster, but the difference in real world performance is very small. It's hard to recommend spending extra for CAS three RAM.
Memory comes in the form of the stick that attaches to the computers motherboard through a memory slot. The memory stick is actually made up of several individual memory chips, that when added up combined to create the storage capacity of the memory stick. Memory sticks come in capacities of 128, 256 or 512 megabytes and 1 or 2 gigabytes.
For more on motherboards see the motherboard component lesson or the installation lessons. There are currently two types of RAM used in computers today. The older type found in most computers made in the last four years is called DDR. The newer type which has been around for two years and is just now going mainstream is called DDR2. DDR2 is able to run at higher speeds and therefore higher bandwidths. We go into speed and bandwidth in a moment.
When you buy a RAM for your computer we recommend you get two sticks of DDR2 memory, 512 megabytes in size, with the same specifications for a total of 1 gigabyte. Since most motherboards have four available slots to add memory, you'll have two more slots available for adding memory in the future, should you need to. The reason for using two sticks of memory is so that you can enable dual channel on the motherboard. Dual channel combines the two sticks of memory to double their bandwidth and increase the speed of which the RAM is accessed. Dual channel support is standard on just about every motherboard made today. The motherboard will detect the matched set of RAM sticks and enable dual channel automatically in most cases. If you have to set manually this would be done in the motherboards BIOS, see the computers setup lessons and your motherboard manual for this. If you want to add more memory in the future you can add another set of matched memory sticks to keep dual channel active. Most memory comes with the options of ECC, or Error Correcting Code, also knows Parity. This type of memory attempts to fix any errors made by the program being run since modern RAM doesn't make many mistakes and ECC almost never is able to correct errors that do happen, the extra money for ECC isn't worth it. Look for RAM without ECC or Parity support.
Here is a breakdown of RAM types, their common names, and the speeds they run at. With DDR and DDR2, the name refers to the bandwidth the memory has. So PC1600 can move 1600 megabytes of data per second. To convert from bandwidth to speed you either multiply or divide by eight. So if you want to find the speed of PC2-6400 RAM, divide by eight and you get 800 or 800 megahertz, which is the actual speed of PC2 6400 DDR2 RAM. Take over from speed to bandwidth you multiply by eight. This is useful to know when you're shopping for RAM and motherboards, some shops list only speed another shop list only bandwidth. By multiplying or dividing by eight you can be sure a motherboard can support the RAM you buy. Also keep in mind that most motherboards support either DDR2 or DDR2. So make sure the motherboard you buy supports DDR2. If you're planning to try overclocking the RAM you might also look at the voltage rating of the RAM.
Overclocking means running the RAM faster than it's meant to be run to get more performance. The standard voltage of DDR2 RAM is 1.8 volts and you can find RAM that will run it up to 2.2 volts. To overclock the RAM you'll be increasing at speed using settings in the motherboards BIOS and upping the voltage of the RAM to keep the system stable and working. See the motherboard component lasting for more on overclocking. Keep in mind that overclocking the RAM will also increase the heat, so look for RAM with built on heat sinks also called heat spreaders if you plan on overclocking the RAM.
When you purchase your computer memory look for 2512 megabyte DDR2-RAM sticks in a package to enable to dual channel on the motherboard. Get the fastest megahertz memory the motherboard you chose can handle by CAS 4 RAM and look for higher voltage support if you planned to overclock and don't spend money on ECC or Parity support.
In installation lessons we'll go over how to install the memory stick on to the motherboard.
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