Lesson 3- Memory component - RAM memory types, speeds and bandwidths
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Overview
In lesson 3 we'll cover RAM memory types, speeds and bandwidths. DDR2 and DDR3 RAM, their advantages and disadvantages, what features and specs to look for when shopping, and how much you can expect to pay.
Your computers 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 needed 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 computer's memory, or RAM, is hundreds of times faster than the computer's hard drive. This allows the computer to perform faster.
The more memory your computer has the more programs and files can be opened at once. For most computers 2GB is more than enough. If you plan to do a lot of picture or video editing you should consider getting 4GB or more of RAM since these types of applications take up more memory than typical programs. The 32bit versions of Windows XP, Vista and Windows 7, can only see 3.5GB of RAM. There is a 64bit version of XP, but you should avoid using it. Windows XP 64 has a lot of compatibility issues with programs and hardware. If you need to use more than 3.5GB of RAM you will need to install the 64bit version of Windows Vista or Windows 7. See Lesson 2 of the Computer setup lessons for choosing the 64bit version of Vista or 7.
Types of RAM
There are currently 2 types of RAM used in computers today.
The older type which has been around for 5 years and is the most prevalent is called DDR2. The newest type, which is going main stream, is called DDR3. DDR3 is able to run at higher speeds and, therefore, higher bandwidths. We go into speed and bandwidth in a moment.
Keep in mind that most motherboards support either DDR2 or DDR3 so make sure the motherboard you buy supports the type of DDR you’ll be using.
Memory comes in the form of a stick that attaches to the computer's motherboard through a memory slot. The memory stick is actually made up of several individual memory chips, that when added up, combine to create the storage capacity of the memory stick. Memory sticks come in capacities of 512MB and 1, 2, 4 or 8GB.
For more on motherboards see the motherboard component lesson or the installation lessons.
Speed of Memory
The speed of the RAM is also important. The speed of memory is measured in Mega Hertz or MHz and ranges from 400 MHz to 2000 MHz or 2 GHz 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 or 7 ns for DDR2 RAM and between 6 and 10 ns for DDR3 RAM. A lower CAS is better, but unless you're building a high end system it's probably not worth paying extra for the lower CAS.
With both DDR2 and DDR3 the name refers to the bandwidth the memory has. So PC2 9600 can move 9600 MB of data per second.
To convert from bandwidth to the speed of RAM, you either multiply or divide by 8. So if you want to find the speed of PC2 9600 RAM, divide by 8 and you get 1200, or 1200 MHz, which is the actual speed of PC2 9600 DDR2 RAM. To go from speed to bandwidth you multiply by 8.
This is useful to know when you’re shopping for RAM and motherboards since some shops list only speed and other shops list only bandwidth. By multiplying or dividing by 8, you can be sure a motherboard can support the RAM you buy.
Dual and Triple Channel
When you buy RAM for your new computer we recommend you get 2 sticks of DDR2 or DDR3 memory, at least 1GB in size with the same specifications, for a total of 2GB. Since most motherboards have 4 available slots to add memory, you’ll have 2 more slots available for adding memory in the future, should you need to.
The reason for using 2 sticks of memory is so that you can enable Dual Channel on the motherboard. Dual Channel combines the 2 sticks of memory to double their bandwidth and increase the speed at which the RAM is accessed. Intel socket 1366 motherboards support Triple Channel memory which triples the memory bandwidth and requires 3 sticks of memory. More on this in a moment.
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. See the installation lesson 2 or your motherboard manual to make sure Dual Channel is enabled.
If you want to add more memory in the future you can add another set of matched memory sticks to keep Dual Channel active.
Intel's socket 1366 Core i7 CPU and motherboards with socket 1366 can use the new Triple Channel DDR3 memory kits. DDR2 is not be supported. These motherboards have 6 RAM slots so you can install 3 RAM sticks and still have 3 more available to add memory in the future and keep Triple Channel enabled.
One more thing about Dual Channel and Triple Channel memory. To make sure the RAM sticks are well matched to each other it's best to buy kits of RAM that say they support Dual or Triple Channel configurations. This will ensure the RAM is stable and won't cause errors or crashes.
Overclocking
If you are 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 performace. The standard voltage of DDR2 RAM is 1.8 volts and you can find RAM that will run at up to 2.4 volts. The standard voltage for DDR3 RAM is 1.5 volts and you can find RAM that will run at up to 2 volts. To overclock the RAM you'll be increasing its' speed using settings in the motherboards BIOS and upping the voltage of the RAM to keep the system stable and working. See the Overclocking video lessons on the website for instructions on how to overclock your RAM. Keep in mind that overclocking the RAM will increase heat so look for RAM with built on heat sinks, also called heat spreaders, if you plan to overclock the RAM.
When you purchase your computers memory, look for:
- 2, 1GB, as a minimum, DDR2 or DDR3 sticks in a package to enable Dual Channel on the motherboard.
- If the motherboard you're using supports Triple Channel memory, get a minimum or 3, 1GB DDR3 sticks in a package.
- Get the fastest MHz memory the motherboard you choose can handle.
- Buy the lowest CAS RAM you can afford and look for higher voltage support if you plan to Overclock.
In the installation lessons we’ll show how to install RAM, processor and CPU cooler onto the motherboard.
Memory Warranties
Computer memory is generally very reliable and will last for many years. That said, it's best to buy memory with at least a 1 year warranty.
Generic RAM typically comes with a 90 day warranty. Branded RAM (Corsair, Kingston, etc.) will come with a 1 to 3 year warranty.
| Manufacturer Links | |
| A-DATA | Mushkin |
| Corsair | OCZ |
| Crucial | Patriot |
| GEIL | PNY |
| G. Skill | PQI |
| Kingston | Super Talent |
Memory Reviews
To find more reviews do a search in your favorite search engine (Google, Yahoo) for the model number of the memory you're interested in.
RAM Memory comes in several sizes, types, speeds and bandwidths. Below are several sites that will help you find the lowest price from a reputable merchant.
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