Replacing Your PC’s RAM – RAM Ads

This post is for those of you who are comfortable replacing RAM in your PC and want to understand how to interpret the RAM ads on the Internet.

Know the Terms – DDR, Buffered, Registered, ECC

• The more RAM that is installed, the faster the PC. Use as much memory as your motherboard and OS can support, within your pocketbook.
• Using DDR/DDR2/DDR3 modules will improve performance. DDR refers to Double Data Rate and processes data twice for each pulse of the system clock, once on the upcycle of the pulse, and once on the downcycle of the pulse. DDR2 is faster than DDR and DDR3 is still faster than DDR2.
• Use buffered or registered modules if the motherboard supports it. Buffers and registers hold the data and amplify it immediately before the data is written to the memory module. Some modules use buffers, some use registers, and there are some that do not use either of them. If a DIMM uses buffers, it is called a buffered DIMM. If the DIMM uses registers, it is called a registered DIMM. If the module does not support the feature, it is called an unbuffered DIMM.
• Use the fastest memory possible that the motherboard will support. If using more than one module, ensure that all of the modules are of the same MHZ speed. If not, the system will default to the slowest module, or with some PCs, will cause system instability.
• Although many PCs use only single channeling, using dual-channel or triple channing will improve performance, providing the motherboard supports it. You must install matching pairs of modules with dual channeling or have 3 modules match with triple channeling.
• If the board supports ECC (error correcting code) memory modules, use them. Although there will be a very slight decrease in performance, it will increase the reliability of the system. If the motherboard supports parity, use modules with parity.
• CAS (column access strobe) and RAS (row access strobe) Latency, refer to the two ways that measure access timing. Both CAS and RAS indicate how many clock cycles required to write or read a column or row of data from the module. The lower the value, the better the speed. These two terms CAS and RAS, are referred to as CL and RL also.

Reading RAM Internet Ads

Let's look at the following advertisement for memory and breakdown the technical specifications so that it is understandable:

• Looking at the first ad, notice the first specification listed: DDR2 PC2 6400. First of all the DDR2 is pretty clear, the module has DDR2 technology.
• The next item listed is PC2. IF you are using DDR2 modules, there will always be a 2 after PC.
• The 6400 means that the speed in bandwidth is 6400 MB/sec (megabytes per second; doing the math: 800MHZ speed X 8 bytes of data per clock tick = 6400MB/sec).
• The CL=6 means that the module uses CAS for measuring the access timing and it takes 6 clock ticks for the module to access data on a memory read or write.
• Unbuffered means that the module does not use buffers.
• Non-ECC means that the module does not use ECC (error correcting code).
• DDR2-800 means that this DDR2 module runs at 800MHZ (system bus speed).
• The 1.8V is the voltage the module uses to operate.
• 256Meg X 64 means that the data path is 64 bits and to find the total amount of ram on the module, multiply them and divide by 8 to convert to bytes. Doing the math, 256Meg X 64 = 16384 Megs. Now we divide by 8 to convert to bytes =2048Megs, which is 2.048Gig (we can drop the .048 portion). So one module contains 2 Gigbytes of memory.
• If you ever see 72 instead of 64 in the advertised formula, that is a clue that the memory is ECC memory. 

To get additional tips on how to speed up your PC, you can view it here.