Choosing your RAM

December 2016




Technical constraints- Factors to be taken into account

RAM type: DDR, DDR2, DDR3


It's your motherboard or rather its memory controller that will determine the type of RAM that can be used.

The memory controller is integrated into the Northbridge on an Intel motherboard Socket 775, but integrated in the processor for AMD model and Intel sockets 1366 and 1156 (and above).

Most motherboards only support one type of RAM, but there were some models that support two types of RAM, with dedicated slots (not simultaneously).
The oldest of all is the DDR, which is now used to update old PCs.

DDR2 had its moment of glory for several years but is currently stalling behind.

As for DDR3, it has become widespread for about a year, with AMD AM3 and Intel 1366/1156 platforms .

The frequency


There are currently various default frequencies, for RAM, besides the ones you can achieve with overclocking. These frequencies range from 133MHz to 2000MHz, but the aeffective frequency ranges from 133/2=66.5Mhz to 2000/2=1000Mhz (1 Gb).

When choosing your RAM, you have to take into account this frequency based on what the motherboard can handle. If your motherboard supports DDR2 in PC-5300/6400/8500, make use of these type and nothing else.

The timings- CAS latency


The timings determine the time in number of clock cycles to perform an operation.
For the more information read: RAM

The most important is CAS Latency (Column Address Strobe) -access time for a column.

The more aggressive (reduced) it is and the more memory will be faster for a given frequency.
For example, timings of 4-4-4-12, will be better than 5-5-5-15 for DDR2, and 7-7-7-21 will be better than 9-9-9-27 for DDR3.

But be careful, because the frequency must also be considered:
For example, with an array of DDR3 1600Mhz CAS 8, having a true frequency of 800Mhz and a CAS of 8, the execution of CAS will beof 8 clock cycles at 800Mhz, or one hundredth of a nanosecond.

With an array of DDR3 2000MHz CAS 10, CAS execution is 10 clock cycles at 1GHz (a hundredth of a nanosecond). It will therfore give the same performance as DDR3 1600Mhz CAS 8 and will not change the bandwidth or stability.

The dual channel


The dual channel technology is managed by the Northbridge to double the bandwidth.

But the situation is quite different in practice.

The gain in bandwidth was obvious in the time of the Pentium 4 (in 2004), by cons on an Intel Core2Duo it is low, at most 5% better according to tests carried out: but why deny it .. .

Since the socket 1366, the Triple Channel has appeared to further improve performance. Unfortunately, comparative tests show no obvious differences compared to the Dual Channel.

Additional Info

The relationship between RAM and graphics card


But what is the relationship between memory and the memory of your graphics card?
There is simply no relationship. You can have a DDR RAM with a HD5770 (DDR5) or DDR3 with an ATI Rage Fury. It's like you want, the 2 systems are independent.



GGDR4 chip by Samsung

The Manufacturers

  • There are plenty of chip manufacturers. Nanya and Hynix are the most popular ones.
  • The best brands (not the manufacturers): Corsair, OCZ, Geil, etc. ...

How much RAM should I use?


Some motherboards with DDR2 are limited to at least 2GB for example, but the DDR3 motherboards to handle all at least 4GB of RAM.

The optimum amount of RAM depends on the OS and applications, in general, we consider that in 2010 that 2GB is a minimum for Windows 7.


Beyond that, it really depends on the applications your're using: for you to read the manual provided by the publisher.


There are two main types of OS (Operating System):
  • 32bits
  • 64bits


Note that: 32bits OS can accept up 3.25Go RAM and 64bits OS beyond 4GB.


Related :

This document entitled « Choosing your RAM » from CCM (ccm.net) is made available under the Creative Commons license. You can copy, modify copies of this page, under the conditions stipulated by the license, as this note appears clearly.