Computer Memory, is more always better?

People often assume that more is always better. A 1G memory computer is better than a 512M computer, 2G is better than 1G. But is this always true?

To answer this you need to know that memory, CPU, motherboard and operating system are all involved and this makes the answer complex.

In order to use the memory the CPU must be able to find it. It relies on the operating system to give each memory location an address. In a 32 bit operating system that means 2 to the power of 32 addresses, which is 4G. This means that on the older operating systems (like XP) and on the new ones which are 32 bit, the maximum amount of memory is 4G. Anything more and the operating system can't find it and it is ignored. (Not quite there are tricks that can be used, but in general that's the way it works).

On 64 bit operating systems (Vista, Windows 7, Mac Snow Leopard, Ubuntu and all modern servers) the system can now address 2 to the power of 64 addresses, or a theoretical limit of 16.3 exabytes. However Windows operating systems have imposed a real limit on the RAM (eg 192G for Professional).

The speed of the computer is not just about how much memory it has, the CPU must get the memory quickly in order to use it. This is all about the speed of the motherboard, or more specifically the bus speed and bus type.

Bus speeds are measured in Mhz and it is important that the motherboard, CPU and memory modules all have the same setting. Usually the motherboard sets this to the optimal setting in the BIOS.

Most CPUs access the memory through one side, called the Front Side Bus (FSB). This means that everything is going through one small bottleneck.

Memory manufactures have tried to speed this up using a technique called Dual Channeling. Here two sticks of memory work as one, theoretically doubling the speed of getting memory to the CPU. In reality it has only made a small increase in performance, not really worth worrying about.

Intel has developed a CPU called Core(TM) which can access the memory from all four sides (though one is disabled). This feature is fully implemented in the Core i7 series. Memory manufacturers have responded to this with Triple Channeling memory, which is now starting to show some performance increases. At present this only works with Motherboards, Memory Modules and CPU specifically designed for Triple Channeling. To gain this on your current computer will cost about $1000 to upgrade the Motherboard, CPU and Memory all at the same time.

There are definite memory minimums that operating systems and software need before they work properly, eg Windows 7 2G memory will be comfortable (1G will run but some things will be VERY slow).