PC Hardware in a Nutshell, Second Edition

Memory Selection Guidelines

The following sections provide guidelines for selecting memory for a new system or to upgrade an existing system. Follow these guidelines as closely as possible to ensure the memory you select functions optimally in your system.

When upgrading an older motherboard, it is sometimes impossible to match the installed memory. Some motherboards have 30-pin and 72-pin SIMM sockets, and many have both SIMM and DIMM sockets. If the installed memory occupies all available sockets of one type, you may have to add memory of a different type.

If so, consult the manual to determine supported configurations. For example, many 30/72-pin motherboards provide four 30-pin and two 72-pin sockets, but allow you to populate both 72-pin sockets only if no memory is installed in the 30-pin sockets. Similarly, motherboards with both SIMM and DIMM sockets may allow using a DIMM only if one or more SIMM sockets are vacant or populated only with single-sided SIMMs.

Mixing memory types may degrade performance. Some chipsets run all memory at the speed of the slowest module. Others, including the 430HX and 430VX, run each bank at optimum speed. Mixed memory configurations are nonstandard and best avoided. Memory is cheap enough that it’s often better to use all new memory.

Warning

But, be very conscious of costs when upgrading older systems. Although older memory types are still available, the cost per MB may be very high. For the same cost as a large amount of old-style memory, you ...