While CPU speed is a major factor in the overall speed of a system, disk
drives have the greatest impact on the potential speed. The faster you can
transfer data to and from disk the quicker the overall operation of the
system will be. It also helps if sufficient RAM exists to load all the
programs and data necessary to carry out your daily tasks. This greatly
reduces the need to use disk space to supplement RAM, thus reducing disk
activity and therefore improving performance. Enabling DMA on all drives
that support it will greatly reduce the CPU workload from over 80% to less
than 1%, freeing it for far more important tasks such as refreshing the
screen. If taken to extremes, it is quite feasible to have a 267MHz with a
fast drive out perform a 1GHz system with a slow drive.
The motherboard bus speeds also have an impact on overall speed because all
data to be processed must ultimately come from and go through it. When
upgrading a CPU it is sometimes necessary to upgrade the motherboard as
well. Before choosing a new CPU check the motherboard documentation for any
CPU speed limitations. Note that a BIOS firmware upgrade (BIOS flash) can
often permit a faster CPU to be fitted than was originally intended, however
this procedure should only be carried out by a qualified technician (don't
be tempted to flash someone else's BIOS unless you are fully prepared to
deal with the consequences of failure). If upgrading the motherboard and CPU
together, it is often best to simply go the whole hog and upgrade the RAM as
well. The old motherboard, CPU and RAM can then be sold together.