Processor speed is generally considered singularly responsible for the performance of a PC by most people. However this is not correct. PC hardware performance come mainly from a combination of factors like Processor, I/O System, RAM and Hard Disk.

If you are a user who often uses applications like autoCAD, 3D Studio or similar processor intensive applications, processor speed can be very important. However most of the people use PCs for office applications like word processing and Internet browsing or e-mail. For these applications to perform optimally, whether the processor is a Pentium 4 or 1 is not significant.

What could make a difference in these circumstances (common use) is a PC which has enough RAM and good hard disk performance even if the processor is slightly outdated.

This is not to mean that the processor speed does not help PC for popular applications. The point is that the common office applications are not processor intensive and hence its affect on performance of those applications is not significant.

The fact is that normally the latest PCs come with the fastest processor, high capacity and high speed hard drives, lot of RAM, and a fast IO bus. Hence performance on all fronts makes a fast PC. However even if your PC is a Pentium II (Pentium 1 can be too old to improve) with good amount of RAM and fast hard disk, it will run almost as fast as a Pentium 4 (for common applications).

Exceptions will be as discussed earlier, processor intensive applications where the processor plays a major role in delivering performance.

Next : Hard Disk Factor.