PC Hardware in a Nutshell, 3rd Edition

Processor Architecture

Clock speeds increase every year, but the laws of physics limit how fast CPUs can run. If designers depended only on faster clock speeds for better performance, CPU performance would have hit the wall years ago. Instead, designers have improved internal architectures while also increasing clock speeds. Recent CPUs run at more than 650 times the clock speed of the PC/XT’s 8088 processor, but provide 6,500 or more times the performance. Here are some major architectural improvements that have allowed CPUs to continue to get faster every year:

Wider data busses and registers

For a given clock speed, the amount of work done depends on the amount of data processed in one operation. Early CPUs processed data in 4-bit (nibble) or 8-bit (byte) chunks, whereas current CPUs process 32 or 64 bits per operation.

FPUs

All CPUs work well with integers, but processing floating-point numbers to high precision on a general-purpose CPU requires a huge number of operations. All modern CPUs include a dedicated FPU that handles floating-point operations efficiently.

Pipelining

Early CPUs took five ticks to process an instruction—one each to load the instruction, decode it, retrieve the data, execute the instruction, and write the result. Modern CPUs use pipelining, which dedicates a separate stage to each process and allows one full instruction to be executed per clock cycle.

Superscalar architecture

If one pipeline is good, more are better. Using multiple pipelines allows multiple ...