Modern computer systems built from the most sophisticated microprocessors and extensive memory hierarchies achieve their high performance through a combination of dramatic improvements in technology and advances in computer architecture. Advances in technology have resulted in exponential growth rates in raw speed (i.e., clock frequency) and in the amount of logic (number of transistors) that can be put on a chip. Computer architects have exploited these factors in order to further enhance performance using architectural techniques, which are the main subject of this book.

Microprocessors are over 30 years old: the Intel 4004 was introduced in 1971. The functionality of the 4004 compared to that of the mainframes of that period (for example, the IBM System/370) was minuscule. Today, just over thirty years later, workstations powered by engines such as (in alphabetical order and without specific processor numbers) the AMD Athlon, IBM PowerPC, Intel Pentium, and Sun Ultra SPARC can rival or surpass in both performance and functionality the few remaining mainframes and at a much lower cost. Servers and supercomputers are more often than not made up of collections of microprocessor systems.

It would be wrong to assume, though, that the three tenets that computer architects have followed, namely pipelining, parallelism, and the principle of locality, were discovered with the birth of microprocessors. They were all at the basis of the design of previous (super)computers. The advances in technology made their implementations more practical and spurred further refinements.