The Unabridged Pentium 4 IA32 Processor Genealogy

The IA32 Data Register Set Was Small

General

Refer to Figure 35-4 on page 849. The IA register set implemented in pre-P6 processors included very few registers that the programmer could use to hold, test and manipulate data items. The small number of data registers permitted the processor (and the programmer) to keep only a small number of data operands close to the execution units where they can be accessed quickly. Rather, the programmer was forced to write back the contents of one or more of the processor's data registers to memory when he or she needed to read additional data operands from memory to be operated on. Later, when the programmer required access to the original set of data operands, they must again be read from memory (perhaps ...