V and U Pipes

The integer pipe on the Pentium(R) processors dual pipe lines that executes only simple instructions.

The Pentium processor has two execution units: the U and the V pipes. When two instructions execute in parallel in the two pipes, the two instructions are considered to have paired.

The U-pipe can execute any instruction in the Intel(R) architecture while the V-pipe can execute only simple instructions.

When two instructions pair, the instruction issued to the V-pipe is always the next sequential instruction after the one issued to the U-pipe.

Simple instructions are entirely hardwired; they do not require any microcode control and, in general, execute in one clock. The exceptions are the ALU mem, reg and ALU reg, mem instructions which are three and two clock operations respectively. Sequencing hardware is used to allow them to function as simple instructions.

The following integer instructions are considered simple and may be paired:

• mov reg, reg/mem/imm

• mov mem, reg/imm

• alu reg, reg/mem/imm

• alu mem, reg/imm

• inc reg/mem

• dec reg/mem

• push reg/mem

• pop reg

• lea reg,mem

• jmp/call/jcc near

• nop