Hardware Reference
In-Depth Information
The Pentium has a 32-bit address bus width, giving it the same 4GB memory-addressing
capabilities asthe386DXand486processors.ButthePentiumexpandsthedatabusto64
bits, which means it can move twice as much data into or out of the CPU, compared to a
486ofthesameclockspeed.The64-bitdatabusrequiresthatsystemmemorybeaccessed
64 bits wide, so each bank of memory is 64 bits.
Even though the Pentium has a 64-bit data bus that transfers information 64 bits at a time
into and out of the processor, the Pentium has only 32-bit internal registers. As instruc-
tionsarebeingprocessedinternally,theyarebrokendowninto32-bitinstructionsanddata
elements and processed in much the same way as in the 486. Some people thought that
Intel was misleading them by calling the Pentium a 64-bit processor, but 64-bit transfers
do indeed take place. Internally, however, the Pentium has 32-bit registers that are fully
compatible with the 486.
The Pentium, like the 486, contains an internal math coprocessor or FPU. The FPU in the
Pentium was rewritten to perform significantly better than the FPU in the 486 yet still be
fully compatible with the 486 and 387 math coprocessors. The Pentium FPU is estimated
