Compaq 850 manual Cpu Fpu, Fsb

Technical Reference Guide

Figure 3-1 illustrates the internal architecture of the Pentium 4 processor.

			Pentium 4 Processor
Branch			Execution	128-bit
Prediction			Trace Cache	Integer
		CPU		FPU
Rapid Exe. Eng.			Out-of-
			Order Core	FSB
	ALUs
				I/F

L1

Data

Cache

256-KB

8-Way

L2

Adv.

Transfer

Cache

ALU Speed: 2.8 GHz w/Pentium 4 @ 1.4 GHz 3.0 GHz w/Pentium 4 @ 1.5 GHz

Core Speed: 1.4 GHz w/Pentium 4 @ 1.4 GHz

1.5GHz w/Pentium 4 @ 1.5 GHz

FSB Speed: 400 MHz (Data transfer rate)

Figure 3–2.Pentium 4 Processor Internal Architecture

The Pentium 4 increases processing speed with higher clock speeds made possible with hyper- pipelined technology that can handle significantly more instructions at a time. Since branch mis- predicts would result in serious performance hits with such a long pipeline, the Pentium 4 features a branch prediction mechanism improved with the addition of an execution trace cache and a refined prediction algorithm. The execution trace cache can store 12k micro-ops (decoded instructions dealing with branching sequences) that are checked when re-occurring branches are processed. Code that is not executed (bypassed) is no longer stored in the L1 cache as was the case in the Pentium III.

The out-of-order core features Advanced Dynamic Execution, which provides a large window (126 instructions) for execution units to work with. A more accurate branch prediction algorithm, along with a larger (4-KB) branch target buffer that stores more details on branch history results in a 33% reduction in branch mis-predictions over the Pentium III.

The L1 data cache features a low-latency design for minimum response to cache hits. The 256-KB advanced transfer L2 cache features a 256-bit (32-byte) interface operating at processing speed. The L2 cache of the 1.5 GHz Pentium 4 can therefore provide a transfer rate of 48 GB/s.

The combined improvements of the Pentium 4’s CPU core the rapid execution engine’s ALUs to operate at twice the processing frequency to handle the steady stream of instructions.

The front side bus (FSB) of the Pentium 4 uses a 100-MHz clock but provides Quad-pumped data transfers. While the Pentium III could transfer 8 bytes of data on a 133-MHz clock cycle the Pentium 4 can transfer 32 bytes of data on a 100-MHz clock cycle for a throughput rate of 3.2 GB/s, balancing the performance of the dual-Rambus memory subsystem. Address information is transferred at a 200-MHz rate.

Compaq Deskpro EXS and Workstation 300 Personal Computers 3-3

Featuring the Intel Pentium 4 Processor

First Edition - December 2000