Processors Toolkit

Intel Prescott: the benchmarks

Kai Schmerer ZDNet Germany

Published: 02 Feb 2004

Caches, pipelines and power dissipation

The new Prescott CPU has more cache memory than its Northwood predecessor: both the L1 and the L2 caches are now twice as large as before, at 16KB and 1MB respectively. The Prescott chip also supports SSE3, which includes 13 extra PNI (Prescott New Instructions) commands. However, no applications yet support the new Prescott instructions, so they are currently irrelevant in practice.

Larger L1 and L2 caches should boost Prescott’s speed. The fact that this is mostly not the case -- Prescott is sometimes slower than previous Pentium 4 variants -- is because the chip’s command pipeline has been extended. Think of the pipeline as an assembly-line with several stages: the more stages assembly line has, the faster can it run, in theory. But if the parts (instructions and data) on the assembly-line are not in the correct order, the line must be stopped, corrected, and restarted.

Intel tries to balance this disadvantage with larger caches, which offer faster access to instructions and data than conventional main memory. But larger caches also mean that the power dissipation of the chip rises. The following tables give the results from a variety of PC systems.

Power dissipation (Watts, with Radeon 7000 GPU)

Motherboard	CPU	Idle (no load)	Maximum (full load)	Cool 'n' Quiet

Asus P4C800	P4 3.2E GHz (Prescott)	114	192	n/a
Asus P4C800	P4 3.2 GHz (Northwood)	76.5	144	n/a
Intel D875PBZ	P4 3.2E GHz (Prescott)	96.9	188	n/a
Intel D875PBZ	P4 3.2 GHz (Northwood)	62.7	127	n/a
Asus K8V Deluxe	Athlon 64 3400+	113	119	71.7
Asus K8V Deluxe	Athlon 64 3200+	106	115	70.6
Fujitsu Siemens D1607	Athlon 64 3400+	107	114	65
Fujitsu Siemens D1607	Athlon 64 3200+	101	105	62

A PC with standard components and the new Intel Prescott chip dissipates nearly 50 Watts more under full load than the same system with the previous-generation Northwood chip. In Idle(no load) mode, the Prescott system still uses nearly 35 Watts more.

Power dissipation (Watts, with Radeon 9800 Pro GPU)

Motherboard	CPU	Idle (no load)	Maximum (full load)	Cool 'n' Quiet

Asus P4C800	P4 3.2E GHz (Prescott)	165	248	n/a
Asus P4C800	P4 3.2 GHz (Northwood)	125	179	n/a
Intel D875PBZ	P4 3.2E GHz (Prescott)	145	242	n/a
Intel D875PBZ	P4 3.2 GHz (Northwood)	113	182	n/a
Asus K8V Deluxe	Athlon 64 3400+	167	174	120
Asus K8V Deluxe	Athlon 64 3200+	158	168	120
Fujitsu Siemens D1607	Athlon 64 3400+	157	166	114
Fujitsu Siemens D1607	Athlon 64 3200+	148	156	110

A high-end system with a 256MB Radeon 9800 Pro GPU and Prescott CPU dissipates nearly 250 Watts under full load. At nearly 200 Watts, the same system with the Northwood Pentium 4 uses considerably less power. AMD’s Athlon 64 3200+ under full load dissipates nearly 80 Watts less than the Prescott system. But the Athlon 64 has a disadvantage: motherboard manufacturers do not yet support all of the AMD chip’s power saving modes, which explains the comparatively small differences between no-load operation and full load. Only if AMD's Cool ' n ' Quiet mode is activated does the Athlon 64's power dissipation drop significantly.