Intel settles Pentium 4 benchmark fudging suit

October 31, 2014 | 11:14

Tags: #cpu #legal #microarchitecture #netburst #pentium-4 #pipeline #semiconductor

Companies: #hp #intel

A long-running lawsuit against Intel which accused the company of massaging the performance figures for its Pentium 4 CPUs has come to a head, resulting in US customers receiving a partial rebate of $15 by way of compensation.

The launch of the Pentium 4 was a pivotal moment for Intel. The processor was based on a fundamentally new microarchitecture dubbed NetBurst, internally known as P68 and designed to replace the ageing P6 microarchitecture used from the introduction of the Pentium Pro through to the Pentium III. Compared to its 10-stage predecessor, NetBurst featured a 20-stage pipeline dubbed Hyper Pipeline Technology, increasing to 31 stages with the Prescott implementation. This allowed Intel to hit higher clock speeds, but at the cost of a loss in instructions per cycle (IPC). Coupled with double-pumped arithmetic and logic units (ALUs) and a slower dedicated shift/rotate execution unit, the result was an architecture that was easily outperformed by its predecessor - and, worse, chips from Intel's main rival AMD - at equivalent clock speeds.

The goal behind NetBurst was to create an architecture that would scale to clock frequencies as high as 10GHz, speeds at which the raw throughput of the chips would more than compensate for its decreased IPC. Sadly, things didn't work out that way: rather than 10GHz, Intel barely made it to 3.8GHz before the power required and the heat generated by the chips became unmanageable. For its next-generation Pentium M mobile processors, the company would abandon NetBurst and return to the P6 microarchitecture before ditching NetBurst altogether and creating a more P6-inspired microarchitecture, still in use today, dubbed Core.

In short: the Pentium 4 was a colossal and costly mistake for Intel. A class action suit brought against Intel and HP claimed that the companies knew from the outset that the Pentium 4 was too slow and ran too hot, and that the companies collaborated on customised benchmarks - WebMark 2001 and SYSmark 2001 - which would concentrate on the things the chip was good at to paint a far rosier picture of its performance compared to the previous generation Pentium III processors which it replaced.

The Register was the first to notice that said case has finally concluded and found in the favour of the class, with the result that Intel is being forced to refund any customers who bought a Pentium 4 PC between the 20th of November 2000 and the 30th of June 2002. No receipt is required to claim, but before you get too excited be aware that the class is exclusively open to residents of US states bar Illinois and will result in a not-exactly-massive $15 payout.

More details are available on the official website.
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