Date: Sat, 02 Aug 1997 02:49:54 -0500 From: Tony Overfield <tony@dell.com> To: FreeBSD Mailing List <freebsd@atipa.com>, Tom Samplonius <tom@sdf.com> Cc: hackers@FreeBSD.ORG Subject: Re: Pentium II? Message-ID: <3.0.2.32.19970802024954.006dfb1c@bugs.us.dell.com> In-Reply-To: <Pine.BSF.3.91.970729115630.9952A-100000@dot.ishiboo.com> References: <Pine.BSF.3.95q.970729100017.26870A-100000@misery.sdf.com>
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At 08:29 AM 7/29/97 -0600, FreeBSD Mailing List wrote: >> > The PPro is still faster for a true 32-bit OS, primarily due to the fact >> > that the L2 is 1:1 with the CPU clock. On the Pentium II, the L2 caching >> > is at 1/2 the CPU clock. On Tue, 29 Jul 1997, Tom Samplonius wrote: >> >> Not, not quite. At the same clock rate, the PPro is faster, but the PII >> can operate at 266mhz, while the PPro maxes at 200mhz. Whoa! Not so fast... Conspicuously overlooked by this whole Pentium II thread is a simple, yet very important, detail. The Pentium II level-one (L1) cache is twice the size of the one in the Pentium Pro. That means you've got a 16+16 KB L1 cache running at up to 300 MHz. This makes a proper comparision a little more complicated because the relative performance of the two processors, even when using the bogus "same clock rate" argument, is dependent on the specific code sequences being run. Since the hit rate of the L1 cache is usually much higher than that of the L2 cache, the effect of the slower L2 cache in the Pentium II is usually offset by the beneficial effect of not having to access it. So even at the same clock rate, the Pentium II can run faster than the Pentium Pro. - Tony
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