Date: Mon, 14 Oct 1996 21:33:42 -0700 From: Chris Browning <cbrown@aracnet.com> To: freebsd-smp@freebsd.org Subject: Re: Which is the better deal Message-ID: <32631426.1B0F@aracnet.com> References: <199610141529.IAA13106@GndRsh.aac.dev.com>
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Rodney W. Grimes wrote: > > > In message <Pine.OSF.3.95.961014095643.1731B-100000@protocol.eng.umd.edu>, Chuc > > k Robey writes: > > >I have two options available to me, in getting the twin cpus for a Pentium > > >Pro smp board. I can't afford the price of 200MHz cpus, they gone past > > >$900 each, but I can get either: > > > > > >166 MHz with 512 K Cache or > > >180 MHz with 256 K Cache > > > > > >I intend this for FreeBSD only, don't bother about things like MS > > >software. I can get either for less than $550 each, what's your guys > > >feelings about which might be better? > > > > > >BTW, this would be on a 64MB system, with 4 GB of scsi disk. > > > > I'd take the 512K cache any time. The PP seems so cache starved to me > > that I have decided never to by a 256k version for my own money. > > And in additon to phk's reason for the 512K version I will add that this > is a 166 chip above, and that is externally clocked at 66MHz, giving > a faster memory bus. Stay away from the ppro 150 and 180 for the simple > fact that it has an external memory bus clock of 60Mhz. I concur with the above statement. The 66MHz host bus for the 166MHz is a definiate advantage. It increases both the memory and I/O bandwidth. Since you are looking at a dual processor system, the larger cache part will also have another effect... it will lower the bus contention. In a UP system, there is only one processor, so bus contention is not as much of a problem. This is why you may not see as much of an improvement in performance, but I haven't done any experiments. With a 2+ processor system, you have a whole new ball game. Now there are 2+ processor all trying to access memory, I/O, and perform consitency operations. All this requires host bus time. A larger cache will mean that the processor is more likely to find information in its L2 cache and will not have to go out on the bus. It is pretty simple, really. There are numerious papers out there explaining this fact. Enjoy! Chris Disclaimer: I don't speak for anyone :-) -- -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.2 mQCNAzJSHeUAAAEEAKQrvftlb+sbnw0hA5vW2Orzq3rCGypldkYxRdXhx0yWx/dY U2PMqxgTwlOeQl3wA1IIWGMaHhbpPp0IegkOm9HIHEvc2G8uWywN5OvkaVFyuIHL juZ6VSem3cd63bqpNe3ZWtWwQdjFivm+YNeQveV220eTPfTuvbz7xZq+b9WZAAUR tCtDaHJpcyBTaGVybWFuIEJyb3duaW5nIDxjYnJvd25AYXJhY25ldC5jb20+ =NxsF -----END PGP PUBLIC KEY BLOCK-----
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