Author: Matt Taylor
Date: 14:40:13 12/04/02
Go up one level in this thread
On December 04, 2002 at 13:32:01, Vincent Diepeveen wrote: >On December 04, 2002 at 11:42:17, Matt Taylor wrote: > >>On December 04, 2002 at 10:43:59, Vincent Diepeveen wrote: >> >>>On December 04, 2002 at 10:21:08, James T. Walker wrote: >>> >>>>On December 04, 2002 at 08:00:35, martin fierz wrote: >>>> >>>>>hi, >>>>> >>>>>i'm on the lookout for a new PC for endgame database computations. i'll probably >>>>>be buying a lot of ram, 2-3GB. i see that there is a big price difference >>>>>between DDRAM and SDRAM. IIRC the main difference is that you get a larger >>>>>bandwidth, but about the same latency with DDR - so i suppose i'm better off >>>>>buying SDRAM for my application. any opinions of the experts? >>>>> >>>>>thanks in advance >>>>> martin >>>> >>>>For what it's worth: I purchased one stick (256M) of DDR ram to compare to my >>>>cheap SDRAM. I found no noticable difference in chess performance (just price). >>>> I did not do any extensive testing. I simply compared Fritz marks. I suspect >>>>that in the future most motherboards will not accept the SDRAM. >>>>Jim >>> >>>I see a big difference. 64 versus 32 bytes cache lines matters >>>a lot for DIEP and all software that doesn't fit within L1 cache. >>> >>>Best regards, >>>Vincent >> >>Cache line size is a part of the CPU, not the ram. There are a number of >>transitional products, both P4 and Athlon, that accept both SDRAM and DDR SDRAM. >>(However, I have never heard of anyone happy with these products.) > >the P4 ended up being a lot faster for DIEP when i tested a p4 with ddr ram >isntead of RDRAM. > >P4 with ddr ram (northwood) is like 1.5 : 1 for a K7 >used to be 1.7 : 1 to a k7 with rdram. > >So 1.7 Ghz P4 rdram == 1.0Ghz K7 for DIEP > 2.4 Ghz P4 ddr == 1.6Ghz K7 for DIEP (both ddr). > >DDR is a big step forward!! > >i don't know where the processor gets 64 bytes instead of 32 bytes in >the design. I just know it gets 64 bytes, versus SDRAM 32. > >Best regards, >Vincent By your figures, DDR SDRAM speed compared to RDRAM speed on a P4 platform is 1.7/1.5 = 113%. I wouldn't call 13% a "big step forward." This also makes the assumption that both the 1 GHz K7 and 1.6 GHz K7 run equally fast. The 1 GHz K7 is the Thunderbird chip. The 1.6 GHz K7 is the AthlonXP 1900. Thunderbirds report that they are model 4, whereas AthlonXP 1900 may report model 6 (palomino) or 8 (thoroughbred). Model 4 and Model 6 are not the same thing, and they differ in MORE than just instructions. One change that I have observed is that the model 6 L2 cache is slightly faster. Other timings have probably changed, too. I will also mention that a 2.4 GHz P4 is the P4 Northwood. The 1.7 GHz P4 may be a Northwood, but I suspect (based on the numbers) that it was probably the older Williamette. The major difference is that the P4 Williamette had a smaller L2 cache (256KB instead of 512KB). I will have to agree with Jeremiah, here. If DDR SDRAM is faster, DIEP is latency-dependant. If RDRAM is faster, it would be bandwidth-dependant. I have measured pc800 RDRAM bandwidth on one of my systems, and it exceeds theoretical bandwidth on any standard part DDR SDRAM. (I am not completely sure, but I don't think pc2700 is part of the JDEC specification.) I am not sure what you're saying about 64-bytes vs. 32-bytes, but I assure you that SDRAM-based, DDR-based, and RDRAM-based P4s all have the cache line size. The information is available from the cpuid instruction. The vector is documented in both Intel and AMD literature, but off-hand I don't know which vector it is. There are many utilities, especially for Windows, that will give this information. I -believe- wcpuid is one such utility, but I usually end up writing a program every time I get curious about cpuid information. If you would like, I will write such a program and post it. -Matt
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