Author: Eugene Nalimov
Date: 22:14:44 10/26/01
Go up one level in this thread
On October 27, 2001 at 01:04:04, Eugene Nalimov wrote: >On October 27, 2001 at 00:24:45, Robert Hyatt wrote: > >>On October 26, 2001 at 23:04:56, Tom Kerrigan wrote: >> >>>On October 26, 2001 at 22:33:47, Robert Hyatt wrote: >>> >>>>On October 26, 2001 at 21:43:35, Tom Kerrigan wrote: >>>> >>>>>On October 26, 2001 at 21:19:11, Robert Hyatt wrote: >>>>> >>>>>>>"The floating point unit has 32 32-bit non windowed registers, which must be >>>>>>>saved on a per-context basis" >>>>>> >>>>>>Memory fails as age increases, apparently. :) >>>>> >>>>>Maybe FPUs are studied in a semester of comp org that you didn't teach. >>>> >>>>Actually FPUS really aren't touched on in a one-semester architecture >>>>course. With pipelines, cache, memory management, plus a few specific >>>>architectures, time runs out pretty quickly. >>>> >>>> >>>>> >>>>>>There is only _one_ data path _into_ the CPU. I was originally talking about >>>>>>the 64 bit chunks that can flow into the cpu from outside. And that is a >>>>>>real bottleneck on Intel boxes, still. IE you can't possible load >>>>>>instructions, int data, and fp data, fast enough if you have to use memory. >>>>>>And the classic SPEC benchmarks tend to stream data like crazy... >>>>> >>>>>This is going off on a tangent; Intel's decision to use a 64-bit FSB is almost >>>>>certainly based on price/performance goals and not the bitiness of any processor >>>>>internals. The FSB is 64-bit, the L2 bus is 256-bit, the SSE datapaths are >>>>>128-bit, the x87 FPU is 64-bit (I believe), the core is 32-bit... all design >>>>>decisions determined by any number of factors. It would have been a small amount >>>>>of work to make the P4 a 64-bit chip instead of a 32-bit chip; this wasn't done >>>>>almost certainly because the need for 64-bit is too small to justify a new >>>>>instruction set. Or they didn't want the P4 to compete directly with the Itanic >>>>>(and kick it in the nuts). AMD seems pretty happy to go the 64-bit route with >>>>>x86-64 and minimal changes to the Athlon design. >>>>> >>>>>-Tom >>>> >>>>In any case, I still believe the _driving_ force for 64 bit machines is not >>>>memory, since I still don't see any > 4gig machines lying around. But I do >>>>see a lot of people comparing FP performance to choose their next >>>>high-performance workstation. The best example here is still the Cray. With >>>>a 32 bit address bus, but a huge data path. Ditto for comparing the processors >>>>made by everybody, to the intel X86. Everybody has done 64 bit processors, >>>>but hardly any go beyond 2^32 address lines. Seems to me that it is for >>>>reasons other than address space, based on that... >>> >>>Well, I know that a lot of noise was made even a few years ago about certain OSs >>>not supporting memory over 2GB. I also know that many of your nicer [non-Intel] >>>MP systems ship with many, many GB of RAM. >> >>Sure. And today, when you ask about large-memory systems, the topic generally >>drops around to the Cray machines, particularly the Cray-2, and now the C90/T90 >>with 32 gigs (4 gigawords). > >Wrong. Probably that's true in the academia and HPC world, but I posted here >some numbers about relative sizes of HPC and DB markets. I can assure you that >*here* nobody talks about Cray. Or almost anybody -- one of our team members >remembers with nostalgia times where he worked with Crays... > >>Most of the "MP systems" are not shared memory, so with 128 processors, and >>128 gigs of ram, you still only need 30 bits of address space. (IE IBM SP >>for one, CM5 for another, big alphas for another, etc.) > >That depends. On HPC -- yes, you are right, as you can modify the algorithm to >run on MIMD machine. But in the DB world you can see all types of animals. Just >go to the www.tpc.org, and look at the some hardware configurations. Here is the >example: >http://www.tpc.org/results/individual_results/Fujitsu/pw2000.082801.128cpu.es.pdf >-- 128CPUs, 256Gb of *shared* RAM. > >>> So somebody out there needs it. It's >>>possible that the demand has been low due to memory prices, but with prices in >>>the basement right now, I expect many more people will want > 4 GB RAM. I only >>>have 512MB myself, but I know many people who are up past 2 GB already. >>> >>>-Tom >> >>I know a _few_ that are at 2 gigs. And I know a couple that are using 4 gigs. >>So the demand is there in very low levels. And no doubt it will grow as >>systems and apps grow. But note that 64 bit architectures were around in >>the middle 60's... (60 and 64 bits). They were obviously done for something >>_other_ than address space... > >Bob, please give up :-). Tom and I know *a lot* about databases. Industry needs >large databases [or at least willing to pay big money for those], and large >databases need large address spaces. > >MS creates Win64 before there is demand for large address spaces *outside* HPC. Sorry, of course I meant "because", not "before". Time to go to bed... Eugene >Eugene
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