Date: Sat, 11 Feb 95 12:23:35 -0800 From: hasty@netcom.com To: hackers@FreeBSD.org Subject: a little bit on bus speeds Message-ID: <199502112023.MAA12495@netcom14.netcom.com>
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If we can at least gather low level performance of systems it may help the users or future users to obtain maximum performance out their systems. I know that when I get ready to upgrade my Pentium most likely I will get an ASUS motherboard :) I found this in comp.windows.x.i >Kendall Bennett (rcskb@minyos.xx.rmit.EDU.AU) wrote: >: Wrong. VLB will never be dead, as long as there are still 486 boxes >: around to run it. >: There is also another area that just about everyone has neglected to look >: into regarding PCI - its performance. Contrary to popular opinion (and >: to what Intel will tell you), PCI local bus video cards have only half >: the raw framebuffer performance of exactly the same VLB card. You may >: find this difficult to believe (I know I did), but we test and develop >: software on over 60 different video cards, and PCI cards consistently >: turn in a maximum of 15-16Mb/s transfer in a Pentium P90 PCI box >: compared to 28-30Mb/s for _exactly_ the same chipset on a 486DX2/66 VLB >: box. You should be able to boost the performance to about 40 MB/s with a good PCI main board. You have simply rediscovered the well known (at least to c't readers) fact that the Opti Pentium chipset has awful PCI performance. The 15 MB is typical for this chipset. Good chipsets reach 30 to 40 MB/s for VLB and up to 65 MB/s for PCI chips together with Intel CPUs. The DEC Alpha CPU with integrated PCI bridge reaches the full 130 MB/s performance of the PCI bus specification. >I find it hard to belive also, but I'm sure you're right. VLB really is local >bus, it's like connecting your video hardware straight to the CPU. PCI is >something completely different, it's more like a minicomputer bus. It _is_ >fast but it will never be as fast as VLB because of the extra facilities it >offers. You can't have extra facilities and maximum performance. VLB is a localbus designed to work together with a 486 CPU. The experience above shows that it does not work well with the Pentium CPU. c't found that identical (except for bus type) video cards got identical (within a few percent) performance when they were compared in a good PCI/VLB 486 Mainboard (Asus VIP with a bus performance of 60 MB/s if run as a pure PCI board and 40 MB/s if run as a VLB board.) btw c't is the leading german pc magazine for in depth technical information. And they tend to test just about every PCI main board. Andreas -- * Andreas Helke, Institut fuer molekulare Genetik, Universitaet Heidelberg ** Im Neuenheimer Feld 230, 69122 Heidelberg, Germany *** WWW: http://orion.mgen.uni-heidelberg.de **** FTP: orion.mgen.uni-heidelberg.de - filemanager and Unix tools for DOS ----------------------------- Enjoy, Amancio
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