Date: Tue, 4 Apr 1995 19:50:19 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: julian@tfs.com (Julian Elischer) Cc: freebsd-hackers@FreeBSD.org Subject: Re: PCI/EISA/ISA performance Message-ID: <199504050250.TAA09440@gndrsh.aac.dev.com> In-Reply-To: <m0rwJ3u-0003vzC@TFS.COM> from "Julian Elischer" at Apr 4, 95 05:35:10 pm
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> > > Whose thumb are you looking at? 8-). > > > > VLB has a speed limit of 40MHz (typical cards die > 33MHz, though) > > PCI has a speed limit of 33MHz > > ISA has a speed limit of 12MHz > > EISA has a speed limit of bus clock (mine runs at 50MHz) > hmmmm (quick check of EISA SPEC) > no, BUS speed on EISA != CPU clockspeed.. > > 1.3 Synchronous Data Transfer Protocol > [bla bla]....Burst cycles with up to 33MB/s data transfer rate. > > table in section 1.4.2 > [chop] > 16bit............16.5MB/sec.........EISA cards only > 32bit............33MB/sec...........EISA cards only > > 2.1.2 > BCLK ... [bla bla]... frequency between 8.333 MHz and 6MHz.....[bla bla] Humm.. what version of the EISA spec is this, mine is ``preliminary'' and it says 8 Mhz +/- 5%. They must have had to relax it on the lower end for some reason :-(. > PLUS > many other references that state that the EISA bus is based around the BCLK > signal.. > > > > > > > > > > For instance, a DX4/75 PCI has the same bus transfer rate as a DX/50 EISA. > > hmm probably the PCI is faster, because most EISA transfers take a number > of clock cycles... So do PCI transfers, infact it is almost the same number of clock cycles per transfer as EISA is. I dug it out once, but don't feel like doing it again right now. PCI is mainly faster because you usually run it at 25 or 33 Mhz in all known implementations. Yes, the spec says DC to 33Mhz, but every board I have ever seen runs the PCI bus at either some frequency directly related to the CPU frequency, or on it's own 33 Mhz crystal. The above sited DX4/75 is probably running the PCI bus at 25 Mhz, which would be 3 times as fast as the DX/50 EISA bus would run. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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