Date: Fri, 7 Apr 1995 13:37:25 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: gurney_j@efn.org (John-Mark Gurney) Cc: hackers@FreeBSD.org Subject: Re: PCI/EISA/ISA performance Message-ID: <199504072037.NAA08323@gndrsh.aac.dev.com> In-Reply-To: <Pine.SUN.3.91.950407132117.7247A-100000@haus.efn.org> from "John-Mark Gurney" at Apr 7, 95 01:25:31 pm
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>
> On Wed, 5 Apr 1995, Rodney W. Grimes wrote:
>
> > >
> > > On Tue, 4 Apr 1995, Rodney W. Grimes wrote:
> > >
> > > [...]
> > >
> > > > ISA does not have a specified clock frequency, I have seen it running
> > > > as fast as 16Mhz. Most boards die above 10Mhz, but some of the more
> > > > specialized industrial applications boards are spec'd upto 12 or 16Mhz.
> > >
> > > actually... I think that I am currently running my isa bus at 16mhz... I
> > > think for a while I was tring to run the bus at 20... but it was falling
> > > over and wouldn't boot... and this is with ne2000 clone cards... and
> > > other generic cards...
> >
> > I suspect you are off by a factor of 2, I haven't seen a ``generic''
> > card of any sort that would run at 12Mhz, let alone 16Mhz. IDE controllers
> > are famous for falling over above 10Mhz (ever done a transmission line
> > simulation of an unterminated ribbon cable :-)).
>
> also... I am running a VL/Bus IDE controler if that makes any difference...
Yea, it can, your IDE disk is not on the ISA bus at all, it is on the
VLB bus.
> > If your basing this on a CPUCLK/N value and you think CPUCLK is 66 Mhz
> > because that is what the crystal is you have made a mistake. Can you
> > tell me what CPU chip you have, what speed is it, and what your BIOS
> > says about ISA bus clock speed settings (list all the valid values).
>
> ok... I have a Intel 486/33DX that I am running at 40Mhz with a cpu
> cooling fan attached... I know that it is running at 40Mhz as I set the
> jumpers (mb used os chip) and sysinfo returns it... I have the CLK set
> to CLK2/2....
^^^^ CLK2 is often 1/2 the cpu clock, CLK2 is not the same as CPUCLK.
So CLK2/2 would be 10Mhz for your system. The only real way to find
this out is to hang a scope on the bus and look at the timing.
> > Also what BIOS is it? AMI, Pheonix, AWARD or someone else.
>
> it is an AMI bios...
>
> > Realize a 486DX33, 486DX2/66 and 486DX4/100** all run with a CPUCLK of
> > 33 Mhz. A 486DX25, 486DX2/50 and 486DX4/75 all run with a CPUCLK of
> > 25 Mhz. A 486DX50 runs with a CPUCLK of 50Mhz.
>
> yup... so my computer is running at 40mhz... no double or anything...
>
> > ** The 486DX4/100 can also be run with a CPUCLK of 50Mhz if the motherboard
> > supports the 1:2 bus/core ratio jumper.
>
> kool... might want to look into this :)
A DX4 running externally at 50Mhz An internally at 100Mhz should do
better than a DX4 running externally at 33.33MHz and internally at 99.99Mhz.
> > Pentium processors are similiar except the CPUCLK values are 50Mhz, 60Mhz
> > and 66Mhz.
>
> possibly 90Mhz?? or is that achived some other way?
THe 90Mhz part runs externally at 60Mhz and internally at 90Mhz (2:3 bus:core
ratio). Likewize the P54C-100 runs externally at 66Mhz and internally at
100Mhz. Accourding to some data I have ``later Pentium CPUs will support
the 1:2 ratio, which will allow a 100Mhz Pentium to run with an external
clock speed of either 50 or 66Mhz''.
>
> thanks for the info though... TTYL...
Your welcome...
--
Rod Grimes rgrimes@gndrsh.aac.dev.com
Accurate Automation Company Custom computers for FreeBSD
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