Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!decwrl!shelby!rutgers!mcdchg!laidbak!botton
From: botton@i88.isc.com (Brian D. Botton)
Newsgroups: comp.sys.3b1
Subject: Re: Seperate HD & FD controllers?
Message-ID: <1991Feb14.004519.1762@i88.isc.com>
Date: 14 Feb 91 00:45:19 GMT
References: <528@trux.UUCP>
Sender: usenet@i88.isc.com (Usenet News)
Organization: INTERACTIVE Systems Corporation, Naperville, IL
Lines: 29

In article <528@trux.UUCP> car@trux.UUCP (Chris Rende) writes:
>I've noticed that the 3b1 can only access one disk at a time. I.e., during
>floppy disk accesses the hard disk is idle - and vice versa. (Especially
>evident during floppy formatting).
>
>However, I've seen references to seperate HD and FD controller chips.
>
>I suspect that there is some common circuitry between the HD and FD interfaces
>which prevents them from operating independantly. (IBM PC clones have seperate
>controllers which can work independantly - 3b1's don't seem to have that
>luxury).
>
>Is this true?
>

  Yes this is true.  The common circuitry is the DMA address and data chips
on the mohterboard.  Those chips are single channel and thus cannot do
transfers to/from two devices at once.  This could be solved by putting
a floppy controller in one of the expansion slots and giving it it's own
DMA controller.  Then the motherboard chips and the expansion chips whould
just have to do arbitration, which is provided for.
  As it stands now there is no way to make the floppy and hard disks work
together better.

--
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