Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!gem.mps.ohio-state.edu!ginosko!uunet!cbmvax!jesup
From: jesup@cbmvax.UUCP (Randell Jesup)
Newsgroups: comp.arch
Subject: Re: *big iron*
Message-ID: <7997@cbmvax.UUCP>
Date: 25 Sep 89 22:43:09 GMT
References: <7981@cbmvax.UUCP> <11538@burdvax.PRC.Unisys.COM> <22488@cup.portal.com>
Reply-To: jesup@cbmvax.UUCP (Randell Jesup)
Organization: Commodore Technology, West Chester, PA
Lines: 37

In article <22488@cup.portal.com> cliffhanger@cup.portal.com (Cliff C Heyer) wri
tes:
>>much of the CPU was chewed up while these transfers were underway? 
>
>If you are running single tasking OS (NOT UNIX), who cares? You have to
>wait until the transfer is done anyway, so it might as well be as fast as 
>possible. Hopefully SCSI does DMA while the CPU is busy elsewhere(comments
>please..)

	Well, I don't want to sound commercial here, but the Amiga (referenced
by the above quote) is multitasking.  I don't have any cpu benchmarks run 
during intense disk I/O handy, but I'll post some when I get time to dig them
out.  BTW, most Unix machines are handicapped by the "standard" unix fs/disk
cache.  This cache requires them to do single-block reads, while under AmigaDos
the filesystem can ask for large blocks and have it transfered by DMA directly
from disk to where the application's read goes to.  This works quite well 
with SCSI.

	On the same hardware, the Amiga Unix (Amix) gets signifigantly lower
I/O throughput because of this, and the extra transfer via CPU to the
application's buffer.

>>I have seen I/O rates at 4000-5000 i/os per second
>>where the CPU is less than 75% utilized.  How many SCSI channels do these
>>micros support? 
>
>One I think. Comments others please!!!!!

	You can add up to 5 SCSI controllers to an amiga (limited by the 5
slots).  The other limit is the bus bandwith of the current Amiga, at about
3.5 Mb/s.  Of course, each scsi controller can talk to at least 7 drives, if
you don't use multi-lun drives.

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.cbm.commodore.com  BIX: rjesup  
Common phrase heard at Amiga Devcon '89: "It's in there!"