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From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: Fish Disk benchmark result
Message-ID: <24006@sun.uucp>
Date: Wed, 22-Jul-87 19:00:35 EDT
Article-I.D.: sun.24006
Posted: Wed Jul 22 19:00:35 1987
Date-Received: Sat, 25-Jul-87 02:01:05 EDT
References: <337@palladium.UUCP> <1638@xanth.UUCP>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 35

In article <1638@xanth.UUCP> kent@xanth.UUCP (Kent Paul Dolan) writes:
>No complaint against the Pal Jr., but just generically; with the state of the
>art in hard disk file transfer in the multiple megabytes per second range,
>why are we still down in the 10K's of bytes?

Ok, the spec for *any* ST-506 compliant drive is 5 megaBITS per second which
is 625K bytes per second. For ESDI drives the data transfer rate is 10 megaBITS
per second or 1.25 MegaBYTES per second. Disk to host adapters (like a lot of
SCSI thingies are) are usually capable of 1.2 megabyte capable with speeds
up to 4 megabytes/second when run 'synchronously'. They basically buffer up
the requested data in an on-board buffer and then squirt it out to you when
they have it all. Some of the new SCSI chips can go faster than this. The
Amiga's fastest transfer rate for bytes is about 600K bytes per second
( mov.b	(a0)+,(a1)+, jmp $ ) 1.2 meg if you transfer words. Disks with DMA
channels win big in this situation, although only 2X to 3X in raw transfer
rate so that is the absolute best you could hope for. Now tack on the over
-head of going from a request for a block in the file system and which is
translated into a device request which is translated into a physical request
which is copies back into the address space of the user and then notified.
It can be done faster, but don't ever expect 'multiple megabytes' per
second on a stock Amiga.

>  Speeds this low make disk based
>virtual memory a real loser (although at today's prices, extended address
>space ramdisk looks like a real possibility for virtual memory on PC's with
>limited personal memory, like the Amiga).

This doesn't parse for me. If you put RAM on the Amiga you can use it, are
you thinking about x86 type machines?



--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.