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From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.hardware
Subject: Re:  GVP Trade-in
Keywords: SCSI, GVP
Message-ID: <14069@cbmvax.commodore.com>
Date: 29 Aug 90 22:45:40 GMT
References: <589@oregon.oacis.org> <38CP09P@dri.com> <02048.002057@thiger.UUCP> <552@DIALix.UUCP>
Reply-To: jesup@cbmvax (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 44

In article <552@DIALix.UUCP> bernie@DIALix.oz.au (Bernd Felsche) writes:
>Another consideration is the speed of the filesystem.  AmigaDOS
>isn't exactly renowned for filesystem performance, even with FFS.
>It involves significant CPU cycles to convert the raw SCSI data into
>something which DOS presents to the user (FFS is a _lot_ better than
>the original FS).  When you measure the average transfer speed, the
>filesystem (and trackdisk.device) get in the way and give you a
>distorted view of what the hardware _can_ do under ideal
>conditions.

	Actually, it does far better at things like that than say, Unix, does.
There's been quite a bit of discussion at times in comp.arch about filesystem
speeds, and even a 68000 amiga with a DMA controller can keep up there with
pretty high-power Unix boxes.  One of the reasons is that FFS allows us to do
direct transfers to the end destination, instead of having to xfer to a buffer
pool and then cpu copy to destination (like most unix implementations).

	If you want to see what they can do, check out floppies under 2.0
trackdisk and FFS.  I've seen >20K/sec reads.  Note that the theoretical
maximum is ~24K/sec, not including seek and settle times or any other overhead.
Trackdisk does 22K/sec via the device interface (including seek/settle) under
2.0.

	Even on a 68000, sustained transfer speed is limited by disk speed
in most cases, not processor handling of the data.  A 680{2,3}0 will improve
rates, but not immensely.

	Unix FS's are faster at some things, like reading directories (assuming
the directories aren't too large - for large directories, AmigaDos is faster
at finding a file).  However, FFS is no slouch at this.  My directory listings
are scroll speed limited.

>bernie
>(Real computers have flashing lights, front panel switches, 8K RAM  and
>hard-sectored floppies - anybody recognize this?)

	Yes, except that's randomly-accessible tape drives, none of those
new-fangled disk things.  To boot them, you have to toggle in a boot
module in octal and run it.  Also, they have 12-bit words. ;-)

-- 
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!"