Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!apple!oliveb!amiga!cbmvax!jesup
From: jesup@cbmvax.UUCP (Randell Jesup)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Floppy speed.
Message-ID: <6407@cbmvax.UUCP>
Date: 28 Mar 89 19:38:46 GMT
References: <9853@polyslo.CalPoly.EDU> <67@microsoft.UUCP>
Reply-To: jesup@cbmvax.UUCP (Randell Jesup)
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 26

In article <67@microsoft.UUCP> w-colinp@microsoft.uucp (Colin Plumb) writes:
>cknight@polyslo.CalPoly.EDU (King Claudius) wrote:
>> What is the speed of the standard 3.5" Amiga drive in bytes per second?
>> 
>Assuming both spin at 300 RPM, both take 0.2 seconds to read a track.
>Because the Atari puts 9x512=4608 bytes on a track, that's 23040 bytes
>per second.  The Amiga puts 11x512=5632 bytes on a track (11x(512+16)=5808
>bytes if you cheat a bit), you get 28160 (29040) bytes per second.
>
>I am assuming the Arari is smart enough to start reading whole tracks
>with the first sector it finds, instead of waiting for sector 1.  If
>it isn't, reduce that figure by 1/3 (to 15360 bytes/sec) to allow for
>the additional 1/2 track (0.1 sec) average latency.  The Amiga never
>waits to start reading.

	Actually trackdisk overhead comes into play here.  Trackdisk
throughput is about 21-22K/sec including decode, checksum, and transfer to
the users buffer for large reads.

	Overhead should be cut for 1.4, but don't forget filesystem gets
in there too, and there isn't a lot of overhead.  Most of the time the disk
is actually spinning or moving the heads.  Even cutting overhead in half
will only add 10% or so to the transfer rate.

-- 
Randell Jesup, Commodore Engineering {uunet|rutgers|allegra}!cbmvax!jesup