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From: binder@dosadi.DEC (The Stainless Steel Rat)
Newsgroups: net.micro.apple
Subject: Re: Apple disk speed -- more info
Message-ID: <1483@decwrl.UUCP>
Date: Thu, 14-Jun-84 08:58:50 EDT
Article-I.D.: decwrl.1483
Posted: Thu Jun 14 08:58:50 1984
Date-Received: Wed, 20-Jun-84 00:33:02 EDT
Organization: DEC Engineering Network
Lines: 43

I don't know how the Mac does it, but the Apple ][ DOS places data on
the disk sequentially backward, thus:

Imagine a 16-sector file, ie one track, to be saved on a freshly
initialised disk. This file will be stored in this order on the disk:

File sector   Disk track/sector   File sector   Disk track/sector
-----------   -----------------   -----------   -----------------
     1             18/15               9             18/ 7
     2             18/14              10             18/ 6
     3             18/13              11             18/ 5
     4             18/12              12             18/ 4
     5             18/11              13             18/ 3
     6             18/10              14             18/ 2
     7             18/ 9              15             18/ 1
     8             18/ 8              16             18/ 0

...and so on for longer files.  What this means in terms of read/write
time is that a simple-minded DOS can have lots of time to read a sector
into a buffer area and then move it to the proper area in memory, and
then do housekeeping before the next sector comes along, almost a full
revolution later.  Thus, it takes DOS 3.3 18 revolutions to read that
16-sector file.  SLOOOOOOOWWW!!!

There are several third-party DOSes available for the Apple ][ machines;
three that I know of are Diversi-DOS, from DSR, Inc.; ProntoDOS, from
Beagle Brothers; and David DOS, from David Data.  All of these are
smarter in that they don't need the massive amount of time between
sectors.  They use a little intelligence to read sectors out of order,
and all of them can load a 16-sector Applesoft or binary programme in
only TWO revolutions.  Text file handling is a little slower but still
vastly faster than DOS 3.3.  All of these DOSes also include extra
functions, some of them rather nice; David DOS has new commands for
direct load and save of text files, Diversi-DOS has a TLIST command that
lists Applesoft directly from the disk, and so on.

Cheers,
Dick Binder   (The Stainless Steel Rat)

UUCP:  { decvax, allegra, ucbvax }!decwrl!rhea!dosadi!binder
ARPA:  binder%dosadi.DEC@decwrl.ARPA

Posted Thursday 14th June 1984, 08:59 Eastern time by DOSADI::BINDER