Re: Disk drive speeds

[Andy McFadden <fadden@fadden.com>]

In comp.sys.apple2 Nicolas Welte <welte_spam@freenet.de> wrote:
> silverdr wrote:
>                         x-factor      time      kB/s
> CMD HD Parallel         57.7         2.2s      20.0
> Professional DOS L2     32.5         3.9s      12.8
> Prologic DOS Classic    28.2         4.5s      11.1
> Dolphin DOS 2.0         26.5         4.8s      10.4
> 
>> I would also be interested in how the fastest Apple][ floppy rigs 
>> performed.
> 
> Me too.

Locksmith "fastcopy" was probably about as fast as it got for 5.25"
floppies.  UCSD Pascal did pretty well too -- if you've ever seen it
load an 8K hi-res image you know how fast it can be.

In theory the data came in at exactly 4us/bit.  Minimum length for a 4K
track is 6384 8-bit bytes if you use the recommended header padding.
That yields 0.204 seconds to read one track.  IIRC, the Apple II is
capable of reading and decoding a track in one pass, though ProDOS
skewed the sectors for a two-pass read because otherwise write performance
was extremely poor.

I don't know how long it takes to seek to a new track.  I know the head
can run across 35 tracks in about a second, so if we're conservative and
call it 0.1 seconds to move one track, we get 0.3 seconds to read a track
and move on to the next.  That means something like 15KB/sec.

I tried to follow this up with an actual experiment, timing LS5.0 fastcopy
as it read a disk, but couldn't get it to work on my IIgs (perhaps it
doesn't like the smartport interface?).  Disk Muncher 1.1 seemed to be
reading about 4 tracks per second, but it didn't read enough at one shot
for me to get an accurate reading.

Perhaps somebody else can do it.  In any event, the maximum conceivable
transfer rate for an Apple II 5.25" floppy is 5 tracks/second, or 20KB/s.
(Unless you jack up the speed and write 18 sectors per track, like
Broderbund did for some of its games.)

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