6 Jun
2007
6 Jun
'07
12:20 p.m.
Date: Wed, 6 Jun 2007 08:34:37 -0500
From: "Dave Dunfield" <dave06a at dunfield.com>
Subject: Re: TESTFDC usage
<snip>
To completely test the FDC, you need to check Single, Double and
Double/128 at each of 250, 300 and 500 kbps rates. These are
represented in a standard PC at:
250 = 5.25 low-density drive only, 3.5" low-density diskette
300 = 5.25 Low-density diskette in high-density drive
500 = 5.25" or 2.5" high-density diskette
So to check all possible data rates without a 300/360 modded drive,
you need to run two tests - either the 5.25" LD and HD drives, or a
5.25" HD and 3.5" drive.
----------------------
I also wanted to do some testing but, despite our off-list correspondence,
I'm still confused:
5.25" drive, 3.5" diskette ???
Either a 5.25" low density drive (and it should be obvious which type
of diskette you need to use with it) - OR -
a 3.5" low-density diskette in either type of 3.5" drive (no I am not
trying to tell you to put a 3.5" diskette into a 5.25" drive)
2.5" diskette ???
Humm.... 5,25" or 2.5" ... obviously the 2.5 is a typo, so it must have
been either:
5.25" or 5.25"
-or- 5.25" or 3.5"
I wonder which one it could be...
Basically, testing HD in either type of drive (with HD diskette) will
test 500kbps.
3.5" drive - LD or HD?
Let me try to explain it all.
All 3.5" drives turn at 300rpm.
to get DD a data rate of 250kbps is used.
to get HD a data rate of 500kbps is used (HD drive only).
- When doing DD, it DOES NOT MATTER what type the 3.5" drive is,
the data rate, rotation speed and head width are all exactly the
same ... this is why 3.5" HD drives do not have the compatibility
problems with DD media sometimes observed with 5.25" HD drives.
All 5.25" low-density drives turn at 300rpm.
to get DD a data rate of 250kbps is used.
HD is not applicable.
Almost-All PC 5.25" high-density drives turn at 360rpm.
to get DD a data rate of 300kbps is used (note1)
to get HD a data rate of 500kbps is used (note2)
note1: 300kbps at 360rpm works out to exactly the same bit
density as 250kbps at 300rpm - this is the "compatibility mode"
to allow single-speed 360rpm 5.25" drives to read/write DD diskettes.
note2: The HD data rate is 500kbps on both 3.5" and 5.25" drives. The
slower 3.5" (300 rpm) drives store more bits on a track, as it takes
longer for the whole track to pass under the head. This is the reason
that 3.5" HD disks store 1.44M which 5.25" HD disks store 1.2M
note3: 360rpm / 500kbps is electrically the same as an 8" drive, which
is why it's fairly easy to replace 8" drives with 5.25" HD drives.
Exactly what tests should be run with what
size/density disk in what size/
density/speed drive in order to get a complete picture?
When I say "drive" I mean that exact type of drive.
When I say "diskette" I mean that type of diskette, and it
does not matter which type of drive (LD or HD) it is in - obviously it
has to be the same physical format as the diskette.
To test 250kbps rate, you need ONE of:
3.5" drive (either type) with 3.5" LOW DENSITY diskette.
5.25" LOW-DENSITY drive (with 5.25" LOW DENSITY diskette)
To test 300kpbs, you need:
5.25" HIGH-DENSITY drive with 5.25" LOW-DENSITY diskette
To test 500kbps, you need ONE of:
3.5" HIGH-DENSITY drive with 3.5" HIGH-DENSITY diskette.
5.25" HIGH-DENSITY drive with 5.25" HIGH-DENSITY diskette.
For most people, who have 3.5" and 5.25" HD drives, running
the full tests available for both those drive types will test
all the possible combinations (in fact it will test 500kbps
twice).
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html