Date   : Fri, 24 Nov 2006 14:14:15 +0000
From   : pete@... (Pete Turnbull)
Subject: BBC Disk Drive?

On 24/11/2006 10:26, Anders Carlsson wrote:
> On Fri 2006-11-24 10:05, Richard Gellman wrote:
> 
>> I remembered that the Amiga has an odd number of pins (by today's
>> standards at least), but forgot that it was 23 rather than 37.
> 
> Don't all DSUB type connectors have an odd number of pins, as
> opposed to an even number of pins? ;-D

But (smiley noted) I think Richard means "odd" as in "unusual" not "not 
even" :-)  Besides, the DD50 has an even number, as do the high-density 
DA26, DB44, DC62, and DD78 connectors.

> Speaking of Amiga, the 3.5" disk drive 1581 for the 8-bit Commodore
> series internally uses an Amiga 500 drive, but it is possible to
> modify most PC drives as well. I suppose almost all 3.5" drives
> are more or less compatible with eachother, with the possible
> exception of Macintosh drives and Unix workstations.

Pretty much, for the most common ones you'll come across nowadays, but 
it wasn't always so.

For example, the original Sony drives were much higher (1.75" high) so 
wouldn't fit a 1" slot, were single-sided, had fewer tracks (77) and had 
no mechanism to open the shutter (original 3.5" disks had no shutter at 
all, and slightly later ones had a shutter that you latched open before 
insertion).  Many early Sony drives ran at 600 rpm (and twice the data 
rate) instead of 300, even when 80-track double-sided came along, and 
had a 26-pin interface instead of 34-pin.  Slightly later 1"-high drives 
were still only 1MB (what PC users wrongly call 720KB, which strictly 
speaking refers to just one particular format scheme) and 34-pin running 
at 300rpm; it was some time before 2MB (what PC users bizarrely call 
1.44MB*) came along.  I have several slimline 3.5" drives that are SD/DD 
only (and work fine on unmodified Beebs), and some 600rpm drives used on 
HP, Sony, and Apricot machines.  Older DD and HD drives sometimes have 
the option of generating READY instead of DISK CHANGED, and usually have 
all four drive selects available; some also have jumper options to 
re-assign some of the connector pins as a power source.  A few have a 
power eject option, controlled by pin 2.

Then of course there are ED drives, which are 4MB unformatted (2.88MB in 
broken PC parlance), using ED disks (they can read/write HD and SD/DD 
disks as well).

The early 3.5" Macintosh drives are variable-speed.  Unix ones are 
sometimes SCSI drives, either TEAC/Toshiba ones with an integrated SCSI 
controller  as used on Sun and SGI kit, or DEC ones with the drive 
mounted on a larger frame with a SCSI adapter (both these came in 5.25" 
versions as well as 3.5").  The TEAC ones sometimes have a power eject 
as well (needed for Sun workstations).  Then of course there are 3.5" 
floptical drives, which can read/write 20MB (formatted) floptical disks 
as well as ordinary DD and HD disks; these are native SCSI.

* 1.44MB is particularly stupid because it's mixing units: 512 
bytes/sector x 18 sectors/track x 160 tracks is 147560 bytes, or 1.44 x 
1024 x 1000.


-- 

Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York