14 Mar
2005
14 Mar
'05
2:27 p.m.
On Sun, 13 Mar 2005, Randy McLaughlin wrote:
I have tried to research the issue further but can I
find no authoritative
references to pin 2 being anything but an RPM select line.
Other websites like mine do claim it is use for write current but provide no
references to show it.
If anyone has an authoritative reference stating it was not used to select
rotational speed I will be happy to change my website stating that it does
have multiple uses.
The first ATs (FROM IBM), and the IBM AT Technical Reference Manual, are
single speed drives with a controller capable of THREE data transfer
rates:
250K for use with 360K drive (300 RPM)
300K for use with 360K disks in 1.2M drive (360 RPM)
500K for use with 1.2M disks in 1.2M drive (360 RPM)
That 300K data transfer rate is NOT needed for a two speed drive. (Which
the first IBM ATs DID NOT HAVE)
With a 300K and a 500K data transfer rate, a two speed drive is not
needed.
Many/most? companies OTHER THAN IBM used a two speed drive, and used the
write current/density select line to control the speed.
Until then I have changed my site to say other sites
state otherwise but
include hyper-links to the manufacturer docs stating that it is for two
speed drives (ala early IBM AT).
Please note I am not looking for what people remember it does but actual
documents from a manufacturer. I tested it with a TEAC FD-55GFR and sure
enough it slowed the RPM when grounded.
Try one of the drives that IBM sold (which did NOT include TEAC FD-55GFR)
BTW, do you know the difference between a 55GFR and a 55G?
It appears to be whether or not it supports 300RPM !
or early Mitsubishi 4854 1.2M (but not the EARLIEST, which had a 50 pin
connector)
IBM AT Technical Reference Manual not official enough?
Howzbout source code of the BIOS?
--
Grumpy Ol' Fred cisin at xenosoft.com