Re: 1.44M 3.5" drive

[dempson@actrix.gen.nz (David Empson)]

In article <24SEP199409145254@utkvx.utk.edu>,
Krishna Madurai Sadasivam <sadasiva@utkvx.utk.edu> wrote:
> 
> Does this drive have a faster transfer rate than 1 MHz, like the ordinary 3.5"
> drive? Or is the same?

The standard Apple 3.5 drive has a raw transfer rate of 500 kbits/sec
(2 microsecond bit cells). The 5.25" drive and UniDisk 3.5 transfer
data to the computer at 250 kbits/sec (raw data for the 5.25, 7-bit
shifted data for the UniDisk 3.5).

720k MFM mode uses 2 microsecond bit cells.  1.44MB MFM mode uses 1
microsecond cells, so data is transferred to the computer at 1
megabit/sec.  This is the data rate used by the SuperDrive with a high
density disk.

A 1 MHz Apple II isn't fast enough to handle the transfer rate of an
Apple 3.5 Drive.  The IIgs uses fast mode, and the IIc+ has an
accelerated processor and hardware support.  The various 3.5"
controller cards use a faster processor and/or hardware support to
handle the higher data rates.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand