Re: Did the Apple II use single-density 5.25" drives?

[Michael J. Mahon <mjmahon@aol.com>]

Michael Black <et472@ncf.ca> wrote:
> On Thu, 6 Jun 2013, ivan@ivanexpert.com wrote:
> 
>> Was GCR chosen because MFM encoding wasn't a viable or economical option
>> > at the time, and it was a higher-density method than FM? And why not
>>> 40 > tracks (which would have yielded 160K per side with DOS 3.3)
>>> instead of > 35? Same reason?
>> 
>> 
> Early drives, as I said in another post, were 35 tracks.  Even when I got
> a Radio Shack Color Computer in 1984, the standard disk controller was
> set for 35 tracks, though I guess by then most drives were 40 track.  YOu
> had to patch the ROM to get the use of 40 tracks.
> 
> So I'm pretty sure that there wasn't the option of 40 tracks when Apple
> first came out with their floppy disk system.  I have no idea why there
> wsa no later upgrade, other than perhaps they didn't want two standards
> floating around.  Or maybe, since standard Apple II drives were custom
> made, Apple never changed the specs.
> 
> As for GCR, we were talking about that some weeks back.  Woz cooked up a
> scheme that used little hardware (the board on the drive is much simpler,
> the controller board in the Apple II is pretty simple, not needing some
> big and expensive IC at the time) that resulted in a much lower cost for
> Apple at the time.  At the time, even the dedicated floppy controller ICs
> required lots of extra parts, making them expensive and bulky.

And Woz's controller is capable of FM (or single-density) operation--in
fact the address fields are encoded as FM, or 4+4 encoding. 

GCR was a nice improvement in data density resulting from using
single-density bit resolution in a cleverer scheme made possible by Woz's
software data encoding/decoding (a scheme later improved from 5+3 to 6+2,
for even better data density. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon