Re: Apple2 disk controller questions

[sales@mainlinebbs.com (John H. Guillory)]

On 12 May 1999 08:49:38 GMT, supertimer@aol.com (Supertimer) wrote:

>Come to think about it, you are right.  It must be the variable
>spin drives that give Apple 3.5" disks the extra 80k, but GCR
>is probably a little less efficient.
  Very possible, as IBM Compatibles use a fixed number of sectors per
track....  Although, IBM's can also make a non-standard disk where we
can get I believe upto 1.8meg, in which case, we bump up the sectors
per track, and go out a few extra cylinders.... Although from what
I've read, the Apple can do the same....  One thing I like about the
Commodore (it may not be able to make non-standard disk easily
but...,) is the fact that I can keep a copy of all my disk on my IBM's
hard drive, or on a CD-ROM, then run 1581copy to re-create the disk at
any time.  What this amounts to is in reality, I only need a handful
of disk, and create them each time I want to play the game, or run the
program, etc.  I could sorta use ShrinkIt to create an image of the
disk, send it via serial port, etc. but not quite as fast as just
making a Commodore disk from the PC....

>What I don't understand is the high density 3.5" Apple II
>format.  Like the Mac, high density 3.5" Apple II disks are
>1.44MB MFM.  However, there is a special 1.6MB GCR
>format that is used by AE's driver for the IIGS.  I'm not
>sure how the AE driver squishes those extra few kilobytes
>into the disk.
  Question is: Why did Mac limit their disk to 1.44mb in the first
place?  Seems like if they just used the same technology that made the
800k disk on the high density disk, they'd naturally get 1.6megs...
Twice the Density, 800k x 2 = 1.6megs ... Don't it seem logical?