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

[Michael Black <et472@ncf.ca>]

On Thu, 6 Jun 2013, slickrcbdnews@gmail.com wrote:

> I got my first computer, an Apple IIGS back in 1988. I don't recall ever 
> seeing single sided or single density disks in the stores back then. I 
> only ever used double sided, double density (DSDD) disks. Years later I 
> added a SuperDrive and was able to use high density 3.5" disks in it.
>
> I think I read somewhere that the Apple II's 5.25" drives could use 
> single sided, single density disks just fine. Was that true and that the 
> "double density" aspect was wasted?
>
> I know for a fact that they were single sided, and the other side was 
> wasted unless you had a hole-punch tool to remove the write protection 
> on the other side. I also know that MS-DOS systems could use both sides 
> simultaneously. Howver, what about the "single density" aspect?
>
> I've never seen such a disk in either 3.5" or 5.25". I know for a fact 
> that 5.25" high density disks will NOT work in the AppleDisk 5.25" 
> drive, given that somebody traded me a blank HD disk at one point for a 
> formatted ProDOS disk that I was unable to format or use (and he gave me 
> several others from the pack.
>
> So, were they single density or double density drives? Did 
> single-density disks even exist, or were they something extremely short 
> lived and quickly replaced with double density the way the 400K disks 
> were replaced with 800K disks on the Mac (400K 3.5" disks was something 
> else I'd only seen as an option with the HFS FST or System 6.0.7 on the 
> Mac).
There wasn't "single density" until "double density" came along, at which 
point they had to put a name on what had existed before.

It's the controller that sets the density.  If you look at 
early floppy disk ICs that do double density, there is a means of 
switching it between single and double.  The same drive could be used. 
Later the ability to switch density generally went away.  I remember 
lookig at single IC controllers in a databook and noticing that, and there 
was at least one operating system, FLEX for the 6809, that needed the 
first sector to be single density for some reason, and the later 
controllers were incompatible.

If I recall properly, High Density needed a different drive, something 
like it ran t a faster speed.

So the average (non-Apple) drives started out with about 90K of storage 
space, single density and single sided.  That doubled when either double 
density or double sided drives came along, I can't remember which came 
first, and then doubled again when the other of the two arrived.

There was also the issue that originally 5.25" drives were 35tracks, and 
when 40track drives appeared (and software to go with them, the software 
had to know to move to the extra tracks), that increased capacity a bit.

There were various attempts at a smaller drive, including small floppy 
disks with a hub like the well known 3.5".  There were 3" disks, I think 
with a hard shell, the poor people who bought into those early likely got 
stuck, and then finally a standardization on the 3.5" with the hard shell 
that we know and love.

Out of the box they had higher capacity 80 tracks per side, so that would 
double the capacity, and no hardware needed.


I guess it was the 1.2meg 5.25" drives that had the faster rotation speed. 
But then the high density drives appeared, they had narrower tracks, which 
meant a need for narrower read/write heads, and a different makeup of the 
coating on the 5.25" floppies, which is why the HD floppies are not seen 
as reliable in double density drives.

I suddenly can't remember how 3.5" drives got to be High Density.

And none of this has much to do with Apple.

  Michael