[Coco] Another drive question

[John E. Malmberg]

Bruce Calkins wrote:
> The impression I have gotten is, that along about the late Pentium one days,
> the motherboards or OS's started reading the drive specifications on
> startup, ignoring the BIOS settings.

Unless you are dealing with a USB floppy drive or one of the rare SCSI 
ones, there are no drive specifications to read except for the BIOS 
settings.

The BIOS or the driver is supposed to use the initial settings as a 
default, but is supposed to know the full range of values.

It is supposed to read the parameters from the loaded floppy for FAT 
formated floppies.

In practice when I had a TANDY 2000, I found that only a IBM PC/AT could 
read the quad density disks.

The PC/AT clones could not, and that meant that their BIOSes were not 
compliant with the then standard specification, As the 720K format was a 
documented in the original BIOS specs.

Electrically with out a floppy in them, the only clue that the software 
has is to see if the LEDs for the 144 or 288 are seeing a signal.  That 
tells it that you have one of those type floppies.

What makes the 5.25 drives special from the 3.5 inch ones is that there 
are two track densities for the 5.25 inch drives, and only 1 for the 3.5 
inch drives.

So if you are reading a COCO 5.25 inch floppy on a high density drive, 
you need to double step the tracks in addition to the other parameters.

The 5.25 inch floppies also have a density line for the controller to 
tell the drive what type of media it has in it.

The 3.5 inch floppies are supposed to have this, but apparently the 
newer drives do not pay attention to it and only go by what their LED 
sensors show.

>  I have had some luck with a 360k (40 track DSDD) drive with a BIOS setting
> of 720k using a 486 board.  This "trick" has not worked for me with any
> Pentium one board computer.

Apparently some of the programs did not set all the parameters 
correctly, and I am having problems locating in my library the 
definitions of them all.

> I have had some luck using the 1.2 Meg 5.25" drives on a Pentium one,
 > using John Collyer's DSKINI and FRESHLY ERASED disks.

John has posted that he fixed the programs to be able to work with those 
drives.

But that issue is becoming moot if you want to work with the newer 
Microsoft operating systems, unless you want to write your own floppy 
driver.

-John
wb8tyw at qsl.net
Personal Opinion Only