Re: IIgs 3.5" disk drive limit

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

Dennis Jenkins <dennis@usb.com> wrote:

> How many 3.5" and 5.25" drives can I daisy chain together on a ROM01
> IIgs?  I assume that I can have no more than 2 5.25" drives.  How many
> 3.5" drives can I have?

There are sevearl limits to consider:

1. The number of drives of each type which can be addressed using a
single disk controller.  (There may also be a software limit on the
total number of drives which may be connected, no matter what type they
are.)

2. The signal loading restrictions, which determine the maximum number
of drives of all types which may be connected to a single disk
controller.

3. The power supply loading restrictions, which determine the maximum
number of drives which may be connected to the entire computer.

4. The operating system may impose a limit on the total number of
drives/volumes.  For example, ProDOS cannot access more than 14 volumes.

Unfortunately the signal and power supply limits are not always well
defined.

The addressing limits for floppy drives are easy:

- There is a limit of two 5.25" drives on any one controller.

- There is a limit of two Apple 3.5 Drives (or equivalent, such as
  SuperDrive) on any one controller.

- There is a theoretical limit of 127 UniDisk 3.5 drives (or other
  intelligent SmartPort devices) on any one controller.

The signal loading restrictions generally restrict you to four drives
per controller, though it may be possible to connect more in some cases.

The power supply loading restrictions vary between computers.  If you
had a heavy duty power supply, you could probably fill all seven slots
of an Apple ][, and have two drives connected to each.

> My current system has 2 of each, with the following slot assignments:
> 
> slot 1)  Apple SCSI Card.  D1 = /HD (32M drive) D2 = nothing
> slot 2)  onboard serial   D1 = 2nd 3.5" drive
> slot 3)  D2 = /RAM
> slot 4)  onboard mouse
> slot 5)  onboard smartport  D1= 1st 3.5" drive, D2 = /RAM5
> slot 6)  onboard floppy  D1/D2 = 5.25" drives.
> slot 7)  onboard appletalk
> 
> If I add a thrid 3.5" drive, and it works, will it become S2D2?

You could connect a UniDisk 3.5 to your built-in disk port (after the
Apple 3.5 Drives and before the 5.25" drives), as long as it didn't
exceed the signal loading and power supply restrictions.  This would
become S2,D2.

You cannot connect a third Apple 3.5 Drive, because the hardware can
only address two of them on a single controller.

You could also add another disk controller card (at the expense of one
of your built-in ports) and connect two Apple 3.5 Drives to that.