Variation #2 - Drives Supported if a Switch block is Fitted


If a switch block were to be fitted, the switches would be set according to the drive/s attached.


Switch Settings

Switches 1 and 2 configure drive 0.
Switches 3 and 4 configure drive 1.

The following table shows the settings for drive 0 (i.e. switches 1 and 2).  The settings for drive 1 (i.e. switches 3 and 4) are the same.

Table Address	Switch Settings for drive 0	Drive Characteristics	Comment
0	1=on  2=on	Cylinders = 306  /  Heads = 2  /  WPC = 0  /  a step rate of 3 ms is valid	Milliseconds, not microseconds.    Not the ST-506 (153 cyls / 4 heads)
1	1=on  2=off	Cylinders = 375  /  Heads = 8  /  WPC = 0  /  step pulses per here are valid
2	1=off  2=on	Cylinders = 306  /  Heads = 6  /  WPC = 256  /  step pulses per here are valid
3	1=off  2=off	Cylinders = 306  /  Heads = 4  /  WPC = 0  /  step pulses per here are valid	What gets selected if no switch block

The information in the above table was sourced from the book: Upgrading and Repairing PCs, Scott Mueller, 5th Edition, page 761/762/763

That matches well with what SpeedStor software reports.
On a computer with variation #2 of the controller fitted, if I activate SpeedStor's ROMLIST switch ( i.e.  A:\>sstor /romlist ), the result is:

Table	Cylinders	Heads	WPC	Control
0	306	2	0	0
1	375	8	0	5
2	306	6	256	5
3	306	4	0	5