Address and Unit Specification on Microsystems

You can select between different ports and drives on the Disk Interface card (12022A). First, the drive Address (DP1) allows you to select between microfloppies, or one of two hard disks. Each microfloppy has its own port, both of which are Address 3. The Unit number (DP2) selects microfloppy unit 0 or unit 1. Note that only one microfloppy, unit 0, is currently provided for the microsystem.

Hard disks have no Unit specifications, and thus this parameter is set to zero. Hard disks are selected by Address 0 or 1. The proper address parameter is factory set and should never be changed.

Special Considerations for the 7906M Disk Drive

The 7906M disk drive has two platters for data storage. One of these platters (the top one) is removable; the other one is fixed in the drive and may not be removed. Each of these platters has two surfaces, with 411 tracks per surface and 24 blocks per track.

The organization of the surfaces and heads of the 7906M disk drive for generation purposes is shown in Figure C4. The four surfaces available for data storage are numbered 0, 1, 2, and 3. Each surface is accessed by one head, also numbered 0, 1, 2, and 3.

Cylinder

0

1

2

3 S S S

 

 

 

 

 

 

 

 

 

 

 

 

Surface 0

 

 

 

Head 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Surface 1

 

 

 

Head 1

 

 

 

 

 

S

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

S

 

 

 

 

 

 

 

 

 

 

 

 

S

Surface 2

 

 

 

Head 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Surface 3

 

 

 

Head 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A cylinder is one track from surface 0, one track from surface 1, one track from surface 2, and one track from surface 3.

Figure C4. 7906M Disk Drive

The 7906M disk drive may be divided into several LUs. There are three modes in which the 7906M LU can operate: surface, cylinder, or shortened cylinder. Surface mode uses only one surface per LU, cylinder mode uses all four surfaces for each LU, and shortened cylinder typically uses two surfaces per LU.

C26 Configuring a Disk Subsystem