CHAPTER 2

Hardware Modifications
200 MB Hard Disk Drive

11

Hard Disk Interface 2

This section describes the interface requirements for the 200 MB hard disk drive. It
provides specifications and signal assignments for the SCSI connector.
Note

The interface requirements for the 120 MB hard disk drive are described
in Chapter 3 of the

Macintosh Developer Notes, Number 2, Macintosh
Duo System

.

◆

Interface Requirements 2

The interface to the hard disk is an ANSC X3T9.2 SCSI interface. It implements the Apple
SCSI command protocol and diagnostic command set. The buffer size supports a 1:1
interleave. The drive supports the SCSI asynchronous information transfer. The transfer
rate is 1.5 MB per second (minimum). An embedded controller provides error recovery
algorithms, which include error check and correction (ECC), seek retry, head offset (for
open-loop systems), and defect management. The SCSI interface provides
hardware-detectable SCSI ID.

SCSI Connectors 2

The 200 MB disk drive SCSI connector comprises two segments, as shown in Figure 2-3.
The first segment has 40 pins, arranged in two rows. It transfers SCSI signals between the
CPU and the hard disk drive, and it also supplies power to the drive. The second
segment of the connector accommodates the SCSI ID.

Figure 2-3

200 MB hard drive SCSI connector
Pin 39 Pin 1
Pin 40 Pin 2
Pin 7 Pin 1
Pin 8 Pin 2
Key
SCSI commands and power SCSI ID