Apple used a DB25 D-sub connector for external SCSI on Mac Plus, SE, II, and early Power Macs instead of the Centronics 50-pin connector used by PCs, for connecting hard drives, scanners, and CD-ROMs.
| Pin | Name | Function | Type |
|---|---|---|---|
| 1 | /REQ | Request active low | I/O |
| 2 | MSG | Message | I/O |
| 3 | I/O | Input output direction | I/O |
| 4 | /RST | Reset | I/O |
| 5 | ACK | Acknowledge | I/O |
| 6 | BSY | Busy | I/O |
| 7 | GND | Ground | GND |
| 8 | DB0 | Data bit 0 | I/O |
| 9 | GND | Ground | GND |
| 10 | DB3 | Data bit 3 | I/O |
| 11 | DB5 | Data bit 5 | I/O |
| 12 | DB6 | Data bit 6 | I/O |
| 13 | DB7 | Data bit 7 | I/O |
| 14 | GND | Ground | GND |
| 15 | C/D | Control data | I/O |
| 16 | GND | Ground | GND |
| 17 | ATN | Attention | I/O |
| 18 | GND | Ground | GND |
| 19 | SEL | Select | I/O |
| 20 | DBP | Data bus parity | I/O |
| 21 | DB1 | Data bit 1 | I/O |
| 22 | DB2 | Data bit 2 | I/O |
| 23 | DB4 | Data bit 4 | I/O |
| 24 | TERMPWR | Terminator power 5V | PWR |
| 25 | GND | Ground | GND |
Apple used a DB25 D-sub connector for external SCSI on Mac Plus, SE, II, and early Power Macs instead of the Centronics 50-pin connector used by PCs, for connecting hard drives, scanners, and CD-ROMs.