A Technical Description of IDE Hard Drives Used in Macintosh Computers

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By Fred Widmer

Interal Harddrive This article describes the Integrated Drive Electronics (IDE ) hard drive, the 40-pin IDE connector pinouts, and IDE signals currently used on the following computers:

Macintosh 630 Family computers**

Macintosh LC 580

Macintosh Performa 5200 series computers

Macintosh Performa 5300 series computers

Macintosh Performa 6200 series computers

Macintosh Performa 6300 series computers

Macintosh PowerBook 150 series computers

Macintosh PowerBook 190 series computers

Macintosh PowerBook 2300 series computers

Macintosh PowerBook 5300 series computers

Power Macintosh 5200/75 LC

Power Macintosh 5300/100 LC

**The Macintosh 630 Family includes the following computers: Macintosh LC 630, Quadra 630, and Performa 630, Performa 635, Performa 636, Performa 637, Performa 638 and Performa 640.

The computers mentioned above all have an internal hard disk using the IDE interface. This cost-effective interface, used on IBM AT-compatible computers, is also referred to as the ATA interface. The implementation of the ATA interface on the Macintosh LC 630 and Macintosh Quadra 630 computers is a subset of the ATA interface specification, ANSI proposal X3T9.2/90-143, Revision 3.1.

An IDE drive does not have any address conflicts, specific cabling, or termination issues normally found in a SCSI chain. Performance of an IDE hard drive will be similar to a comparable SCSI hard drive.

Any hard drive utilities you may have for SCSI drives will likely have to be revised to function properly with an IDE drive. Check with the vendor of the utility for compatibility information.

Hard Disk Connectors

The internal hard disk has a standard 40-pin IDE connector and a separate 4-pin power connector. The 40-pin connector cable is part of the cable harness attached to the main logic board by the internal chassis connector. The power cable is attached directly to the power supply.

Pin Assignments

The Table below shows the pin assignments on the 40-pin IDE hard disk connector. A slash (/) at the beginning of a signal name indicates an active-low signal.

Pin number Signal name Pin number Signal name

1 /RESET 2 GROUND

3 DD7 4 DD8

5 DD6 6 DD9

7 DD5 8 DD10

9 DD4 10 DD11

11 DD3 12 DD12

13 DD2 14 DD13

15 DD1 16 DD14

17 DD0 18 DD15

19 GROUND 20 KEY

21 Reserved 22 GROUND

23 DIOW 24 GROUND

25 DIOR 26 GROUND

27 /IORDY 28 Reserved

29 Reserved 30 GROUND

31 INTRQ 32 /IOCS16

33 DA1 34 /PDIAG

35 DA0 36 DA2

37 /CS0 38 /CS1

39 /DASP 40 GROUND

Pre-Formatted Text Pin Assignments Chart

Note: The IDE data bus is connected to the I/O bus through bidirectional bus buffers. To match the big-endian format of the MC68030-compatible bus, the bytes are swapped. The lower byte of the IDE data bus, DD(0-7), is connected to the high byte of the upper word of the I/O bus, IOD(24-31). The higher byte of the IDE data bus, DD(8-15), is connected to the low byte of the upper word of the I/O bus, IOD(16-23).

The Table below describes the signals on the IDE hard disk connector.

IDE Signal Descriptions

Signal name	Signal description
DA(0-2)	IDE device address; used by the computer to select one of the registers in the IDE drive. For more information, see the descriptions of the CS0 and CS1 signals.
DD(0-15)	IDE data bus; buffered from IOD(16-31) of the computer's I/O bus. DD(0-15) are used to transfer 16-bit data to and from the drive buffer. DD(8-15) are used to transfer data to and from the internal registers of the drive, with DD(0-7) driven high when writing.
CS0	IDE register select signal. It is asserted high to select the additional control and status registers on the IDE drive.
CS1	IDE register select signal. It is asserted high to select the main task file registers. The task file registers indicate the command, the sector address, and the sector count.
/IORDY	IDE I/O ready; when driven low by the drive, signals the CPU to insert wait states into the I/O read or write cycles.
/IOCS16	IDE I/O channel select; asserted low for an access to the data port. The computer uses this signal to indicate a 16-bit data transfer.
/DIOR	IDE I/O data read strobe.
/DIOW	IDE I/O data write strobe.
INTRQ	IDE interrupt request. This active high signal is used to inform the computer that a data transfer is requested or that a command has terminated.
/RESET	Hardware reset to the drive; an active low signal.
Key	This pin is the key for the connector

Text IDE Signal Descriptions Chart

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