TITLE
    Macintosh Desktop & PowerBook Computers: IDE Hard Drive
Article ID:
Created:
Modified: 		15826
7/15/94
4/13/00
TOPIC

    This article describes the IDE (integrated drive electronics) hard drive, the 40-pin IDE connector pinouts, and IDE signals currently used on some Macintosh and PowerBook computers. To find out if your computer uses an IDE hard drive, check the specification article for your computer model.

DISCUSSION

    Some Macintosh, Performa, Power Macintosh and PowerBook computers use an internal hard disk using the IDE interface. This cost-effective interface 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.

    Note: The internal hard disk in the Macintosh 630 Family computers is an IDE drive, not a SCSI drive. To avoid possible problems in formatting, be sure to use the supplied Internal HD Format software with the internal IDE drive.

    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 assignments on the IDE hard disk connector:
    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

    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(0ð7), is connected to the high byte of the upper word of the I/O bus, IOD(24ð31). The higher byte of the IDE data bus, DD(8ð15), is connected to the low byte of the upper word of the I/O bus, IOD(16ð23).

    IDE Signal Descriptions
    The Table below describes the signals on the IDE hard disk connector.
    Signal name
    Signal description
    DA(0ð2)
    		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(0ð15)
    		IDE data bus; buffered from IOD(16ð31) of the computer's I/O bus. DD(0ð15) are used to transfer 16-bit data to and from the drive buffer. DD(8ð15) are used to transfer data to and from the internal registers of the drive, with DD(0ð7) 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.

Document Information
Product Area: Peripherals
Category: Magnetic Storage Devices
Sub Category: General Topics

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