The document describes the ATA (Advanced Technology Attachment) interface for connecting storage devices like hard drives to a computer motherboard. It details the ATA connector and specifications, including the 40-pin connector layout and cable. It explains that ATA supports up to two devices on each cable, designated as a master or slave, and that the cable select pin is used to automatically configure a device's master/slave status based on its position on the cable.

1. ATA Features

2. ATA Connector on the Left, with two
ATA Connectors on the Motherboard
on the Right.

3. ATA Specifications
● Hot pluggable: no
● External: no
● Width: 16 bits
● Bandwidth: 16 MB/s originally, later 33, 66, 100
and 133 MB/s
● Max devices: 2 (master/slave)
● Protocol: Parallel
● Cable: 40 wire ribbon cable
● Pins40

4. ATA Plug

5. Pin Description
● Pin 1 Reset ● Pin 21 DDRQ
● Pin 2 Ground ● Pin 22 Ground
● Pin 3 Data 7 ● Pin 23 I/O write
● Pin 4 Data 8 ● Pin 24 Ground
● Pin 5 Data 6 ● Pin 25 I/O read
● Pin 6 Data 9 ● Pin 26 Ground
● Pin 7 Data 5 ● Pin 27 IOCHRDY
● Pin 8 Data 10 ● Pin 28 Cable select
● Pin 9 Data 4 ● Pin 29 DDACK
● Pin 10 Data 11 ● Pin 30 Ground
● Pin 11 Data 3 ● Pin 31 IRQ
● Pin 12 Data 12 ● Pin 32 No connect
● Pin 13 Data 2 ● Pin 33 Addr 1
● Pin 14 Data 13 ● Pin 34 GPIO_DMA66_Detect
● Pin 15 Data 1 ● Pin 35 Addr 0
● Pin 16 Data 14 ● Pin 36 Addr 2
● Pin 17 Data 0 ● Pin 37 Chip select 1P
● Pin 18 Data 15 ● Pin 38 Chip select 3P
● Pin 19 Ground ● Pin 39 Activity
● Pin 20 Key or VCC_in ● Pin 40 Ground

6. ATA Cables

7. Multiple devices on a cable
If two devices attach to a single cable, one is commonly
referred to as a master and the other as a slave.
The master drive generally appears first when the
computer's BIOS and/or operating system enumerates
available drives

8. Cable Select
A drive set to "cable select" automatically
configures itself as master or slave, according to
its position on the cable. Cable select is controlled
by pin 28. The host adapter grounds this pin; if a
device sees that the pin is grounded, it becomes
the master device; if it sees that pin 28 is open,
the device becomes the slave device.
This setting is usually chosen by placing a jumper on the
"cable select" position, usually marked CS, rather than on
the "master" or "slave" position.