ATA/IDE Internal connector pinout

Advanced Technology Attachment (ATA), is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. Many terms and synonyms for ATA exist, including abbreviations such as IDE, ATAPI, and UDMA. ATA standards only allow cable lengths in the range of 450 to 900 mm, so the technology normally appears as an internal computer storage interface. It provides the most common and the least expensive interface for this application.

Pin	Name	Dir	Description
1	/RESET		Reset
2	GND		Ground
3	DD7		Data 7
4	DD8		Data 8
5	DD6		Data 6
6	DD9		Data 9
7	DD5		Data 5
8	DD10		Data 10
9	DD4		Data 4
10	DD11		Data 11
11	DD3		Data 3
12	DD12		Data 12
13	DD2		Data 2
14	DD13		Data 13
15	DD1		Data 1
16	DD14		Data 14
17	DD0		Data 0
18	DD15		Data 15
19	GND		Ground
20	KEY	-	Key (Pin missing)
21	DMARQ	?	DMA Request
22	GND		Ground
23	/DIOW		Write Strobe
24	GND		Ground
25	/DIOR		Read Strobe
26	GND		Ground
27	IORDY		I/O Ready
28	SPSYNC:CSEL	?	Spindle Sync or Cable Select
29	/DMACK	?	DMA Acknowledge
30	GND		Ground
31	INTRQ		Interrupt Request
32	/IOCS16	?	IO ChipSelect 16
33	DA1		Address 1
34	PDIAG	?	Passed Diagnostics
35	DA0		Address 0
36	DA2		Address 2
37	/IDE_CS0		(1F0-1F7)
38	/IDE_CS1		(3F6-3F7)
39	/ACTIVE		Led driver
40	GND		Ground

Each cable has two or three connectors, one of which plugs into a controller that interfaces with the rest of the computer system. The remaining one or two connectors plug into drives. Parallel ATA cables transfer data 16 or 32 bits at a time. One occasionally finds cables that allow for the connection of three ATA devices onto one IDE channel, but in this case one drive remains read-only (this type of configuration virtually never occurs).

For most of ATA"s history, ribbon cables had 40 wires, but an 80-wire version appeared with the introduction of the Ultra DMA/66 standard. The 80-wire cable provides one ground wire to each signal wire. This reduces the effects of electromagnetic induction between neighboring wires and enables the 66 megabyte per second (MB/s) transfer rate of UDMA4. The faster UDMA5 and UDMA6 standards require 80-conductor cables. This was done to reduce crosstalk. Though the number of wires doubled, the number of connector pins remains the same as on 40-conductor cables. The physical connectors are identical between the two cable types.

If two drives attach to a single cable, the configuration generally sees one as a master and the other as a slave. The master drive generally shows up ahead of the slave drive when the computer"s operating system enumerates available drives. The master drive arbitrates access to devices on the channel. Because of this, latency-sensitive devices such as early CD-RW drives often benefitted from functioning as a master, and each channel must have a master in order to function properly.
In a drive setting called cable select the drives automatically configure themselves as master or slave. This is achieved by cutting wire 28 (on 40 wire cables, or wires 56 and 57 on 80 wire cables) between the two HDD/CDROM connectors. Some newer cables have this done internally in the connectors. In this case, the two connectors are of different colours.

Note: Direction is Controller relative Devices (Harddisks).