IDE 40-pin Pinout

Parallel ATA (PATA) 40-pin ribbon-cable interface for hard drives and optical drives.

Overview

The 40-pin IDE/PATA connector is the classic dual-row header (two rows of 20 on 2.54 mm pitch) used by parallel ATA drives. It carries a 16-bit data bus, three address lines, ATA read/write strobes, DMA handshaking and control signals.

Pin 20 is the keying position (removed). The later 80-conductor cable keeps the same 40-pin connector but interleaves a ground between every signal for UDMA, with pin 34 used to detect the 80-conductor cable.

Pinout

Pin	Name	Function	Description
1	-RESET	SIGNAL	Drive reset, active low
2	GND	GND	Ground
3	DD7	DATA	Data bus bit 7
4	DD8	DATA	Data bus bit 8
5	DD6	DATA	Data bus bit 6
6	DD9	DATA	Data bus bit 9
7	DD5	DATA	Data bus bit 5
8	DD10	DATA	Data bus bit 10
9	DD4	DATA	Data bus bit 4
10	DD11	DATA	Data bus bit 11
11	DD3	DATA	Data bus bit 3
12	DD12	DATA	Data bus bit 12
13	DD2	DATA	Data bus bit 2
14	DD13	DATA	Data bus bit 13
15	DD1	DATA	Data bus bit 1
16	DD14	DATA	Data bus bit 14
17	DD0	DATA	Data bus bit 0
18	DD15	DATA	Data bus bit 15
19	GND	GND	Ground
20	KEY	SIGNAL	Keying position (pin removed)
21	DMARQ	SIGNAL	DMA request
22	GND	GND	Ground
23	-DIOW / STOP	SIGNAL	Write strobe (Ultra DMA: STOP)
24	GND	GND	Ground
25	-DIOR	SIGNAL	Read strobe / Ultra DMA ready
26	GND	GND	Ground
27	IORDY	SIGNAL	I/O channel ready / Ultra DMA ready
28	CSEL	VIDEO	Cable select / spindle sync
29	-DMACK	SIGNAL	DMA acknowledge
30	GND	GND	Ground
31	INTRQ	SIGNAL	Interrupt request
32	-IOCS16	SIGNAL	16-bit I/O (obsolete in ATA-3+)
33	DA1	SIGNAL	Address bit 1
34	-PDIAG / CBLID	SIGNAL	Passed diagnostics / 80-conductor cable detect
35	DA0	SIGNAL	Address bit 0
36	DA2	SIGNAL	Address bit 2
37	-CS0	SPI	Chip select for command-block registers
38	-CS1	SPI	Chip select for control-block registers
39	-DASP	SIGNAL	Drive active / slave present (LED driver)
40	GND	GND	Ground

Notes

Pin 20 is keyed (no pin) for orientation.
Some control pins take Ultra DMA dual functions.
The 44-pin 2.5-inch variant adds power pins beyond these 40.

Reference: ATA/ATAPI (PATA) 40-pin interface pinout· verified 2026-06-27