IDE Internal (old) pinout

Often, the control circuitry is built into the motherboard, eliminating the requirement for a separate Host Adapter. There are 2 types of IDE interfaces...those for the 8-bit XT bus, and those for the 16-bit AT bus .
The cable for IDE contains 40 conductors and has no twists. Like an SCSI cable, the IDE cable uses a Dual-row Pin connector for both ends. A single cable may be used to connect two drives, or two cables may be Daisy-Chained.
Most IDE Host Adapters will support two hard drives. The first drive should be jumpered as the Master drive, and the second as the Slave drive. Plug-in IDE Host Adapters are often called Paddle-Boards, and may contain a floppy controller, and serial and parallel ports.

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
21	n/c	-	Not connected
22	GND		Ground
23	/IOW		Write Strobe
24	GND		Ground
25	/IOR		Read Strobe
26	GND		Ground
27	IO_CH_RDY
28	ALE		Address Latch Enable
29	n/c	-	Not connected
30	GND		Ground
31	IRQR		Interrupt Request
32	/IOCS16	?	IO ChipSelect 16
33	DA1		Address 1
34	n/c	-	Not connected
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

Note: Direction is Controller relative Devices (Harddisks)