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

Nominally called the IDE (Integrated Drive Electronics) bus; how ever it"s more correctly known as the ATA (Advanced Technology Attachment) [Parallel bus] specification [ATA Bus]. The IDE bus is used in Personal Computers [PCs] as a hard-drive or peripheral bus to interconnect the PC mother board and a hard drive. With the introduction of Serial ATA [SATA], Parallel ATA is now being called PATA. The specification has been up-graded a number of times each building on the past specification. ATA-1 and 2 were single documents, but like SCSI, after ATA-2 the specification was divided into a number of different documents. Data is passed Single-Ended. Only the 40 pin connectors are referenced below, which are used on 3.5-inch drives, but there is also a 50 pin connector used on 2.5-inch drives. The 50 pin connector adds the power and Master/Slave functions. PCMCIA uses a 68 pin connector. Most maintain backward compatibility, keeping in mind the cable changed. A graph showing the difference between ATA and Ultra ATA timing is shown on the Strobe page. The IDE, ATA connector pinout is listed in the table below. There are a number of versions: [Serial ATA: is listed on its own page.]

ATA-1 (IDE), [Obsolete] 8.3MBytes/sec, 8 or 16 bit data width, 40 pin data ribbon cable/connector. With a maximum of 2 devices on the bus. Using PIO Modes 0, 1 or 2. Preformed no bus error correction.

ATA-2 (EIDE, or Fast ATA), [Obsolete] 16.6MBytes/sec, 8 or 16 bit data width, 40 pin data ribbon cable/connector. With a maximum of 4 devices on the bus. Using PIO Modes 0, 1, 2, 3, or 4

ATA-3, 16MBytes/sec, 16 bit data width, 40 pin data ribbon cable/connector. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2. Runs with 120nS Strobes (rising edge to rising edge). Includes CRC.
ATAPI (ATA Packet Interface)is the CD-ROM side of the interface. It uses the same connector as ATA, and adds 1 for analog and 1 for digital audio.

ATA-4 Ultra-ATA/33, 33MBytes/sec, 16 bit data width, 40 pin data ribbon cable/connector. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, and 2. Runs with 120nS Strobes (rising edge to rising edge), but used both edges of the Strobe producing an effective 60nS Strobe rate. 33MBps Transfer speed = [(1/120nS) x 2 bytes x 2]. Where 120nS cycle time is 4 clock periods at 30nS each. Added CRC checking.

ATA-5 Ultra-ATA/66, 66MBytes/sec, 16 bit data width 40 pin data connector/80 pin cable, with the additional 40 new pins being Ground. The new cable allows ATA/66 to run at a faster rate then ATA/33. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, 2, 3 and 4. Runs with 60nS Strobes (rising edge to rising edge), but uses both edges of the Strobe producing an effective 30nS Strobe rate. 66MBps Transfer speed = [(1/60nS) x 2 bytes x 2]. Where 60nS cycle time is 2 clock periods at 30nS each.

ATA-6 Ultra-ATA/100, 100MBytes/sec,16 bit data width 40 pin data connector/80 pin cable, with the additional 40 new pins being Ground. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 1 and 2 and Ultra DMA modes 0, 1, 2, 3, 4 and 5. 100MBps Transfer speed = [(1/40nS) x 2 bytes x 2]. Where 40nS cycle time is 2 clock periods at 20nS each

ATA-7 Ultra-ATA/133, 133MBytes/sec,16 bit data width 40 pin data connector/80 pin cable, with the additional 40 new pins being Ground. Using PIO Modes 0, 1, 2, 3, or 4 and Multiword DMA modes 0, 1 and 2 and Ultra DMA modes 0, 1, 2, 3, 4, 5 and 6. 133MBps Transfer speed = [(1/30nS) x 2 bytes x 2]. Where 30nS cycle time is 2 clock periods at 15nS each

Serial ATA: (Ver 1.0) High Speed Serialized AT Attachment
Serial version of the IDE [ATA] spec. Uses a 4 conductor cable with two differential pairs [Tx/Rx], plus an additional three grounds pins and a separate power pin. Data runs at 150MBps [1.5GHz] using 8B/10B encoding and 250mV signal swings.
ATA-# interface for disk drives; defines the Physical layer, Electrical layer and Signaling protocol. The speed of data transfer depends on the Transfer mode used. There are 3 main Transfer modes: PIO, Multiword DMA, and Ultra DMA. All transfer rates listed above are best case [Mulit-word/DMA transfers].

PIO Modes: 0 [3.3MB/s], 1 [5.2MB/s], 2 [8.3MB/s], 3 [11.1MB/s], 4 [16.7MB/s]
Multiword DMA Modes: 0 [4.2MB/s], 1 [13.3MB/s], 2 [16.7MB/s]
Ultra DMA Modes: 0 [16.7MB/s], 1 [25.0MB/s], 2 [33.3MB/s], 3 [44.4MB/s], 4 [66.7MB/s], 5 [100.0MB/s]

Power (+5 / +12volts) is supplied over a four pin connector (unless the 50-pin connector is used). There are a number of power (down) modes defined: Active, Idle, Standby, and Sleep.
Active: normal drive operation.
Idle: the electronics power down but still receives commands.
Standby: the drive spins down and the electronics power down.
Sleep: every thing is powered down, the electronics will not respond except for a power reset.

The early specifications defined the data cable as a normal 40 pin ribbon cable with a 40 pin IDC connector. The latest standard(s) define the same 40 pin connector, but have increased the ribbon to 80 pins - the additional 40 pins being dedicated to ground pins. Data transfers are made at either 8 or 16 bits.
The normal PC cables have three connectors, one for the mother board (at one end) and two for device attachment. One at the opposite end, the other about 6 inches away.