IDE (Integrated Drive Electronics), standardised as ATA (AT Attachment) by the T13 technical committee of INCITS, is a parallel interface for connecting storage devices such as hard disks and optical drives to a PC host. The interface uses a 40-pin IDC header on both host and device, with pins arranged on 2.54 mm (0.100 in) centres and pin 20 physically removed as a keying feature. A flat ribbon cable carries all 40 conductors straight through from connector to connector; the standard 40-conductor variant supports Ultra DMA modes 0–2 (up to 33.3 MB/s), whilst the 80-conductor variant — which interposes a ground wire between each signal wire — is mandatory for Ultra DMA modes 3 and above (ATA/66 and ATA/100). The interface governed by ATA/ATAPI-5 (NCITS 340-2000) and ATA/ATAPI-6 (INCITS 361-2002) remained the dominant desktop storage bus through the early 2000s.
The IDE ribbon is a straight-through cable: conductor 1 (the marked edge) connects to pin 1 at every connector, wiring the controller to drive 1 and drive 2 in parallel with no crossovers.
40 PIN IDC FEMALE to the Controller
40 PIN IDC FEMALE to the Drive 1
40 PIN IDC FEMALE to the Drive 2
| Controller | Drive 1 | Drive 2 | |
|---|---|---|---|
| Wire 1-40 | 1-40 | 1-40 | 1-40 |
Notes
All 40 conductors are wired straight through (pin 1 to pin 1, pin 2 to pin 2, and so on). The cable carries up to two devices; one must be jumpered as Master (Device 0) and the other as Slave (Device 1). If only one drive is fitted, jumper it as Single where that option exists, or as Master otherwise.
Pin 20 is physically absent on both the cable and the header and serves as a mechanical key to prevent reversed insertion.
For Ultra DMA modes 3 and above (ATA/66, ATA/100), an 80-conductor cable with the same 40-pin connectors is required. The 80-conductor cable is colour-coded: blue connects to the host/motherboard, black to Device 0 (master), and grey to Device 1 (slave). The blue host connector grounds pin 34 (CBLID–) internally, allowing the host to detect which cable type is fitted.
Maximum cable length for both variants is 457.2 mm (18 inches).