Compare 2.5-3.5" HDD Pins
N.B. All the information in this page is intended only for guidance. It is believed to be correct and not everyone adheres to standards. The information is used at your own risk.
40-pin IDE/ATA Connections for 3.5" Desktop Hard Drives
Fig 1. Female slots
Fig 2. Male pins
1. Pin/Slot 20 (arrowed above) may have an absent pin or be blanked of as a key identifier. It carries no data nor power.
2. The outside notch beside Pins/Slots 19 and 21 may or may not be present.
3. The ribbon cable normally has a red line going to Pin/Slot 1.
44-pin IDE/ATA Connections for 2.5" Laptop Hard Drives
Fig 3. Female Slots
Fig 4. Male Pins
The first 40 are the same as their desktop cousins but there are an additional four pins (41 to 44) which use 5V power normally carried by a molex connector on a desktop hard drive.
Don't confuse the four pins (41 to 44) with another bank of four pins (- usually separated from the other 44 pins by a gap -) which are for jumpering the laptop hard drive. These are usually not jumpered at all on laptop hard drives.
Complete end-view of 2.5" Hard Drive (inc. 4-pin jumper block)
Fig 5. End-view of 2.5" drive - (PCB on top here).
The four-pin jumper block seldom actually has any jumpers on it and this is commonly the Master setting. There is however much variation and the drive itself should be examined carefully for the correct jumper settings or the internet browsed for supporting documentation for the make and model in question.
Dont confuse the above layout with the less commonly seen 60-pin blocks, where the first six pins are customisable and the last 44 are the same as the 44-pin ATA/Power layout as in Fig 5. The absent pin (if it is absent) for Key at posn 20 can often be very useful in orientation.
The ATA Pin-Outs consist of:
Pin Name Dir Description 1 /RESET OUT Reset 2 GND ------ Ground 3 DD7 IN/OUT Data 7 4 DD8 IN/OUT Data 8 5 DD6 IN/OUT Data 6 6 DD9 IN/OUT Data 9 7 DD5 IN/OUT Data 5 8 DD10 IN/OUT Data 10 9 DD4 IN/OUT Data 4 10 DD11 IN/OUT Data 11 11 DD3 IN/OUT Data 3 12 DD12 IN/OUT Data 12 13 DD2 IN/OUT Data 2 14 DD13 IN/OUT Data 13 15 DD1 IN/OUT Data 1 16 DD14 IN/OUT Data 14 17 DD0 IN/OUT Data 0 18 DD15 IN/OUT Data 15 19 GND ------ Ground 20 KEY - Key 21 n/c - Not connected 22 GND ------ Ground 23 /IOW OUT Write Strobe 24 GND ------ Ground 25 /IOR OUT Read Strobe 26 GND ------ Ground 27 IO_CH_RDY IN 28 ALE OUT Address Latch Enable 29 n/c - Not connected 30 GND ------ Ground 31 IRQR IN Interrupt Request 32 /IOCS16 ? IO ChipSelect 16 33 DA1 OUT Address 1 34 n/c - Not connected 35 DA0 OUT Address 0 36 DA2 OUT Address 2 37 /IDE_CS0 OUT (1F0-1F7) 38 /IDE_CS1 OUT (3F6-3F7) 39 /ACTIVE OUT Led driver 40 GND ------ Ground 41 +5VL ----> +5VC (Logic) 42 +5VM -----> +5VC (Motor) 43 GND ------ Ground 44 /TYPE -----> Type (0=ATA)
Ribbon Cables (40 versus 80 wire)
80-wire data cables, when used, still only attach to pins 1 to 40. They are part of the UDMA (Ultra DMA) Transfer Mode specification of the ATA/ATAPI-4 standard. The extra wires are interposed between the original 40 wires and all run to earth to prevent stray signals crossing over between adjacent wires. This allows for faster trouble-free data transfer and automatically supports the CableSelect feature. The same standard allows for colour-coding of the connectors on the cable. Blue to motherboard, Grey (in the middle) to any Slave Drive and Black to the Master or to a Single Drive. Under the specification it is not allowable to attach a single drive to the middle connection.
Smaller and Smaller Drives
More and more Solid State (NAND and CompactFlash) as well as Spinning 1.8" Hard Drives are coming on stream. These usually have a 50-pin interface for which we don't yet have the specifications. Some come with a ZIF (zero force clip on connections) and some with mini-ATA or micro-ATA 50 pin sockets. The latter can be quite easily interfaced using a 1.8"-to-2.5" converter. There is also an adapter to connect these small 1.8" drives inside a 2.5" USB external enclosure.