Learning Resources

Drive Connector and Cables


The desktop computer hard-drive connector is pictured here. It has 4 conductors, with the standard pinout as follows:

Pin # Color Function
1   Yellow +12 V
2   Black Ground
3   Black Ground
4   Red +5 V

Sometimes, especially in older computers, the colors differ. The pins are 0.200 in (5.08 mm) apart (center to center). The connector housing has chamfered corners on one side to prevent the user from plugging it in incorrectly. The connector that provides power (e.g., on a power supply) has female pins and a male housing; the connector that receives power (e.g., on a peripheral) has male pins and a female housing.

The connector is standard on all PATA disk drives and low-end SCSI disk drives; however, newer SATA disk drives will employ a more advanced interconnection with 15 contacts. These new, advanced connection systems are being developed by Molex and other connector companies, often working together to develop interconnection standards.

Despite its widespread adoption, the connector has problems as a 30-year-old product. It is cumbersome and difficult to remove because it is held in place by friction instead of a latch, and some poorly constructed connectors may have one or more pins become unattached from the connector when plugged in.

Insertion may also be difficult due to the tendency for the loosely inserted pins to come askew, preventing easy insertion into the female connector.

Additionally, over a long period of time the receiving socket can spread, making the connection imperfect and subject to arcing. It is strongly advised that, whenever working with these connectors, you check for any sign of blackening or browning on the white plastic shell: This is often a sign that arcing is happening and the connector needs replacing. In extreme cases (for example in vintage pinball machines which often use this style of connector) the whole connector can melt due to the heat from arcing.

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Hard disk drives have basically two connectors, one for power and other for exchanging data with the computer. This second connector is better known as “interface”. The most common hard disk drive interface for end-users is called ATA (Advanced Technology Attachment), while SATA (Serial ATA) interface was created to replace ATA and is becoming more popular these days. After the released of SATA, ATA interface started being also called PATA (Parallel ATA). Another famous interface is called SCSI (Small Computer Systems Interface), but it is targeted to servers and rarely seen on PCs targeted to end-users.

The master/slave jumper on ATA hard drives can be configured in three different ways:

  • Master: this means that this drive will be the only one attached to the cable that connects the hard drive to the computer or will be the first drive in a two-drive configuration.
  • Slave: this means that this drive will be the second drive attached to the cable that connects the hard drive to the computer.
  • CS (Cable Select): this means that you will use a “special” cable (called CS cable) that the configuration of whether a drive will be master or slave will be made by the position of the hard drive on the cable and not by a jumper configuration on the drive.


HDDs are accessed over one of a number of bus types, including as of 2011 parallel ATA (PATA, also called IDE or EIDE; described before the introduction of SATA as ATA), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to buses with which they cannot communicate natively, such as IEEE 1394, USB and SCSI.

Modern hard drives present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally. Typically a DSP in the electronics inside the hard drive takes the raw analog voltages from the read head and uses PRML and Reed–Solomon error correction90] to decode the sector boundaries and sector data, then sends that data out the standard interface. That DSP also watches the error rate detected by error detection and correction, and performs bad sector remapping, data collection for Self-Monitoring, Analysis, and Reporting Technology, and other internal tasks.


  • Small Computer System Interface (SCSI), originally named SASI for Shugart Associates System Interface, was standard on servers, workstations, Commodore Amiga, and Apple Macintosh computers through the mid-1990s, by which time most models had been transitioned to IDE (and later, SATA) family disks. The range limitations of the data cable allows for external SCSI devices.