Computer interfaces

Most internal drives for personal computers, servers and workstations are designed to fit in a standard 5.25" drive bay and connect to their host via an ATA or SATA interface. External drives usually have USB or FireWire interfaces. Some portable versions for laptop use power themselves off batteries or off their interface bus.

Drives with SCSI interface exist, but are less common and tend to be more expensive, because of the cost of their interface chipsets and more complex SCSI connectors.

When the optical disc drive was first developed, it was not easy to add to computer systems. Some computers such as the IBM PS/2 were standardizing on the 3.5" floppy and 3.5" hard disk, and did not include a place for a large internal device. Also IBM PCs and clones at first only included a single ATA drive interface, which by the time the CDROM was introduced, was already being used to support two hard drives. Early laptops simply had no built-in high-speed interface for supporting an external storage device.

This was solved through several techniques:

* Early sound cards could include a second ATA interface, though it was often limited to supporting a single optical drive and no hard drives. This evolved into the modern second ATA interface included as standard equipment
* A parallel port external drive was developed that connected between a printer and the computer. This was slow but an option for laptops
* A PCMCIA optical drive interface was also developed for laptops
* A SCSI card could be installed in desktop PCs for an external SCSI drive enclosure, though SCSI was typically much more expensive than other options