There are many different interfaces used.
For internal hard drives, older drives use/used PATA (Parallel ATA, originally just called ATA, and commonly referred to as IDE). Newer drives generally use SATA (Serial ATA).
For external drives, connections include USB (1.0, 2.0, and 3.0), eSata, and Firewire (IEEE 1394).
SCSI (Small Computer System Interface) is not typically used for internal tape drives, as most modern internal tape drives utilize SATA (Serial Advanced Technology Attachment) or SAS (Serial Attached SCSI) interfaces. SCSI was more common in older tape drive models, while SATA and SAS offer better performance and compatibility with current hardware systems.
Integrated Drive Electronics (IDE) refers to a standardized interface that provides slots for connecting hard drives to the motherboard of a computer. SCSI, known as Small Computer Systems Interface, provides a universal interface for connecting such devices as disc drives, hard drives, plotters and scanners.
Floppy drives do not typically need drivers. Any operating system on a typical PC can interface with the floppy controller integrated into the motherboard. All modern operating systems include drivers to interface with drives connected via USB.
backbone
SCSI Harddrive:80-pin Connector The SCA interface was designed to provide a standard connection for systems using hot swappable drives. SCA interface drives connect to a SCSI backplane that provides power, configuration settings such as SCSI ID, and termination of the SCSI bus.
Hard disk drives
Most external hard drives can be used as internal ones. Provided that the IDE, SATA, or SCSI interface of the external hard drive is the same as the desktop's system board hard drive interface. Users can remove the USB casing and proceed to plug the data and power cables into it. The external drive, just has an additional component, that's used to hook up with the USB port.
SAS (Serial Attached SCSI) interfaces can connect various types of devices, primarily storage devices such as hard disk drives (HDDs) and solid-state drives (SSDs). Additionally, SAS can interface with tape drives and expanders, allowing for the connection of multiple devices in a storage network. It is commonly used in enterprise environments for high-performance and reliable data storage solutions.
External drives require additional controllers to adapt the signals to the chosen interface. The drives themselves are manufactured as ordinary IDE or SATA drives, and are simply placed in an enclosure. The enclosure adds a great deal to the cost. Another factor is that external drives are more prone to damage, so the company may need to charge more to offset RMA costs.
in internal bays
Enhanced Integrated Drive Electronics (EIDE)
In the early take up period of computer cdrom drives, Pc's required an interface to drive the unit itself. Later on, the drives were created able to utilise the IDE interface.