ASPI: Advanced SCSI Programming Interface, a specification that Adaptec developed and that programmers can use to write device drivers and other programs that communicate with devices such as scanners. ASPI defines a common set of communications that can be sent from SCSI devices to host adapters to carry out tasks such as data transfer.

ASPI layer: A standard software interface between the ASPI device drivers and the ASPI software manager, which programmers write for a specific host adapter. Commands from the ASPI device drivers pass through the ASPI layer.

ASPI software manager: Also called the ASPI manager; a program tailored for a specific host adapter and operating system that interprets commands from ASPI devices and relays this information to the host adapter. ASPI software managers are sometimes called system-level drivers.

Device driver: A program that controls a piece of hardware, such as a scanner. Scanners usually require two drivers to work: one for the host adapter and a second to control the scanner. The host-adapter driver is often called a system-level driver (usually a *.sys file); the scanner driver is called a source driver. Source drivers that comply with the ASPI specifications are called ASPI device drivers.

Host adapter: Hardware that lets the computer communicate (using software such as ASPI managers and device drivers) with the SCSI device. Host adapters can be either a printed circuit board card or a built-in bus on the system motherboard.

ISIS: Image and Scanner Interface Standard, an API for the design and development of scanner drivers. Developed by Pixel Translations and now adopted by other vendors, ISIS is an alternative to the TWAIN standard, specifically for scanners. The ISIS standard is usually used for optical character recognition (OCR) software.

SCSI: Small Computer Systems Interface, a standard developed in the late 1980s. It lets up to seven SCSI devices be daisy-chained onto a single SCSI bus. The most common standard is SCSI-2, which was finalized in 1992 and among other things, added support for CD-ROMs and scanners.

SCSI devices: Peripherals such as disk drives, CD-ROM drives, scanners, and tape drives.

TWAIN: An image and scanner interface standard for the design and development of scanner drivers. TWAIN is an alternative to the ISIS standard.