SCSI background sources include:
http://www.techweb.com/encyclopedia/defineterm.jhtml?term=scsi

SCSI - Small Computer Systems Interface.  Pronounced "scuzzy."

SCSI is an ANSI standard for connection peripherals/devices to your computer
via a hardware interface, which uses standard SCSI commands.

In the early 1980's, Adaptec's founders, while at disk drive manufacturer
Shugart Associates, developed a parallel I/O interface called SASI for Shugart
Associated System Interface.  When this specification was finalized, it was
released to several different manufacturers and enjoyed commercial success.
In 1982, SASI was presented to ANSI as a basis for standard.  Because of the
commercial success and widespread market use of SASI, ANSI formalized and
extended the SASI specification and changed the name to SCSI (in part to
separate the specification from any one vendor in particular).  In June 1986,
SCSI was formally adopted by ANSI.

The following hardware interface devices allow SASI/SCSI devices (such as hard
disk drives) to be connected to the Atari:

==> ICD Multi I/O (MIO)
- Parallel printer interface
- Serial interface, for modem or serial printer.  will handle 19.2Kbps
- 256K or 1 MB RAM, for RAMdisk or printer spooler
- SASI/SCSI interface, supports up to 8 controllers.
- Limited to drives with 256-byte sectors.
Attaches via PBI, or ECI with adapter.

==> CSS Black Box
- RS-232 Serial Modem Port (19.2Kbps) w/ hardware flow control
- Parallel Printer Port
- SASI/SCSI Hard Disk Port
- Operating System Enhancements
- optional 64K printer buffer
- Supports drives with 512-byte sectors
PBI/ECI device.
Available: http://www.nleaudio.com/css/products/black.htm

Mathy van Nisselroy's Black Box page:
http://www.mathyvannisselroy.nl/blackbox.htm


ASPI - Advanced SCSI Programming Interface
Originally developed by Adaptec.  It is a software layer that enables programs
to communicate with SCSI (and ATAPI) devices.

Mathy van Nisselroy's Atari ASPI page:
http://www.mathyvannisselroy.nl/aspi.htm