In most cases when a product is described as conforming to SCSI 2, They are talking about the second implementation of the SCSI Parallel interface (SPI), it is also known as Fast SCSI. SCSI 2 introduces 16 (wide) bit operation, to accompany 8-bit (narrow] operation, and 10MHz (fast {more then 5 MB/s, though commonly thought of as being attached to the operating frequancy}) yielding bandwidth ceilings of ten (wide SCSI), and twenty megabytes per second{fast wide SCSI}. With the addition of "wide" scsi, SCSI-2 introduces the (high-voltage) differential (some may call it balanced) signaling method to accompany the original single-ended (or unbalanced) signaling standard.

The Adaptec page found at: adds that SCSI-2 reduces some of the SCSI timing margins "in order that faster handshaking could occur. The result is that asynchronous transfers can run at up to 3.0 bytes/Sec and synchronous transfers at up to 10.0 Mbytes/Sec."

SCSI-2 also tightens the termination standards, and I believe introduces active-termination, though in some cases where the SCSI chains are short, and there are few devices, passive termination will work.

The standard connector used when wiring a chain for use with 16 bit SCSI is called a SCSI-3 connector. It was not standardized in time to be included in the SCSI-2 standard, but it is the connector used to connect wide SCSI-2 cables, and devices (host bus adapters, drives, and other miscelaney{sp?}).

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