Penguin
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SCSI is an Acronym for Small Computer Systems Interconnect - a method of attaching peripherals to a computer motherboard. People generally consider SCSI to be more reliable (and more expensive) than IDE.

SCSI allows better throughput than IDE by allowing commands to be sent asynchronously - that is, you can send a "read" or "write" request and return immediately, and sometime later (when the device has finished reading or writing) do something with the data. In contrast, for IDE the read request doesn't return until the data has been physically read from the disk.

The SCSI protocol requires a host card (called an adapter). SCSI peripherals are then attached to this card. In theory (ha!) up to 127 devices in one chain can be attached to each host card. SCSI cables require a special terminator at each end.

People sometimes describe SCSI as requiring black magic (including sacrifricing goat's blood, or occasionally Lusers).

Note: Do not underestimate the black majick involved in SCSI! If you don't have a terminator on the non-controller end, it might work for a while, and then never work again. Or it might work under some OS's but not others. Put a terminator on it already. While you're at it, ensure BOTH ends of each channel are terminated. Most modern cards have "Auto" termination, and this almost always works these days, but if unsure, set to "Enabled", terminate the end of the cable, and if you're unsure if your cable terminator is active or passive, enable "term. power" on at least one of the devices on the channel.

SCSI over IP is called iSCSI.

Debian doesn't detect my SCSI card

Go to http://people.debian.org/blade/install/preload/ and download the bf24 SCSI driver disc. Modules for the kernel included with Debian's bootfloppy-2.4 kernel are on this disc. It will make the woody install nice and smooth.