SCSI Computer Devices

Though most people won't run into SCSI devices when dealing with computers, it doesn't hurt to know how to work with them.

Unlike IDE which can only have 2 devices on each cable (master and slave), SCSI can have many devices on a cable in a daisy chain. Each device has to have a unique number assigned to it (there can't be any duplicates). How do you assign your SCSI device a number? Use the jumpers. On the back of all SCSI devices there should be a set of jumpers (like regular IDE devices). Read the manual to see exactly which ones are which, but each set of pins should have a certain value and the values should go in order like this: 0,1,2,4... You can put more than 1 jumper on, so if you want to assign a device as 3, jumper both 1 and 2.

Keep in mind that hard drives usually are lower (0s and 1s) than other things. Also remember that SCSI devices are daisy chainable, so the end of the cable needs a terminator.

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SCSI is a type of interface for peripherals. Most modern SCSI devices are much speedier than their USB, FireWire, or IDE equivalents. But SCSI is not only beneficial for its speed, but also its much reduced dependence on the main CPU. For operations like CD Burning, this is a godsend. The number of coasters produced is much, much smaller when compared with an equivalent IDE or FireWire CD-R drive. And then Plextor introduced BurnProof technology. But still, if you like having a useable system while burning something SCSI is a better way to go. In recent times, though, I can't recommend it for anything more than that. A 12X SCSI burner just doesn't compare with a 40X IDE burner.

I was amazed and stunned that E2 had very little in the way of biased SCSI brain washing nodes, so I took it upon myself to take care of this. Please enjoy, won't you?:

Low Voltage Differential
High Voltage Differential
Single-Ended
SCSI-1
Differential
Fast SCSI
Ultra SCSI
Wide SCSI
Ultra Wide SCSI
Ultra 160 SCSI

Please note that all iterations of SCSI have to be properly terminated.

SCSI is also, like all wiring, susceptable to EMF and Magnetic Flux interference. Because of this, new ways to shield the precious wiring have been developed and popularized. These include ThermoPlastic Elastomer and Teflon, which is also labeled as FEP (Fluorinated Ethylene Propylene). All SCSI cabling has maximum length limits, which depend on the version used (feel free to explore the nodes above for specifics). Cabling can be custom-made and may be fairly expensive, especially the afforementioned Teflon. In general, people report up to a 10-20% gain in throughput when using high-quality cabling.
scruffies = S = SCSI voodoo

SCSI n.

[Small Computer System Interface] A bus-independent standard for system-level interfacing between a computer and intelligent devices. Typically annotated in literature with `sexy' (/sek'see/), `sissy' (/sis'ee/), and `scuzzy' (/skuh'zee/) as pronunciation guides -- the last being the overwhelmingly predominant form, much to the dismay of the designers and their marketing people. One can usually assume that a person who pronounces it /S-C-S-I/ is clueless.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

A bit more on SCSI, to build on ivan37's wu above.

You may have one or more SCSI ports on your motherboard, or you may be using one or more SCSI adaptors (usually a PCI card). If you're using a card, the one that's plugged in closest to the power supply will probably be card 1, and so on accross the motherboard.

The machine will try to boot off SCSI devices in order, so your boot drive should be on card one, with a low SCSI ID, such as 0. ID 7 will be occupied by the adaptor itself. Beyond this, SCSI IDs are largely unimportant. You can attach as many devices as will fit (ie. 13). If you have two devices which you know will talk to each other a lot, such as a CD-ROM and a CD-RW, try to put them on the same SCSI bus.

A SCSI bus is made up of the adaptor, the cable and any devices. The bus needs to be terminated, either by setting the termination jumper on a device attached to the last connector on the cable (ie. furthest from the adaptor), or by attaching a dongle-type terminator. There should be a label on the disk telling you which one is the termination jumper.

The connectors, cable and devices can be one of two types (your adaptor or motherboard may even have both types on it) - these are Narrow SCSI and Wide SCSI. Narrow SCSI connectors are wider then Wide SCSI connectors - the name comes from the number of pins (Narrow = 50 pins, wide = 68 pins). You can get adaptors which allow you to plug a wide SCSI connector into a Narrow SCSI device, but not vice-versa. Check wangmu's wu for more on eclectic SCSI connectors

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