I see a lot of people here having trouble with SCSI cards and devices, so why not do a little crash course on SCSI:

Some facts:

A SCSI (host)adaptor is a device controller much like an IDE controller found in every modern PC today. It has the abillity to control datastreams flowing to and from a number of devices, provided these are equipped with SCSI-interfaces/connectors.

Whereas a normal IDE controller handles harddrives, CD-ROMs, DVD-drives and other storage devices, SCSI controllers may also control other devices like scanners and CCD-cameras.

You average IDE controller will handle up to 2 devices (master/slave), and since a PC is normally equipped with a primary and a secondary IDE controller, this sums up to a max of 4 devices.

A SCSI controller will handle up to 7 or 15 devices, depending on the type of controller. With a SCSI controller there is no such thing as master/slave - instead SCSI-IDs are used, numbering from 0 to 7 (15) - The adapter usually has the ID #7 reserved for itself.
Another notable difference between IDE and SCSI controllers is that SCSI contr. most often have an external connector allowing the user to connect external devices to the controller. Some controllers have several different internal connectors to allow different types of SCSI devices to be connected (SCSI, SCSI-2, fast-SCSI, ultrawide-SCSI, LVD-drives, just to mention a few. I suggest you read here for further information: http://www.scsifaq.org/ ).

All these devices connected to the SCSI controller - internal as well as external - comprise the so-called SCSI-chain.

An IDE connector is 40 pins wide, SCSI connectors can be 50 pins, 68 pins or 80 pins. The ribbon cables are accordingly wider (except for ultra-cables). External cables are round and connectors are usually 50- or 68-pins high density (HD) - and quite expensive....some devices (like my old external ZIP 100 drive) require the old-type (or Mac?) 25 pin cable.

SCSI has throughout the years been known for its abillity to transfer data faster than IDE (due to a wider data-bus), but this speed difference gap has diminished noticable in recent years with the introduction of ATA66 and ATA100 in the IDE-world. And the introduction of USB 2.0 sends a third player onto the field.


When using SCSI there are some things/rules you should be aware of:

- All devices connected to a SCSI controller must have unique SCSI-IDs assigned. This goes for internal as well as external devices!

- Each end (internal <-> external) of a SCSI-chain MUST be properly terminated. Most modern SCSI devices have builtin termination, but this option must be enabled in order to work. External devices usually have 2 (HD) connectors - one FROM the previous device in the chain and one TO the next device (if any - which connector you use is normally up to you) - and a switch for termination.
Internal devices only have one connector allowing for connection with a ribbon cable. If the device you attach is the last one on the internal chain, you must connect this device to the LAST connector on the ribbon cable in order to obtain termination of the chain.

- In order to be able to boot from a SCSI device, the device must be defined (in the adaptor settings = SCSI-bios) as bootable. Also, this may have to be defined in the motherboard's bios.

- Some older SCSI harddrives require that a startup signal is sent to them during boot, to set them spinning. This may also be set up in the adaptor settings.

- Some external SCSI devices (fx. scanners) may be switched off. In order to be able to use these devices they must be detected by the adaptor during boot, which is why SCSI devices should ALWAYS be switched on before the PC is powered up. Sometimes a re-scan (with a piece of software like Adaptec's EZ-SCSI) from inside Windows will find such devices later, when they have been switched on, but personally I don't rely on that.
Internal devices naturally don't have any such power-on problems.

Once SCSI devices like harddrives, CD-ROMs ect. have been properly installed (incl. drivers) and are detected during boot, they can be handled like any other device in the system, and don't require any special software to work.


Well, quite a bit of writing here - I could go on, but that would probably become too boring for most. This is, after all, just a crash course intended to give an overview and maybe prevent the most common erros encountered when using SCSI.

If you have questions, feel free to post them here at VDr.

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Karl, Denmark
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"..and may The Force be with you too..."

[This message has been edited by kallikru (edited 05-24-2001).]