Keith:

I don't think you should hesitate to thank Oso at all. He answered your question. His surprise is that the question is extremely basic for the level of computer user normally associated with this site.

However, many people who have used computers have not played with the hardware much. If you open your case you will notice a cable going to your hard drive. If your hard drive is a standard drive then it is EIDE (unless it is very old in which case it might be IDE). There are two EIDE connectors on most motherboards (connector 0 and 1). They can support two devices each, a master and a slave. So your computer can initially support 4 IDE devices.

You can add cards that give you more IDE ports for more devices.

SCSI is also a device controller but it can support 7 or 15 depending on the type of SCSI controller you have.

IDE advantages are cheaper devices, decent performance, easy to set up and use, almost always integrated into the motherboard (no extra cards to buy).

IDE disadvantages Fewer Devices

SCSI advantages: More devices, higher data rates, better data utilization

SCSI disadvantages: More expensive devices, Usually not integrated into the motherboard, steeper learning curve to set up.

Hope this helps clarify a bit.

For my home system I use IDE due to price and because performance is not critical. At work we use SCSI since cost is less important than performance. If you are going to use SCSI make sure to set up your LUNs (check Whatis.com) correctly. Also you should realize that *nix usually is happier if certain devices use certain lun numbers.

BTW, SCSI is much easier to set up now than it was in the past. Like many things they have worked to become much more user friendly. My recommendation though is that if you are going to purchase a SCSI interface card get a well known one like Adaptec. It simplifies its integration with OS's like Linux. Personally I wouldn't buy one that wasn't Adaptec but I am prejudiced by past problems.