SCSI Frequently Asked Questions (FAQ)

Q. What is SCSI?
A. SCSI is an acronym for Small Computer System Interface (pronounced “scuzzy”) and is one of several high speed data transfer protocols that were developed in the late 1980s. There are also other types of data transfer protocols like IDE that are used by the computer community, however, the music community almost always uses SCSI.

The term SCSI is used in all kinds of terminology. There are SCSI ports on the back of a Macintosh and some samplers like the Kurzweil K2500 and Roland S-760. There are SCSI cables. There are SCSI devices, SCSI IDs, SCSI conflicts, SCSI controller chips ….the list goes on. You can have SCSI hard drives, CD-ROMs, removable hard drives, CD Recorders, etc.

Q. What is a SCSI ID number?
A. When you connect several SCSI devices together you create a “SCSI bus”. A bus is a path through which electrical signals are transmitted and received. An example of a simple SCSI bus would be a Macintosh computer connected to an external hard drive. The SCSI protocol allows you to have up to 8 devices connected together on the SCSI bus. Each device on the SCSI bus, including the CPU, is identified by a SCSI ID number. Each device must have a unique SCSI ID number. If two devices share the same SCSI ID# you will most likely experience a crash. It doesn’t matter what ID# you choose for your new SCSI drive as long as you don’t have two devices on the same ID#.

Q. How do I change a SCSI ID number?
A. Changing the SCSI ID number of your new hard drive is very simple. External hard drives have an ID selector on the back of the drive with two buttons. The number by the two buttons is the ID number. Pressing the top button with increment the the ID # by one and pressing the bottom button will decrement the ID # by one. If you change the ID# of the drive with the drive turned on you MUST turn the drive off and back on again before the change will take place.

Internal drives set their SCSI ID number via a series of jumpers on the hard drive’s PCB. This is a little more difficult that with an external drive and if you are not experienced in dealing with electronics (or Binary) you should refer the job to a trained technician.

Somewhere on the hard drive’s PC board you will find 3 sets of jumper pins (6 pins) labeled A0, A1, and A2. The ID # is set by placing a shorting jumper across one or more of these 3 sets of jumper pins. See the chart below to determine which set of pins to short or open to establish the ID you require.

O = open, X = jumper installed (shorted)

A0 A1 A2
0 0 0 = ID#0 – Normally used for internal boot HD in a MAC.
X 0 0 = ID#1
0 X 0 = ID#2
X X 0 = ID#3 – Normally used for internal CD-ROMs
0 0 X = ID#4
X 0 X = ID#5
X X 0 = ID#6 – Kurzweil’s default SCSI ID # (Can be changed from MIDI Receive page.)
X X X = ID#7 – MAC SCSI ID #
Q. How many SCSI ID numbers can I use at once?
A. Theoretically, all eight SCSI IDs can be used simultaneously, however, real world experience tells us that a more reasonable number is about 5 devices in the chain.
Each device in the chain (including internal hard drives) must have its own unique SCSI ID #. The default K2000 ID is #6. Macintoshes use ID #7 & ID #0.

Q. What is Termination?
A. Termination acts like a stop sign at each end of the SCSI bus. A terminator is a series of resisters that prevent SCSI signals from reflecting when they hit the end of the SCSI bus. You will get data reflection and data echoes that will corrupt the data if a terminator is not installed on each end of the SCSI bus. You MUST have termination on each end of the SCSI bus.

Most computers and SCSI equipped keyboards have termination installed internally so you only need to worry about the external drives that you add to the SCSI chain. Some SCSI devices have “active termination” which can be enabled by sliding a switch.

Q. Can I remove or switch SCSI Cables while my computers/keyboards are on?
A. If you remove any SCSI cables or SCSI terminators while data is being written you will mess up your drive and it will need to be Reformatted. Even if you are not writing data, removing or connecting SCSI cables is a very risky behavior. You won’t get bitten every time, but there’s always a chance that you may do serious damage to your computer, keyboard or SCSI drives.

Q. What is the longest length I can go with SCSI?
A. Here are some basic guidelines to follow when configuring a SCSI chain:

1. Including a minimum of 1 foot for internal cabling of each device in the chain, the total length of the SCSI chain should not exceed 18 feet.

2. No single cable length in the chain should exceed 8 feet.

Q. Can I use any Cable if it has the right connectors?
A. Use only true SCSI cables – high quality, twisted pair, shielded SCSI cables.
Do not use RS-432 or other non-SCSI cables.

Also, impedance mismatching between cables from different manufacturers may cause problems. Try to avoid this whenever possible.

Q. If there are two SCSI connectors on a drive, which is the In and which is the Thru?
A. With only a few exceptions the two SCSI ports on a drive are identical. As long as one end is correctly terminated (unless you’re going on to other drives) then the other end will work fine.

Q. Sometimes, when using my CD-ROM drive with my sampler, the drive locks up if I try to load from the CD right after I put it in the drive. Is something wrong?
A. Optical media (like CDs and Magneto Optical discs) needs a little time to be read by the drive before you try to access it. Just watch the little LED when you first put the CD-ROM in. After the light has changed you may proceed freely. If you do hang your drive, you’ll need to restart both your keyboard and CD-ROM drive.

We hope this Q&A sheet has helped you get up and running with you new SCSI equipment. All of us would like to thank you for making Sweetwater your music technology experts.

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