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Troubleshooting the Hard Disk
SCSI overview
SCSI stands for Small Computer System Interface. Every Macintosh and clone since the Mac Plus has had SCSI. Look on the back of your machine. It is probably the widest plug there, followed in size by the monitor port. SCSI allows your Macintosh to expand. You can add an additional hard drive, CD ROM drive, scanner, Zip drive, or anything designed to use this high speed connection.
SCSI has become somewhat of an industry standard for expanding a computer's useability. A standard Macintosh or clone can typically have six devices available to it. To keep track of these many devices, SCSI identification numbers are used. There can be a total of seven devices, with your Macintosh always reserving ID 7 for itself. Most any Macintosh has a hard drive built into the casing of the machine. This "start-up" drive (even if it is an IDE drive) uses ID zero (0). A built in CD ROM drive would typically use ID one (1), although newer PCI based PowerMacs often have it set at ID three (3). Additional devices are then set with sequential numbers, based on their position in the SCSI chain. One important catch to SCSI chains is that they need to be "terminated." Think of the chain as a line of people playing "telephone." The Mac sends out a message along the chain. "Hello, who's out there?" This message is relayed to each person in the chain. The last person in line is the terminator. (The good one, from T2!) This person receives the message and then sends a message back, saying essentially, "I'm the last one here. Send another message when you're ready."
Without a terminator, the last person in line would relay the message from the Mac to nobody. That person might simply repeat the question back, or provide some wacky information that is irrelevant. The Mac gets really confused, and things literally come to a halt. A terminator is a plug that attaches to the open SCSI port on the last external device. Some external devices, like a Zip drive, have a built in terminator that can be activated with a switch. The reason there isn't a plug on your Macintosh's SCSI port is that it terminates itself; it also has an internal terminator that activates itself when needed. SCSI can be a very powerful tool for expanding the functionality of your Macintosh. Here are some VERY important tips to remember when using SCSI.
- NEVER detatch or attach SCSI devices when your Macintosh is on. Always turn off BOTH the Mac and the SCSI device (unplug your ZIP drive) before doing anything with the cables. There are great amounts of electricity travelling through SCSI devices. Interrupting that flow of power can literally blow your Macintosh, releasing the dreaded "blue smoke."
- Use the shortest, fattest SCSI cables you can find. Pay extra for good ones, especially if many devices are to be used. Think of it in terms of our line of people playing "telephone." When you have good, short cabling, it is similar to these people standing right next to eachother. Cheap, long cables makes it as though they were standing very far apart, not able to clearly understand one another.
- Before turning on your Macintosh, first turn on your external SCSI devices. When your Mac starts up, it "puts out a shout" to see who is out there. (No, connecting yourself to a SCSI chain will not allow you to talk to your Macintosh!)
- When connecting SCSI devices, make sure you have set the Identification numbers correctly. If you don't know what numbers are already being used, download either SCSI Probe, or Mt. Everything from the MacintoshOS.com shareware library. Remember, as the chain extends itself, the numbers get higher, up to ID 6. ID 7 always belongs to your Mac!
How do I use SCSI?
The SCSI port on the back of your machine is a 25 pin connector. If your SCSI device is not like this, you will need the correct cable. The next most common SCSI connection is 50 pins, often in a form called "Centronics." A SCSI device using Centronics 50 connectors typically needs a terminator. If your new device has the same connections as your Mac, it will most likely have a built-in terminator. Another type that is occasionally found is a mini SCSI connection found on Iomega's new Jaz drive. Used mostly for space saving measures, these connectors can require the purchase of an external terminator, if it will be the last SCSI device in the chain. Don†t leave the store with your new SCSI device until you are sure you have the right cables and terminator.
Now make sure your SCSI ID number is set. The device will typically have a switch near the SCSI connector that allows you to set your own ID. Start high, keeping in mind that the Mac itself needs ID 7 to work.
My Macintosh isn't recognizing my SCSI device.
1. Hard drives
• Is the hard drive Macintosh formatted?
• Was the external drive turned on before the Mac?
• Is the hard drive terminated?
• Are the SCSI ID numbers conflicting?
• Is the device connected? Plugged in? Using good cables?
• Can you hear the hard drive spinning?
2. Removable cartridge drives (ZIP, EZ, Syquest, etc.)
• All of the above
• Is the cartridge Mac formatted?
• Can the Macintosh read other cartridges? (are you unknowingly trying to use a bad cartridge?)
• Try mounting the cartridge with SCSI Probe or Mt. Everything
3. CD ROM drives
• All of the hard drive checks which apply
• Do you have proper CD ROM software drivers? (These are included in the Macintosh operating system, or typically with the drive itself. If the drive is not made by Apple, you may need a CD mounting program.)
I've tried everything, and my SCSI chain is just not working.
SCSI chains are very sensitive. One weak link can take down the whole line. As a last resort, try connecting one device at a time. Try an intelligent terminator. Borrow or use cables that are known to work. Try the device on a friend's Mac. These kinds of troubleshoots are not often needed. Chances are you're just being picked on. Be patient, spend time away from the problem, and post your troubles on MacintoshOS.com's Discussion Forum for other's to think about too. Before long you'll be slapping your forehead and saying "oh man, I can't believe I didn't think of that before!" You'll be smarter for it, and better looking too.
The SCSI port on my Mac is different from the one on my external device.
Your Macintosh has a 25-pin connection built in called DB25. External devices typically use Centronics 50 connections. Other smaller devices use a mini connector. There are cables for all of these. As always, the better quality cable will give you less hassle. Remember also that if your external device doesn†t have internal termination, you will need a terminator. (No, not Arnold.)
What is SCSI docking, and how do I use it?
SCSI docking is a really cool way to connect your Apple PowerBook to your desktop Macintosh. Many PowerBook models support this, but you need to verify for yourself that yours is or isn't one of them. Once you are sure that yours is, you only need the appropriate connections. There are special docking adapters that allow you to connect an external device to your 'Book as well as switch to docking mode. Apple recommends buying their special cable which, in conjunction with a terminator, connects to another cable attached to your Mac. Before the connection is made, set the SCSI ID switch (a control panel) on your PowerBook. Shut it down, and the desktop Mac, and make the connection. Turn on your PowerBook, and then turn on your desktop Mac. Your PowerBook should display a SCSI symbol on the screen with it's ID number. BE WARNED: you can really screw up both machines if you do this incorrectly. The information provided here is meant only to inform you of the option. BE CAREFUL!
How do I put my old internal hard disk in an external case?
Alliance Peripheral Systems, 800-443-4199/816-483-6100 sells cases for old internal 3.5 inch drives for $179.95 plus shipping and handling (about ten to fourteen dollars). The price includes instructions and technical support for the installation.
What's the best CD-ROM Drive?
There are three features you should look for in a CD-ROM drive. First and most importantly you want at least a double-speed drive. If cost is your only concern single speed drives are available for less than one hundred dollars, but they're painfully slow for most applications. You'll also sacrifice many other bells and whistles. Triple-speed drives ar available for less than $200 from many sources and may be useful if you mainly retrieve text, graphics and other data files from CDs.
However most multimedia applications and games designed to be run from a CD are optimized to work best at double-speed and will gain little if any advantage from a triple-speed drive. Quadruple speed drives are also available for $200 and up. Most manufacturers and software vendors are jumping straight to the quadruple speed format and will skip the triple speed drives completely. Thus for maximum compatibility with future applications (and for some more speed now) consider spending the extra money for a quad-speed drive. Sextuple speed drives are also available, but like the triple speed drives this format will probably be an interim format unsupported by most publishers. Further down the road the next big jump will probably be to either 20-speed drives or to quad speed drives that can also write CDs or both. However these won't become real consumer-priced items until at least summer 1996 so by all means buy a CD-ROM drive now if you haven't already.
Secondly the drive should be "multi-session, PhotoCD compatible." Some drives on the market advertised as "PhotoCD compatible" but can only read the first set of photos on a PhotoCD.
Finally you want a drive with excellent audio capabilities including playback of audio CD's and digital copying of audio CD's to your hard disk. That last capability is the kicker. It's available out of the box only with the various versions of the Apple CD-300 and CD-600, but FWB's CD-ROM Toolkit adds support for digital audio extraction on drives based around the following mechanisms: the Chinon 535, Compaq CR-503BCQ, NEC CDR 400, 500, 501 and 900, Sony CDU-55S, 561, 561SUNCD, 75S, 76S and 920S, Plextor PX-43CH, 45CH, 43CS, 45CS, 63CS and 65CS, the Toshiba 3301, 3401, 3501, 3601, 4100, 4101, the Yamaha CDR-100 and possibly others.
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