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Tech Tips: SCSI, Drives and All That Jazz
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Everything you ever wanted to know about SCSI problems, drives and loads more besides
How do I setup a non-Apple hard drive?
What's the 'hard drive interleave'?
How big a hard drive can I install?
My hard drive has given up - help!
Can I add a CD Writer to my Mac?
What's the best way to diagnose a SCSI error?
Is there a limit on how many SCSI devices I can connect?
My floppy drive won't read a disk - what's up?
[Q]: How do I setup a non-Apple hard drive?
[A]: Installing hard drives in Macs is a doddle and Apple branded drives simply need plugging in and initialising with Apple's Hard Disk Setup application. Non-Apple drives though can cause problems. While there are versions of Apple's tools that will accept non-Apple drives, the vast majority won't. In these cases you need a third party application to do the job. Plug the drive in as normal, fire up the Mac and then run something like MicroNet Utility or FWB and your drive should be ready to go.
[Q]: What's the 'hard drive interleave'?
[A]: Early Macs had issues with reading/writing to hard drives and to solve the problem the hard drive could be initialised in such a way as to avoid the problem. Apple's HD SC Setup automatically sets this based on the machine's gestalt ID but if you do have to set it manually (i.e. via a hard drive management application), the following values should be used: Mac SE, Mac Classic - Interleave=2:1, Mac Plus - Interleave of 3:1. All other Macs should use an interleave of 1:1.
[Q]: How big a hard drive can I install?
[A]: The answer is more to do with the OS instead of the hardware. Anything before OS 7 is limited to 2Gb. OS 7 to OS 7.5.1 is limited to 4Gb, and OS 7.5.2 (and upwards) raised the limit to a stupid 2Tb!
[Q]: My hard drive has given up - help!
[A]: Assuming that your hard drive HAS totally given up... If you want to try to recover any data from it then with the machine powered up, hold the drive in one hand and swing it downwards. This can sometimes 'jump start' a 'stuck' drive - If it does, get the data off of it and onto another drive as quickly as possible. Once you've retreived everything that you need (or can) switch off, replace it and go through the whole process of installing and initialising a new drive - sorry.
[Q]: Can I add a CD Writer to my Mac?
[A]: As long as it's a SCSI drive then yes. You'll need some burning software (e.g. Adaptec/Roxio's Toast) but creating CDs on a 68K Mac is definitely possible. DVD drives on the other hand...
[Q]: What's the best way to diagnose a SCSI error?
[A]: First of all, check that everything on the SCSI chain has a unique SCSI ID (the internal hard drive is usually ID 0, and the system is usually ID 7). If this doesn't work, try connecting each device on its own, directly to the Mac. Then (starting with a device that's Ok) start building up the chain until you identify the problem. SCSI chains can be tricky and sometimes the device order, physical order or even the connecting cables can cause problems. You might also want to try adding a SCSI terminator to the end of the chain.
[Q]: Is there a limit on how many SCSI devices I can connect?
[A]: Yes. There's a limit of 8 SCSI IDs in total but the system takes ID 7 (and if there's an internal hard drive, it takes one too).
[Q]: My floppy drive won't read a disk - what's up?
[A]: Firstly, make sure that it's not the disk. If you can try it in another Mac then this is ideal - if not, try other disks in the drive that's causing problems. If the disk is OK then try cleaning the floppy drive using a 3.5" disk cleaner. If this fails then you can try removing the drive from the machine and checking that the drive mechanism is free of dust and is moving smoothly (if not, try relubricating it with either penetrating oil or WD-40 until it works smoothly). If you still have no joy, try the drive itself in a different Mac. If the drive is STILL playing up it's probably time to replace it.
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