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Always shut the power off before unplugging SCSI cables: Hot-swapping can fry the circuits. To make mistakes less likely, plug your PC and all your external SCSI devices into the same outlet strip, and use its switch to turn them all on and off.
A standard SCSI adapter can hold up to seven devices. Each time you add a device to the chain, you must assign it a unique SCSI ID number from 0 to 6. (The adapter normally gets 7.) If you're not sure what IDs you've used, check your SCSI software for a scanning utility, like Adaptec's SHOWSCSI.EXE. If you can't find one, download a copy of System Census for Windows (available on CompuServe's WINSHARE forum): it'll scan the bus and display the info.
Are the manuals that explain how to change your CD-ROM drive's SCSI ID missing or incomprehensible? No problem. Most use three jumpers or sets of pins representing 1, 2 and 4. Add the jumpered values to get the SCSI ID. A tiny black plastic-wrapped copper shunt is used to close the jumper gap. Most CD-ROM drives usually come with only one, if that, so you may need to purchase extras to close the jumpers. Some 3.5-inch drives use special mini-jumpers.
Some SCSI devices offer little or no choice of ID numbers, occasionally leading to irreconcilable conflicts. You can fix that by adding a second SCSI adapter. Just be sure to buy a card that can coexist with the old one.
For easier upgrading, buy an extra-long SCSI ribbon cable with seven sockets. You won't have to replace the cable to add another drive, and you'll have room to maneuver when drives aren't adjacent or wrong-way-up connectors demand cable twists.
The two devices at each end of the SCSI chain must be terminated. The first is normally the drive at the end of the internal ribbon cable. If all your SCSI devices are internal, the second is the host adapter. Remove the terminating resistors from all other drives. (If you tape the resistors to the drives, they'll be easy to find if you need them later.) With external devices, disable termination on the adapter, and plug a terminator into the end of the daisy-chain.
Some SCSI devices insist on being at the end of the chain. If you've got two such devices, disable termination on the adapter, move it to the middle of the chain and put the problem units at each end (be sure to terminate the new end devices). Or install a second adapter.
If you want to use an external SCSI device but your adapter doesn't have an external port, add one. (If your board vendor doesn't sell such a kit, try TTS Multimedia Systems, 619-942-5393, info@ttsnet.com.) For proper termination, you must put the new port at the *end* of the ribbon cable, and cap it with a terminator when it's not in use. Turn off termination on the host adapter and bump it to the next socket on the cable.
Installation utilities often waste memory by loading unneeded SCSI drivers. If your SCSI board is running only hard or removable disk drives, the adapter's BIOS may be able to mount them without additional SCSI drivers. Windows 95 Setup sometimes leaves unrequired real-mode drivers in CONFIG.SYS and AUTOEXEC.BAT. To check for these, REM out all the SCSI stuff and reboot. If your drives don't work, restore real-mode drivers as necessary.
Products that come with a full set of memory-hogging drivers often work fine with your existing ASPI stack. Iomega's Zip drive, for example, works with Adaptec's EZ-SCSI using this CONFIG.SYS entry: DEVICE=C:\SCSI\ASPIDIS.SYS /D
Windows 3.1 Setup erroneously installs SmartDrive's double-buffering option with some Future Domain SCSI adapters that don't need it. To get top performance from your TMC-820, 830, 840, 850, 860, 870, 875, 880, 885, 850M, 860M, 885M, 1650, 1660, 1670 or 1680 adapters, remove the double buffer reference from this line in CONFIG.SYS:
DEVICE=C:\WINDOWS\SMARTDRV.EXE /DOUBLE_BUFFER
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