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Installing An External Hard Drive On A Mac Plus


This tutorial also applies to any SCSI Mac.

The Mac Plus was the first Mac with built in SCSI hard drive capabilities. If you plan on running system 6 on the Plus, (and you should as anything newer will be slow just as running OS X on a pre-G3 Mac is slow), you can easily put all the programs you'll need on an 80 meg drive. You can go all the way up to a 1 gig and up to 4 gigs if you are running system 7, 10 gigs if you are running 7.5.5.

What you need

Hard drive case with power supply - see the pic above. The phone book size box is the drive case with power supply. This case has scsi connectors on the inside and attaches to the scsi port of the Mac. If you can find one, you should buy the Apple brand SCSI hard drive case - they are built like tanks and the power supplies last forever. Of the hundred or more that came into Goodwill when I worked there, 99% of them worked fine, some were almost 13 years old. The case pictured above is an Apple case. Some older cases have BD 25 connectors and not Centronics 50 pin connectors. You'll need a DB 25 pin to DB 25 pin scsi cable for these cases.

The rear of a typical scsi case.

SCSI Cable


A typical Centronics 50 pin to DB 25 pin SCSI cable.

A Drive

You can use pretty much any SCSI drive, Mac or PC in a Mac, but if it's not an Apple brand, you'll need a third party (Non-Apple) drive formatter program such as LIDO, Anubis, FWB, etc.. You can also d/l the patch to Apple's HD SC Setup which allows it to see and format 99% of third party drives.

A typical SCSI hard drive.



Open the drive case. If it's an Apple brand, you'll need a tiny flat head screwdriver to pop back the plastic tabs on the sides and rear of the case. This is not easy to do without breaking the tabs, but if you do, the case will still snap shut securely. On other drives, unscrew the screws as necessary. When you get it open, you should see a ribbon cable, power supply, possibly a hard drive lite connected to a cable and a scsi ID selector cable. You'll need to unscrew the present hard drive and remove it if there is one. Just detach the cables and pull it out. Now put the new drive in in the same way. Attach the ribbon cable to the rear of the drive. There is only one way the cable will go in. If your case has a scsi id selector cable, see if it will fit onto the SCSI ID jumpers on the rear of the drive. Some drives don't have these. They are usually six pins sticking straight out of the bottom of the drive. If you connect the SCSI ID cable, you can change the SCSI ID by switching the switch on the rear of the case. If you do not attach teh SCSI ID connector to the drive, you'll have to open the drive and change the ID with jumpers. If you are using a drive from a PC, you may have many pins. If this is the case, do a search on the web for the part number of your drive and you'll probably find the pinouts. For a quick and dirty test of the drive, leave the scsi id connector off and attach just the ribbon cable (scsi) and power cable to the rear of the drive. Don't put the case back together yet, you may still need to fool around inside it.

Attach the scsi cable to the back of the Mac with the DB 25 pin connector. Attach the Centronics 50 connector to the rear of the drive case.

**IMPORTANT** If you are using a Mac Plus, you'll need a terminator connected to the second Centronics port of the hard drive. This terminates the signal. The Mac Plus does not have built in termination, all other Macs do. You may or may not need termination on other Macs, you WILL need one ALWAYS on a Plus. If you have more than one SCSI device attached to your Plus, the terminator is usually on the last item.

A typical Centronics 50 pin terminator


If you get a flashing question mark on your Mac's screen, you either have a bad hard drive, no operating system on the drive or the operating system has been damaged. You'll need to boot off a floppy and reinstall the OS. Get your Mac OS 6.08 floppies here, 7.5.3 here. You'll need 4 megs of ram in the Plus to boot and load 7.5.3.

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