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Überhacker II, Chapter 3: How to Get Many Operating Systems on One PC, continued ...

Hard Drives

IDE hard drives are the ones that usually come with PCs. SCSI drives are faster, and you can place many more SCSI drives on one PC. The disadvantage is that SCSI drives cost more and, in order to run them, you usually have to add a SCSI card and cables to your PC. Also, today most BIOSes only offer the choice of one generic boot from a SCSI drive, yet allow you to specify any IDE drive. This chapter will assume IDE drives for booting operating systems.

The disadvantage of IDE drives is that you can have no more than two IDE busses (the cables that connect drives to the motherboard) and each IDE bus can have no more than two drives. This includes the total of hard and CD or DVD drives.

If you are using old hard drives, be careful. They have a tendency to crash when it is most inconvenient, and take a lot of work to make halfway safe to use. One problem is that it could have an infected master boot record. Some of these boot sector viruses are subtle but will really mess you up in ways that don't obviously point to a viral culprit. Or there could be errors in the disk geometry - the way it has been formatted - that could give you endless headaches. Worst of all, it could have been zapped by a power surge or for any other reason could have lots of bad blocks. This could mean it is nearing a disk crash. A disk crash is basically impossible to fix.

The best safety measure is to do a low-level format. This is a type of formatting that is specific to each manufacturer. To get the appropriate software for this, write down the product data printed on the disk, then go to the manufacturer's web site and download whatever they advertise for testing and erasing that drive. They may not necessarily call it "low level format" and they may require more than one program to do the job. If during testing you find bad blocks, watch out for an impending crash.

I've used Partition Magic (http://www.powerquest.com) to test and clean old hard drives, with mixed results. If a hard drive is too messed up, it labels it bad and gives up. Yet I've made a "bad" drive good - even one zapped by lightning - by using the manufacturer's software for a low level format.

How to Install More than One IDE Hard Drive on the Same Computer

On the back of your hard drives and CD drives, next to the power connector, there should be two rows of little pins with one or more jumpers (little rectangular boxes) across them. Only the most ancient hardware lacks those pins. If the pins aren't there, the drive is not likely to be useful to you.

In theory, the drive on the last connector on an IDE cable should be jumpered to be a master, and the one in the middle a slave. The BIOS may not even detect a drive unless it has been properly jumpered.

I found a PC that only worked when both drives on the same cable were jumpered slave, but its BIOS was probably designed by a mad scientist.

Here's the fun part. One IDE cable is primary, and the other secondary. There also is usually a cable for a floppy and compatible devices such as tape backup drives. This is important because when the BIOS to chooses from which drive will boot, knows which cable is which. How do you know which cable is primary, and which is secondary? If your computer has a CD or DVD drive, it will most often be installed as the secondary master. You can make sure of this by watching BIOS detection of drives on boot. It will say something like (depending on the BIOS)
Detecting Primary HDD Master
Detecting Primary HDD Slave
Detecting Secondary HDD Master
Detecting Secondary HDD Slave

As it detects each device, a BIOS typically labels it on the screen with the manufacturer's part number. If the screen flashes by too fast to read, that is a good sign because it means the BIOS figured out what everything was. If you want to stop things and read them, try the scroll lock key.

Here's how to tell apart the cables inside your computer. The cable for floppies and related hardware like tape drives is narrower than the IDE cable. Just before the end connector it is split and half of it is twisted. If you have a SCSI cable, it is much wider than the IDE, and the connector(s) on it have holes that are much closer together.

New hard drives normally come out of the box jumpered to be either the only hard drive or the master. Normally some sort of instructions are on the hard drive itself. If not, or if they are confusing, it doesn't hurt to try all sorts of jumper combinations. Cable select is an option that won't matter to you unless you install a NIC that is designed to accept a network signal to your hardware to boot the operating system from that hard drive.

How do you know what way to attach the IDE cable to the hard drive? Often the cable is physically able to fit two different ways. Fortunately, it doesn't damage anything to connect it the wrong way. Here's how to get the connector right: the red line on the edge of the connector cable belongs on the side next to the hard drive power connector.

If you want to get really geeky about how you install multiple hard drives, here's a tip from Stuart Carter.

A system I once set up used a DPDT (double-pole, double-throw) switch wired to where the jumpers would normally attach to two hard drives. The way it worked was to switch the two drives between primary master and primary slave - one containing Windows, and one Linux. That way, it was like a disk caddy, but without having to remove the drives, plus the other system was available as a slave drive to the booted system. I can't remember exactly what happened when I tried flipping the switch while it was powered up...

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