Classic Computer Magazine Archive COMPUTE! ISSUE 131 / JULY 1991 / PAGE 50

How To Install a Hard Drive. Four Steps to Hard Disk Power
by Mark Minasi

A couple of years ago, 20 megs seemed like a lot of storage. But nowadays everything burns up disk space at a furious rate. Windows 3.0 takes up 5 or more megabytes, Lotus several more--heck, even Wing Commander, a game with unbelievable graphics, can only manage those graphics by taking up 5 megs on your disk.

So it's time for an upgrade. You buy a larger disk and don't want to pay to have it installed. Here's how to put in your first hard drive or add a second hard drive.

One caveat before we go further. There is a wide variety of controllers, drives, and interfaces, so one article can't cover them all. What follows will tell you how to install most hard drives. Here are the basic steps to the process:

* Gather the information you'll need before you start.

* Configure the hard drive.

* Install the hard drive.

* Install the drive controller.

I'll also assume that you know that a drive system needs a hard drive, a circuit board called a hard drive controller, and cables. The controller has to be compatible with the hard drive, or this whole operation isn't going to work.

If you're not clear on how to buy a controller and drive, take a look at "How to Choose a Hard Disk" in the May 1991 issue.

Getting Ready

There are a few things you'll need to know about your drive later on, so let's get this information together before we go any further.

Find whatever documentation came with the drive, controller, and PC. You want to know the heads, cylinders, sectors per track, and write precompensation cylinder for your drive because the controller needs to know that data in order to support your drive. So get this from your vendor and write it down somewhere--you'll probably have use for it even after the drive is installed.

Most drives have a paper label pasted on them with a bad track table or error map. It described exactly where the disk's surface has some kind of defect. I'm looking currently at a Seagate ST251-1, a popular 42MB drive. It has a white paper label atop it marked Error Map. The label looks like this:

Error Map 251/Serial #26956413

Cyl Hd BFI

137 3 2463

140 3 2463

141 3 2463

142 5 3722

The three columns are labeled Cyl (Cylinder), Hd (Head), and BFI (Bytes From Index). As the disk spins, there is an arbitrary staring point that is the index--BFI is the distance from this index. (Note an oddity of the table: It sees an error on head 3 for tracks 137, 140, and 141 at the same BFI. It seems highly likely that an error exists also on tracks 138 and 139. Personally, I'd treat head 3, BFI 2463 as bad for cylinders 138 and 139.)

The last suggestion for this installation phase is to collect documentation. There's no sense in tearing the computer apart only to realize that you never got the information on configuring the controller and that you won't get any further until you beg the company to send you that information. And besides, even if you convince the company to send it, you'll look strange lurking around the mailbox waiting for the mail carrier. (Actually, most controller vendors have 24-hour-a-day BBSs from which you can download your controller documentation and other information.)

Opening the Computer

There's a good chance you'll have to get into your computer before going much further, since most AT-class machines (286-, 386SX-, and 486-based PCs) have their hard disk controller and hard disk cables already in the machine. Here are some tips on getting inside the machine with a minimum of trouble. Take your time, and write everything down.

Make a bootable DOS disk. If you don't have a bootable DOS floppy, make one now with everything on it that you'll need to boot the system. If you're replacing a hard disk, you probably always boot from the hard disk and don't have a bootable floppy handy. Make one, and make sure that it has the things you'll need for software preparation: SETUP if it's an AT machine, whatever low-level format program you'll be using, FDISK, and FORMAT.

Park your drive's heads. If you're removing an old hard disk, park it first. You should have a head-parking program around somewhere.

Turn the computer off, and remove the cover. Leave the PC plugged in, however, but be sure to provide antistatic protection, as I'll explain in a minute.

Be especially careful when removing the cover that you don't rip any ribbon cables on the edge of the cover. The ribbon cables for the floppies and hard drive often pop up as the cover is removed, making them easy prey for any sharp edges on the inside of the case.

Also, find an egg carton and use it to help you organize the screws that you take out of the computer. You can use the compartments in the carton to keep the different screws separated. You'll probably find two or three sizes of screws in your PC: large ones that secure the cover, small ones that secure the hard drive, and medium-sized ones that fasten everything else.

Ground yourself. Before you touch anything in the computer, touch the case of the power supply. (Don't know which is the power supply? It's the silver box with the fan in it and the power switch on the side. It's also got a label on it that says--sometimes in several languages--"If you open me, I'll kill you.")

Touching the power supply case drains away any static electricity that you might have built up. This only works if the power supply is plugged in.

Heed this warning. In 1989, I lived in The Condo from Hell for three months. It had the most static-attracting carpet I've ever seen in my life. I was working on a computer and absent-mindedly shuffled my feet on the carpet while trying to work out a problem. I reach over to remove a memory board from the system, and zap! A blue spark leapt about a centimeter from my hand to the board. Killed two memory chips and probably weakend others.

Get in the habit of touching the power supply case. (No, you won't get electrocuted by touching the case of the power supply. Just don't open it up--that can kill you.)

Remove the hard drive. If you already have a hard drive, remove it and the controller. You can find the controller easily--just follow the ribbon cables from the back of the hard disk to a circuit board. That circuit board is the controller. It'll probably look like a pincushion, as it usually sports a 34-pin connector and two 20-pin connectors.

Before you do any of this, however, please make good diagram so you can put things back the way you found them!

Circuit boards are held into the system with a single screw near the back of the PC. Remove the screw, and the board will come out. Rock the board gently back and forth to remove it from the system board. See the figure "Removing Circuit Boards."

Drives in XT-class systems are generally held in place with screws that bolt the drives right into the chassis. AT-class systems typically have rails fastened to the sides of the hard drives; the drives slide right into the AT chassis like drawers into desks. Metal tabs hold the drives in place.

If you ordered a hard drive with an installation kit for AT-class machines, the installation kit probably consisted of the plastic drive rails and screws to mount them on the drive.

Configuring the Drive

Next, you'll need to adjust two things on your hard drive: the terminator and the drive select jumper. If the drive is the only hard drive (floppies don't count), you don't need to mess with the terminator.

The drive select jumper gives a drive an address as far as the controller is concerned: either address 0 or address 1. Ordinarily, your first hard drive (let's call it drive C) is addressed 0, and the second, if present, is addressed 1.

Let's call the second hard drive D, and ignore for the present that it's possible for a single drive to own more than one drive letter.

The drive is addressed by placing a jumper--a tiny plastic box (usually black, but I've seen white and blue) over two metal pins.

Drives generally have pins for drive addresses 0 through 5, but we only use addresses 0 and 1 in the PC business. There are set of pins to jumper for address 0, another set for address 1, and so on.

The address your drive responds to is determined by where you put the jumper. There are two examples of drive select jumpers (and terminators, which we'll discuss present) on "Hard Disk Drive Select Jumper." Just remember that the drive select jumper only goes on one address.

So we've said that the drive can have address 0 or 1. But which should it use? It depends on whether or not there's a twist in the cable. Your system probably uses two cables to connect the hard disk to the hard disk controller--a wider 34-wire cable and a skinnier 20-wire cable. The 34-wire cable carries the control signals; the 20-wire cable the data signals.

Take a look at the 34-wire cable. It should have a 34-wire connection on one side that attaches to the controller and a 34-wire connection on the other side that attaches to the drive. Is there also another 34-wire connection in the middle of the cable? If so, that is intended to support a second hard drive.

If you have the middle connector, look between the middle connector and the hard drive connecton on the end. Is there a twist in the cable? Some cables are cut, twisted, and reconnected between lines 24 and 29 on the 34-wire hard disk cables. Knowing whether your cable is twisted or not determines how you set the drive select jumper.

If your cable isn't twisted, you set the drive select jumpers as I've already explained: Drive C is drive select 0, and D is drive select 1. On the other hand, if the cable has a cut and a twist, you set both drives to either drive select 0 or drive select 1, as you see in "Hard Disk Cabling."

The Terminator

The last adjustment on the drive is the terminating resistor chip, or terminator.

You only need to mess with this if you're installing a second drive. The terminator is a group of resistors packaged in a chiplike housing. It will look like either a chip or half of a chip, and it can be any color, though it is generally not black so it will stand out from the rest of the board.

Limited space prevents a complete explanation of the terminator, but basically it's a resistor needed to complete a bus circuit. Drives connected to a controller are on a bus much like the bus that your PC has--the slots of the PC motherboard. Something's got to hold up one end of the bus (termed an open collector bus), and that's a resistor called the pull-up or terminating resistor.

The problem arises when the controller sees two drives with terminators--the circuit then ends up with half the resistance that it's designed for, and twice as much current runs through the controller and drive electronics. Result? You slowly cook the drive and controller.

So remove the terminator from the drive attached to the connector in the middle of the cable. Again, the arrangement is pictured in "Hard Disk Cabling." Look back to the figure "Hard Disk Drive Select Jumper," and you can see two examples of common hard drive terminators.

Installating the Drive

Now the drive's configured. Let's physically install it in the chassis.

The easiest way to install a drive is to insert it partway into the chassis and then attach the ribbon cables.

Stop at this point; don't get over-anxious to screw in the drive. The difference between a good installation and a bad installation (as students in my PC troubleshooting classes hear over and over again) is how the cables are routed.

Now that the cables are attached to the drive, take a minute and figure out where to put them. They go from the drive to the controller, but there's nearly always some slack. Sloppy installers just stuff the cables into the case and then slap the cover on. This is a time bomb. The next time you take the cover off the PC, you'll end up catching the cables on something sharp, and you'll rip them. So take a minute and see if you can tuck them down out of the way.

Don't forget to provide power to the drie with the power connector. That's the white plastic connector with four wires running back to the power supply. You'll see several of these four-wire power connectors. they're pretty universal, and they'll connect to a floppy drive,, hard disk, or tape drive. It doesn't matter which one you connect to the drive--they're all equal. There isn't a special one for A and one for C, or anything like that, so use whatever power connector is handy. If they're all in use, you'll need a Y splitter to convert one of the power connectors into two power connectors. Contact your hard disk dealer to buy a Y connector, if necessary.

Now secure the drive. As we saw before, with most systems you either bolt the drive directly to the chassis or secure it with metal tabs that keep it from sliding out of the box. See "Securing Hard Drives" for deatils.

Install the Hard Disk Controller

If the controller isn't already installed, put it in now. Installing the board is just the reverse of removing it; push the board's edge connector down into an expansion bus slot on the PC motherboard and then secure it with a screw on the board's back bracket.

A common question at this point is My PC has five 9ore eight or three) expansion slots. Does it matter which slot I put the board in? The answer is Basically, no Some boards are 8-bit boards. They're identifidable because they have a single edge connector.

Other boards are 16-bit boards. they have two edge connectors. A-bit board should go in a 16-bit slot, but an 8-bit board can go in either an 8-or a 16-bit slot.

Now hook up the cables from the hard drive. If you've got an AT system, the controller will probably be a combination floppy and hard disk controller, so be sure to hook up the cable for the floppy drives, too.

Introduce the Controller and

the Drive

Seems only polite, hmmm?

The controller needs to know what kind of drive it's dealing with. On XT-style systems you give it that information during the first part of the software installation--a step called low-level format, so we won't worry about that here.

On AT systems, the system BIOS has a table of drive types built into it. Most clones know of 47 different hard drives. Why 47? Who knows? The earliest IBM ATs only knew of 14 drive types, and later ones knew 25. The last batch had 47 drive types. Cloners just copied IBM from that point on.

You just figure which drive type most closely describes your hard disk--remember I told you to have heads, cylinders, number of sectors, and write precompensation handy?

For instance I use a 60MB hard drive with 1024 cylinders, seven heads, 17 sectors per track, and no write precompensation. There isn't a drive type in my clone's ROM that matches that, but there's one that's close--977 cylinders, seven heads, 17 sectors per track, and no write precomp. That's drive type 18.

Once I figured that out, I ran my clone's SETIP program and told the system that I had drive type 18, and then I was ready to format the disk. I lost a little space, as I'm only using 977 of my 1024 cylinders, but that's not a big deal.

Well, that's how to do a hardware installation of most PC hard disks. Again, not every drive installation works as I've described, but this is the procedure for installing drives in most XT-and AT-class systems these days. Good luck and have fun-it's a great feeling to do a hard drive installation by yourself!