IBM Personal Computing

Donald B. Trivette

Hard Disks And The Home PC Technology marches on: The price of a hard disk drive--a $2,000 luxury just a few years ago--has fallen to a point where it's becoming affordable for home-based computers. Mail-order houses are offering internal hard disks for less than $400, and prices of hard disk cards are coming down as well. If you're thinking about upgrading your IBM PC with one of these super storage devices, here are some points to consider.

Hard disk, fixed disk, and Winchester disk are all names for the same thing--a device with a rigid magnetic disk permanently sealed in a box. Because it's sealed from airborne contaminants and has a hard rather than a flexible surface, it can record larger amounts of data than a floppy disk, and-the data can be read or written much faster. The smallest hard disks commonly in use store 10 megabytes of data-- that's 10,240 kilobytes, or 10,485,760 characters. In comparison, a standard IBM floppy disk stores only 360 kilobytes---368,640 characters. Hard disks are available for the PC with capacities of 20, 50, and even 100 megabytes, although a home user isn't likely to need more than 10 megabytes.

Hard disks come in two forms: the internal type that fits into one of the spaces once occupied by a floppy disk drive (half-height or full-height), and a newer configuration called a hard disk card that squeezes the disk onto a printed circuit board which plugs into one of the PC's expansion slots.

Can You Spare A Slot?

Every hard disk must have a hard disk controller. An ordinary internal hard disk requires a separate controller board connected via cables to the drive. One advantage of the hard disk cards is that both the disk and the controller are a single compact unit. Either way, one expansion slot is used. But there is an alternative for internal models. For about $50 extra, you can order a controller that runs existing floppy disk drives as well as. the hard drive. This allows you to remove (and scrap) your floppy disk controller board and free up one expansion slot. None of the hard disk cards introduced so far can control floppy disk drives.

Another factor to consider is power consumption. Hard disk cards are designed to work with the 63-watt power supply found in the IBM PC; many of the internal hard disks were designed for the PC-XT, which has a larger power supply. Frankly, if your PC is already brimming with boards--parallel, serial, color/graphics, and game ports as well as memory expansion--you should strongly consider replacing the old power supply no matter which type of hard disk you install. The operation is as simple and safe as removing some screws and unplugging some wires. A new 135-watt power supply can be purchased for as low as $90.

Of course, speed and reliability are prime considerations when investing in a hard disk. Although reliability is difficult to measure without an industry-wide mean-time-between-failure test, there are some things you can check. An oxide coating on the disk surface is more stable and thus more reliable than plated or sputtered media. The type of actuator that moves the read/write heads across the surface of the platter not only affects speed, but also influences accuracy. A voice-coil actuator is faster and more reliable (and more expensive) than the more common steppermotor actuator. Therefore, look for a hard disk with an oxide coating and voice-coil actuator.

Fast, Faster, Fastest

Speed varies greatly depending on the make and model. Consider the results of a test which measures a mixture of 1,000 sequential and random accesses--a test that is typical of how real computer programs use a hard disk. The times range from 12 milliseconds for a high-performance internal drive like Core International's AT line, to more then 100 milliseconds for some of the inexpensive hard disk cards. A hard disk for home use-- where you don't need top performance--should have a sequential/random access time in the 30-to 60-millisecond range.

Cost is usually a major consideration when selecting a hard disk for home use. Hard disk cards cost as little as $550 for a 10-megabyte unit to as much as $1,200 for 20 megabytes. Internal 20-megabyte drives, including the controller board, are generally in the $400--$600 range; 10-megabyte models cost about $100 less. The best advice here is not to choose a disk by cost alone. Consider all the factors.

My own PC has a 20-megabyte internal Seagate drive, a new 135-watt power supply, and a controller that also runs two half-height floppy drives. It cost about $650 and took two hours to install. An alternative I'd be comfortable with is Plus Development's 10-megabyte Hardcard; it's designed for those who want a quick, simple installation and who don't want to fool with a new power supply. The Hardcard, at about $900, is a wellengineered solution to upgrading your computer's mass storage capabilities.

One final caveat: Whether you spend ten minutes or two hours installing the hardware, plan to spend lots more time learning to use the DOS commands that are necessary to manage files on a hard disk.