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IBM PC Clones

An introduction to the less expensive brothers of the IBM PC/XT.

The terms "compatible" and "clone" refer 10 computers functionally identical to IBM's PC and PC/XT—such computers can use the same hardware and software as the PC. This article hopes to explain a little bit about the extremely popular IBM Personal Computer compatibles, used more and more in amateur radio. It discusses some things the prospective buyer should look for, and look out for. This .trticlc doesn't pretend to give enough information for the buyer to rush right out and buy one, but it's a start for more in-depth research.

Why Not a Commodore 64?

It's true the Commodore 64 is so far the most popular computer in use in ¡amateur radio. There's more amateur radio software written for it than any other computer.

The C-64, however, was designed as a hnme rather th;in a businesv computer It s priced reasonably but there are some drawbacks, The disk drive is slow, and doesn't hold much data I he screen is hard to read, i he power supply is unreliable. Furthermore, it's tough to expand with externa! hardware.

In contrast, the PC is designed as a business computer. Although the early PCs suffered from many of the problem the C-64 did, it was designed on a highly expandable foundation, The PC has survived basically unchanged for more than 5 years—many times a microcomputer's normal lifetime.

The PC was designed with expansion in mind. There are expansion "slots'* or connectors built into ihe computer, capable of connecting many different kinds of equip ment, such as high capaciiy fixed (hard) disks» many different kinds of video displays» extra memory, modem cards, and networking cards. The PC 's solid metal ease gives the PC much better RFI immunity than a C-64 with its power supply and disk drive cables exposed to the high RF environment found in a typical shack. The PC uses a more powerful microprocessor than the one used in the C-64, The PC s 8088 microprocessor can access a total of I MB (1 Megabyte) of memory, of which 640KB (640 kilobytes) the PC can use. That much memory lets the PC run much more sophisticated software than the C-64,

IBM puts a high price on all of this sophistical ion. l-ortunatel) , clones are often much less expensive and fuller-featured alternatives.

by Steven K. Stroh N8GNJ

I he Clones

Get over the aversion of buying a computer without the initials IBM on the front panel The clones are often as well engineered and reliable as the IBM PC. Clone manufacturers often buy components, such as microprocessors and floppy disk drives, from the same sources IBM uses. The one major advantage to owning an EBl^ PC is that it s possible to gel it serviced anywhere. A clone buyer has to be careful to choose a clone for which he can get good service.

Most Clones Now Fully Compatible

Shortly after the IBM PC first came oui in I981t many manufacturers came out with clones that were almost compatible with the IBM PC Early clones had incompatibility problems with certain hardware and software that ran fine on the IBM PC, These problems dwindled us the IBM PC's architecture became more thoroughly understood- Software and hardware manufacturers make more effort to ensure their products w ill work on the more popular clones as well as the IBM PC, because the clones now have a big market share.

Make Sure It's FCC Certified

One of the latest problems to emerge for clones is the issue of FCC certification. The FCC has been cracking dow n hard on computer manufacturers whose computers exceed the FCCs RF noise specifications, and have shut down some manufacturers umil they are in compliance, i he owner of an uncertified clone is liable for the RFI it causes! Hams should be especially interested in this, since RFI is a major hamshack issue.

( he More the Merrier

Many of the clones now come with i>4QK of RAM. If possible, get at least 640K of RAM when buying the computer Many of the larger programs, such as dBase II and Lotus 1-2-3, work much better when more memory is available, "Memory resident^ utility programs—those which stay permanently in a sectored-off seel ion of RAM (while the computer is powered up)—are extremely useful because they require almost no access time and save wear on the disk drives. Having 640K of RAM is well worth ihe modest cost.

Dual Clock Speeds

Dual clock speeds are a handy feature of most of the clones. The clock is the master timing system in the computer regulating the speed at which all operations are performed. IBM never made a PC using the 8088 microprocessor with a clock sjieed greater than 4.77 MHz, The clones, on the other hand, take advantage of the ability of the Intel 8088^

2 (faster version of the 8088) microprocessor to run at 8 MHz, and process data faster. Programs running at 8 MHz scream along compared to running at 4,77 MHz. Although most software and hardware has no problem running at the increased speed, some do, so the clone computers offer the 4.77 MHz speed to accommodate those few fussy programs.

Dual Floppy Disk Drives

So far the most common data storage device is the 5 ^ floppy disk, which can store up to 360K of data. Most of the clones come with a single 5 W floppy disk drive. Even in a system with a hard disk drive, dual 5 floppy disk drives really come in handy. Backing up 5 xk " floppy disks is a real chore without iwo drives, yet the user will see the need of this the first time he accidentally erases the disk that contained the program he's worked on for 3 weeks. Buy a name brand floppy disk drive, such as Teac or Panasonic, Half-height drives are a better choice than full-height drives for the simple reason that the user can ha\e two half heighl drives in the same amount of space as one full height drive.

3 tt* Disk Drives

With the introduction of IBM Convertible Computer (IBM's "laptop'')t the 3 disk is now standardized in the PC world. A3 W disk is much more reliable than a 5 ^ " floppy disk, and holds up to 800K of data—at least tw ice that of a floppy.

I deliberately didn't say "3 S4* floppy disks. " These disks aren't all that floppy— The actual disk is well protected inside a hard plastic shell, with a covcr that is spring loaded to covcr the medium access slot, and normally is opened only when the disk is inserted into the drive. The 3 Vin disk is here to stay, and will become increasingly popular in the coming months. Many users now equip tlicis clones with both 3 and 5 W " disk drives the 3 h" drive allows them to use the much more reliable 3 disks, and the 5 lA " drive allows them to continue using their old software and exchange disks u ith other users.

Hard Disks f won't go into why hard disk drives are such fantastic devices for PCs—rest assured it is one of the main reasons for buying a PC or clone. Keep in mind for now that they move data in and out of the computer much more rapid I > than, and store many times the data of, floppies.

Software that's irritatingly sluggish to read from a floppy disk loads in a fraction of a second from a hard disk. Also, the operator will eventually tire ot switching floppy disks every time he wants to load up a different program. One hard disk drive that is wel[ thought of in the PC industry is the Seagate ST-225 which has a storage capacity of 20 Megabytes. It's very reliable and reasonably priced. The user needs also buy a hard drive controller card to plug into one of the expansion slots—I suggest the Western Digital hard disk controller. The 20M hard drive and controller card runs 200-300 dollars,

A Legal BIOS

The IBM PC BIOS ROM (Basic Input Output System Read Only Memory, or bootstrap ROM) is at the heart of the compatibility issue. The BIOS is the lowest level of software in a PC or clone—it's the "glue" that interfaces the the computer's hardware and DOS (Disk Operating System)

Avoid buying a clone from a company who installs BIOS ROM that are direct copies of the IBM PC BIOS ROM. This is a copy right infringement. Once discovered, the company erther ha\ to change the chip immediately or suffer a lawsuit from IBM. Rather, look for a clone that has. or *ill accept either Phoenix or Award ROM BIOS chips. They are the best combination of PC ROM BIOS compatibility without copyright infringement, and price.

8fl#7 Math Coprocessor Socket

Most clones, and the PC. have an empty socket beside the microprocessor reserved for the Intel 8087 math coprocessor. The buyer should make sure this is, in the clone lie's considering. The 8087 is a special pro* ccssor optimized for fast, efficient execution of math calculations, With softw are designed to take advantage of the 8087 s features, the difference in execution speed can be startling. If the 8087 is not present, the calculations can be done using the microprocessor, but this slows down overall processing speed.

The coprocessor is especially useful in spreadsheet programs that do a lot of number crunching, and programs such as AM SAT's latest IBM PC satellite tracking software. When buying an 8087 chip, make sure that it's specified for an 8 MHz clock if the clone has dual speeds.

Automatic Time and Date

A nice feature of the IBM PC is that every lime a file is written to disk, it's stamped with the time and date. It's hard to appreciate this feature until the computernik has a hard disk full of files, and can't remember the name of the letter he typed up last night. With the stamp, he needs only to look at the date and time of each file. Whenever the user turns on or reboots the computer, it asks for the time and date. Many expansion boards that include memory, serial communication, and parallel printer pons C'combo'" or "multifunction 1 boards) come with a battery-backed real time clock calendar chip takes care of this chore when the user runs a small program inserted on the start-up disk. A battery-backcd real time clock is a very worthwhile feature.

Reset Switch

Sometimes a user u ishes to reboot the system. Rebooting means clearing everything out of RAM, including the DOS system, and reinstalling the DOS. A very common reason for rebooting is because a software crash has locked-up the computer.

A user can reboot his computer several ways. The reboot least stressful for the system—and the one the user should try first—is keystroking the <Ctrl>, <Del>, and < Alt> keys simultaneously. Some software crashes are so major, however, that the computer won ! accept any commands from the keyboard. At this point. the user should press the reset button. As a last resort, he should turn off the computer, put the system disk in, and switch it back on.

The IBM PC and ail other IBM Personal Computers don't have a master reset switch. Look for this on a clone. Those debugging their ow n software will appreciate having the reset switch, because the recovery cycle is much shorter than with a power down, and much gentler on the computer.


Those who type a lot, such as those who have discovered the joys of word processing and packet radio communications, quickly lire of using a keyboard with the same layout as the original PC's keyboard. Fortunately, when IBM introduced the PC's bigger brother, the PC/AT, it introduced a keyboard with u much improved layout. Many clone manufacturers, in their ongoing quest to go IBM one better, now include a keyboard with the same layout as the AT with their PC clones.

The PC 8700 keyboard from DataDesk International has received excellent reviews. Another DataDesk keyboard is the Turbo-101 Enhanced keyboard, which features the improvements that IBM has implemented in their latest keyboards (separate function, cursor, and number pad keys) while retaining the large backwards "L' shaped return key. The DataDesk keyboards work with any IBM PC, and vinualh all clones. I also heard good words about the Maxi-Switch, a keyboard with the same layout.

Which Display?

There are many articles devoted to the van-ous display options available for the PC.'! he r*C doesn't come with circuitry to drive a video monitor like the C-64 does. What follows is a summary of the wide variety of display options.

The most basic display is the monochrome text adapter. (The adapter is another name for the circuit card that plugs into the expansion slots in a PC or clone and generates the signal for the monitor in use.) The mono text adapter doesn't allow graphics, hut di>es have nice sharp text display. 1 he color of the mono screen is determined by the color of the phosphor of the monitor. Hercules came out with a mono adapter card that could do graphics, but only for those programs written specifically for it—it's not compatible with the color graphics adapter mentioned in the next paragraph. Nonetheless, the Hercules card has become a standard in its own right, in addition to the IBM cards.

The color graphics adapter can display text, graphics, and color and can only be used with a color monitor. Its text display, however, is very grainy and hard to look at for a long time. Those who intend to work mainly with text shouldn't get this card.

IBM then came out with its Enhanced Graphics Adapter (EGA), at a much enhanced price. This, however, greatly improved graphics and text resolution. Fortunately, reasonably-priced EGA clones soon appeared. The EGA is quite usable for both text and graphics.

For all-around use. a Hercules-type mono system is likely the best choice- it's the cheapest and easiest to read.

Selecting a suitable display is one of the few items in buying a computer best left to do personally at a computer store.

Specific Clones

There are some very good deals out there on clones, especially for those willing to deal by mail, Good deals are also possible, however, at the local dealer

The first is Tandy/Radio Shack. Some of Tandy's computers have the Radio Shack label, others the Tandy label. Tandy, the parent company, has learned a lot about making IBM PC compatible computers. There are many randy. Radio Shack Computer Center nationw ide that will ser\ ice these clones.

The user should know, however, of which peripherals he wants to interface with the Tandy, Tandy's 1000 series computers iiave a reputation of being very hardware incompatible.

Don't think that the only place to buy Tandy/Radio Shack computers is at the local Radio Shack store or Radio Shack Computer Center, Pick up an issue of 80 Micro magazine and look at the classified ads, There are also several companies selling Tandy/Radio Shack computers by mail as Radio Shack Associate (as opposed to Tand> owned) stores. The same ease of sen icing is available to a Tandy/Radio Shack computer purchased through the mail as one purchased locally.

The second is Epson, Epson started out making a very successful line of printers and has now branched out into IBM PC clones. Epson has been fairly successful in getting store and mail-order dealers to carry their line.

The third is Leading Edge. Leading Edge made a big splash with their "Model D'h computer—it was even rated a best buy by Consumer Reports magazine! One can also buy Leading Edge's computers through the mail and have them serviced locally. The Leading Edge company, however, are sometimes difficult to get through to for technical support. They refer the great majority of technical inquiries to their dealers, which is a problem when (he system or software in question has a problem about which the dealer has no experience.

The fourth is Heath kit/Zenith, Heath/ Zenith computers are good, rugged, compatible, and reliable workhorses. Zenith has been doing a booming business selling their computers to the government in large numbers, beating out even IBM with great regularity. The Heathkit counterparts can be built by a hobbyist, just like other Heathkit products, Heath/Zenith computers can be bought through the mail and serviced locally at Heath/Zenith Electronics Centers, or in-crcasingly by local dealers (Zenith only),

The fifth, and last discussed here, is PC Source, sometimes called CompuAdd, Although strictly a mail order vendor, they have some innovative policies that make buying from them a more promising than usual proposition. They offer a free one-year warranty , one year of free technical support on an 800 number, good quality, and reasonable prices.

Although their technical support responsiveness has become more sluggish as the company has sold more systems, it's still head and shoulders above the great majority of mail-order clone vendors.

Build It!

Many people build their own computers. All of the components to build a PC are readily available on the open market.

Be aware of several potential trouble areas. The builder performs the function of a systems integrator, insuring that all pieces of the system work together with every other piece. It's sometimes impossible to know exactly what one gets when buying strictly by maiL There's no dealer tech support service to which to resort. The builder has to scrounge documentation from all quarters. On the flip side, those who select their components carefully and have a mentor can save a bundle of money. Byte and Computer Shopper magazines are good parts sources.

What Vln Cleveland?

Just to give you some examples of what might be available through a local dealer in your area, here are some of my experiences with Cleveland-area computer dealers. One computer distributor sells a clone they themselves assemble. The buyer has no idea who manufactured the components in it, nor does he really care. The main points are that it's IBM PC compatible and locally serviceable.

Another company in the area that used to sell only typewriters is now a dealer for several well respected clone manufacturers, This dealer services the lines they sell, of course, and has many sales offices throughout the Cleveland metropolitan area. Another local computer dealer is run by a ham and distributes a clone that almost no one has ever heard of; but they support it, and it's compatible with the PC, so again, it's a pretty good deaL

Three Vital Accessories

I consider these next few items absolutely indispensable for those thinking about buying (or who already own) a ck>rie, These accessories will end up saving the owner untold amounts of aggravation and money.

The first is PC Magazine . Twenty-two issues—one year's worth—is only $25, PC is literally an encyclopedia of PC knowledge, updated every .two weeks or so.

The second is the local PC User Group, User groups provide ongoing support and encouragement, usually a newsletter, occasionally a Bulletin Board System, and almost always a public domain software library.

The third is the PC-Software Interest Croup, PC-SIG is an organization that gathers, organizes, and distributes public domain software for the PC for a modest fee,

Final Words of Wisdom

Many people get in a pattern of constantly waiting for the prices of personal computer systems to go down, since it does so regularly. For example, IBM recently announced their new Personal System/2 line of computers, which has an unusually good price/performance ratio. The PS/2s, however, don't really offer any features of practical use for the average PC user.

The point is this: If a particular combination of software and hardware will accomplish what the user wants now, he should buy now. Otherwise, he should wait.


■Make sure it's FCC certified! •Make sure it has at least 64QK of RAM. •Look for dual clock speeds (4.77 & 8 MHz typically).

•Get dual floppy disk drives. •Don't try out a hard disk unless you can afford to get one—they're too addicting! •Make sure the BIOS is legal. The user isn't liable, but it's difficult to get any support. •Make sure it has an 8087 socket. •Keep in mind the battery backed clock/calendar option,

'A reset switch, though not necessary, is very handy,

'Look for a keyboard with the same (or better) layout as an IBM PC/AT keyboard. The PC type keyboard is the pits! •Define the text/graphics use balance before buying the video card. •Subscribe to PC magazine. •Join a PC users group. Computer Shopper magazine publishes a list of users groups nationwide,

♦Check out PC-SIG. It's quite possible to fmd all the needed software, except DOS, in public domain software.

-If there's a need, buy the clone now, rather than waiting for something better to come along.

Good luck! If you have specific ques tions about PCs, feeï free to write—SASE please!®

Further Reading

For further reading about IBM PC clones, check out the following articles, books, and magazines:


Guttman, Michael, "Zenith 151 Computer,'1 ComputerLand Elect tonics August 1984, pgs 32-33,91-93.

Kanter, Elliot S/'PC Compatible Computer," Radio Electronics, July î985h pgs 4346, 82.

l4IBM Compatible Computers*' Consumer Reports, October 1985, pgs 576-580, Call, Barbara. "XT Compatibles/' PC Week, July 15, 1986, pgs 57-67,73-78. Stafford, Paul M. "The Cheapest PCs Ever," PC, October 14, 1986, pgs 122-146. Rutch, Edwin, The IBM XT Clone Buyers Guide, $9.95 from Modular Information Systems.


PC Clones, 5211 S. Washington Avenue, Titusville, Florida 32780, (305) 269-3211. PC Resource, 80 Elm Street, Peterborough, New Hampshire 03458. Addresses 80 Micro, 80 Elm Street, Peterborough, New Hampshire 03458. Byte Magazine One Phoenix Mill Lane, Peterborough, New Hampshire 03458, (603) 924-9281.

Computer Shopper Magazine Computer Shopper, Inc., 407 South Washington Avenue, Titusville, Florida, 32796, (305) 269-3211.

DataDesk International 7650 Haskell Avenue, Van Nuys, California 91406, (818) 780-1673.

PC Magazine Ziff Davis Publishing Company , PO Box 2445, Boulder, Colorado 80322, (303)447-9330.

PC SIG 1030-D East Duane Avenue, Sunnyvale, California 94086, (408) 730-9291 or (800) 245-6717,

Microcomputer Companies

Epson America, Inc, 2780 Lomita Boulevard, Torrance, California 90505, (213) 5399140.

Heath Company, Benton Harbor, Michigan


Leading Edge Hardware Products, Inc. 225

Turnpike Street, Canton, Massachusetts

02021,(617) 828-8150.

Maxi-Switeh Company, 9697 East River

Road. Minneapolis, Minnesota 55433. (612)


Modular Information Systems, 431 Ashbury Street, San Francisco, CA 94117,. (415) 5528648.

PC Source/Compu Add, 12303-G Technology Boulevard, Austin, Texas 78727, (800) 643-0092.

Tandy Corporation, 300 One Tandy Center, Fort Worth, Texas 76102, (817) 390-3700 Zenith Data Systems, 1000 North Milwaukee Avenue, Glen view, Illinois 60025, (312) 699-4800.

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