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Clone Wars: IBM Edition
If you search the Internet for “Clone Wars,” you’ll get a lot of Star Wars-related pages. But the original Clone Wars took place a long time ago in a galaxy much nearer to ours, and it has a lot to do with the computer you are probably using right now to read this. (Well, unless it is a Mac, something ARM-based, or an old retro-rig. I did say probably!)
IBM is a name that, for many years, was synonymous with computers, especially big mainframe computers. However, it didn’t start out that way. IBM originally made mechanical calculators and tabulating machines. That changed in 1952 with the IBM 701, IBM’s first computer that you’d recognize as a computer.
If you weren’t there, it is hard to understand how IBM dominated the computer market in the 1960s and 1970s. Sure, there were others like Univac, Honeywell, and Burroughs. But especially in the United States, IBM was the biggest fish in the pond. At one point, the computer market’s estimated worth was a bit more than $11 billion, and IBM’s five biggest competitors accounted for about $2 billion, with almost all of the rest going to IBM.
So it was somewhat surprising that IBM didn’t roll out the personal computer first, or at least very early. Even companies that made “small” computers for the day, like Digital Equipment Corporation or Data General, weren’t really expecting the truly personal computer. That push came from companies no one had heard of at the time, like MITS, SWTP, IMSAI, and Commodore.
The IBM PC
The story — and this is another story — goes that IBM spun up a team to make the IBM PC, expecting it to sell very little and use up some old keyboards previously earmarked for a failed word processor project. Instead, when the IBM PC showed up in 1981, it was a surprise hit. By 1983, there was the “XT” which was a PC with some extras, including a hard drive. In 1984, the “AT” showed up with a (gasp!) 16-bit 80286.
The personal computer market had been healthy but small. Now the PC was selling huge volumes, perhaps thanks to commercials like the one below, and decimating other companies in the market. Naturally, others wanted a piece of the pie.
Send in the Clones
Anyone could make a PC-like computer, because IBM had used off-the-shelf parts for nearly everything. There were two things that really set the PC/XT/AT family apart. First, there was a bus for plugging in cards with video outputs, serial ports, memory, and other peripherals. You could start a fine business just making add-on cards, and IBM gave you all the details. This wasn’t unlike the S-100 bus created by the Altair, but the volume of PC-class machines far outstripped the S-100 market very quickly.
In reality, there were really two buses. The PC/XT had an 8-bit bus, later named the ISA bus. The AT added an extra connector for the extra bits. You could plug an 8-bit card into part of a 16-bit slot. You probably couldn’t plug a 16-bit card into an 8-bit slot, though, unless it was made to work that way.
The other thing you needed to create a working PC was the BIOS — a ROM chip that handled starting the system with all the I/O devices set up and loading an operating system: MS-DOS, CP/M-86, or, later, OS/2.
Protection
IBM didn’t think the PC would amount to much so they didn’t do anything to hide or protect the bus, in contrast to Apple, which had patents on key parts of its computer. They did, however, have a copyright on the BIOS. In theory, creating a clone IBM PC would require the design of an Intel-CPU motherboard with memory and I/O devices at the right addresses, a compatible bus, and a compatible BIOS chip.
But IBM gave the world enough documentation to write software for the machine and to make plug-in cards. So, figuring out the other side of it wasn’t particularly difficult. Probably the first clone maker was Columbia Data Products in 1982, although they were perceived to have compatibility and quality issues. (They are still around as a software company.)
Eagle Computer was another early player that originally made CP/M computers. Their computers were not exact clones, but they were the first to use a true 16-bit CPU and the first to have hard drives. There were some compatibility issues with Eagle versus a “true” PC. You can hear their unusual story in the video below.
One of the first companies to find real success cloning the PC was Compaq Computers, formed by some former Texas Instruments employees who were, at first, going to open Mexican restaurants, but decided computers would be better. Unlike some future clone makers, Compaq was dedicated to building better computers, not cheaper.
Compaq’s first entry into the market was a “luggable” (think of a laptop with a real CRT in a suitcase that only ran when plugged into the wall; see the video below). They reportedly spent $1,000,000 to duplicate the IBM BIOS without peeking inside (which would have caused legal problems). However, it is possible that some clone makers simply copied the IBM BIOS directly or indirectly. This was particularly easy because IBM included the BIOS source code in an appendix of the PC’s technical reference manual.
Between 1982 and 1983, Compaq, Columbia Data Products, Eagle Computers, Leading Edge, and Kaypro all threw their hats into the ring. Part of what made this sustainable over the long term was Phoenix Technologies.
Rise of the Phoenix
Phoenix was a software producer that realized the value of having a non-IBM BIOS. They put together a team to study the BIOS using only public documentation. They produced a specification and handed it to another programmer. That programmer then produced a “clean room” piece of code that did the same things as the BIOS.
This was important because, inevitably, IBM sued Phoenix but lost, as they were able to provide credible documentation that they didn’t copy IBM’s code. They were ready to license their BIOS in 1984, and companies like Hewlett-Packard, Tandy, and AT&T were happy to pay the $290,000 license fee. That fee also included insurance from The Hartford to indemnify against any copyright-infringement lawsuits.
Clones were attractive because they were often far cheaper than a “real” PC. They would also often feature innovations. For example, almost all clones had a “turbo” mode to increase the clock speed a little. Many had ports or other features as standard that a PC had to pay extra for (and consume card slots). Compaq, Columbia, and Kaypro made luggable PCs. In addition, supply didn’t always match demand. Dealers often could sell more PCs than they could get in stock, and the clones offered them a way to close more business.
Issues
Not all clone makers got everything right. It wasn’t odd for a strange machine to have different interrupt handling than an IBM machine or different timers. Another favorite place to err involved AT/PC compatibility.
In a base-model IBM PC, the address bus only went from A0 to A19. So if you hit address (hex) FFFFF+1, it would wrap around to 00000. Memory being at a premium, apparently, some programs depended on that behavior.
With the AT, there were more address lines. Rather than breaking backward compatibility, those machines have an “A20 gate.” By default, the A20 line is disabled; you must enable it to use it. However, there were several variations in how that worked.
Intel, for example, had the InBoard/386 that let you plug a 386 into a PC or AT to upgrade it. However, the InBoard A20 gating differed from that of a real AT. Most people never noticed. Software that used the BIOS still worked because the InBoard’s BIOS knew the correct procedure. Most software didn’t care either way. But there was always that one program that would need a fix.
The original PC used some extra logic in the keyboard controller to handle the gate. When CPUs started using cache, the A20 gating was moved into the CPU for many generations. However, around 2013, most CPUs finally gave up on gating A20.
The point is that there were many subtle features on a real IBM computer, and the clone makers didn’t always get it right. If you read ads from those days, they often tout how compatible they are.
Total War!
IBM started a series of legal battles against… well… everybody. Compaq, Corona Data Systems, Handwell, Phoenix, AMD, and anyone who managed to put anything on the market that competed with “big blue” (one of IBM’s nicknames).
IBM didn’t win anything significant, although most companies settled out of court. Then they just used the Phoenix BIOS, which was provably “clean.” So IBM decided to take a different approach.
In 1987, IBM decided they should have paid more attention to the PC design, so they redid it as the PS/2. IBM spent a lot of money telling people how much better the PS/2 was. They had really thought about it this time. So scrap those awful PCs and buy a PS/2 instead.
Of course, the PS/2 wasn’t compatible with anything. It was made to run OS/2. It used the MCA bus, which was incompatible with the ISA bus, and didn’t have many cards available. All of it, of course, was expensive. This time, clone makers had to pay a license fee to IBM to use the new bus, so no more cheap cards, either.
You probably don’t need a business degree to predict how that turned out. The market yawned and continued buying PC “clones” which were now the only game in town if you wanted a PC/XT/AT-style machine, especially since Compaq beat IBM to market with an 80386 PC by about a year.
Not all software was compatible with all clones. But most software would run on anything and, as clones got more prevalent, software got smarter about what to expect. At about the same time, people were thinking more about buying applications and less about the computer they ran on, a trend that had started even earlier, but was continuing to grow. Ordinary people didn’t care what was in the computer as long as it ran their spreadsheet, or accounting program, or whatever it was they were using.
Dozens of companies made something that resembled a PC, including big names like Olivetti, Zenith, Hewlett-Packard, Texas Instruments, Digital Equipment Corporation, and Tandy. Then there were the companies you might remember for other reasons, like Sanyo or TeleVideo. There were also many that simply came and went with little name recognition. Michael Dell started PC Limited in 1984 in his college dorm room, and by 1985, he was selling an $800 turbo PC. A few years later, the name changed to Dell, and now it is a giant in the industry.
Looking Back
It is interesting to play “what if” with this time in history. If IBM had not opened their architecture, they might have made more money. Or, they might have sold 1,000 PCs and lost interest. Then we’d all be using something different. Microsoft retaining the right to sell MS-DOS to other people was also a key enabler.
IBM stayed in the laptop business (ThinkPad) until they sold to Lenovo in 2005. They would also sell them their server business in 2014.
Things have changed, of course. There hasn’t been an ISA card slot on a motherboard in ages. Boot processes are more complex, and there are many BIOS options. Don’t even get us started on EMS and XMS. But at the core, your PC-compatible computer still wakes up and follows the same steps as an old school PC to get started. Like the Ship of Theseus, is it still an “IBM-compatible PC?” If it matters, we think the answer is yes.
If you want to relive those days, we recently saw some new machines sporting 8088s and 80386s. Or, there’s always emulation.
