Jury Still Out on Best Inner Design

Richard O'Reilly designs microcomputer applications for The Times

Should you really care about how the inside of your computer is designed?

That question was brought to the fore recently when two new and conflicting ways to build PC-compatible computers were announced separately by IBM and by a group of its competitors. The debate really began nearly 18 months ago when IBM introduced its new PS/2 line of personal computers and quit building the old PCs, XTs and ATs.

The new IBM models were remarkable in several ways. They use a smaller (3 1/2-inch) diskette than their predecessors, which has made swapping data and programs between old and new IBM computers difficult.

The higher performance PS/2 machines, Models 50, 60, 70 and 80, have a different internal structure, something called “Micro Channel architecture.” It promised performance advantages, but none of the expansion circuit boards designed for the earlier machines could be used in the new models.


These expansion boards are used for a wide variety of computer system enhancements such as additional memory, hard disk controllers, modems, local area network connections, higher resolution video displays and laser printer control.

During the ensuing months, IBM’s new PS/2s have generated a lot of controversy, a lot of compatibility problems for users and for independent expansion board makers and a lot of sales for IBM. Including September’s results, the company says it has sold 3 million PS/2 computers. About half those sales have been for Micro Channel-equipped machines.

With its announcement of the new PS/2 line in April, 1987, IBM also issued a stern warning to other manufacturers that it intended to vigorously protect its designs from clone makers. Earlier this year, IBM finally said it would license to other manufacturers at least some of the technology to build Micro Channel computers--but at royalties of up to 5%. Among major manufacturers, Tandy was one of the few to take IBM up on its offer.

Many others, Compaq Computer being among the loudest, criticized the Micro Channel design and continued to build computers compatible with IBM’s earlier PC-AT or PC-XT architecture.


Now two new factors have emerged--IBM’s announcement of a new computer compatible with its PC-AT architecture and the announcement by a group of IBM’s competitors that they will develop computers with yet another internal design.

IBM this month introduced the Model 30-286, an enhancement of the PS/2 Model 30 design. Incorporating some of the old-style architecture, Model 30-286 accepts expansion cards compatible with the abandoned PC-AT architecture while increasing video graphics resolution to match that of the higher-end PS/2 computers.

Some observers have viewed this new machine as evidence that IBM made a mistake in launching the Micro Channel-equipped designs and that the Model 30-286 is the path by which the computer giant will return to the PC-AT standard that most of its competitors never left. IBM also reportedly is considering bringing out next year yet another PC model without the Micro Channel.

Another way to look at it is that IBM has sold 1.5 million Micro Channel-equipped computers and another 1.5 million PS/2 computers patterned after its earlier internal designs. Although its performance doesn’t match that of IBM’s Micro Channel machines, the new Model 30-286 provides more power and performance at about the same price as the standard Model 30 that sold so well.


The new computer will be more software-compatible with the MCA-equipped models of the IBM line than its predecessor because it uses the same video standard and because it will run the new OS/2 operating system.

Nine IBM competitors that are major makers of PC-compatible computers--supported by 50 other key computer, peripheral and software makers--recently announced the Extended Industry Standard Architecture, or EISA.

EISA-design computers, which won’t be available for another year, are IBM competitors’ answer to the Micro Channel and represent a resounding “no” to Big Blue’s royalty requests for its MCA design.

The EISA group--AST, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse and Zenith--made a big point of their design’s compatibility with current PC and AT expansion cards.


But to get the full performance potential inherent in the EISA design one will have to invest in a new generation of expansion cards for such things as memory, networking, high-speed communications, fast graphics video and the like, so compatibility with current cards is more a symbolic benefit than a real benefit.

The common challenge that both the MCA and EISA designs had to meet was how to expand the internal architecture of the basic PC--the so-called bus--so that it could make full use of the latest Intel 80386 microprocessor. (The bus is simply the electronic pathway by which all the devices inside the computer are connected.)

The original PC had an Intel 8088 chip, and it moved data internally eight “bits” at a time. (A bit is a binary digit, the zeros and ones that are the smallest units of information that a computer can process. A combination of eight bits creates a byte, which is used to represent a single letter of the alphabet or other single on-screen symbol.)

When IBM brought out the PC-AT, it equipped that computer with Intel’s 80286 chip that not only ran faster but could process data 16 bits at a time. Consequently, IBM expanded the internal design of that computer to accept expansion cards that processed data either eight or 16 bits at a time.


Bits not only represent on-screen characters, they also are combined to represent “addresses” in the computer’s memory where data is stored. The original PC’s eight bits allowed a maximum of about 1 million separate addresses. The PC-AT’s 16 bits upped that maximum to about 16 million bits.

Intel’s 80386 chip can process data 32 bits at a time and address an astronomical 4 billion memory locations, if it is installed in a computer that will transfer data among the memory, disk storage, communications chips and other devices at the full 32-bit limit.

Both IBM’s MCA design and now the EISA design provide that full 32-bit internal data path and allow maximum performance for 386-based computers.

Is one better than the other? It is far too soon to tell. What is true is today’s application software and operating systems cannot take full advantage of the features of either architecture.


That will change over the next several years as new computing challenges and capabilities emerge. What is thought to be state-of-the-art design today will soon enough be outmoded.

I wouldn’t worry much what the inside of the machine looks like. Buy whatever best performs the tasks you want done now at the price you can afford. Even if you could buy today the capability you’ll need in three to five years, it will be outdated by then.

Just think back to what you would have bought five years ago if you were looking forward. Three possibilities that were highly touted in their time, but have all but disappeared from use today, are Apple’s Lisa, the Vector Graphic and the Osborne Portable.