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5. MicroChannel Architecture

With the burgeoning popularity of the IBM PC, everyone and their brother got into the hardware game. This was made possible by the fact that the bus used was well documented, and knowledge about it was not encumbered by proprietary agreements. (As was common for other buses in the past; as is becoming virtually extinct today.)

Quality of products was often pretty slipshod, but the fact of the matter is that now anyone could get into the "hardware game," and many did. Unfortunately for IBM, this meant that IBM could not substantially control the peripheral market. Worse still, the "IBM PC" BIOS was able to be reverse-engineered, and additional computer vendors could enter the market. Ultimately, a set of these vendors defined a "standard" bus known as ISA, "Industry Standard Architecture." Later enhanced to "EISA." "VESA" was a further extension of this to an Intel 486-oriented bus. (And the latest bus, "PCI," is at last processor-neutral so that "PC" cards can be used with Macs, Alphas, and other CPUs. But I digress...)

MCA (Micro Channel Architecture) was IBM's attempt to take things over again. At the time, it could provide somewhat better system performance (keeping CPU and RAM configurations equal) than the equivalent ISA system. (We'll ignore the consideration that the corresponding ISA system would cost less, thus allowing the purchaser to afford to buy more RAM and/or a faster CPU, more than making up for the ISA disadvantages.) Since IBM put a certain amount of forethought into licensing this time, critical portions would require licensing from IBM.

Vendors of course did not come to the MCA architecture in droves. In the "good old days," joint ventures with IBM were tantamount to the smaller vendor providing "free organ transplants." (Today that would be a good description of a joint venture with Microsoft.)

The "industry reaction" was naturally to reject this attempt to take the market back, and vendors got together to create the EISA standard which was just slightly more successful in the marketplace than MCA. Neither bus ever supplanted ISA. This meant that prices never did come down on peripherals, and the more esoteric peripherals were seldom available for MCA. Tandy is about the only computer vendor aside from IBM that ever built MCA machines.

Later buses like VESA "Local Bus" and PCI have been very popular. The PCI bus in particular is well enough designed that it has proved adequate for most "minicomputer/RISC/server" system configurations. Unix vendors commonly use PCI which now permits them to support commodity video, networking, and SCSI cards rather than having to design them from scratch.

The more recent I2O initiative to build a "newer, faster" I/O bus system hearkens to the proprietary approach taken with MicroChannel. The main difference is that I2O has a fairly sizable group of participants, including Microsoft, Intel, and a variety of other vendors.

It remains to be seen whether this approach will break again.


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