Information Technology Reference
In-Depth Information
3.8
The fall of the MCA bus
The leading computer companies of 1987 were Intel, IBM, Compaq, and Microsoft, but a
special mention must go to Apple, Commodore and Sun Microsystems, who fought bravely
against the growing IBM PC market. With the release of the IBM AT and now the PS/2,
IBM had presented Intel with a large market for their 80286 design, but it was Compaq who
increased it even more with the release of the DeskPro 386. The new Intel processors were
now so successful that Intel had little to do, but try to keep up with demand, and try to stop
cloners from copying their designs. They could now consolidate on their success with other
support devices, such as the 80387- math coprocessor. By the end of the year, their only real
mass-market competitor was Motorola, who released their excellent Motorola 68030 micro-
processor, which would become the foundation of many Apple Mac computers. Within a few
years, Motorola would become extremely reliant on the Apple Mac, while Intel held onto the
PC market.
At IBM, things were hectic. They were phasing out their IBM PC range, and introduced
their new computer range, the PS/2. IBM realised that the open architecture of the IBM PC
held little long term advantages for them, as clone manufacturers could always sell com-
puters at much less cost than themselves. IBM had large development teams, sales staff, dis-
tribution centres, training centres, back up support, and so on. They thus need to make
enough profit on each computer to support all these functions. The PS/2 was their attempt at
trying to close the open system, and make one that required to be licensed through them-
selves. It was also an attempt at trying to reduce some of the problems that were caused with
the limited technology of the IBM PC. One of the main problems was the PC bus, which
allowed users to easily add peripherals to the computer, by plugging them into the system
with a standard card which had a standard edge connector. Initially this used an 8-bit data
bus, and operated at 8 MHz, which gave a data throughput of 8 MB/s (as one byte is 8 bits).
This was upgraded on the AT computer with the AT bus, which used a 16-bit data bus, giv-
ing a data throughput of 16 MB/s. The great advantage of the AT bus, was that it was still
compatible with the PC bus, where PC bus cards could still be slotted into AT bus connectors
(soon to be renamed the ISA, or Industry Standard Bus).
The AT bus was fine for slow devices, such as printer, modems, and so on. However, for
colour graphics it was far to slow. For example, a colour monitor with a resolution of
640·480, with 256 colours (8 bits per colour), and a screen refresh of 25 Hz, requires a data
throughput of 7 680 000 B/s (640·480·1·25 B/s).
IBM's concept was to use a bus, which, intentionally, had a different connector to the PC
and the AT bus, which did not use a fixed clock rate, and could thus operate at the speed of
the processor, which was now moving above 20 MHz. The MCA (Micro Channel Architec-
ture) bus also used a 32-bit data bus, which allowed data throughputs of 100 MB/s.
The PS/2 was an excellent concept, and was boosted by an extensive advertising cam-
paign that boosted performance improvement over previous systems. It was the right move,
and the system looked well, with 3.5-inch disk drives, and a rugged gray plastic case. Com-
puters had never look so professional. For many businesses, they were heaven sent. How-
ever, the fly-in-the-ointment for IBM was Compaq, who had previously released their Desk-
Pro 386. The big problem with the PS/2 range was that the lower-end PCs were based on the
8086 and the 80286, and against the 80386-based Compaq they seem slow. The initial range
was:
Model 30, which used the, at the time, relatively slow, 8 MHz 8086. IBM also intro-
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