Another setback in the roll-out of Motorola’s much-delayed 68040 microprocessor was emerging last week as sources at Concurrent Computer Corp, the financially-worried Tinton Falls, New Jersey-based manufacturer, claimed that multi-processing 68040s delivered to it so far are deficient, and do not conform to the original product specification. And Concurrent went further, saying that Motorola, which has only recently begun to deliver good uniprocessor versions of the 68040 to system manufacturers – nearly two years after the launch – may have thrown in the towel completely on a planned multi-processing version of the part, abandoning multi-processing 68040 system-builder hopefuls entirely. The missing element, it says, is the copy-back cache, crucial to the effective working of multi-processing systems. Motorola, it says, is not going to develop the multi-processing 68040 chip, and is re-writing the original product specification, omitting any reference to that [copy-back cache] part. To ensure the integrity of a multi-CPU environment, each processor needs to know that the information it holds about a given piece of data is the same as that held by its companion processors. Write-cycles carry these details to and from memory. Conventional write-through cache techniques used in a multi-processing environment would mean each processor having to address memory simultaneously, taking up large and valuable amounts of space on the system bus to perform what are essentially administrative tasks, reducing overall system performance drastically. Copy-back cache elements pre-empt much of this traffic and, using bus-snooping techniques, stop so many write-cycles occurring. Concurrent, whose engineers are reported to have been working closely with Motorola’s 68040 development team on multi-processing features, says it is having to build its own gate-arrays, clocks and other enhancements into the processor environment to get around the problem with the processor. However delays in receiving initial 68040 parts from Motorola and the extra development work needed mean that deliveries of multi-processing 7000 boxes will not now begin until some time after the summer – a five month delay. Another firm staking much on a multi-processing 68040 future is Arix Corp. While not aware of the lack of a copy-back element, Arix officials said its own wider bus system enables write-through caching to be supported on its architecture in a dual-processor environment. Backing this up, it says it will preview a dual-processor System 90 68040 box at this week’s CeBIT Hannover Fair. Unis ys Corp, Groupe Bull SA, Siemens Nixdorf, NCR Corp and Thomson CSF SA’s Cetia are others planning 68040 multi-processors. Calls to Motorola in the US were not returned, but Clive Gay, European product manager for high-end microprocess ors, said that although it had been a point of discus sion, Motorola would ret ain the copy-back feature on the 68040 and 68050.
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