Editing Micro Channel architecture (section)

=== Data transmission ===
The basic data rate of the Micro Channel was increased from ISA's 8&nbsp;MHz to 10&nbsp;MHz. This may have been a modest increase in terms of clock rate, but the greater bus width, coupled with a dedicated bus controller that utilized [[burst mode (computing)|burst mode]] transfers, meant that effective throughput was up to five times higher than ISA. For faster transfers the [[address bus]] could be reused for data, further increasing the effective width of the bus. While the 10&nbsp;MHz rate allowed 40 [[MB/s]] of throughput at 32-bit width, later models of RS/6000 machines increased the data rate to 20&nbsp;MHz, and the throughput to 80 MB/s.<ref>[https://www-01.ibm.com/common/ssi/rep_ca/9/877/ENUSZG92-0339/index.html RISC System/6000 POWERstation/POWERserver 580]</ref> Some higher throughput functions of the Micro Channel bus were available to RS/6000 platform only, and were not initially supported on cards operating on an Intel platform.<ref>[https://books.google.com/books?id=KzsEAAAAMBAJ&dq=microchannel+rs/6000+differences+intel&pg=PA1 Infoworld March 5, 1990, p1]</ref>

With [[bus mastering]], each card could talk to another directly.  This allowed performance that was independent of the CPU.  One potential drawback of multi-master design was the possible collisions when more than one card would try to bus master, but Micro Channel included an arbitration feature to correct for these situations, and also allowed a master to use a ''[[burst mode (computing)|burst-mode]]''. Micro Channel cards had complete control for up to 12 [[millisecond]]s. This was long enough to permit the maximum number of other devices on the bus to [[data buffer|buffer]] inbound data from over-runnable devices like tape and communications.

Multiple bus-master support and improved arbitration mean that several such devices could coexist and share the system bus. Micro Channel bus-master-capable devices can even use the bus to talk directly to each other ([[peer-to-peer]]) at speeds faster than the system CPU, without any other system intervention. In theory, Micro Channel architecture systems could be expanded, like [[mainframe]]s, with only the addition of intelligent masters, without periodic need to upgrade the central processor.

Arbitration enhancement ensures better system throughput since control is passed more efficiently. Advanced interrupt handling refers to the use of level-sensitive interrupts to handle system requests.  Rather than a dedicated interrupt line, several lines can be shared to provide more possible interrupts, addressing the ISA-bus interrupt line conflict problems.

All interrupt request signals were "public" on Micro Channel architecture permitting any card on the bus to function as an I/O processor for direct service of I/O device interrupts. ISA had limited all such processing to just the system's CPU. Likewise, bus master request and grant signals were public, such that bus attached devices could monitor latency to control internal buffering for I/O processors. These features were not adopted for PCI, requiring all I/O support to come uniquely from the system board processor.

The final major Micro Channel architecture improvement was '''POS''', the ''Programmable Option Select'', which allowed all setup to take place in software. This feature is taken for granted now, but at the time setup was a huge chore for ISA systems. POS was a simple system that included device IDs in firmware, which the drivers in the computer were supposed to interpret. (This type of software-configuration system is known as ''[[plug and play]]'' today.) The feature did not really live up to its promise; the automatic configuration was fine when it worked, but it frequently did not - resulting in an unbootable computer - and resolving the problem by manual intervention was much more difficult than configuring an ISA system, not least because the documentation for the MCA device would tend to assume that the automatic configuration ''would'' work and so did not provide the necessary information to set it up by hand, unlike ISA device documentation which by necessity provided full details (however having to physically remove and check all [[interrupt request|IRQ]] settings, then find and set the new IRQ for a new device—if a suitable one was available—for ISA was no fun at all, and beyond many users... it is obvious why the attempt was made to move to software-arbitrated configuration, and why this was to later succeed in the form of [[Plug and play|PnP]].)