CDC disk drives (was Re: what IBM system is this?)

On 07/09/2015 06:49 AM, Paul Koning wrote: "Multiple Access Controller"--pretty much just a software-programmable switch. At one time, was strictly a QSE--we used them extensively on 4-Cyber configurations sharing 4MW of ECS and multiple peripherals. The idea was that any CPU could get to any peripheral. So a site with 4 CPUs might be equipped with a couple of 512 printers; but any CPU could use any printer. This extended to the disk drives, IIRC. Mostly it involved an extra FCN instruction ahead of the usual code. So one could take a stock SCOPE deadstart, and just key in the FCN from DSD to get to an available printer not the default. Sometimes COMSOURCE would run on one of the systems, while our project was using another in the same configuration. It annoyed the COMSOURCE operators no end when their peripherals would be "stolen" by our system. But don't get me started on COMSOURCE... On our big setups, the 844s had their own filesystem--keeping over 100 drives online (not as PF drives) using the usual RBR/RBT scheme would have eaten up a lot of CM. In our case, we used them for an indexed database, so the database itself had the block linking information embedded, so all that was needed was a simple bitmap to indicate used blocks. --Chuck