The Alliant computer is a parallel machine with four 68020 processors. It has a local VME bus architecture which runs through the whole machine. The one we have installed has it's harddisks connected to this VME bus, which is standard (I think) for this type of computer.
Though the machine is a parallel computer, it doesn't need all four processors to run. We have had a problem with one of the boards, and pulled it out. The computer had no problem with the loss of this one processor, and continued it's duty. The scheduler is a mystery at the moment. I assume there must be a way to reschedule it's procedures, but I am at a loss how to do this. Any documentation is appreciated.
Now, as to other kinds of gadgetry which is put onto this machine... We have a tape drive and a floppy drive on the machine. These devices both are on a scsi controller, which has no DMA at all. So every time one of these devices has read one byte, it triggers an interrupt after which one of the CPU's must attend to this byte and put it somewhere in the memory (or dump it) and tell the device to continue. This is somewhat slow, I know. But it is the only way to make it work, I think.