Basic Machine Architecture
The Burroughs B5500 was a 48-bit stack based computer with either one or two CPU's, and up to 32k words of memory. Only the first CPU could preform I/O operations, the second CPU was used only as an auxiliary processor. The system could have up to 4 I/O channels that could talk to any device. All data was accessed via segments, segments could be loaded or swapped out to disk based on usage. This allowed a form of virtual memory. Also the B5500 was programmed mostly in high level languages rather then assembly languages which were common for the time.
The B5500 supported up to 16 tape drives, 10 or 20 disk units, 2 drum units, 2 line printers, 2 card readers, 1 card punch, console typewriter and a terminal controller.
Disks consist of 1 or 2 controllers, and up to 10 disk drives each. Each disk drive had up to 5 Electronic Storage Units to hold data. Disks could also be shared by both controllers to increase access time. The maximum amount of disk space that could be configured per controller was about 960 million characters of data. The B5500 simulator supports two types of disk units, Mod I or Mod IB. ModI held 48 Million Characters, ModIB held 96 Million Characters. The simulator supports up to 2 disk controllers, the default is shared. To run the system in an unshared mode requires the operating system be rebuilt. Disks can be added once the system is built, however they can't be removed.
Under the simulator disks are attached to esu units, the dk units are disk controllers and used to route I/O requests. There is no order requirement for esu units to be added, however once attached they can't be removed without reloading the entire system. Other system units can be enabled or disabled without changing the configuration. The simulator supports the full expanded system if the user desires. Generally 2 esu units are all that is required to make a usable configuration.