I am continuing my exploration of the SacState 8008 boot PROM code (using James Markevitch's listing), and have a little more understanding of the escape codes I was asking about previously (in the thread 'identifying terminal by escape codes') It looks like the SacState machine was built as a card that plugged into a 4023 terminal motherboard. My current assumption is the data going out of the 8008 card (i.e. where the code on the PROM is running) is interacting with the other cards on the 4023 bus directly. My further assumption is that there must have been some kind of block device (tape or disk?) that was also on that same bus, and that some of the escape codes must be doing some sort of device selection (i.e. signalling that the next chunk of data is intended to be read from, or written to, a specific device, not read from keyboard or displayed on screen). I am not clear as to whether the other devices are interfacing via - a commercial 'dedicated' I/O card, e.g. a drive controller (if any existed?) - a commercial 'generic' I/O card, e.g. a serial I/O and an 'intelligent' device is being controlled - a custom made I/O card that plugged directly into the 4023 bus The only 4023 documentation I can find online is the User Manual, which has: - a list of bus signals, which confirm there are enough signals available to construct complex device I/O - a list of accessory cards, including a serial 'Data Communications Interface', a 'hard copy unit', and 'audio recorder card' (tape controller ). - a reference to a 4023 service manual, which has a 'theory of operation' which may describe enough of the bus protocol to work out how the 8008 PROM could be interacting with other devices on that BUS. So my questions are - - were any commercial accessory cards available for the 4023 other than the ones listed in the back of the user manual? If so, does any documentation for them exist? - is the 4023 "service manual" available through any means? Cheers Jonno