Talk:KS10

Second UBA also 18-bit?

I'm trying to figure out whether the "second" (i.e. not disk) Unibus was also operated in 18-bit mode. I have a vague recollection that only the disk controller needed 18-bit data transfers, but I can't confirm this. I read the technical manual, but it doesn't seem to indicate any difference between the two. Larsbrinkhoff (talk) 10:58, 6 February 2025 (CET)

I haven't checked the documentation/code, but my strong recollection is that the second UNIBUS is operated in 16-bit mode only. For one thing, very few UNIBUS devices can operate in 18-bit mode - the only ones I know of are the RH11 MASSBUS controller and the RK11-E. (Note that the RH11 also needs MASSBUS devices that can operate in 18-bit mode, to operate in 18-bit mode; the TM02 magtape controller apparently did not have that capability, because the drives that could connect to it only operated in 8-bit mode - again, I have not checked the prints to be certain.) Which would explain why the TM02 and its RH11 are connected to the second UNIBUS. Everything else on that bus was a 16-bit device. Jnc (talk) 15:42, 6 February 2025 (CET)

Note to later readers: see Talk:UNIBUS parity for extended research on this point. The "drives that could connect to it only operated in 8-bit mode" supposition is 'confused' (as we used to say at MIT); the TM03 magtape controller could function in 18-bit mode, using 8-bit drives - it just threw away half of every 5th byte on the tape. Jnc (talk) 14:00, 7 February 2025 (CET)