I have an HP 9830A desktop computer, circa 1972, which runs BASIC using a custom bit-serial processor built out of TTL, with an architecture similar to the HP 2116 minicomputer. I’m planning to use the 9830A in my RetroChallenge entry, but it was configured with insufficient RAM, and I’ve now upgraded it from 3520 bytes available to 11,712 bytes.
The 9830A has two slots for RAM boards. Each board has either 4K or 8K bytes of dynamic RAM, using 32 or 64 Intel 1103 dynamic RAM chips of 1 Kbit each. My 9830A has the base configuration of 4KB, of which 3520 bytes are available to the user. The “LIST” command will show the free memory; at power-up it shows 1760 words (3520 bytes).
RAM expansion was possible by replacing the 4KB RAM board (p/n 09830-69584) in slot 1 with an 8KB RAM board (p/n 11275-69584), and installing a 4KB or 8KB board in slot 2.
My 9830A came with a spare 8KB RAM board, which does not work correctly. However, a friend gave me a non-working 9830A which contained a single 8KB board. I removed that, installed it in slot 1 of the working 9830A, and put the 4KB board in slot 2, and now the 9830A LIST command reports 5856 words of memory available (11,712 bytes).
The 9830A processor can actually address 32KB of RAM, but the address decoder is set up for only 16KB. The 9830B uses higher-density RAM boards and a different decoder to allow for 32KB. At some point I might build a custom RAM board for my 9830A, and jumper the necessary additional address lines to the M register board (09830-66582).
Online 9830A resources:
- The Museum of HP Calculators
- HP Computer Museum, includes scanned documents, and Tony Duell’s reverse-engineered schematics
- Brent Hilpert’s HP 9830A page, includes Brent’s reverse-engineered schematics, and interfacing projects