(IMS 6100) A single chip design of the DEC PDP-8 minicomputer. The old PDP-8 design was very strange, and if it hadn’t been popular, an awkward CPU like the 6100 would never been designed.
The 6100 was a 12-bit processor, which had three registers: the PC, AC (accumulator), and MQ. All 2-operand instructions read AC and MQ and wrote back to AC. It had a 12-bit address bus, limiting RAM to only 4K. Memory references were 7-bit, offset either from address 0, or from the PC page base address (PC AND 7600 oct).
It had no stack. Subroutines stored the PC in the first word of the subroutine code itself, so recursion required fancy programming.
4K RAM was pretty much hopeless for general purpose use. The 6102 support chip (included in the 6120) added 3 address lines, expanding memory to 32K the same way that the PDP-8/E expanded the PDP-8. Two registers, IFR and DFR, held the page for instructions and data respectively (IFR was always used until a data address was detected). At the top of the 4K page, the PC wrapped back to 0, so the last instruction on a page had to load a new value into the IFR if execution was to continue.
- Intersil 6120
processor (IMS 6120) An improved version of the Intersil 6100. The 6120 was used in the DECmate. [Details?] (1994-11-23)
[in-ter-puh-zish-uh n] /ˌɪn tər pəˈzɪʃ ən/ noun 1. the act or fact of or the condition of being . 2. something . 3. the doctrine that an individual state of the U.S. may oppose any federal action it believes encroaches on its sovereignty. /ˌɪntəpəˈzɪʃən/ noun 1. something interposed 2. the act of interposing or the […]
[in-ter-pohz] /ˌɪn tərˈpoʊz/ verb (used with object), interposed, interposing. 1. to place between; cause to intervene: to interpose an opaque body between a light and the eye. 2. to put (a barrier, obstacle, etc.) between or in the way of. 3. to put in (a remark, question, etc.) in the midst of a conversation, discourse, […]
[in-tur-puh-leyt] /ɪnˈtɜr pəˌleɪt/ verb (used with object), interpolated, interpolating. 1. to introduce (something additional or extraneous) between other things or parts; interject; interpose; intercalate. 2. Mathematics. to insert, estimate, or find an intermediate term in (a sequence). 3. to alter (a text) by the insertion of new matter, especially deceptively or without authorization. 4. to […]