The HER/12 minicomputer assumes a historical retro-context located between mid 1960s and early 1970s and it is meant to be a minicomputer
in the historical sense.
The following constraints have been established by design:
* Strict 12-bits architecture.
* Only SSI and MSI integrated circuits of the series 7400 must be employed.
* Not use of ROM memory chips of any kind.
* Peripherals connect to the CPU by the mean of "I/O Channels" rather than external bus.
* Construction must be agile and low cost.
The machine is designed to achieve high performance within these limitations by optimizing instruction encoding and execution for minimum clock cycles. Also, sufficient resources to programmers has been put in place, such as indirect addressing, one index register and hardware support for BCD arithmetic.
I have to admit that using fast static RAM semiconductor memory is historically incorrect. Memory were very slow in the 70s; the one employed by HER/12, in contrast, is as fast as the CPU electronics itself.