Signetics 2650

According to Adam Osborne's classic book "An Introduction to Microprocessors Vol 2: Some Real Products", the 2650 was "the most minicomputer-like" of the 8-bit processors.

The manufacturer, Signetics, was not an expert in manufacturing complex MOS chips. They did however bring out a very good prototyping board at a reasonable price, so the chip found use with a limited number of hobbyists. The chip contained 7 8-bit registers, although only 4 were visible at once. It was limited to a 15-bit address space (thereby addressing a maximum of 32KB of memory), since the upper bit of a 16-bit memory reference was reserved to indicate that the indirect memory addressing mode was to be used (a minicomputer-like feature).

While there were many addressing modes, the lack of any 16-bit registers and the 15-bit address space prevented widespread use. Despite this, an operating system ("2650 DOS") was available, along with a BASIC interpreter, and many games of the "Hunt the Wumpus" style. Most programs were written in assembler.