Hands-On Embedded Programming with C++17

TMS 1000

The first commercially available MCU was Texas Instrument's TMS 1000, a general-purpose 4-bit, single-chip system. It was first made available for sale in 1974. The original model had 1 KB of ROM, 64 x 4 bits of RAM, and 23 I/O pins. They could be clocked at speeds from 100 to 400 KHz, with each instruction executing in six clock cycles.

Later models would increase the ROM and RAM sizes, though the basic design remained largely unchanged until production ceased in 1981:

The size of the MCU die was roughly 5 x 5 millimeters, small enough to fit in a DIP package. This type of MCU used mask-programmable ROM, meaning that you could not ...