In the late 60's and early 70's, the technology and market were emerging to set the stage for production of monolithic, single-chip CPUs. In 1969, A terminal equipment manufacturer met with Intel to design a processor that was smaller and would generate less heat than the dozens of TTL chips they were using. The resulting design was the 8008, which is well known as the predecessor to the x86 line of processors that are ubiquitous in desktop PC's today. Less well known though, is that Texas Instruments came up with a competing design, and due to development delays at Intel, beat them to production by about nine months. [more inside]
"This realistic simulator of a 4-function Texas Instruments calculator from 1974 runs the calculator's source code instruction by instruction by simulating the processor. The unusual processor has 11-bit opcodes, 44-bit BCD registers, and a 9-bit address bus. To use the simulator, slowly click keys on the calculator image and you can watch how the calculator performs operations step by step. Since the processor doesn't do multiplication or division, it does these operations by repeated addition or subtraction."
This is a video of a game which replicates Portal's physics system in 2 dimensions on the TI-83 graphic calculator. The game was developed by a 20 year old student studying game design. A download link is available here.