NOS IMSAI 8080 - Part-1 - Unboxing and Inspection - RTR100

In this video we start looking at the IMSIA 8080 New Old Stock (NOS) kit I recently acquired. The system was released for sale in 1975, this example is from 1976.

We remove all the part and take an initial look at them.

The IMSAI 8080 is considered the first clone home / hobbyist computer. It was cloned from the Altair 8800 however the mechanical design was improved to provide easier construction and to provide a more stable system. The front panel was improved to move away from small toggle switches to paddle toggle switches and was perhaps the best looking machine from the era.

The initial system provided a front panel which was the only way for the user to interact with the system. In the base configuration the user had the front panel, an intel 8080 CPU and a small amount of RAM (1K bytes). All interaction with the system was through the front panel. There was no monitor in ROM. There was no mass storage provided, not even a cassette interface. Users added RS-232/Current Loop expansion cards that could talk with an ASR (Teletype) terminal that included a paper tape reader and punch that allowed program loading and the ability to save programs and data.

The design of the front panel is interesting in that it injects 8080 instructions directly onto the CPUs data bus which provided the methods to read and write to memory. The design of this tied the front panel tightly to the Intel 8080 CPU, as CPUs evolved such as the Zilog 8080 there was enough differences in CPU timing that the front panel typically wasn't compatible with the newer CPU card.

The design is so minimal that there was no Power On Reset. After power on the user had to manually reset the system to get it to a known state.

Many systems were upgraded to provide Power On Reset and ROM to allow the system to automatically or with minimal user interaction to boot an OS, application or start a BASIC interpreter.

In my opinion the Intel 8080 CPU was the first CPU that provided sufficient speed and instructions to be used as a general purpose CPU that could support a wide variety of software.

The system can run CP/M, various versions of BASIC from ROM and supported various compilers such as C.

S-100 systems went on to provide word processors and business software.

S-100 systems found their way into manufacturing as machine controllers and provided various other functions within manufacturing and industry.

The Altair 8800 defined the S-100 bus standard which later evolved into the IEEE-696 standard that allowed 16-bit CPUs. The IMSAI followed this path as well.

There is an active group of collectors for S-100 machines and an active community designing newer boards and clones of existing boards.