The machine also includes a bootstrap ROM that makes it easier to start up, including code for running basic input/output and allowing input through a front-mounted octal keypad and front panel display, instead of the binary switches and lights used on machines like the Altair 8800.

Sales were so much greater than expected that MITS was unable to clear the order backlog for the better part of the year.

[3] The company had considered designing a kit computer as early as 1974, but concluded that it was not a good fit for their traditional market.

[4][5][6] For full functionality, the system also requires a 4 KiB SRAM card ($139) and some form of storage controller; at a minimum this would be the H10 paper tape punch/reader or the H8-5 Serial I/O card ($110) which controls a cassette tape, using a 1200-baud variant of the Kansas City standard format.

The H9 is limited to upper case characters and 12 display lines, and uses a cheap array of switches for its keyboard.

It was eventually superseded by the H19 terminal, a more ergonomic design, and capable of lower-case and graphic-like characters.

The H8 can run CP/M, and often did, but early machines require either a special version of CP/M that was "org'd" at 8 KiB instead of zero, or a small hardware modification and an updated ROM to do so.

In 1978 Heath introduced the Heathkit H88 which integrated the H19 terminal and a new Zilog Z80-based single-board processor into the case of the H19.

The machines bear a strong resemblance to the TRS-80 Model III and similar all-in-one computers.

Eventually, Zenith Data Systems (Heathkit plus the computer division of Zenith) was purchased by Bull HN (CII Bull, Honeywell and Nippon Electric) because they needed a US maker of microcomputers to comply with government purchase requirements.

The H8 is packaged in a box-like chassis with pressboard sides and metal sheeting for the rest of the case.

The machine is built up from the backplane mounted on the right-hand side panel of the case, with ten 50-pin card slots.

Another notable change is the replacement of the front-panel toggle switches and lights of a standard early-model S-100 system with a keypad and seven-segment LED display (early S-100 machines like the Altair or IMSAI 8080 contain no ROM and when they are started, the user "keys in" a program via the toggle switches to read a paper tape.

The ROMs interfere with the operation of standard CP/M, which assumes it can write the memory near location 0, in particular the interrupt handler pointers.