Ohio Scientific

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Ohio Scientific was a computer company that built and marketed computers from the late 1970's to the early 1980's.

One of their first products, launched in 1978 was the OSI Model 500 system, a very simple single board computer based on the MOS Technology 6502 microprocessor, but lacking a Video Display Controller. It needed an external video terminal such as the VT100, or the CT-64 terminal system from SWTPC, to create a useful system. Their later products were also 6502-based, the Superboard II, Challenger 1P, Challenger 4P and Challenger 8P, introduced in 1979 and discontinued in 1981.

The company had some rather unusual design practices. Most every design was minimal, uncluttered, feature-scant. Think of their hardware and software along the lines of a Model T. Examples:

A typical Ohio Scientific motherboard used a minimum number of 7400-series TTL chips. No fancy MSI chips, just lots of basic logic, hand-designed. So minimal, there were bare spots on the motherboard where they'd laid down the circuit paths for a serial port, but not bothered to solder in the requisite IC's. Instead of a proper floppy-disk controller, they used the 6850 serial-port UART chip! Which made their 8 and 5 inch floppies unreadable on any other system.

The company supplied full schematics of their hardware. That and the simple design, made their motherboards easy and friendly to modify. Some examples:

It was easy to jumper around a divide by two flip-flop, effectively doubling the CPU clock speed from 1 to 2 MHz!. At least on the C1P, the hardware was quite capable of running at double the basic rate. You did have to burn a new BIOS EPROM, otherwise the cassette interfae would try to read and write tapes at double the basic rate, which would not work.

It was also easy to change some jumpers and double the number of characters per line to a (then) whopping 64. (You did have to change some constants in the BIOS so the write-a-character routines knew the new screen geometry).

No fancy color-graphics like the Apple II, just very basic upper-case text, and some pseudo graphical characters, (comparable to the "PETSCII" character-set of the Commodore PET) for drawing lines and supporting simple games. They hadn't figured out how to write to the video memory without glitching the display, so the hardware would blank the screen for a few microseconds while it accessed the video memory. Not too obtrusive at 1MHz, but if you doubled the CPU speed, it became noticeable.

The software was also very minimalist. A cassette boot loader in ROM and Microsoft BASIC in ROM. If you bought the optional floppy or hard disk, you also got a really bare-bones "Disk Operating System". So bare-bones, it didn't even have named files!. You accessed the disk by asking the DOS to read or write absolute track numbers. They suggested you reserve track 40 as a text area where you'd manually keep a directory of what tracks held what information. That was it. Even so, the disk was a blessing, being much handier than reading and writing cassettes at 1200 baud.

All in all, a cheap and fun system for the real hard-core hacker, but not a warm and fuzzy end-user system, like the Apple II.