Professor Mark Csele: Ohio Scientific Computers

Posted on Feb 5, 2014

This machine was near-and-dear to me as it was my first real computer, an Ohio Scientific Superboard II. In 1979 I got my machine, a 6502-based single-board computer with a whopping 8K of RAM and BASIC in ROM. The board was completely self-contained, requiring only a 5V, 3A power supply to run (I built my own using a 78H05 regulator). Ohio Scienti

Professor Mark Csele: Ohio Scientific Computers
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fic (OSI) started business in 1975 and through the late 1970`s and early 1980`s produced a series of 6502-based machines called the "Challenger" series. Like contemporaries (including the Apple and the Commodore machines), OSI systems used the low-cost 6502 processor. Created as a low-cost response to Motorola`s 6800 processor, and commercially available (in production quantities) in 1976, the 6502 could use all readily-available and inexpensive 6800 peripheral chips (as OSI did to save cost). The 6502 achieved low costs through a number of design features including the fabrication in NMOS technology and use of "zero-page" memory which allowed reduction of the number of on-chip registers to six. The 6502, in a design reminiscent of the PDP-8 processor, allows fast access to the first 256 bytes of RAM from most instructions (making the 6502 almost RISC-like). The next 256 bytes (0x100 through 0x1FF) are prewired as the stack. All 6502 systems, therefore, require at least 512 bytes of RAM located in the lowest memory page and unlike the contemporary Z-80 processor, programs cannot simply be located at address zero (the 6502 actually fetches a vector for the start program from the highest two bytes - a ROM must be located there). The earliest catalog I could locate was the spring 1978 issue. That year, OSI offered several models based on a single-board CPU, the model 500 card. This card featured 8K BASIC-in-ROM, 4K of RAM on...

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