Ohio Scientific, Inc. (OSI, originally Ohio Scientific Instruments, Inc.), was a privately owned American computer company based in Ohio that built and marketed computer systems, expansions, and software from 1975 to 1986. Their best-known products were the Challenger series of microcomputers and Superboard single-board computers. The company was the first to market microcomputers with hard disk drives in 1977.

The company was incorporated as Ohio Scientific Instruments in Hiram, Ohio, by husband and wife Mike and Charity Cheiky and business associate Dale A. Dreisbach in 1975. Originally a maker of electronic teaching aids, the company leaned quickly into microcomputer production, after their original educational products failed in the marketplace while their computer-oriented products sparked high interest in the hobbyist community. The company moved to Aurora, Ohio, occupying a 72,000-square-foot factory. The company reached the $1 million revenue mark in 1976; by the end of 1980, the company generated $18 million in revenue. Ohio Scientific's manufacturing presence likewise expanded into greater Ohio as well as California and Puerto Rico.

In 1980, the company was acquired by telecommunications conglomerate M/A-COM of Burlington, Massachusetts, for $5 million. M/A-COM soon consolidated the company's product lines, in order to focus their new subsidiary on manufacturing business systems. During their tenure under M/A-COM, Ohio Scientific was renamed M/A-COM Office Systems. M/A-COM struggled financially themselves and sold the division in 1983 to Kendata Inc. of Trumbull, Connecticut, who immediately renamed it back to Ohio Scientific. Kendata, previously only a corporate reseller of computer systems, failed to maintain Ohio Scientific's manufacturing lines and subsequently sold the division to AB Fannyudde of Sweden. The flagship Aurora factory, by then only employing 16 people, was finally shut down in October 1983.

Ohio Scientific was founded in Hiram, Ohio, in 1975 by Dale A. Dreisbach (c. 1909 – June 16, 1987) and husband and wife Michael "Mike" Cheiky (January 1, 1952 – December 7, 2017) and Charity Cheiky (born c. 1954). Mike Cheiky had worked at the Solon-based Ohio Nuclear Company—makers of medical equipment—as director of engineering, while Charity Cheiky had been employed at Western Reserve Academy as a professor of math and computer science. Dreisbach meanwhile was a chairman and professor emeritus of Hiram College's chemistry department; the Cheikys had met at Hiram College. The three founded Ohio Scientific with between $5,000 and $25,000 of start-up capital.

The company was originally outfitted from the Cheiky's garage and was dedicated to the production of electronic teaching aids. The company's original name—Ohio Scientific Instruments, Inc.—reflected this initial purpose. The first products the company released included a calculator that also taught the basics of statistics and a single-board microcomputer. The latter, called the Microcomputer Trainer Board and incorporating a MOS Technology 6502 microprocessor, was designed by Mike, inspired by his experience with microprocessor-based minicomputers at his Ohio Nuclear job.

Most of the educational products sold poorly due to the lack of a strong local market for them, according to Mike. However, the Microcomputer Trainer Board saw high demand. Most fruitful was a quarter-page advertisement in an early issue of Byte—a magazine for microcomputer hobbyists—with orders for the board totaling $100,000 within a few months. The board generated $20,000 in sales for the trio, much more than they had originally anticipated. To keep up with growth, Cheikys moved the company to a 700-square-foot storefront in Hiram, Ohio, last occupied by a barbershop and right next to a pizza parlor.

With the release of their microcomputer systems and hardware in the mid-1970s, Charity Cheiky became the first woman at the helm of a personal computer manufacturer. In June 1976, Ohio Scientific had logged their first $1 million in revenue. In late January 1978, the company moved from Hiram to Aurora, Ohio, occupying a 72,000-square-foot factory formerly occupied by Custom Beverage. By that point, the company had employed 35. Within six months, the number of employees had reached 100. Cash flow increased in tandem: between 1977 and 1978, the company grossed $10 million, and between 1978 and 1980, it logged sales of $20 million. In 1980, Ohio Scientific generated $18 million in revenues — $14.8 million between January and October 1980 and $3.2 million to the end of the year.

The Cheikys meanwhile felt that Ohio Scientific was growing too fast for them to adequately manage. Stan Veit, a business partner of Ohio Scientific as well as the founder of the first computer store in New York City, called the company poorly organized and hard to contact. In his words, the company was "undercapitalized and very slow to deliver ordered equipment. This lost them a lot of the business they could have obtained because of their technical ability". In order to appease chagrined dealers who complained of long development times for the company's software, Ohio Scientific initiated a cooperative centralized software dealership program to spur the development of business applications for their computers in late 1978. In 1980, the company opened up two facilities in Cleveland: the first, a manufacturing plant early in the year; and the second, a 15,000-square-foot salesman training center opened in fall 1980. Ohio Scientific additionally opened a printed circuit board manufacturing plant in Puerto Rico around the time of their expansion into Cleveland, incorporating Ohio Scientific of Puerto Rico, Inc., in the process. In November 1980, the company acquired the hard drive manufacturing division of Okidata in Goleta, California, which manufactured the company's C-D74 drives that were used with their Challenger series of microcomputers. After acquiring the division, Ohio Scientific folded it into their wholly owned Ohio Scientific Memory Products division. By 1980, Ohio Scientific had 300 employees overall.