You could buy the Model 500 as a single-board system (the 500), as a bare-bones BASIC computer in an enclosure (the 500-1), or as an expandable BASIC computer in a larger OSI Challenger enclosure (the 500-8).
<text>OSI had been selling the core components of the Challenger since 1975, but didn’t integrate them into a single package until 1977. The OSI Challenger uses a non-standard Molex connector for its S-100 bus. The company believed that it provided a more reliable contact.

The Challenger II was housed in a large enclosure and required the addition of a terminal for keyboard input. It also did away with the BASIC in ROM, relying instead on the floppy drive. A Challenger II single-board computer, sans case, was also available. With the Challenger series you could have the biggest hard drive on the block–74MB–but it would set you back a cool $6,000.

Based on the Model 500 electronics, the Challenger IIP had a full-size, integrated keyboard housed in a case similar to the Sol-20. Subseqent IIP models came in different enclosures depending on configuration and expansion capability. The main floppy-disk-based C2-8P system, for example, was housed in a large enclosure with a separate keyboard.

With the Challenger III, OSI promised a system that could run all the popular software of the day. Challenger IIIs came in different enclosures depending on options and expansion capability.

Much like the Sol-20, the Challenger 4P had an aluminum case with wooden sides. It was more of a home-user-friendly system than its predecessors with several options for home security. An 8P model used a larger enclosure and offered options for a hard drive, voice I/O, and telephone interface.

The Challenger I Series 2 was introduced after OSI had been sold to M/A-Com Office Systems.

OSI Model 500 Series (1977, early micro)
Original Retail Price: $298 to $629
Base Configuration: 1MHz 6502 CPU, 4K RAM, 8K ROM, RS-232C port, BASIC
Size/Weight: 12 x 15 x 4 inches (500-1) or 15 x 17 x 10 inches (500-8) Important Options:eight-slot chassis, power supply, two terminal connectors

OSI Challenger (1977, early micro)
Original Retail Price: $439 to $675
Base Configuration: 6502A CPU, OS-65, eight S-100 slots, 1K RAM (192K max), up to 16K ROM, external 5.25-inch floppy disk drive, serial interface, BASIC, editor/assembler
Video: 16-line x 64-column text
Important Options: 6502C or 6800 CPU; CPU expander board; external dual 5.25-inch floppy disk drives; keyboard terminal; Sanyo monitor; ADC, DAC, parallel, serial, and cassette interfaces

OSI Challenger IP (1978, early micro)
Original Retail Price: $349
Base Configuration: 6502 CPU, 4K RAM (8K max), 8K ROM, cassette interface, integral keyboard, BASIC in ROM
Video: 24-line x 24-column text, 256 x 256 graphics
Important Options: expander board, floppy disk drive interface, port adapter, editor/assembler

OSI Challenger II (1977, early micro)
Original Retail Price: $1,964
Base Configuration: 1MHz 6502 CPU, four S-100 slots, 16K RAM (192K max), 8-inch floppy disk drive, integral keyboard, serial or video interface, BASIC
Video: 16-line x 64-column text
Important Options: second 8-inch floppy disk drive, 74MB hard disk drive, video interface, line printer

OSI Challenger IIP (1977, early micro)
Original Retail Price: $598
Base Configuration: 2MHz 6502 CPU, four S-100 slots, 4K RAM (40K max), 8K ROM, cassette interface, integral keyboard, BASIC in ROM
Video: 32-line x 64-column text
Important Options: single or dual 8-inch floppy disk drives, 74MB hard disk drive, video interface, line printer

OSI Challenger III (1977, early micro)
Original Retail Price: $3,481
Base Configuration: 6502A, 6800, and Z80 CPUs; OS-65D, 32K RAM, two 8-inch floppy disk drives, serial interface

OSI Challenger 4P (1979, desktop)
Base Configuration: 6502 CPU; accessory bus; 8K RAM (48K max);  integral  keyboard; two RS-232, parallel, four game, and cassette ports; BASIC
Video: 32-line x 64-column text, 512 x 256 graphics, 16 colors
Important Options: 6502A CPU or 6502C “GT Option,” external 5.25-inch floppy disk drive, Home Color TV set, joysticks, remote security console, modem

OSI Challenger I Series 2 (desktop)
Original Retail Price: $479
Base Configuration: 6502 CPU, OS-65, 4K RAM (32K max), RS-232C port, BASIC
Video: 24-line x 24-column text, 256 x 256 graphics

OSI Challenger II Series 2 (desktop)
Original Retail Price: $879
Base Configuration: 6502 CPU, OS-65, 8K RAM (48K max), integral keyboard, RS-232C and parallel ports, BASIC, music synthesizer
Video: 32-line x 64-column text, 15 colors