Operating system IBM PC DOS 2. IBM’s first attempt to enter the home computer market. From a software perspective, the PCjr video hardware is an upward-compatible extension of the Cga p 18 pdf, but differences in the hardware that affect mode and color selection make it incompatible from a strict hardware perspective.
In general, the PCjr video hardware can do anything that a CGA can, but the design of hardware-control registers and the programming rules and techniques are different. The PCjr’s sound is provided by a Texas Instruments SN76496 which can produce three square waves of varying amplitude and frequency along with a noise channel powered by a shift register. 77 MHz Intel 8088 CPU is faster than that of other computers that were aimed at the home market at the time, though the stock PCjr usually does not run at the full rated 4. The detached wireless infrared keyboard promised a degree of convenience none of its competitors had, eliciting visions of word processing wirelessly from one’s couch with the computer connected to a TV set as a display. For infrared wireless operation, it was powered by common AA cells. The PCjr Color Display sold by IBM included an internal amplified speaker, being the only IBM monitor in the PC line to do so. Further reinforcing the “home-friendly” goal, the PCjr also introduced two ROM cartridge slots on the front of the unit, meant to load software quickly and easily.
Cartridges can also replace the system BIOS and other firmware. A number of patches from various vendors are included on a single “combo-cartridge”, licensed and sold by PC Enterprises, to support add-on hardware, bypass certain limitations of design, and keep up with changing OS requirements. PCjr are provided via add-on “sidecars” that attach to the side of the PCjr. Multiple expansions are stacked together, increasing the width of the machine.
The PCjr’s video uses 32 KB of RAM as shared graphics memory, which prevents using additional memory with the built-in 128 KB under DOS. The PCjr initially shipped with a wireless chiclet keyboard called the “Freeboard”, powered by four AA batteries to provide infrared line-of-sight wireless communication. The PCjr also has a light pen port. Mouse Systems optical mouse of the same design as those for Sun workstations. For my grandmother, and for millions of people like her, IBM and computer are synonymous.