It was developed by IBM after the comparatively expensive PC had not established itself as a computer for the average home user. The computer presented to the public on November 1, 1983, however, was a failure due to its limited scope of performance and still high price, which IBM later tried in vain to make up for with the IBM PC JX .
Like the PC, it had an Intel 8088 CPU (sometimes a replica in the form of an AMD D8088 was installed), which was clocked at 4.77 MHz . The memory configuration was also 64 KB, but could (officially) only be increased to 128 KB. The DMA controller was saved compared to the PC, which means that some hardware-related programmed applications for the IBM PC do not run on the PCjr. There was also no official option for retrofitting a second floppy disk drive or installing a hard disk.
The possibility of adding new functions to the computer using expansion cards was limited to a so-called sidecar connection, for which memory expansions up to a total of 512 KB were available. Sidecar extensions were flat housings that could simply be plugged into the computer on the right side. Programs could be loaded via the 5.25 " floppy disk drive or a cassette recorder input , just like on a PC . In addition, there were two slots on the front for cartridges that could contain, for example, an extended version of the integrated Microsoft BASIC or games.
Another special feature was the keyboard, which was wirelessly connected to the computer via an infrared interface on the front. For cost reasons, it was not the buttons but the space above the buttons that were labeled - which made it difficult to use. Further points of criticism were the often unreliable infrared connection and the imprecise stop.
The graphics system was integrated onboard on the motherboard and therefore could not be upgraded. It is compatible with the CGA standard, but for better positioning on the home user market it also has two additional graphics modes that provide 16 colors at 320 × 200 pixels and four colors at a resolution of 640 × 200 pixels, but at the expense of what is available for programs RAM. The PCjr was delivered complete with a monitor. Another concession to the home user market was the integrated sound system, which was based on a TI 76496 chip from Texas Instruments, was able to reproduce three voices at the same time and was an enormous improvement over the system loudspeaker of the IBM PC and PC XT.
The PCjr came in two versions: the Model 4 , which is the original PCjr, and the Model 67 , an expanded version with u. a. an additional floppy disk drive.