The IBM PCjr (type 4860 ) was a home computer-like and cheaper version of the IBM PC.
It was developed by IBM, after the comparatively expensive PC could not prevail as a computer for the average home user. The November 1, 1983, the public for the computer, however, was due to its limited scope of services and the still high price of a flop, who was later tried in vain with the IBM PC JX to make amends.
He decreed as the PC has an Intel 8088 CPU as ( to some extent a replica in the form of a AMD D8088 was built ), which was clocked at 4.77 MHz. Memory capacity also was 64 KB, however, was ( officially ) be increased only to 128 KB. The DMA controller has been compared to the PC saved, whereby some hardware at programmed applications for the IBM PC will not run on the PCjr. Also, there was no official way to retrofit a second floppy disk drive or to install a hard drive.
The possibility of the computer by means of expansion cards to add new functions added, was limited to a so-called sidecar connection (English for sidecar ) were available to a total of 512 KB for memory expansions. Sidecar extensions were flat case that could be plugged into the right side of the computer easy. Programs could be loaded on the 5.25 " floppy disk drive or a tape recorder input as on a PC. Additionally, there was on the front two slots for cartridges that could include, for example, an enhanced version of the built-in Microsoft BASIC or games.
Another peculiarity was the keyboard that was connected wirelessly via an infrared port on the front with the computer. For cost reasons, were not the keys, special room labeled above the keys - which use difficult. Other criticisms were often unreliable and imprecise Infrarotverbindunng stop.
The graphics system was onboard integrated on the motherboard and therefore could not be upgraded. It is the CGA standard compatible, features for better positioning on the home user market but also has two more graphics modes, which provided 16 colors at 320x200 pixels as well as four colors at a resolution of 640x200 pixels, but at the cost of memory available for programs memory. The PCjr was supplied with the monitor. Another concession to the home user market was the integrated sound system, which was based on a TI 76496 chip from Texas Instruments, three votes could play simultaneously and represented a vast improvement over the speaker system of the IBM PC and PC XT.
The PCjr came in two variants: the model 4, which represents the original PCjr, and the Model 67, an extended version with uA an additional disk drive.