The IBM PCjr (read "PC junior") was IBM's first attempt to enter the market for relatively inexpensive educational and home-use personal computers. The PCjr, IBM model number 4860, retained the IBM PC's 8088 CPU and BIOS interface for compatibility, but differences in the PCjr's architecture, as well as other design and implementation decisions, eventually led the PCjr to be a commercial failure in the marketplace.
Additionally, its 4.77 MHz Intel 8088 CPU was faster than other computers aimed at the home market (though the PCjr actually ran slower than the stated 4.77 MHz, because every 4th clock cycle of the 8088 CPU was designated to refresh the PCjr's RAM as it had no dedicated memory controller), and its detached wireless infrared keyboard promised a degree of convenience none of its competitors had. Two cartridge slots promised easy loading of games and other software.
Two joystick ports were built into the PCjr, evidence of IBM's goal for marketing the PCjr as a home-friendly machine. Other than the Tandy 1000 and Amstrad IBM PC compatible lines a few years later, the dual built-in joystick ports introduced by the PCjr never became standard on IBM PC compatibles, and haven't been seen since. Also, in addition to the joystick ports having a different connector than used on the "game adapter" ISA card for PC compatibles, they required joysticks that had a different electrical resistance range in their X/Y access controllers, necessitating the use of PCjr-specific joysticks (or generic joystics that had a dual-mode switch).
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. The cartridge(s) would be plugged in from the front, prompting the computer to automatically reboot and run the software. Loading and saving data from cartridge software was possible via the floppy drive. The cartridge BASIC for the PCjr, in particular, gave programmers the advantage of a real programming language always ready without taking up system memory, as it was firmware, with its own address space. Being stored in ROM, the BASIC would load very quickly, not needing access to the floppy disk or other storage.
The two front cartridge slots were also used with third-party cartridges to update the system BIOS and other firmware. A number of patches from various vendors were 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.
Expansions (such as additional parallel ports, serial ports, memory, etc.) to the PCjr were provided via add-on "sidecars" that attached to the side of the PCjr. Multiple expansions were stacked together, increasing the width of the machine.
The PCjr shipped with a chiclet type keyboard powered by AA batteries to provide infrared line-of-sight wireless communication. The keyboard could also operate with a modular telephone-style cable if so desired, eliminating battery usage. The PCjr also shipped with a lightpen port, which worked with a small number of applications designed for it. The lightpen port was later used in combination with the serial port to supply voltage to a Mouse Systems optic mouse of the same design as Sun workstations.
The PCjr launched with an enormous amount of advance publicity, including live news-broadcast coverage of the product announcement. Ziff-Davis, publisher of the successful PC Magazine, printed the first issue of PCjr Magazine even before the first PCjr units shipped. Observers expected the PCjr to change the home-computer market in a similar way to how the IBM PC had singlehandedly changed the business market in the two years since its debut. PCjr advertising featured a Charlie Chaplin character from The Tramp connecting it to the successful campaign for the business model.
However, the PCjr was never well received. A prime target of criticism was its keyboard; IBM chose to use an infrared wireless chiclet keyboard, similar to that of a pocket calculator, with wide spaces between keys to leave room for instructional overlays bundled with software packages. It was widely criticized as feeling cheap and being difficult to type on. IBM eventually replaced it for free with a different wireless keyboard with more conventional keys. Regardless of the keys' design, with only 62 keys, it lacked the numeric keypad and separate function keys of the IBM PC, and the layout was more awkward than that of most of its competitors.
At $669, the PCjr's price was not competitive. It cost more than twice as much as the Commodore 64 and the Atari 8-bit family; its price was close to that of the Coleco Adam, but the Adam also included two tape drives, a printer, and software. With the exception of the Apple II, it was possible to purchase a complete system (computer, disk drive, printer, and monitor) from almost any of IBM's competitors for less than the PCjr's entry price.
Many people compared the PCjr unfavorably to the IBM PC rather than to the machines against which it was directly competing. While compatibility with the IBM PC's large software library was a key selling point, in practice the PCjr proved incompatible with many popular PC applications, in part due to memory limitations and in part due to architectural differences.
The PCjr was often purchased by business people as a lower-cost alternative to the PC, but then was quickly abandoned for business use. The BIOS was produced by the same company that wrote the BIOS for the PC, IBM, with published differences. At the time, it was popular for many programmers to use direct hardware BIOS "pokes" and "peeks" and process with assembly language as this offered performance advantages and compilers for PCs were limited. Programmers had to keep the PCjr in mind when developing code, which most didn't. So, while most PC software would work, including the "acid test" for PC-compatibles at the time, Microsoft Flight Simulator, business packages competing for features and performance would often have odd hardware related crashes.
The keyboard issue alone was enough to sink the PCjr, but not having the same expansion slot type was really the death of the PCjr. When an expansion came out to add a hard drive, it would only work on the PC. The PC with a built-in hard drive came out next, known as the XT. No further development was done with the PCjr. The PCjr was not a PC clone as the first Compaq would be. It was a separate computer, technically linked by being from the same vendor, that, like an unusual mutation of early species, would just die out.
Arguably, the PCjr's technical capabilities may have justified its higher price tag: it was a 16-bit machine competing in an 8-bit world. It offered better memory expansion, had a built-in 80 column display, and was faster than any of its competition. However, reviewers of home computers at the time cared much less about raw power and more about price, available software, and the quality of the keyboard. Moreover, while the PCjr may have been superior to its competitors in running office suite software, it was clearly inferior to the Commodore 64 and the Atari 8-bit family as a gaming platform; unlike them, it had very limited color capabilities (due to its CGA-derived graphics chip) and no support for hardware sprites. Also, the sound chip was nowhere near as advanced as the MOS Technology SID found in the C64 (although it rivaled Atari's POKEY). Since gaming capabilities were important to many home computer buyers of the time (who often purchased the machines as replacements for older game consoles), this was another strike against the PCjr.
The PCjr was more difficult to expand than many of its intended competitors. It was not designed to add a second floppy drive, a hard drive, or easily expand memory beyond 256K, which made it difficult to deliver on the promise of running business software for the IBM PC. Third parties created PCjr add-ons, including a second floppy drive or a 20-megabyte hard drive, but were not available right away. One particular company, PC Enterprises, produced several useful expansion kits, including a CPU speedup board, SCSI controller for hard drives, VGA video card, 3.5" floppy drive, SoundBlaster sound card, and also many software products that shipped on floppy and on plug-in cartridge that enhanced the PCjr's compatibility with the IBM PC. Many of these products ended up being fairly costly due to the limited PCjr expansion market; for example, the Combo Cartridge, a cartridge which simply improved BIOS compatibility and sped up certain BIOS calls, was $89 when it was last sold. PC Enterprises no longer provides PCjr products so these items are increasingly harder to find today. PC Enterprises' online catalog of PCjr products is still available for viewing.
Many IBM and third-party add-ons attached to an expansion slot on the computer's right side (dubbed "Sidecars"), similar to the design of the discontinued TI 99/4A; thus, as with the TI, multiple add-ons proved very clumsy. In addition, it was necessary to purchase additional power supplies for every few expansion modules attached to the computer; it was not unheard of for the computer to require three separate power bricks just to run with its expansions.
The PCjr also lacked a DMA controller. Thus, the 8088 CPU had to service standard system interrupts such as the serial port or the keyboard directly. Hence, the PCjr couldn't be used with modems faster than 2400 baud, and it would refuse to process keyboard input if its buffer was full.
King's Quest, a popular adventure game series, was originally developed for the PCjr, as IBM had commissioned Sierra On-Line for a game that would take advantage of the PCjr's expanded graphics and sound capabilities for the product's launch.
IBM returned to the home market in 1990 with its much more successful IBM PS/1 line. Unlike the PCjr's radical departure from the IBM PC, the PS/1 line concentrated on IBM brand-name compatibility and affordability.
"PCjr magazine" ran articles written by many of the legends of the computer industry from back in their early days. This comprises a collection of entry level PC articles, from such people as Peter Norton, that could be considered mentionable.
Several upgrades for the PCjr were designed by IBM/Teledyne but never reached the store shelves before the IBM PCjr was canceled. These included a wireless joystick and various memory/drive upgrades.
PC Enterprises became the last of the major third party vendors to supply full service, parts, and add-ons, extending the functional life of the PCjr to about 10 years, often buying out inventory and rights for PCjr support.