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Old 24-09-2018, 04:31 PM   #1
Super Freak

Join Date: Apr 2008
Location: Lerida, Spain
Posts: 153
Default IBM PCjr and Tandy 1000, the almost PC compatibles.

I already mentioned these two computers in a previous guide, but since many DOS games offer some kind of support for them, I think a more in-depth explanation could be of interest to the readers.

The IBM PCjr.

When IBM launched the first PC models around 1981, they had little in common with the PC clones we use these days. They employed MDA and CGA display cards, 8088 CPUs running at 4.77 Mhz and could have as little as 16 Kb. of RAM. Their prize was around $1.565 and they found success in office use, especially after the release of spreadsheet software.

By the end of 1983, IBM announced the PCjr. The PCjr was designed with the intention of becoming a home variant of the IBM PC, competing with other computers such as the Commodore 64, the Atari 8 bit family or the Apple II.

The PCjr would use the same CPU 8088 @ 4.77 Mhz of the IBM PC, but changes were made to the display and sound systems. The CGA display now supported several 16 color modes, and the PC speaker had three sound channels rather than one. The first "King's Quest" game by Sierra Online was ordered by IBM as an example of a game taking advantage of these extra features.

However, when the PCjr was finally released in 1984 it was poorly received. There are several reasons for that:

- It was competing with 8 bit computers, which were much cheaper than the PCjr, which sold at $669, and already had an stablished market.

- IBM had promised a fully PC compatible machine. However, with only 128 Kb. of RAM and limited expansion possibilities, many IBM PC programs wouldn't run in the PCjr.

- Accesories such as the wireless keyboard were widely criticised. Originally, the PCjr was shipped with a rubber keyboard that made typing at a reasonable speed almost impossible.

In 1985, IBM stopped manufacturing the PCjr after 250.000 units had been sold. IBM would not try to sell a home-oriented PC until the PS/1 in 1990.

IBM PCjr legacy and emulation.

Or the reason you may be interested in this system.

- Cartridge games: A handful of games were released in this format for the PCjr. Many of them were also released for DOS or in PC Booter format, but won't run in regular PCs.

- PC Booter games: These type of games were designed to run by booting the computer with their disks. This allowed for games to use different OSes than DOS or to implement their own copy protection schemes.

Some games from this era had either different CGA, PCjr and Tandy releases or are PCjr / Tandy exclusive, such as "Ghostbusters" or "Pitfall II". You may need an specific version to obtain PCjr benefits.

- Regular DOS games with PCjr support: This is the most common situation. A DOS game released during or after the PCjr era that has some kind of PCjr support. Normally this will mean plain CGA graphics, but some games such as "Pit Stop II" or "Super Boulder Dash" will show better graphics if they detect a PCjr machine.

"Super Boulder Dash" and "Montezuma's Revenge" in CGA and PCjr modes.

DOSBox can run PCjr software by setting machine=pcjr. It can also run PCjr cart dumps (files with a JRC extension) with the command BOOT name of file.JRC.

PCem offers one profile to run a PCjr machine, but doesn't support (yet) booting from a cartridge image.

Last edited by Neville; 24-09-2018 at 06:22 PM.
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