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IBM JX.jpg
IBM JX Personal Computer (IBM 5511)
Developer IBM
Release date October 1984 (1984-10)
Operating system PC DOS 2.1, Microsoft Disk BASIC, Advanced BASIC
CPU Intel 8088 @ 4.77 MHz

The IBM JX (or JXPC) was a personal computer released in 1984 into the Japanese, Australian and New Zealand markets. Designed in Japan, it was based on the technology of the IBM PCjr and was designated the IBM 5511. It was targeted in the Australian market towards the public education sector rather than at consumers, and was sold in three levels - JX (64Kb), JX2 (128Kb) and JX3 (256kb). Upgrades were available to both 384kb and 512kb.


The IBM JX's main difference from the PCjr was a professional keyboard (rather than IBM PCjr's disparaged chiclet), dual 3.5" floppy drives, a 5.25" floppy drive option (as a bolt-on unit that sat above the main box) and a hard drive option (ditto). The JX did not have the support for the sidecar add-on's that the PCjr was designed to support for hardware expansion. In common with the PCjr it had no DMA controller. It also supported the otherwise unique in the IBM PC world ECGA (Enhanced CGA - 16 simultaneous colors, but only at 320x200 resolution) and the 4-channel sound functions. Support for these two features was utilised by only a handful of software developers - Sierra On-line being the most well-known.


It had several innovative features:

In Japan, both white and black units were available, but elsewhere all IBM JXs were black—very unusual in the days of the standard color of IBM "beige boxes".

However, one disadvantage it shared with the IBM PCjr was that it could not use the standard ISA bus cards of the PC XT.

The system operated PC DOS 2.11 as well as, Microsoft Disk BASIC and Microsoft Advanced BASIC. Like the IBM PC, if the system was left to boot without inserting a diskette into one of the drives the Microsoft Cassette BASIC interpreter would be loaded, which was compatible with IBM PCjr BASIC, including Cartridge BASIC. PC DOS 2.11 could only use half of the tracks of a 3.5" drive, however, since it didn't really understand what a 3.5" drive even was. The PCjx's BIOS could only address the first 40 tracks like a 5.25" drive.

The PCjx later had a BIOS upgrade chip, sold together with PC DOS 3.21, which could use the full 720 KB capacity of the diskette drives. Some popular options for the PCjx were a 5.25" 360 KB capacity diskette drive, a 10 MB external hard disk (both as a stackable unit the same size as the JX itself) and a joystick. IBM never released a 3270 emulation adapter for the PCjx in order to steer enterprise customers to more expensive IBM PCs and XTs.

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