The IBM PCjx

[Joshua]

I'd like to talk a bit about the IBM PCjx. From what I understand, this odd beast was sold in Japan and Australia. The Australian version ran in 100% (American) English.

My first computer growing up was a jx. Here's what I remember from it:

- We got the computer in 1985.
- We upgraded it to 512kB. My neighbour's jx had 448kB. As a young child, I informed them their computer was "broken" because it didn't count all the way up.
- The machine had a joystick (custom made for the jx - dark grey colour scheme with light grey buttons, unlike the regular PC or the Jr's.)
- Initially, we had just used two 3.5" drives and ran DOS 2.11. This supported the 3.5" drive but only with 360kB drives. The BIOS made them look like 5.25" drives. According to my dad, they skipped every other track. I'm not sure if this is actually the case, or if they actually just didn't use the last 80 tracks. The old 360kB diskettes don't work with a modern 3.5" 1.44MB drive.
- Sometime (I believe late 1986), we bought an upgrade which allowed the full use of 720kB drives. It was a BIOS chip and a copy of DOS 3.21.
- In 1987, we bought a 10MB hard disk. It made a distinctive "chirping" sound, so my family called it The Bird. The attachment looked like another jx stacked on top of the main system. It didn't quite look like a sidecar.
- We used an IBM branded RGB monitor it. Like the joystick, it had the same colours as the jx.

According to my dad, the main appeal of the jx was that there wasn't a 3270 emulator card for it, so businesses wouldn't buy it and then cut into revenue from the more expensive 5150 series PCs.

When my family moved away from Australia, we sold the jx to friends, which has since been resold.

I'll ask my dad for any more info on the system next time I speak with him.

I still have a few items from it:

- Most notably, I still have the original pre-720kB BIOS chip. I'd like to find a way to get this in to a ROM socket and read the contents off.
- IBM PCjx DOS 2.11 Technical Reference, which includes interesting references to running in double-byte character sets.
- IBM PCjx DOS 2.11 User's Guide
- IBM PCjx DOS 3.21 Technical Reference
- IBM PCjx DOS 3.21 User's Guide
- IBM PCjx BASIC Reference

Diskettes:
- IBM PCjx DOS 2.11 (oddball 360kB 3.5" format)
- IBM Personal Editor II (in oddball 360kB 3.5" format)
- IBM PCjx DOS 3.21 (720kB)

Back when my family owned this computer, diskettes were worth about $12. That means, unfortunately, we have some diskettes overwritten with other data. A notable example would be IBM Typing Tutor for the PCjx and the PCjx starter diskette, which had a couple example programs.

The DOS 3.21 is fairly standard. It will boot on a modern computer or a PS/2.

These manuals have numerous references to the IBM PCjx Technical Reference, which I unfortunately never had.

[Joshua]

I don't remember a lot from the hardware, but here's what I do remember:

- It had two cartridge ports, but we never owned any cartridges.
- The graphics options and audio options were the same as the PC jr.
- The documentation is littered with references to 48k and 64k options. While our jx had 512k, I am reasonably certain the 320x200x16 and 640x200x4 graphics modes were not accessible to 64k customers.
- We used an IBM ProPrinter with the machine. It was branded in the dark grey, unlike the "normal" ProPrinter which was a lighter IBM beige grey. This connected using a normal parallel port, as we later used this printer on a PS/2.
- The machine had some sort of modem option, but my dad stopped using it because it was too slow. I'm guessing this means it was 300 baud. (He chose to lug home a giant IBM PC from work with a 1200 baud modem to work from home some nights.) I am going on my recollection as a six year old, so I may be completely wrong on this point.
- The keyboard was an odd beast. We didn't have a numeric keypad, which made inputting ASCII codes quite difficult.
- You can approximately see a picture of it here (plus keypad): en.wikipedia.org/wiki/File:IBM_JX.jpg
- Notice the arrangement of the Fn keys. This was a harbinger of things to come with the IBM PS/2 Model F keyboard, and did not require the Fn key for nearly as many combinations (such as PF keys). However, it did still have an Fn key, which was required for certain operations.

Next time I'm visiting my parents, I'll find some pictures of the machine in action. We do have pictures both with and without the later additions such as the hard disk.

Of particular note of the jx is that the PS/2 adopted both the 3.5" diskette drives and the jx's keyboard layout, which have dominated the PC industry for 24 years since.

[Joshua]

Software on the jx was not overwhelmingly unusual. Programs compatible with the TANDY 1000 or the PC jr generally were able to use the extra graphics and audio features.

We played Microsoft Flight Simulator 2.13 (I believe). Getting a 3.5" copy of the software was difficult. My dad took it to work and ran it on a PC that had both a 5.25" and a 3.5" drive, and then ran the normal Flight Simulator make copy program (which can only be run once). The resultant disk was formatted like a 3.5" 360kB disk.

The game generally ran fine, and was able to use the TANDY 1000 video modes in addition to having an option to use a PC jr style keyboard layout, which worked fine on the jx. It would seem to follow that the copy protection on Flight Simulator did not use floppy DMA.

The jx needed newer versions of DOS, but mostly to support the 3.5" disks. PC-DOS 2.10 came out to support the jr, but didn't know about 3.5" disks. 2.11 supported 3.5". Likewise, PC-DOS 3.20 supported 3.5" 720kB drives, but will not boot on a jx. 3.21 works fine on an 8086 PS/2 Model 25, so it would seem to follow that newer versions of PC-DOS probably worked on the jx.

[Joshua]

As a final note on the keyboard, the jx did have the infrared option. We quickly tired of replacing the rather expensive AAA batteries and dealing with the questionable reception and range, and simply ran in corded operation.

All in all, the jx was a capable machine. It felt faster than comparable jr's I have used. I suspect it had a mechanism to dual port the video memory. Some minor design differences made the machine much more usable than the jr, such as the improved keyboard layout. The 3.5" drives were a significant improvement, both in terms of speed and reliability. They were an inconvenience, however, when it came to exchanging data in a 5.25" world at the time.

The jx did have a cassette port. We never had it in action. I vaguely recall seeing an IBM branded (and jx[/u]-coloured) cassette deck.

Further analysis will have to wait until I get a chance to dump the 360kB 3.5" ROM BIOS. I welcome your comments and any input about this odd machine, which I haven't seen since my 7th birthday.

[MattCarp]

It's definitely an interesting machine. It appears to have had the benefit of being developed a year after the jr (is that right?) so they were able to make incremental improvements that ultimately led to a "better" machine.

Was the actual PCjr available in Aus/NZ/Japan?

[Joshua]

I certainly never ran into a PC jr in Australia. I can't find any evidence of them having been marketed there.

We bought our PCjx in 1985, and I believe we bought it right when it was available for pre-order by IBM employees. (Ours certainly came with a half-finished BIOS.) One interesting angle of the order was that 512kB was an option.

Anyone interested in the ROM dump?

[alanh]

A few people asked about the JX I previously mentioned. The front panel was destroyed in shipping when I bought the machine - as well as some other dents and dings. I took some photos here:

https://www.retrotronics.org/2020/05/ib ... e-version/

I was thinking of selling it. But I'm going to hang on to it instead. I should be able to swap out the Japanese ROMs for the Australian versions, right?

[Trixter]

Holy Schnikes, that's one amazing system. It's as weird to the PCjr as the PCjr was to the PC. Nonstandard ports, this time labeled in Japanese... non-standard card connectors...