I never had a PCjr; my first IBM compatible PC was a Wyse 8MHz 286 (1MB RAM total, 1.2MB and 360KB 5.25" floppies, whopping 40MB MFM HDD) from around 1986 that had an EGA graphics adapter in it, which of course was a whole generation newer than the original 8088/8086 IBM PC/PCjr technology. I could only view text, CGA and EGA modes as high as 640x???x16c (*). I recall trying to make it run in Tandy modes and either got garbage or an error message. Eventually the monitor blew out around 1989 due to my brother and I carelessly leaving our Epson MX-80 printer sitting on top of it. For the next year or so we were stuck with an amber Hercules monochrome setup, although we could play CGA games using a TSR that emulated CGA on Hercules via dithered patterns. Around 1990 we upgraded to a 256KB Paradise SVGA card and I was finally able to play all those 320x200x256c games I had been missing out on (and a few SVGA games like Steve Moraff's games). I also got an ISA joystick card and cheap 2-button flightstick. I believe the video card and joystick bundle were each in the $100 range. Sound cards were still too primitive and expensive - I remember seeing Creative Game Blaster and Adlib cards locked away in glass cases the way $300 video cards are these days, and being that I was just under 12 years old in 1990, they may as well have been on the moon.

Questions:
- When and why was the PCjr released, especially in relation to the original IBM PC and the Tandy PC-compatible series?
- Do you remember which model of Intel CPU was in the original IBM PC and the PCjr (and the Tandy's for that matter)? I get the 8088 and 8086 confused as I don't know the difference between them.
- Also, how does the PCjr compare with the original IBM PC and their Tandy contemporaries?
- Did they actually have IDE and SCSI drive interfaces back then (for the PC anyways)? As I mentioned, my 286 used an MFM drive (I think - it certianly had a different connector on it), so I thought that IDE came a bit later.

Also, a nitpick: You contradicted yourself in regards to math coprocessors.

* Don't remember if the vertical max for EGA was 200, 400 or 480. Also, I'm not sure if I was able to put it in a Hercules monochrome-compatable mode, although I do remember the monitor had a switch on it that could set it to amber or green only modes (the purpose of said switch escapes me to this day).

The difference between a 8088 and 8086 was like that between a 386SX and 386DX. They both supported the exact same instruction set, but the 8088 had an 8bit databus, whereas the 8086 had a 16bit databus (for the 386s that was 16- and 32bit respectively). Both the IBM PC, XT and PCjr had a 4.77MHz 8088 (8086 models were available, but not for the PCjr)

SCSI was developed in 1981, officially standardised by ANSI in 1986. So it was available when the PCjr came out. IDE was invented by Compaq around 1986 and standardised in 1990, so it's doubtful that could be found in the 1983 PCjr (which didn't actually become available until 1984). PCjr wasn't intended to have a hard disk anyway, but third party addons were available.

EGA was max 640x350.

The PCJr. was announced in 1983 and available in 1984 and discontinued in 1985. Tandy cloned the PCjr. instead of the PC because it had more powerful graphics and sound capabilities. But by the time the Tandy 1000 came out, the PCjr. had just been discontinued. Hard drives had to be added by sidecars and few came out during the PCjr.'s life and would have supported MFM and RLL drives only. IDE and SCSI were late 80s innovations for the PCjr.

If we want to compare a contemporary (1984-85) IBM PC Model 5150 and the IBM PCjr., here is what we would get:

Keyboard:
PC: 83 Key Corded Keyboard
PCjr.: 62 Key Wireless Chicklet Keyboard

Floppy Drives:
PC: 1-2x360KB 5.25" Full Height Floppy
PCjr: 1x360KB 5.25" Half Height Floppy

Hard Drives:
PC: 10MB XT Hard Drive Upgrade (ISA controller)
PCJr: None Available

Serial Port:
PC: Asychronous Communications Adapter
PCJr: 1xSerial Port (proprietary)

Video:
PC: CGA, MDA, EGA or Hercules
PCJr: Enhanced CGA

Monitors:
PC: 5151 and/or 5153 or 5154
PCJr.: 4863 or 5153 + adapter

Parallel Port:
PC: MDA or Printer Adapter
PCJr.: Printer Port Sidecar

Modem:
PC: Third Party
PCJr.: 300 baud internal Modem (not Hayes compatible)

RAM:
PC: 256KB on MB, + ISA Memory Expansions
PCJr.: 64 or 128KB on MB, + 128KB sidecars - 16 or 32KB for Video

Audio:
PC: PC Speaker
PCJr.: PC Speaker + PCJr. Sound Chip + Speech Sidecar

Joysticks:
PC: Game Control Adapter
PCJr: 2xjoystick connector (proprietary)

Power Supply:
PC: 65 Watts
PCJr: 33 or 45 Watts

Miscellaneous:
PC: math co-processor socket, DMA controller
PCJr.: 2xcartridge ports, lightpen support

But the true question remains, how compatible is Enhanced CGA with CGA and Tandy Graphics (with mod)? I cannot say that no commercial game that works on an IBM PC with a CGA will refuse to work properly on a PCJr. (I'm pretty sure that the color composite modes would work as well.) As for Tandy Graphics, even with the mod it may be somewhat hit and miss.

I had a Tandy 1000TX. Lot like a PCjr. Rocked for the game on the left too! Beautiful 16-color and great sound.

I actually had one when I was a kid (seem like I'm one of the few). In fact, I currently have two, one in semi-working order (the keyboard is malfunctioning when both wired or wireless...so I suspect the keys have gone bad). Aside from the funky compatibility issues with the PC and the lack of support, I loved my PCjr and created quite a few images, songs, and even PCjr BASIC games supporting PCjr-specific features. In fact, I'm still trying to bring them over to my PC...and have been playing around with DOSbox in the hopes I'll finally be able to view / hear them again.

The first two King's Quests were my favorite games for a long time...and I was depressed when Sierra started upping the memory requirements above the 128KB I had in my PCjr. Playing games on my dad's PC in CGA composite mode with monotone audio just wasn't the same.