Mike's PCjr Page

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/ibm-5511-pcjx-japanese-version/ I was thinking of selling it. But I'm goi...

I only consider it a fiasco because if you envision a scale where at one end - the family that owned the warehouse was forced to liquidate for $0 or even negative expense, and at the other end they got top dollar for every individual item in the place - they family received 10%? maybe 20% of the ful...

That's because jrconfig.sys is using the BIOS to do it, specifically Int 10/AH=05h. More info: http://www.ctyme.com/intr/rb-0095.htm As Jim points out... It's done in jrconfig.sys in the function _reset_video_page. The location of the active video page is set in the global variable _video_page. The...

Also we should just jump on Jay's Discord server one night and hack out a plan.... I'm on a planet that is currently in world-wide lock down. So I'm available anytime!

If moving 0x415 to 0x413 fixes the double boot, great. But are you still using jrconfig? Is it detecting that 0x413 has been adjusted and not making the second boot as a result? jrconfig.sys is still a must. Sorry, I mis-stated. I move 736 into both BDA fields and jrconfig.sys skips the double boot...

Going to go back and read the latest replies when I have more caffeine. Let me re-iterate... the only thing I'm trying to solve is the double boot issue. The only thing necessary to prevent jrconfig.sys from double booting is the fix-up patch code you have been manually adding to (eg) DOS 5.0's MBR ...

Assume you have a PCjr that can run DOS 5 unmodified. Now it's not compatible with any other PCjr in the house, and you still need two sets of boot floppies. The second boot required by jrconfig also doesn't take a lot of time or break anything so I don't understand the need to fix it. I completely...

It's the BIOS responsibility to tell DOS where the top of usable RAM ends via the BDA. The Jr system BIOS doesn't scan past 640KB. An option ROM on an adapter providing extra memory above 640K and fully aware of the system BIOS scan limitations should verify it's upper memory works correctly and (IM...

It really should just be done in the option BIOS. My $.02

I'm still slammed with the project that sucked up all my time last fall. I guess I'm happy to have a guarantee'd job for the next 2-3 months at least; and one that is entirely WFH. But I haven't wanted to work on anything vintage in a while. I actually just ordered a guitar and going to try and pick...