Tanner has New In Box IBM PC Juniors

Hackerspace
#1

As the title states, whole New In Box IBM machines for a mere $60. Comes with a joystick, keyboard, parallel expansion, and some extra ram. I think they even have new copies of OS/2.1 to pair it with.

4 Likes
#2

No seriously, who do I talk to and where am I sending my paypal?

1 Like
#3

Awe that was my first computer. I remember playing king’s quest and having to switch cartridges for dos and not dos.

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#4

That would have to be PC-DOS 2.1; OS/2 requires a 286 processor or better.

The PC/Jr has a couple of engineering tradeoffs which make it a less than desirable PC. The main one is the lack of DMA for the floppy disk, so that during a disk access, the keyboard beeps and ignores characters.

#5

I got a response from someone else in the Retro Community

Question: Is it true that if the floppy drive is running, everything freezes like the keyboard?

JB Langston: not entirely. The keyboard has the highest interrupt priority (NMI) so it will never get preempted. It is true that at higher speeds, the serial port would drop data if the floppy was accessed or you type on the keyboard. This is because ibm skimped on a dma controller so everything has to be handled by the cpu.

#6

I have to disagree.

It has been a long time since I used mine, but the machine beeped and refused keystrokes while the disk was active.

#7

Since it is beeping, it sounds like it might have something to do with the OS or the program running.

#8

This says I am right:

:stuck_out_tongue:

1 Like
#9

I did a bit more research and found this …

The keyboard still functions and still generates the NMI, but it does not reach the CPU while NMIs are masked by port A0. The keyboard latched bit at port 62h can tell the system that there was a missed key while NMIs were ignored and the error beep will sound.

#10

I have some memory expansion sidecars and will pick up some more Saturday morning.

They will take the Jr. to 640K.

1 Like
#11

Apparently, someone made an expansion that added DMA …

Racore_ocr.pdf (1.3 MB)

#12

I have a PCjr with that second drive installed. Still need to hook it up and see what all is installed on it. :slight_smile:

1 Like
#13

Any chance any of the pcjr’s are still available?
I’m looking for any peripherals anyone has available as well.

#14

Unfortunately Tanner’s closed earlier this year.

#15

@vonHelmst Try the FB group for Computer Reset and retro machines