Patching IBM DOS 5 for the PCjr

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Re: Patching IBM DOS 5 for the PCjr

Postby Brutman » Fri Nov 02, 2012 3:51 pm

Trixter wrote:I see we're changing the value at 40:13 which is "size of memory in kbytes", but why are we setting it from the contents of 40:15? How is 40:15 getting the correct value in the first place?

Also, is this to force 640k, 768k, both, or neither?

(I ask these questions because I will likely write a patcher that will work with any DOS 4.x and higher)


Look in the memory map. 40:13 is the amount of memory on the motherboard, excluding the video buffer. 40:15 includes expansion memory too, but still not the video buffer. So the value in 40:15 is a better indication of how much memory is installed, but never completely accurate because the BIOS only scans up to 640K. (If you have 736K it will not be reflected in that value.)

I had the patch utility on a todo list, but if you get to it first that isn't going to bother me ...
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Re: Patching IBM DOS 5 for the PCjr

Postby Brutman » Fri Nov 02, 2012 3:55 pm

Tempest wrote: ... I'm starting to wonder if my problem is that the high density floppy drive I'm using isn't writing to the boot sector properly. Using a HD floppy to write 360K disks is kind of iffy to begin with, even if you tell the drive to format disk as 360K. Then again, maybe this is just a wild goose chase and something else is amiss?


Argh! Don't do that. Use real DD diskettes, not HD diskettes.

One problem is that the HD drives have a head that is half as wide as a DD drive. That's going to be a potential problem whether you have DD or HD media, but depending on your drives your 360K drive might be ok with it.

The other problem is that HD media and DD media require different amounts of "force" to write, and if you use the wrong media or the wrong drive it's flaky at best. The early boot process does not tolerate media errors, so it just stops.
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Re: Patching IBM DOS 5 for the PCjr

Postby jmetal88 » Fri Nov 02, 2012 5:14 pm

Yeah, if you don't have a DSDD drive available for your 360k disks, it's actually better to swap the PCjr's floppy drive between your PCjr and PC than to try to write the disks with a high density drive.
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Re: Patching IBM DOS 5 for the PCjr

Postby Tempest » Fri Nov 02, 2012 6:26 pm

Nope, just the one in my PCjr. I've been scanning ebay for one cheap. I am using DD media however which is probably why it works some times.
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Re: Patching IBM DOS 5 for the PCjr

Postby Tempest » Sat Nov 03, 2012 7:39 am

Is there a debug.com available for DOS 3.3? I can do the work on my jr, but I need a version of Debug that works with dos 3.3
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Re: Patching IBM DOS 5 for the PCjr

Postby Brutman » Sat Nov 03, 2012 8:48 am

If you have DOS 3.3 it should be on two 320KB diskettes. DEBUG.COM and a lot of other utilities are on the second diskette.

If you are missing something, then do you have the ability to receive electronic images of diskettes? (ie: Receive via email or FTP, write the image to a DD 360KB diskette, and then boot in the Jr?) If so, it's easy to get what you need.


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Re: Patching IBM DOS 5 for the PCjr

Postby Tempest » Sat Nov 03, 2012 9:22 am

Brutman wrote:If you have DOS 3.3 it should be on two 320KB diskettes. DEBUG.COM and a lot of other utilities are on the second diskette.

If you are missing something, then do you have the ability to receive electronic images of diskettes? (ie: Receive via email or FTP, write the image to a DD 360KB diskette, and then boot in the Jr?) If so, it's easy to get what you need.


Mike

I never had the DOS 3.3 disks, I just had a boot disk. If you have the disk images then that would be great, I can transfer files to my jr from my PC using 3.5" disks.
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Re: Patching IBM DOS 5 for the PCjr

Postby Tempest » Sat Nov 03, 2012 9:32 am

I think I just found some. Stay tuned!
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Re: Patching IBM DOS 5 for the PCjr

Postby Tempest » Sat Nov 03, 2012 9:46 am

No dice. I patched it all on a PCjr and it still hangs after loading my jrConfig. The drive is spinning, but no one is home.
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Re: Patching IBM DOS 5 for the PCjr

Postby Brutman » Sat Nov 03, 2012 11:27 am

Ok - send me email at mbbrutman at yahoo dot com and I'll send you bootable images for DOS 5.


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