offensive_Jerk
Veteran Member
Just wondering if it is possible to replace the useless Cbasic in rom on 5150s to even disk basic or DOS or cp/m.
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Is it possible to replace cassette basic with dos or cpm?
- Thread starter offensive_Jerk
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krebizfan
Veteran Member
It is possible to replace CBASIC with other ROMs. That has been done before. But remember the CBASIC ROMs are only 32KB so the system that can be installed has to be small. Disk BASIC 86 would need the contents of CBASIC or equivalent code plus the disk code so it would not fit in the space available.
CBASIC isn't useless. BASICA requires it. By having the CBASIC in ROM, IBM BASIC loaded from disk needs 32KB less RAM so a 64K 5150 is actually somewhat useful.
I have long thought that the PS/2 lineup should have removed cassette BASIC and used the space for a larger system ROM.
CBASIC isn't useless. BASICA requires it. By having the CBASIC in ROM, IBM BASIC loaded from disk needs 32KB less RAM so a 64K 5150 is actually somewhat useful.
I have long thought that the PS/2 lineup should have removed cassette BASIC and used the space for a larger system ROM.
offensive_Jerk
Veteran Member
Ah that's right, I forgot that basica uses it.
What other ROMs have people swapped for Cbasic do you know of?
What other ROMs have people swapped for Cbasic do you know of?
krebizfan
Veteran Member
The one ROM expansion I remembered didn't replace the CBASIC but instead uses the spare ROM socket. http://boginjr.com/it/sw/dev/bootlpt-86/
I thought I read about a Forth ROM that was installed in place of CBASIC as a proof of concept. I can't remember where it was though.
Some of the Soviet PC compatibles replaced CBASIC with a cassette driven monitor program which could be used to load software from cassette including cassette BASIC. I do not know of anyone converting that into a ROM that could be installed in a 5150.
I thought I read about a Forth ROM that was installed in place of CBASIC as a proof of concept. I can't remember where it was though.
Some of the Soviet PC compatibles replaced CBASIC with a cassette driven monitor program which could be used to load software from cassette including cassette BASIC. I do not know of anyone converting that into a ROM that could be installed in a 5150.
I did some experimentation with this recently; added a 2K option ROM (the smallest BIOSes will actually handle sanely) that just mapped requests for tracks on Drive A to bits of the ROM address space. The problem is getting enough disc image space-- your limiter there is almost certainly the sockets an 5150 board offers. I use a machine with a custom memory card that uses a 39SF010 (128k flash) for E000 and F000, so I had 90k left once the "real" BIOS stuff was added. This holds a DOS 2.11 image with DEBUG, EDLIN, FORMAT, and SYS, so you could theoretically black-start a machine with no formatted media. Alternative payloads would be boot-to-game, boot-to-specific-application, etc.
I could see using a larger ROM still, say a 39SF020 (256k) but enabled at C800-F7FF to give 192k of usable ROM, that's definitely enough to hold an unretouched 180k single-sided disc image.
I could see using a larger ROM still, say a 39SF020 (256k) but enabled at C800-F7FF to give 192k of usable ROM, that's definitely enough to hold an unretouched 180k single-sided disc image.