Timeline for How did an IBM 5150 with 16KB RAM work?
Current License: CC BY-SA 4.0
17 events
| when toggle format | what | by | license | comment | |
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| Mar 15, 2020 at 1:12 | comment | added | supercat | @Raffzahn: Even if the first boot stage is located in low memory, that won't interfere with the real system starting low in memory. | |
| Mar 15, 2020 at 0:32 | comment | added | Raffzahn | @supercat And your point is? | |
| Mar 14, 2020 at 23:37 | comment | added | supercat | @Raffzahn: Many systems use a multi-phase boot; the original boot sector doesn't have enough intelligence to fully boot the system, but has enough code to read in another few sectors of boot code. The first boot sector would then no longer be needed after that point. | |
| Dec 13, 2018 at 23:29 | comment | added | roolebo | @Raffzahn your theory looks very reasonable, thank you. The page cites that Dr. David Bradley wasn’t considering 16K systems at all: glamenv-septzen.net/en/view/6 and for 32K systems it makes sense to give as much room as possible. Interestingly, 8086 CPU monitor loaded boot sector into 200h, and example boot loader for 86-DOS loaded the program into 400h: patersontech.com/dos/docs/86_dos_prog.pdf | |
| Dec 13, 2018 at 22:44 | comment | added | Raffzahn | @supercat I would go for marketing. Most logical load adress would be 0500h as 0400h is the BIOS area. 0500h is the first unused address. Then again, loading it at the upper end of available memory is an easy way avoide the need of a double copy, as the final DOS (with the boot block no longer needed) should reside as low as possible. So 7C00h seams like a compromise to allow the second boot stage to load more than 14.25 KiB DOS code (30.25 KiB max) as 14 KiB may have already looked too little when the BIOS was made. | |
| Dec 13, 2018 at 20:16 | comment | added | supercat | @Raffzahn: I wonder if there's any particular reason the boot sector is read just before the 32K mark, rather than at address 0:0x200, since interrupts 128-255 aren't needed for anything at that point, and the boot sector code itself won't be needed after it has fetched a more complete loader. | |
| Dec 13, 2018 at 20:10 | comment | added | supercat |
@Raffzahn: Perhaps one could type in a program like 1 READ Q:IF Q>=0 THEN A$=A$+CHR$(q):GOTO 1 ` 2 CALL VARPTR(A$):DATA ..,..,..,..,-1` every time one starts the system, and that could then do something useful with a floppy, but having to type that every time one wanted to use the machine would seem annoying. Maybe less annoying than having to use the Altair's toggle switches to enter 15 bytes of machine code to start MSBASIC from paper tape, but still pretty horrible.
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| Dec 13, 2018 at 19:59 | comment | added | Raffzahn | @supercat Looking at the presented information would reveal that it only crashes when the IPL switch is set. Having it cleard would still allow to use the all disk related functionality via INT 13h, So, not as useless as assumed. | |
| Dec 13, 2018 at 16:19 | comment | added | supercat | @Raffzahn: A system with only 16K RAM isn't going to have a usable floppy drive. I'm not sure whether trying to install a drive in a 16K system would result in it simply ignoring the drive or crashing on bootup, but the question of which useless behavior would result doesn't seem very interesting. | |
| Dec 13, 2018 at 14:20 | history | edited | roolebo | CC BY-SA 4.0 |
move RAM mapping description next to ROM mapping
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| Dec 13, 2018 at 10:17 | comment | added | Raffzahn | Sorry, but No. It doesn't aswer the question, just piles up much information and then somewhere inbetween saying 'The System Doesn't Boot'. All of this was already part of the question. It does, as well not target the underlaying question of what happens with a disk drive in a 16 KiB system. Last but not least, Effort is no indicator for quality nor is the amout posted. | |
| Dec 13, 2018 at 6:54 | comment | added | wizzwizz4♦ | @Raffzahn "So, if the system didn't have a diskette or diskette drive" and then a description of how it boots. I'd say that it hits the nail on the head. It's a different interpretation of the question to yours, but I think it is an answer. (Careful that you don't assume the intentions or effort of the answerer.) | |
| Dec 13, 2018 at 1:45 | review | Low quality posts | |||
| Dec 13, 2018 at 7:35 | |||||
| Dec 13, 2018 at 1:33 | comment | added | Raffzahn | Worthy description of the minimum system, but not an answer to the question asked. | |
| Dec 13, 2018 at 1:31 | history | edited | roolebo | CC BY-SA 4.0 |
added 4 characters in body
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| Dec 13, 2018 at 1:30 | review | First posts | |||
| Dec 13, 2018 at 4:37 | |||||
| Dec 13, 2018 at 1:26 | history | answered | roolebo | CC BY-SA 4.0 |