New answers tagged ibm-pc
7
The standard text mode for VGA DOS was 80 by 25 characters, which translated to a resolution of 720 by 400 (characters of 9 by 16 pixels) per the table on VGA text mode page in Wikipedia.
One option would be to change the mode and see if you can get the resolution high enough for your converter, but that would depend on the capabilities of the graphics ...
47
The manual says that the smallest resolution it can handle is 800x600.
That is almost certainly the key. Original VGA supported 640x480 16-colors and 720x400 (essentially a small step up from the 720x350 monochrome (MDA) text, but with color). While VGA has come to mean "any video card and monitor that uses a blue 15-pin connector" that's not what ...
answered Sep 6 at 1:58
manassehkatz-Moving 2 Codidact
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22
DOS is almost surely not outputting 800x600 or up, and is probably in the ballpark of 720x350 or thereabouts. Further, it's likely 70Hz, which this adapter may not like.
I'd recommend you get a display that can use the signal from card natively -- any old multiscan CRT and lots of early LCDs can do this -- but if you're determined to use this adapter, you ...
2
For PC XT types, there were multifunction cards using a MC58167 from National Semiconductors. Other RTC chips were also used.
4
If the latter, was it common to lose clock accuracy if the timer rate was changed by a running program?
It was certainly possible, yes; it's hard to say how common this kind of distortion was, but it was fairly easily avoidable. A well-behaved program that hooks the timer interrupt needs to call the original handler at its original rate. If it changes the ...
13
Or was the clock maintained in software, and based off of something like the 18.2 Hz system timer interrupt?
Exactly that. It is a 32 bit counter incremented by one every time INT 8 is triggered by the 8253 counter #3 (via INT 0).
If the latter, was it common to lose clock accuracy if the timer rate was changed by a running program?
That depends much on ...
27
Or was the clock maintained in software, and based off of something like the 18.2 Hz system timer interrupt?
This is exactly how time was tracked; you can see the implementation of the timer tick handler in the IBM PC Technical Reference, page A-77. It updates a counter, stored in memory as a double word at 0x0040:0x006C, and checks for elapsing days, ...
2
Diagnostics have changed
Modern machines have far more built-in diagnostic capability. The first couple of generations didn't even have any interactive setup pages - you set everything with dip switches and jumpers. As later machines added built-in Setup routines, it gradually became practical to include enhanced diagnostics as well, so a typical machine now ...
answered Aug 27 at 19:07
manassehkatz-Moving 2 Codidact
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2
It was not only about the memory itself, but also other required hardware.
For example, the first IBM PC model 5150 used a timer chip to periodically trigger a DMA chip to perform a memory refresh cycle. So it was not only about the memory chips.
If the memory was not good, it is possible that at some point you try to load an operating system and the code or ...
2
Why did they do this "test"?
.1 No error checking
Memory at the time did not have any error checking. It does now, if an error is found now it will create an exception. At the time, without error checking, things would go silently wrong. Hence checking every bit of memory (also see below).
.2 Lots of memory chips
Computers typically had lots and ...
0
I don't know to which games this might apply, but I'm sure that some programmers simply did not consider an exit feature to be important. Back in the early DOS days, your program may not have been the product of a team, but the output of a single programmer with an idea. Some were self-taught and had not programmed long enough to recognize that some of ...
12
Back then, the operating system was much less powerful than you are used to today.
MS-DOS was a disk operating system. It primarily took care of the disk (floppy disks, mostly), including reading, writing and executing files, and handling directory structures. Sure, it had a few other functions which would wrap around lower level features of the system, but ...
5
Because reset times were negligible
Having to reset the PC is only an issue if the PC takes a long time to boot afterwards.
Assuming you had the memory check turned off in your BIOS, the time from powering on your PC to the DOS shell running was single-digit seconds. There really wasn't any inconvenience to it.
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If a program hooks or disables all interrupts, and never invokes any DOS or BIOS functions, it may use all of RAM following the last enabled interrupt vector (typically the keyboard vector at address 0x00024-0x00027) in whatever manner it sees fit, without regard for what portions of RAM might have been reserved for use by DOS or BIOS functions. If a game ...
6
One possible explanation could be: because the game has corrupted or leaked the memory or resources (video modes, sounds) and you'd need a reboot to get back the system in a clean state anyway, so better not give a false hope to the user.
It's not as easy as it seems to cleanly exit from a program, specially on old OSes.
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Paratrooper was originally a “PC booter”. All PC booters run without DOS or any other operating system¹ — to start them, you would insert the floppy into the drive, and switch the computer on (or reboot it). There was nothing for such a game to exit to — once you’d finished playing, you’d switch the computer off, or reboot it from a different floppy (or from ...
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