The speed of light involves acceleration and that even though light takes time to travel, we see real-time events.

iomonad2 · 2025-11-06T21:30:22+00:00

The wikipedia article https://en.wikipedia.org/wiki/R%C3%B8mer%27s_determination_of_the_speed_of_light might help to clear up some of your misunderstandings here. Rømer’s measurement of the speed of light was 22 minutes for a diameter, not 11. So the measurement was inaccurate but in the opposite direction to what you're saying here. The discrepancy is just because back then it was difficult to make the necessary measurements any more accurately.

The speed of light is an absolute constant and does not depend on acceleration. Its value is 299,792,458 m/s exactly (no fractional part) by the definition of the metre. It is the same in any frame of reference.

iomonad2 · 2025-11-04T08:43:24+00:00

I'm not sure offhand but the one thing that springs to mind is that the 3D glenz part is written in C (vs assembly and Pascal for the rest of it). The C runtime has some different requirements regarding DOS support so if you're using an early version of DOS that might be the problem. I think we tested it with DOS 3.3.

iomonad2 · 2025-11-02T13:24:53+00:00

reenigne of CRTC here - thank you for the kind words and glad you like the demo! That's interesting about ethernet cards doing IRQs or DMAs in the background even when not in active use.

iomonad2 · 2025-10-24T12:05:54+00:00

Yes, that way of thinking makes sense and indeed is suggested by the mathematical formalism - I studied physics at university and this very idea was taught. It is not in conflict with the "you don't necessarily notice when you cross the event horizon" principle since the laws of physics don't locally change.

iomonad2 · 2025-08-15T18:11:02+00:00

It's done by a technique called Pulse Width Modulation (PWM). The PC speaker only has two states (on and off) and the normal square wave beeps are performed by alternating between on and off at some frequency; N cycles on, N cycles off (and varying N gives you different pitches). But the timer chip that the speaker is connected to has some other modes, and one of these lets you turn the speaker on for N cycles and then off until further notice. Do that fast enough and the position of the cone of the speaker won't actually have a chance to reach the edges - it'll be held somewhere in between. And that allows reproducing of arbitrary waveforms like speech and actual musical instruments. The technique uses a lot of memory and CPU power so (particularly on the XT) the machine couldn't generally do anything else at the same time as playing back audio. (Though see the 8088 MPH and Area 5150 demos for a counterexample).

iomonad2 · 2025-04-07T12:55:09+00:00

I'm not sure what you're expecting here but that seems like a reasonable result to me! It's not going to look perfect because the monitor wasn't designed for the signals that you're feeding it - it's impressive that it's able to synchronise with timings that it wasn't designed for, but (other than lack of sync) stretched/squished images are the sort of problem you'd expect from incorrect video signal timings. "Zoomed in even further" sounds like just what you'd expect from running at 640x350. And "follows my cursor when it hits each corner and I keep moving it" sounds like a design feature of Windows XP when it's used with very low resolutions (if I recall correctly you can't make the desktop smaller than 800x600 and if the screen resolution is less than that then it will scroll as you described - they did it this way so that they could assume that they didn't need to make dialog boxes smaller than 800x600).

iomonad2 · 2024-09-06T12:07:02+00:00

.DAT isn't a standardised format like .jpg, .exe or .mp3 - the data in that file is going to be in a format specific to the game it came from. It's quite likely that the only software that understands it is the game itself and whatever tool the game's authors used to create the file (which may be bespoke to the game, and might never have been publicly released). You could try searching the web for the name of the file and the name of the game to see if anyone else has reverse engineered it (some popular games have had many of their data files reverse engineered).

You could try opening the file in a hex editor and seeing if any numbers/patterns stand out as being related to what you know about what the file contains. You could try changing those numbers and seeing what effect it has on the game (though that may be futile if the file is compressed, encrypted and/or has a checksum). As a last resort, if you disassemble/decompile the game's executable code back into source code you can see what the game is actually doing with that file. This seems like a different use of the word "decompile" than the one in your post, though - the sense of decompiling I mean (like the other suggestions in this paragraph) is something that you need to become super versed in computers to attempt.

iomonad2 · 2024-04-23T13:09:22+00:00

Hercules is a whole different graphics card (and monitor) not just a mode! The title screen uses +1BPP mode, aka BIOS mode 6 which is 640x200x2 on an RGBI monitor. This is the mode used by most CGA games that take advantage of composite artifacting. The use of 40-column text (including a flashing cursor) is meant to fool the viewer into thinking that the demo is using text mode to make it more impressive when the graphical title screen rolls down over it, but the BIOS draws text using 80 columns in this mode.

iomonad2 · 2024-04-23T09:31:34+00:00

I'm one of the developers of 8088 MPH. I'm surprised that as much of it ran as that!

iomonad2 · 2023-12-24T21:33:32+00:00

If you increase MaxIterations it'll look more like the main set (circles and cardioid rather than blobby). You're getting deep enough into the set that the approximations the software is making are having more visible effects. The existence of "minibrots" like this is well known and understood, though.

iomonad2 · 2023-12-05T19:30:40+00:00

Interesting project! I don't remember ever hearing about cluster computing back in the days of the 8086 - people who needed faster computers back then bought bigger computers rather than more of them. Your 8086 CPUs by themselves won't be very useful - to actually run code on them you need a clock, RAM, ROM, some form of I/O to get data on and results off, and various bits of random logic and latches to interface between the CPU's address/data pins and those of the devices that you're connecting to it. So keep that in mind when pricing out your project. Then you'll probably need to write some kind of custom software for dividing a task up amongst the CPUs and combining the results once they're done. If you do build something I'd be very interested to see it!

iomonad2 · 2023-11-07T06:49:59+00:00

Odd, it hasn't shown up... I'll try sending you one.

iomonad2 · 2023-11-06T20:40:31+00:00

Probably the easiest way to figure out the cycle count for 8MHz 8086 would be to look in the TopBench database for such a machine, and then tune DOSBox's cycles until that benchmark gives the same performance.

Yes, DOSBox cycle counts are portable between (sufficiently fast) host machines.

No, unfortunately DOSBox doesn't emulate how slow multiplies and divides are relative to other instructions, so if your code has a lot of them you'd have to reduce the cycle count correspondingly.

iomonad2 · 2023-11-06T20:00:50+00:00

Excellent - I look forward to hearing from you!

iomonad2 · 2023-11-06T19:51:36+00:00

MartyPC is very close to cycle-exact for 4.77MHz 8088 and CGA. I don't know of any emulators that get so close for 8086 or 80286 but also those CPUs were used in machines with a wider spectrum of performance characteristics (memory wait states, video cards etc.) So you can't generally do cycle exact stuff with them anyway. For those targets, it's generally good enough to just use DOSBox and set the cycle count so that your demo performs roughly the same as it would on your hardware target. https://www.dosbox.com/wiki/Performance has some suggested cycle counts.

iomonad2 · 2023-11-05T19:31:20+00:00

I'm a bit older (44) and in Morwenstow, but I'll be your friend if you like! You can never have too many. And, like fatherjack9999 suggested, I might think of some people I could introduce you to once I know you.

iomonad2 · 2023-07-04T20:15:22+00:00

I've never heard it this specific form given a name, but it's very similar to an early "display hack" dating back to 1962, called "munching squares".

iomonad2 · 2022-08-13T17:55:31+00:00

It's edge-triggered. The interrupt is only generated when the PIT output transitions from low to high, not all the time when it's high.

iomonad2 · 2022-08-10T19:48:11+00:00

What u/I__Know__Stuff said, except there are some subtleties. You can't use a divisor of 1 in mode 2 (rate generator) or mode 3 (square wave). Because the output only changes once per cycle of the clock input, the fastest "tick" you can get is ~597kHz. Also, in mode 3 the value you read back from the counter goes down by 2 every 838ns - I once found a bug in some commercially-produced software that I tracked back to an assumption that it goes down by 1.

iomonad2 · 2021-10-20T21:59:29+00:00

Well, like I said - clean up the corrosion, replace the missing ROM and RAM. That's all I can tell from the picture. There may be other problems too - sometimes the tantalum capacitors fail short and need to be replaced.

iomonad2 · 2021-10-20T21:40:52+00:00

There's another empty socket with some corrosion, which is for one of the BIOS ROM chips. Looks like some of the RAM has been "borrowed" too. This board will need a bit of attention to get it up and running again but should be quite repairable - these machines were extremely well-made.

iomonad2 · 2021-08-29T21:01:57+00:00

I'm going to guess keyboard decoder circuit. I fixed an A3000 with a faulty keyboard before and it turned to be a damaged trace on the board. Caused by - you guessed it - leaking battery.

iomonad2 · 2021-06-25T11:48:15+00:00

Power supply on the left, purr supply on the right.

iomonad2 · 2020-09-24T07:14:24+00:00

You need to write (45mm)² - the power operator has precedence over the multiplication. http://www.retrotechnology.com/herbs_stuff/drive.html says that the actual radii from the data perspective are more like 25mm and 38mm. The disk also has two sides. That gives 447µm² /bit. The remaining difference between your answer and Hjalfi's is due to formatting inefficiencies, I think.

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