Oh and if you know me IRL: yes I'm a weird furry and yes I'm trans. Now you know :-D... are you even surprised?
...the video rate of 8bit consoles was often a ratio from the 3.579545 megahertz NTSC colour clock. Since the horizontal frequency of the common NTSC standard is 15734 hertz, this gives the following amount of pixels per line:
| Ratio | Clock | Per line | Visible | Pixel aspect ratio | Examples |
|---|---|---|---|---|---|
| 1:4 | 0.894886 MHz | 56.8125 | ~40 | CPU: RCA Studio II | |
| 4:15 | 0.954545 MHz | 60.6 | ~42 | ||
| 2:7 | 1.022727 MHz | ~64.928 | ~45 | ||
| 3:10 | 1.073864 MHz | 68.175 | ~48 | ||
| 4:13 | 1.101398 MHz | ~69.923 | ~49 | ||
| 6:19 | 1.130383 MHz | ~71.7631 | ~50 | ||
| 1:3 | 1.193181 MHz | 75.75 | ~53 | CPU: Atari 2600 | |
| 6:17 | 1.263369 MHz | ~80.2058 | ~56 | ||
| 4:11 | 1.301652 MHz | ~82.636 | ~58 | ||
| 3:8 | 1.342329 MHz | ~85.2187 | ~60 | ||
| 2:5 | 1.431818 MHz | 90.9 | ~64 | ||
| 3:7 | 1.534091 MHz | ~97.3928 | ~68 | ||
| 4:9 | 1.590908 MHz | 101 | ~71 | ||
| 6:13 | 1.652098 MHz | ~104.884 | ~73 | ||
| 1:2 | 1.789772 MHz | 113.625 | ~80 | CPU: Atari 8-bit, Intellivision | |
| 8:15 | 1.909090 MHz | 121.2 | ~85 | ||
| 6:11 | 1.952479 MHz | ~123.954 | ~87 | ||
| 4:7 | 2.045454 MHz | 128? | ~91 | 6:2 | AY-3-8500 Pong systems |
| 3:5 | 2.147727 MHz | 136.35 | ~96 | 20:7 | |
| 8:13 | 2.202796 MHz | ~139.846 | ~98 | 39:14 | |
| 2:3 | 2.386363 MHz | 151.5 | ~106 | 18:7 | |
| 8:11 | 2.603305 MHz | ~165.272 | ~116 | 33:14 | |
| 3:4 | 2.684657 MHz | 170.4375 | ~120 | 16:7 | CPU: SNES slow rom |
| 4:5 | 2.863636 MHz | 181.8 | ~128 | 15:7 | RCA Studio II (?) |
| 6:7 | 3.068181 MHz | ~194.785 | ~137 | 2:1 | |
| 8:9 | 3.181817 MHz | 202 | ~142 | 27:14 | |
| 1:1 | 3.579545 MHz | 227.25 | ~160 | 12:7 | NTSC colour clock, Atari 2600, CPU: SNES |
| 8:7 | 4.090908 MHz | 256? | ~182 | 3:2 | AY-3-8710 "Battle" Game |
| 6:5 | 4.295454 MHz | 272.7 | ~192 | 10:7 | |
| 4:3 | 4.772726 MHz | 303 | ~213 | 9:7 | |
| 3:2 | 5.369315 MHz | 340.875 | ~240 | 8:7 | NES, SNES, Master System, TMS-9918 |
| 8:5 | 5.727272 MHz | 363.6 | ~256 | 15:14 | |
| 16:9 | 6.363635 MHz | 404 | ~284 | 28:27 | Teletext data rate |
| 2:1 | 7.159090 MHz | 454.5 | ~320 | 6:7 | C64 |
| 8:3 | 9.545453 MHz | 606 | ~426 | 9:14 | |
| 3:1 | 10.73863 MHz | 681.75 | ~480 | 4:7 | |
| 4:1 | 14.31818 MHz | 909 | ~640 | 3:7 | CGA, Apple II |
| 6:1 | 21.47727 MHz | 1363.5 | ~960 | 2:7 | |
| 8:1 | 28.63636 MHz | 1818 | ~1280 | 3:14 | 720p anyone? :-P |
So, say you want to make a system with a certain horizontal resolution, spanning the display fully horizontally.
Just pick one that matches closely to the one you want
It is intentionally vague on the visible pixel count, overscan matters. See the NES that renders in a 240-wide resolution but overscans to 256
Then you simply take for the CPU a frequency that has a logical ratio to the former, and you're game!
This way you won't choose a random resolution or CPU frequency that's unrealistic to get.
Obviously, PAL is different but the idea is the same.
4.43361875 MHz is the magic number here, except for PAL-N (Argentina, Paraguay and Uruguay, 3.58205625 MHz) and PAL-M (Brazil, which has the NTSC colour carrier)