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==MAME==
By default [[MAME]] allows you to change the clock speed of the systems it emulates (including consoles) to anything between 50% to 200250% of the original clock speed, the only requirement is that you enable cheats for that game/system.
==NES==
==SNES==
===Main CPU===
For an NTSC SNES, the master clock rate is approximate ~21.477 MHz, but the CPU's effective clock rates are ~3.58 MHz, ~2.68 MHz, or ~1.79 MHz. This is because any CPU operation takes 6 master cycles (i.e. 21.477/6 = 3.58) and memory access can take 6, 8, or 12, depending on the area of RAM is accessed. In the case of ROM access, it also depends on whether bit 0 of CPU register 420D is set to 0 (SlowROM, 8) or 1 (FastROM, 6).<ref name="Fullsnes - Nocash SNES No$SNS Specs">http://problemkaputt.de/fullsnes.htm#cpuclockcycles</ref>
In testing overclocks on the original hardware, the following issues occur (speeds listed represent the maximum effective clock rate):
* 7.6 MHz: Color palette errors; sprites fail to render. Freezes after a few minutes.<ref name="SNES overclock">http://web.archive.org/web/20070629163744/http://www.undergroundcm.com/index.php?option=com_content&task=view&id=15&Itemid=38</ref>
Only MAME has an option to change the main CPU frequency, which requires you to enable cheats. MAME SNES emulation is very demanding by default and activating the overclock only makes it worse. It is more stable than the real hardware while overclocked and won't exhibit the same issues, but it is still very unstable especially if you adjust the frequency multiple times. It also does not allow you to go over 200250% clock speed, which isn't enough to fully get rid of slowdowns in some games.
The latest builds of all [[Snes9x]] libretro cores can overclock by reducing the number of emulated CPU/memory access cycles from 6, 8, and 12 to either 4, 5, and 6 (Compatible) or 3, 3, and 3 (Max) respectively. Just for comparison, that means the Max option is effectively 7.16 MHz. Gameplay is not sped up (assuming the game is not in a constant state of some slowdown, to begin with, like Out of This World) and the issues experienced on real hardware are not present, though stability will vary depending on the game and which option you use. Also to note, some games may work better with the Max option rather than Compatible, as appears to be the case for Mega Man X1 which has a bit of graphical corruption under very specific conditions when using the Compatible option, so try both if you encounter issues.
