I have no idea myself, but I found somewhere that says

The Z80 in the TI-83 runs at a low 6 Mhz and is underclocked. According to the Z80 user Manual, the Z80 is capable of running at 20Mhz without exceeding the operating temperatures. So, it is possible to make your TI-83 run at 20 MHz. This isn't a smart thing to do though, the LCD driver wouldn't be able to handle all the instructions because it would still run at the same speed as it used to do, thus resulting in f*cked up display. It is possible to overclock your calc to 8 or 10 Mhz, but you might want to use a switch to switch between normal and boosted speed (overclocking drains your batteries faster than normal speed).

Ah, I see. Thanks.

IIRC for the 83+ you have to mess with a resistor, it limits the processor's clock speed, dunno if it's the same with the 84+.

Also if you run into an old calc on which it is possible, be careful because it's apparently risky. If you overclock it too much I have heard about fried calcs before. Typically, people will not go above 15 MHz and there are even some people who install a switch on the side of their calc like this guy http://www.yaronet.com/hook.php?sl=0&s=39406&f=1384&h=3 (yes, Omnimaga used to be hosted on yAronet) so they can switch back and forth between 6 and 15.

I think you need an account there to click direct post links