In prior centuries, it was common practice to tie the operation of a program to a computer’s clock speed. As computers got faster and faster, the programs tied to that slower clock speed sometimes had trouble running. To patch the issue temporarily, some computers in the early 90s included a “TURBO” button which actually slowed the computer’s clock speed down in order to help older software run without breaking in often unpredictable ways. [Ted Fried] decided that he would turn this idea on its head, though, by essentially building a TURBO button into the hardware of old computers which would greatly increase the execution speed of these computers without causing software mayhem.
To accomplish this, he is running CPU emulators on Teensys (Teensies?), but they are configured to be a drop-in replacement for the physical CPU of several retro computers such as the Apple II, VIC-20, and Commodore 64 rather than an emulator for an entire system. It can be configured to run either in cycle-accurate mode, making it essentially identical to the computer’s original hardware, or it can be placed into an accelerated mode to take advantage of the Teensy 4.1’s 800 MHz processor, which is orders of magnitude faster than the original hardware. This allows (most of) the original hardware to still be used while running programs at wildly faster speeds without needing to worry about any programming hiccups due to the increased clock speed.
The video below demonstrates [Ted]’s creation running in an Apple II but he has several other cores for other retro computers. It’s certainly a unique way to squeeze more computing power out of these antique machines. Some Apple II computers had a 4 MHz clock which seems incredibly slow by modern standards, so the 800 MHz Teensy would have been considered wizardry by the standards of the time, but believe it or not, it’s actually necessary to go the other direction for some applications and slow this computer down to a 1 MHz crawl.
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