IBM PC Model 5150 in JS – jsmachines.net via Waxy.

The PCjs simulation above is limited to a maximum simulated clock speed of 4.77Mhz. When the simulation isunlimited (click the “Fast” button twice), it can reach simulated clock speeds over 80Mhz (tested on a 3.4Ghz Intel Core i7). However, speed is very dependent on the browser. Safari performs best, initially reaching 60Mhz, and then after a minute or so, jumping to 80Mhz. Firefox and IE9/IE10 are more consistent, with speeds just over 60Mhz.