It can be really frustrating if you want to switch back and forth between Scratch, Python and Minecraft, as Minecraft will automatically pause when you leave the window. While this is good when you’re playing normally, it stops us from seeing what’s happening in the Minecraft window when we’re working elsewhere. Follow these instructions to stop Minecraft from pausing.
Open up the options.txt file in a text editor(img)
Search for a line that reads:
pauseonLostFocus:False, and change it to read
pauseonLostFocus:True (img)Save and close options.txt
Now you’ll find that when you ALT-TAB (Win) or CMD-TAB (Mac) away from Minecraft to another program, Minecraft won’t pause on you.
Minecraft can be pretty resource intensive on any computer that you're running. I'd advise to turn some of the advanced graphic features down or off, as indicated by the screenshot below.