Way back I had a friend that wanted his (maybe) "Sargon" chess program to run faster. Luckily it was on the Atari 8-bit and I knew a thing or two. The program seemed to use standard b/w hires graphics nothing super fancy, so I thought I could make a pre-boot loader.
The theory was that the Atari spends a good chunk (30%) of its time for display memory access. That can be disabled (making a black screen) and re-enabled. My pre-boot program installed a vertical blank interrupt handler reading the 2nd joystick port: up/down for display on/off. After installing the handler, the program waited for diskette swap and pretended to be the original program loader reading the disk layout into memory and jumping to the start. Worked like a charm first go.
The theory was that the Atari spends a good chunk (30%) of its time for display memory access. That can be disabled (making a black screen) and re-enabled. My pre-boot program installed a vertical blank interrupt handler reading the 2nd joystick port: up/down for display on/off. After installing the handler, the program waited for diskette swap and pretended to be the original program loader reading the disk layout into memory and jumping to the start. Worked like a charm first go.