I remember issuing "call -151" on an Apple IIe to enter the monitor. I was too young to understand how it worked, but I was using the examples from the manual t

I remember issuing "call -151" on an Apple IIe to enter the monitor. I was too young to understand how it worked, but I was using the examples from the manual to define fast-drawing code for shapes (defined with an existing language made of combinations of down, left, right, up etc. commands) that could be called from Basic.