Lab 2 context: why PC timers exist

The CPU is much faster than many I/O devices and than human-visible time. A program needs to ask "has enough time passed?" without a busy loop. Older PCs used timer hardware such as the i8254 PIT: program a divisor, receive periodic events, and count ticks.

What you learn

Hardware time derives from a base clock. You program a divisor so the counter produces events at the requested frequency, then count events. Time becomes measurable independently of CPU speed.

Programming a controller also means writing bytes in a required order. A divisor is 16 bits, but the interface writes a low byte and a high byte. Wrong order configures a different value while every port write succeeds.

Why this comes before graphics

Animation needs a timing policy: when to update state, draw, wait for input, and stop an idle loop. Without one, a graphical program runs as fast as the CPU or sleeps in a way that is hard to test. The handler records ticks; the main program decides what they mean.