The Video Card

A video card is a device that turns memory and commands into display output. Modern GPUs are large parallel processors, but older educational interfaces keep the visible model simple:

Concept	Role
mode	resolution and pixel format
framebuffer	memory backing the visible image
pitch	bytes from one row start to the next
color format	how color channels are packed
present	make the prepared frame visible

The mode describes the dimensions and pixel format. The framebuffer is the memory region that stores pixels. The pitch tells you how many bytes separate the beginning of one row from the beginning of the next. These values must come from mode information, not from guesses in drawing code.

Text Mode vs Graphics Mode

Text mode stores character cells. It is small and efficient for terminals because the hardware or firmware interprets bytes as glyphs and attributes. Graphics mode stores pixels. It gives applications control over every point on the screen, which makes sprites, games, image viewers, and visual tools possible.

Why Pitch Exists

Rows may include padding for alignment or device constraints. Therefore:

offset = y * pitch + x * bytes_per_pixel

not:

offset = (y * width + x) * bytes_per_pixel

This is one of the most important formulas in the lab. If it is wrong, everything built on top of it will look random: rectangles tear, sprites drift, and writes near the right edge corrupt the next row.