How does the cpu/gpu tell each individual lcd in a monitor to do? And how does it understand without 2.1M+ wires?
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Each pixel in the screen has a tiny memory cell. OLED displays have an analog memory cell with a simple current controller for the LED. In LCD screens, the LCD cell itself has some relapse time. The memory is short-term, and has to be renewed regularly – otherwise it looses data.
There is column wires, that run vertically – they are used to store data in the pixels. There is also row wires, that run horizontally – they seal and unseal electrical “valves”, that connect the cells to the column wires. Row wires select a row, that will be updated.
The video port sends pixel values one at a time – row by row, column by column. The monitor accumulates them into an internal row buffer memory. When the buffer is full – it sets the voltages on the column wires and then activates one of the row wires.
The GPU and CPU do not directly work with the screen: they work with its virtual copy – the framebuffer. The framebuffer is a RAM chip, and it organized exactly like a real screen – with rows and columns and a row buffer. The difference – GPU and CPU can activate rows in any order by sending a “row select” command with a row number, and then request or modify individual columns with a “column select”. The video port controller chip will periodically read the entire framebuffer and send the data to the monitor.
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