Possibly, on a real computer. But not necessarily true for a hypothetical one.rurwin wrote:Writing a dot to the screen is, in fact, not the simplest operation of a computer, it is one of the most complex. You wont find any information on how to do that in any assembler manual. All you will find is how to move numbers about, how to add and subtract numbers, and so forth. To write a dot on the screen, first of all you need to get access to the screen, (by writing the right numbers into the memory locations used as control registers by the memory management unit), put it into the right mode, (by writing the right numbers into the memory locations used as control registers by the video hardware), and work out where the dot is in memory and what value it should have. That is a significant number of assembler instructions.
Consider the memory management unit - is it part of the computer, or is it part of the peripherals? One could imagine a computer without a MMU.
In that case, the address bus comes out of the computer, and is decoded in hardware - gates, a mixture of NANDs and inverters. We could decide that 1k of the address space will be for the screen, and route the bottom ten address lines to our screen hardware. The rest of the address bus goes into a large NAND gate, to select that 1k of address space
Our screen hardware will consist of a small dual-port ram and a Teletext chip, with appropriate electronics to light up the CRT
To write to the screen, we only need to write to that 1k of address space. We can do it from boot-up in bare-metal with almost no coding.