Comment by PlunderBunny
1 year ago
I taught myself to program on an 8-bit BBC micro-computer in the mid-80s by typing in BASIC listings. I understood BASIC quite well, and could write my own structured BASIC programs, but machine code was always a bit out-of-reach. I would try to read books that started by demonstrating how to add, subtract etc, but I couldn’t see how that could build up to more complicated stuff that I could do in BASIC, like polling for input, or playing sounds, or drawing characters on the screen. Only once I got an advanced users guide and discovered the operating system commands, then it started to click with me - the complicated stuff was just arranging all the right data in the right bits of memory or registers, then (essentially) calling a particular OS command and saying ‘here’s the data you want’.
Yeah the issue is that the pedagogy doesn’t make it clear how to bridge the “calculator” with the OS stuff. I had this issue when I was a kid. How does adding eventually make something draw on the screen? Of course, it doesn’t, you need some hardware or OS specific information
It wasn't until I read Petzold's CODE that this stuff, especially the role of the the motherboard bridging processing, memory and I/O and what an OS is for, that it started to click for me.
Yeah my stepdad bought me CODE as a kid and that really helped. A similar book that took a "top down" approach as much as possible would have also helped though, but would be much harder to pull off
But if this doesn't satisfy your curiosity, you might realize this is just pushing the magic blackbox/question mark a little further down the chain
How does the OS and the hardware draw on the screen, actually? All they have is also just calculator stuff, super basic primitives. You can't even do loops in hardware, or even real branches (hardware always "executes both sides" of a branch at once)
Anyways, if you keep digging long enough you eventually end up finding this XKCD https://xkcd.com/435/ =)
> hardware always "executes both sides" of a branch at once
Unless you're talking about quantum hardware, that is very much not true. The whole point of transistors is to choose whether to power one part of a circuit or another.
Plus, even for hardware, the solution to all this is to modularize all the way down. One piece of hardware sets up the right state and powers up another piece of hardware - this type of logic doesn't stop at the OS level. For drawing on the screen, ultimately you reach a piece of hardware that lights up in one of three colors based on that state - but all the way there, it's the same kind of "function calls" (and even more indirection, such as communication protocols) on many levels.
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