ELI5. If a computer is made up of preprogrammed circuits, then how does it display anything on its screen, even if that particular thing hasn’t been preprogrammed in its circuits?
In: Technology
Think of it like an old school Lite Brite only way better. Instead of you reading an instruction manual to know which peg goes in which hole to get which color for the bigger, there is a computer doing it and the monitor is a super lite brite
The pre-programmed circuits are more indirect than that.
The basic display circuit takes some cell of memory and makes some pixel on the screen a color defined by the contents of the cell. Then there are other circuits that read and write those memory cells.
Pretty much the same way you are just a bunch of cells. But, like each cell is actually doing a very different and specific thing, in a computer each preprogrammed circuit is doing a very specific and different thing.
Now, some of those preprogrammed circuits are part of the screen of the computer. These circuits control 1 thing and only 1 thing: depending on what they receive, they will light up differently.
The screen is connected (probably) to something else (unless it’s an All in One). The many types of preprogrammed circuits inside the other part of the computer are in charge of several things including, remembering things at the moment (RAM), long term memory (Hard Drive) and coordinating all the different preprogrammed circuits that work with the computer (CPU).
You, using input devices, change the input available in the RAM, Hard Drive, and sometimes even CPU. Stored applications in the Hard Drive, and running applications in the RAM, also change the input that goes to the screen. All of these interactions create a lot of different combinations of input, received, stored, and translated on your screen as different patterns of light.
This means, of course, that everything you see in your screen is simply the preprogrammed circuits on it cycling in very specific ways between all available possibilities between an all-black screen and an all-white screen.
It might be easiest to think of computer circuits as hardcoded ways to transform or change voltages (data). The input data you give it can be different, and therefor the output data can be different. You get different images on screen in a word processor by typing different characters on your keyboard, and the data of “you pressed a Y” is combined and transformed with a bunch of other data (“you are in a word document” for example) to eventually arrive at the output data “turn on these pixels”
A computer is made up of preprogrammed circuits that allow it to interpret instructions from a program and display the results on a screen (or do one of many, many other things with the output, whether it be music, instructions to a peripheral device, whatever). The computer is at its heart a giant set of millions of If / Then statements. It takes input, does something with it, and displays the results.
The standard english alphabet is made up of 26 predefined letters, but you can still type sentences much longer than that. Computers have options in which circuits to use, and in what order. This flexibility gives it the chance to f.i display a specific image of a bird by sending power down some pathways, but not others. It doesn’t need to have a “bird circuit” to do that, it just has to follow instructions that tell it which pixels need to be lit up in which order in order to display that image, similar to how you can use a keyboard to arrange the 26 letters in a specific order to write a question regarding how computers work.
Think of it like a bunch of clouds and how we humans tend to see patterns/shapes in clouds.
The circuits are kinda like air molecules. They know nothing about the pattern being formed, or whether or not the cloud looks like a giant banana. Each electronic circuit follows a set of very specific rules, much like the air molecules.
But when combined together, and given the right conditions, those air molecules can creates shapes in the sky that we humans interpret as a banana. Same thing with electronic circuits. Each individual circuit is designed to turn specific pixels on the screen on/off. The job of a programmer is to give the circuits the right set of instructions so that the eventual outcome is a banana on your screen.
In general, it can be thought of as [data]-[scene]-[render]-[screen]
Part of the computer maintains the data that needs to be displayed to the user and processes inputs. Part of the software and perhaps some hardware is dedicated to rendering the inputs and outputs, such as a screen display with touchscreen input.
In reverse order, a calculator that displays 2+5=7 on screen has a part of the hardware that translates the data of two plus five equals seven, into the display string [2 + 5 = 7]. In a similar manner, there are parts of the data processing the user doesn’t see, and there is also a portion of the data that keeps track of what needs to be displayed to the user. In math terms, the [data] includes the scratch sheet where the math is done, but the [scene] is just the question and resulting answer.
Answering this requires a few steps:
*Preprogrammed circuits can give different results, because they transform data they were given into something else.*
Those preprogrammed circuits don’t simply give you 1 result all the time, they can take an Input, a chunk of data stored electronically, and the circuit physically alters it into different data, giving out a different chunk of data called an Output. All that certain preprogrammed circuit does is take one or more Inputs, and transforms them into the Output.
Example: One such circuit can add 2 numbers in binary. 2 chunks of 1s and 0s representing the 2 numbers are sent to the circuit, and the circuit gives the result. This is all happening through tricky layouts and physics, the circuit doesn’t need to “understand” that it’s adding, or that what it was given are numbers.
How does this give you images on the screen?
*Your display is given chunks of data that are simply long lists of numbers, each representing one pixel, the display has circuits built in that turn those numbers into electric signals that light up specific parts of the screen in specific colors in different degrees, according to the numbers.*
How does this chunk of data get sent?
This is the part not explicitly asked in the question, but I believe is a key piece to understand what’s going on.
Computers can really only do one thing: handling data. They can handle single pieces of data, they can put pieces of data together, they can split data into smaller pieces, etc. Processors are just really complicated chips that have many preprogrammed circuits, and what some of those circuits do is forward data to specific circuits, so this way, the processor can be “told” what you want it to do with the data you give to it, by giving it an Instruction Code(this is just a number, therefore a simple chunk of data, that will make the other chunk of data you actually want to work with “flow” into the specific circuit you want). You want to add 2 numbers? You use the code number for adding, and put the number you want afterwards. You do the same with the second number. You want to multiply them, you use the code for multiplication and then your number. The Outputs of the circuits are stored in Memory, and can be used to do work with afterwards.
Since computers have been a thing, computer scientists and programmers have worked on creating layers of programs that contain sets of the above instructions detailed above in ways that they create more complex pieces of data. Programming Languages were created this way, so people can write specific human readable words that then get translated into a list of commands for the Processor to execute.
*Some of these layers deal with translating specific commands into specific numbers on the lists that then get sent over the cable to the display.*
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