How computers actually work

I was always curious to understand how these tiny boxes (computers) work. Its insane to believe that they're just bunch of electrical switches, literally.

gogle

Binary

Computers can understand only two things either something is done or its not done, like i said they're just bunch of switches, a switch has only two states On or Off nothing in between. So computers only understand 0 (off) and 1 (on) which is called binary

Bits and bytes

To represent a piece of information we use the word bit (a binary digit)

0 or 1 would be considered a bit

bit can only represent very small amount of information for example if a bulb is on or off, a single state. but if you want to represent big chunk of information like writing your pet's name, now you would need multiple bits to represent here comes bytes in the picture.

01001011 -> K

as you can see grouping these 8 bits makes a byte which can represent numbers, letters, colors, even pictures which can be understood by humans.

Example: the letter "A" is agreed (by a standard called ASCII) to be represented as the byte 01000001.

The cpu

Storing these bits / bytes in the computer won't help us in any way so there has to be something which can do things like adding, comparing and moving the numbers somehow, that doer is cpu.

cpu has a single job, to follow the instruction and execute a given task. It could be multiplying or adding two numbers. cpu follows a three step loop always to do something

Fetch -> Decode -> Execute

  • Fetch the next instruction to be executed.
  • Decode the instruction to understand what exactly needs to be done.
  • Execute the instruction, actually do it.

Then it moves to the next instruction and repeats . Forever. Billions of times per second.

Memory

for our computer to store the bits and bytes and make some operation on them it needs a place to sit somewhere, we call it memory.

a memory is of two types RAM and ROM

RAM (Random Access Memory)

  • short term
  • fast
  • wipes everything out when power is off.

ROM (Read Only Memory)

  • long term
  • slower
  • keeps things even when power is off.

But why two types, not one?

  • Computers need constant power to hold data and do any operation — which is expensive
  • RAM is fast but short-lived → good for active work
  • ROM is slower but long-lived → good for storage
  • You rarely need all your data at once — just the chunk you're working with right now
  • So keep the unused stuff in ROM, and load only what's needed into RAM

eg. chatGPT keeps all your chat histories ("memory") but you only use one conversation at a time. Loading everything into RAM at once would be wasteful, better to keep unused history in ROM and pull in only what's needed right now.

Stack vs Heap

computers can't just store anything anywhere, there has to be a structured way and different use cases right? So the RAM is organized in two structures with a different use cases:

Stack

  • small data
  • short lived operation
  • ordered data
let age = 49; // small, static → STACK

Heap

  • huge data
  • long lived operation
  • flexible data
let user = { name: "James" }; // bigger, flexible → HEAP

Processes vs Threads

Your computer's CPU has cores the parts that actually do the work.

Open Chrome, and the computer starts a process for it. Think of it as a separate box just for Chrome. Open Spotify, and it gets its own separate box too. One box can't see inside the other.

Inside each box, the work gets split into smaller pieces called threads

Process

one app running, in its own isolated box / environment.

Threads

a smaller task inside that box, like 1 tab playing a video and 1 rendering a webpage in chrome

Just fyi: one core can do one task at a time and when you try to open multiple processes (programs) it tries to switch between the processes to handle them parallely (fake parallelism)