The instruction follower itself
When a laptop ad says "3 GHz, 8 cores", it is describing the chip this lesson explains, and when your code someday feels slow, the fix starts with knowing what the machine is actually doing per instruction.
The CPU, or central processing unit, is the chip that actually follows instructions. It understands only a small set of primitive operations called machine code: load a value from a memory address, add two values, store a result back, jump to another instruction. Each is encoded as bits from lesson 6-1, and programs sit in RAM from lesson 6-2 as long sequences of them.
The CPU runs one relentless cycle:
- Fetch the next instruction from RAM
- Decode it, working out which operation those bits encode
- Execute it, then move to the next instruction
That is all a computer does, but it does it billions of times per second, since a 3 GHz CPU cycles about 3,000,000,000 times each second.
Your Python code is not machine code. The interpreter you met in lesson 1-2 is itself a program, made of machine code, that reads your text and performs it instruction by instruction. Python's if and while become jumps, and your arithmetic becomes add and multiply operations.
The CPU cycle in order
The order is fetch → decode → execute.
The CPU fetches the instruction's bits from RAM, decodes which operation they encode, executes it, and immediately fetches the next one.
Everything your computer appears to do is this cycle repeated absurdly fast. There is no larger plan anywhere in the hardware, and no part of the chip knows it is running a browser.
The cycle is also the reason lesson 6-2's RAM matters so much for speed. Step 1 is a trip to memory on every single instruction, so a CPU that can execute billions of operations per second spends a great deal of its time waiting for values to arrive.
What runs your Python text
It is the interpreter.
It is a machine-code program that reads Python text and performs it, line by line, which is why it appeared in lesson 1-2 right before your first print.
Some languages instead use a compiler, which translates the whole program into machine code ahead of time, and then the CPU runs that output directly with no translator present. C works this way, and you will meet compilers later in the curriculum.
The trade-off is worth knowing now. An interpreter starts instantly and can run a one-line program, and a compiler does its translation work once up front so the resulting program runs faster. That is most of why Python is pleasant for learning and C is used where speed decides the outcome.