This mini-lesson covers how a computer works inside: hardware & software, the CPU and von Neumann architecture, the fetch-decode-execute cycle, registers, memory & storage, logic gates & Boolean logic, and embedded systems.
Work through each screen, answer the questions (some wordy, some logic tables) and collect ⭐ stars. Press Start when you're ready.
System · hardware & software
Hardware & software
Hardware — the physical parts you can touch: CPU, RAM, hard drive, keyboard, monitor.
Software — the programs and instructions that run on the hardware.
System software — runs the machine: the operating system (manages memory, files, hardware, users) and utilities.
Application software — lets the user do a task: browsers, games, word processors.
Key idea: the operating system sits between the hardware and the applications, so apps don't have to control the hardware directly.
Quick check
Hardware or software?
?Which of these is an example of system software?
Processor · CPU & von Neumann
The CPU & von Neumann architecture
The CPU (central processing unit) is the "brain" that processes instructions. In the von Neumann architecture, program instructions and data are stored together in the same memory.
The CPU contains the control unit, the ALU and registers, and swaps instructions/data with memory over the buses.
Control unit (CU) — directs the flow of data and decodes instructions.
ALU (arithmetic logic unit) — does the calculations and logical comparisons.
Registers — tiny, very fast stores inside the CPU used during processing.
Processor · the FDE cycle
The fetch-decode-execute cycle
The CPU repeats this cycle over and over, once per instruction:
Fetch → Decode → Execute, then loop back and repeat for the next instruction.
Performance factors: a higher clock speed (more cycles/second), more cores (do cycles in parallel) and a bigger cache all make the CPU faster.
Quick check
The FDE cycle
?In the fetch-decode-execute cycle, what happens in the fetch stage?
Calculate
Your turn — clock speed
1A CPU has a clock speed of 3 GHz. 1 GHz = 1 billion cycles per second. How many billions of cycles can it do each second?
billion
Hint: 3 GHz = 3 × 1 billion cycles per second.
Memory · RAM, ROM & storage
Memory & storage
RAM — volatile (loses data when powered off) read/write memory that holds the programs and data currently in use.
ROM — non-volatile, read-only memory holding start-up (boot) instructions.
Cache — small, very fast memory inside/near the CPU storing frequently used data.
Secondary storage — non-volatile, large capacity, keeps files permanently: HDD (magnetic), SSD (flash), optical, magnetic tape.
Volatile vs non-volatile: "volatile" means it loses its contents without power. RAM is volatile; ROM and secondary storage are non-volatile.
Sort it
RAM, ROM or storage?
Tap a statement, then tap where it belongs.
🧠 RAM
🔒 ROM
💽 Secondary
Quick check
Which memory?
?When you turn a computer off, the data in this memory is lost. Which type is it?
Logic · gates & Boolean
Logic gates & Boolean logic
Inside the CPU, circuits are built from logic gates that work on 1 (true) and 0 (false). The three you must know:
AND: 1 only when both inputs are 1. OR: 1 when at least one is 1. NOT: flips 0↔1.
Remember: AND = 1 only if both inputs are 1. OR = 1 if either input is 1. NOT has one input and reverses it.
Quick check
Work the gate
?An AND gate has inputs A = 1 and B = 0. What is the output?
Quick check
Now an OR gate
?An OR gate has inputs A = 1 and B = 0. What is the output?
Calculate
Your turn — a NOT gate
2A NOT gate has an input of 0. What is its output? (Type 0 or 1.)
Hint: NOT reverses the input, so NOT 0 = 1.
Systems · embedded
Embedded systems
An embedded system is a computer built inside a larger device to do one specific job. It usually has fixed software stored in ROM and doesn't need a general operating system.
Examples: a washing machine controller, a microwave, car engine management, a digital camera, a smart thermostat.
They are typically cheaper, smaller and use less power than a general-purpose PC because they only do one task.
Contrast: a laptop is general-purpose (runs many different programs); an embedded system is dedicated to one function.
Match it
Match the role to the component
Tap a role on the left, then its matching component on the right.
Role
Component
Quick check
Spot the embedded system
?Which of these best describes an embedded system?
Recap
The big ideas to know
Hardware = physical parts · software = programs (system vs application)
CPU: control unit + ALU + registers · von Neumann = instructions & data share memory