Two Blueprints for Computers
Computers need a plan to work, called an 'architecture'. It decides how the brain of the computer (the CPU) talks to its memory. The two main types you need to know are Von Neumann and Harvard. They have a key difference in how they handle instructions and data.
Von Neumann Architecture
This is the most common design, used in your PC, laptop, and phone. Its defining feature is that it stores both program instructions and the data for those instructions in the same memory (RAM).
- Uses one main memory for both data and instructions.
- Simpler hardware design.
- Instructions and data are fetched one after the other using the same bus, which can create a bottleneck.
Harvard Architecture
Often found in smaller, specialized devices called embedded systems (like a microwave or washing machine). It keeps instructions and data in completely separate memories, with their own connections to the CPU.
- Separate memories for data and instructions.
- Allows fetching instructions and data at the same time.
- Generally faster and more efficient for specific tasks.
The Brain: The Central Processing Unit (CPU)
The CPU is where all the thinking happens. It has several key parts that work together to run your programs. Think of it as a tiny, super-fast factory carrying out billions of tasks every second.
Core CPU Components
Control Unit (CU)
The director. It manages the flow of data inside the CPU and tells all the other parts what to do and when.
Arithmetic Logic Unit (ALU)
The calculator. It performs all maths (add, subtract) and logic (AND, OR, NOT) operations.
Registers
Tiny, super-fast memory spots inside the CPU that hold data or instructions being worked on right now.
Cache
A small amount of very fast memory. It stores frequently used instructions and data to save the CPU from fetching them from the slower main memory (RAM).
Registers are vital, temporary storage locations right inside the CPU, making data access incredibly fast.
How It All Connects: The System Bus
The CPU and Main Memory (RAM) are constantly talking. They communicate using a set of wires called the System Bus, which is split into three different jobs.
CPU
Carries memory addresses from the CPU to RAM.
Carries the actual data between the CPU and RAM.
Carries commands and status signals from the CPU.
Memory (RAM)
The CPU's Main Job: The Fetch-Decode-Execute Cycle
The fundamental job of the CPU is to run a cycle over and over, billions of times a second. It fetches an instruction from memory, decodes what it means, and then executes it.
1. Fetch
The CPU fetches the next instruction from the address in RAM that is stored in the Program Counter (PC) register.
2. Decode
The Control Unit decodes the instruction to figure out what operation needs to be performed.
3. Execute
The instruction is carried out. This might involve the ALU doing a calculation or moving data between registers.
What Makes a CPU Fast?
Not all CPUs are created equal. Three main factors determine how powerful a processor is. A higher number is generally better for each of these, leading to more instructions being processed per second.
Clock Speed (GHz): How many cycles the CPU runs per second. Higher speed = more cycles = more instructions executed.
Number of Cores: A core is like a mini-CPU. More cores allow the processor to work on multiple tasks at the same time (multitasking).
Cache Size (MB): A larger cache means more frequently used data can be stored close to the CPU, reducing trips to slower RAM.