Course: From Basic Science to Web Hosting

Module 03 — Computer Fundamentals

What Is a Computer?

Difficulty: Beginner → Intermediate
Prerequisites: Lesson 013 — What Is Binary?
Estimated time: 30 minutes

---

1. The Big Question

We now know:

Transistor
 ↓
Switch
 ↓
0 / 1
 ↓
Bit
 ↓
Data

But how do billions of these tiny electrical switches become something that can:

• run Linux,
• run WordPress,
• process network traffic,
• execute PHP,
• store databases,
• and serve websites?

The answer is:

A Computer Is a System for Processing Information

A simplified model is:

INPUT
  ↓
PROCESSING
  ↓
MEMORY
  ↓
OUTPUT

But a real computer is more accurately understood as several cooperating subsystems.

---

2. The Basic Computer Model

A simplified computer contains:

                 COMPUTER
                    │
       ┌────────────┼────────────┐
       ↓            ↓            ↓
     CPU          Memory       I/O
       │            │            │
       └────────────┼────────────┘
                    ↓
                 Storage

The major components are:

CPU
RAM
Storage
Input/Output
Interconnects
Power

---

3. CPU

CPU means:

Central Processing Unit

The CPU executes instructions.

Conceptually:

Instruction
    ↓
CPU
    ↓
Operation
    ↓
Result

The CPU contains structures such as:

Control logic
Arithmetic logic
Registers
Caches
Execution units

---

4. The CPU Is Made From Transistors

Remember:

Transistor
 ↓
Logic gate
 ↓
Digital circuit
 ↓
CPU

So the CPU is ultimately a highly complex semiconductor circuit.

Conceptually:

Silicon
 ↓
Transistors
 ↓
Logic gates
 ↓
Functional units
 ↓
CPU

---

5. What Does the CPU Actually Do?

A CPU repeatedly performs operations according to instructions.

A simplified instruction cycle is:

FETCH
  ↓
DECODE
  ↓
EXECUTE
  ↓
WRITE BACK
  ↓
NEXT INSTRUCTION

This happens extremely rapidly.

---

6. Fetch

The CPU needs to obtain an instruction.

Conceptually:

Memory
  ↓
Instruction
  ↓
CPU

The CPU uses a special register called the:

Program Counter

It indicates where the next instruction is located in the program’s address space.

---

7. Decode

The CPU determines what the instruction means.

For example, conceptually:

Instruction
     ↓
Decode
     ↓
ADD

or:

Instruction
     ↓
Decode
     ↓
LOAD

or:

Instruction
     ↓
Decode
     ↓
JUMP

The exact instructions depend on the CPU architecture.

---

8. Execute

The CPU performs the operation.

For an addition:

5 + 3

Conceptually:

Registers
   ↓
ALU
   ↓
Addition
   ↓
Result = 8

---

9. ALU

ALU means:

Arithmetic Logic Unit

It performs operations such as:

Addition
Subtraction
AND
OR
XOR
Comparison
Bit operations

Conceptually:

        ┌─────────────┐
Input → │     ALU     │ → Result
        └─────────────┘

---

10. Registers

Registers are very fast storage locations inside the CPU.

They hold values needed during computation.

Conceptually:

Register A → 5
Register B → 3

        ↓

ALU

        ↓

Register C → 8

Registers are much smaller than main memory but extremely important for CPU execution.

---

11. Memory

The CPU needs somewhere to store instructions and data.

This is where memory comes in.

A simplified hierarchy:

CPU registers
     ↓
CPU cache
     ↓
RAM
     ↓
SSD / storage

As we move downward:

Capacity generally increases
Access speed generally decreases

There are important architectural nuances, but this is a useful beginner model.

---

12. RAM

RAM means:

Random Access Memory

RAM is working memory used by the computer while programs are running.

For example:

Linux
 ↓
RAM

Nginx
 ↓
RAM

PHP
 ↓
RAM

WordPress
 ↓
RAM

RAM is generally volatile.

That means its contents normally disappear when power is removed.

---

13. Storage

Storage keeps data persistently.

Examples:

SSD
Hard disk
Flash storage

Conceptually:

Storage
 ↓
Files
 ↓
Operating system
 ↓
Applications
 ↓
Website
 ↓
Database

Unlike ordinary RAM, persistent storage retains information when power is removed.

---

14. RAM vs Storage

This distinction is extremely important for server administration.

RAM	Storage
Working memory	Persistent data
Usually volatile	Non-volatile
Very fast	Slower than CPU registers/cache
Smaller	Usually larger
Running programs use it	Files are stored here

For example:

WordPress files
      ↓
SSD

Running WordPress/PHP processes
      ↓
RAM

---

15. Input and Output

A computer also needs to communicate with the outside world.

Examples:

Keyboard
Mouse
Display
USB
Network interface
Disk controller

For a server, the network interface is particularly important.

Internet
   ↓
Network interface
   ↓
Server

---

16. Interconnects

Computer components need to communicate.

For example:

CPU
 ↕
Memory
 ↕
Storage
 ↕
Network

These connections use electrical signaling and protocols.

At the lowest level:

Transistors
 ↓
Electrical signals
 ↓
Digital interfaces
 ↓
Computer buses/interconnects

---

17. The Motherboard

In a traditional physical computer, the motherboard provides much of the physical infrastructure connecting components.

Conceptually:

             CPU
              │
       ┌──────┼──────┐
       ↓      ↓      ↓
      RAM   Storage  Network

Modern systems can integrate many of these functions into a smaller number of chips, but the conceptual organization remains useful.

---

18. Power

None of this works without energy.

The power system converts electrical energy into appropriate voltage/current rails for the components.

Conceptually:

Electrical supply
      ↓
Power supply
      ↓
Voltage regulation
      ↓
CPU / RAM / SSD / Network

---

19. Computer Hardware vs Software

This distinction is essential.

Hardware

Physical components:

CPU
RAM
SSD
Motherboard
Network interface

Software

Instructions and data:

Operating system
Applications
Libraries
Configuration
Website
Database

So:

Hardware
   +
Software
   ↓
Computer system

---

20. What Is an Operating System?

The hardware needs software that manages resources and provides useful abstractions.

That software is the:

Operating System

Examples:

Linux
Windows
macOS
Android

For your web hosting environment, the important one is:

Linux

---

21. What Does Linux Do?

Linux manages hardware resources and provides interfaces for applications.

Conceptually:

Applications
      ↓
System calls
      ↓
Linux kernel
      ↓
Hardware

For example:

Nginx
 ↓
Linux
 ↓
Network hardware

---

22. What Is the Kernel?

The kernel is the central privileged part of an operating system.

It manages resources such as:

CPU
Memory
Processes
Devices
Networking
Filesystems

Conceptually:

Applications
      ↓
Kernel
      ↓
Hardware

---

23. What Is a Process?

When you start a program, the operating system creates a running execution context called a process.

For example:

Nginx program
      ↓
Nginx processes

Similarly:

PHP program
      ↓
PHP-FPM processes

A process has things such as:

Code
Memory
State
Resources
Identifiers

---

24. What Is a Program?

A program is a set of instructions and associated data that can be executed by a computer.

Conceptually:

Program
 ↓
Machine instructions
 ↓
CPU
 ↓
Execution

---

25. What Is a File?

A file is a persistent representation of data managed by a filesystem.

Examples:

index.html
style.css
wp-config.php
image.jpg
database backup

On Linux:

/storage/websites/

is simply part of the filesystem hierarchy.

---

26. What Is a Filesystem?

A filesystem organizes persistent data into structures such as:

Directories
Files
Metadata
Permissions

Conceptually:

Disk
 ↓
Filesystem
 ↓
Directories
 ↓
Files

For example:

/storage/websites/templates.cresignsys.com/public/

can be understood as a path through the Linux filesystem.

---

27. What Is a Server?

A server is not necessarily a special type of physical machine.

A server is fundamentally a system that provides a service to clients.

For example:

Web server
DNS server
Database server
Mail server
File server

Your computer can technically act as a server.

---

28. What Makes a Computer a Web Server?

Install web-server software.

For example:

Computer
   ↓
Linux
   ↓
Nginx
   ↓
Web service

Nginx listens for network requests and sends appropriate responses.

---

29. Client and Server

Suppose you open:

https://templates.cresignsys.com

Your browser is the:

CLIENT

Your hosting machine is the:

SERVER

Conceptually:

Browser
   │
   │ Request
   ↓
Internet
   │
   ↓
Server
   │
   │ Response
   ↓
Browser

---

30. The Web Server Stack

Your website can involve several software layers:

Internet
   ↓
Network interface
   ↓
Linux
   ↓
Nginx
   ↓
PHP-FPM
   ↓
WordPress
   ↓
MySQL

Each component has a different responsibility.

---

31. Nginx

Nginx is web-server/reverse-proxy software.

It can:

Receive HTTP/HTTPS requests
Serve static files
Proxy requests
Handle TLS
Route requests
Manage connections

---

32. PHP

WordPress is primarily written in PHP.

Conceptually:

Browser
 ↓
Nginx
 ↓
PHP-FPM
 ↓
WordPress PHP code
 ↓
Response

---

33. MySQL

WordPress needs a database.

Conceptually:

WordPress
    ↓
Database query
    ↓
MySQL
    ↓
Data
    ↓
WordPress

The database can contain:

Posts
Pages
Users
Settings
Metadata
Plugins' data

---

34. Your Hosting Stack

The system you are building can therefore be visualized as:

PHYSICAL / CLOUD INFRASTRUCTURE
             ↓
        Virtual Machine
             ↓
           Ubuntu
             ↓
          Linux Kernel
             ↓
         File System
             ↓
           Nginx
          /     \
       HTTPS    HTTP
         ↓
      PHP-FPM
         ↓
     WordPress
         ↓
       MySQL
         ↓
       Website

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35. The Complete Journey

You have now travelled from basic physics to a real web-hosting architecture:

Matter
 ↓
Atom
 ↓
Electron
 ↓
Electric charge
 ↓
Electric field
 ↓
Voltage
 ↓
Current
 ↓
Circuit
 ↓
Semiconductor
 ↓
Transistor
 ↓
Logic
 ↓
Binary
 ↓
CPU
 ↓
Computer
 ↓
Operating System
 ↓
Linux
 ↓
Networking
 ↓
Internet
 ↓
HTTP/HTTPS
 ↓
Nginx
 ↓
PHP
 ↓
WordPress
 ↓
MySQL
 ↓
Website
 ↓
Web Hosting

This is the CresignSys Learn technology path.

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36. Next Level

The next lesson should not jump directly to web hosting yet.

We should understand the layer immediately above the computer hardware:

Lesson 015 — What Is an Operating System?

We will go deeply into:

Computer hardware
       ↓
Boot process
       ↓
Firmware
       ↓
Bootloader
       ↓
Linux kernel
       ↓
Operating system
       ↓
Processes
       ↓
Memory
       ↓
Filesystems
       ↓
Users
       ↓
Permissions
       ↓
Services
       ↓
Commands

Then we will connect it directly to the commands you are already using on your Ubuntu web-hosting server.