Computer components

%%{init: {"flowchart": {"htmlLabels": false}} }%%
graph LR
    A[Input] --> B[Processing] --> C[Storage] --> D[Output]

Think of lightbulbs…

%%{init: {"flowchart": {"htmlLabels": false}} }%%
flowchart LR
    S0[Switch OFF: 0]:::off --> L0[Light OFF]:::off

    classDef off fill:#ff4d4d,color:#ffffff,stroke:#b30000,stroke-width:2px;
    classDef on fill:#4dff88,color:#000000,stroke:#00802b,stroke-width:2px;

%%{init: {"flowchart": {"htmlLabels": false}} }%%
flowchart LR
    S1[Switch ON: 1]:::on --> L1[Light ON]:::on

    classDef off fill:#ff4d4d,color:#ffffff,stroke:#b30000,stroke-width:2px;
    classDef on fill:#4dff88,color:#000000,stroke:#00802b,stroke-width:2px;

Combining switches

%%{init: {"flowchart": {"htmlLabels": false}} }%%
flowchart LR
    %% Define styles
    classDef off fill:#ff4d4d,color:#ffffff,stroke:#b30000,stroke-width:2px;
    classDef on fill:#4dff88,color:#000000,stroke:#00802b,stroke-width:2px;
    classDef S1 fill:#A7D13D,color:#000000,stroke:#b30000,stroke-width:2px;
    classDef S2 fill:#3DD1B6,color:#000000,stroke:#00802b,stroke-width:2px;


    %% State 00
    S1_0[S1: 0]:::off --> ST00[00]:::S1
    S2_0[S2: 0]:::off --> ST00


    %% State 01
    %% subgraph STATE01[State 01]
    S1_0b[S1: 0]:::off --> ST01[01]:::S2
    S2_1[S2: 1]:::on --> ST01
    %% end

%%{init: {"flowchart": {"htmlLabels": false}} }%%
flowchart LR
    %% Define styles
    classDef off fill:#ff4d4d,color:#ffffff,stroke:#b30000,stroke-width:2px;
    classDef on fill:#4dff88,color:#000000,stroke:#00802b,stroke-width:2px;
    classDef S3 fill:#5884CC,color:#000000,stroke:#b30000,stroke-width:2px;
    classDef S4 fill:#A958CC,color:#000000,stroke:#00802b,stroke-width:2px;

    %% State 10
    %% subgraph STATE10[State 10]
    S1_1[S1: 1]:::on --> ST10[10]:::S3
    S2_0b[S2: 0]:::off --> ST10
    %% end

    %% State 11
    %% subgraph STATE11[State 11]
    S1_1b[S1: 1]:::on --> ST11[11]:::S4
    S2_1b[S2: 1]:::on --> ST11
    %% end

Representing Data

Data in a computer is represented using binary code (0s and 1s). Each switch (bit) can be in one of two states, allowing us to represent different values.

8 bits = 1 byte (typical unit of digital data storage)

%%{init: {"flowchart": {"htmlLabels": false}} }%%
flowchart TD
    A[7] -->|Binary| B[00000111]

• Numbers: binary counting system

• Text: ASCII/Unicode (e.g. A = 65 → 01000001)

• Images: pixels stored as numbers (colors = binary values)

Switches as Decisions (Logic Gates)

• One bulb = 2 states: ON (1) / OFF (0)
• Connect switches in clever ways → logic gates

From Switches to Circuits

Circuits (“chips”) - Building blocks

• Circuits perform operations:
  • Add numbers
  • Compare values
  • Make decisions
• Control external devices (e.g., motors, displays)
• Store data

CPU is a Giant Switchboard

• CPU = Central Processing Unit
• Network of billions of transistors - the brain of the computer
• Executes instructions by switching on/off rapidly
• There are also GPUs (Graphics Processing Units), but we won’t discuss them here (extra slide for quick reference).

CPU v/s GPU

Storage Types

• RAM (Random Access Memory): Fast, temporary storage
• Storage drive: Slower, permanent storage

RAM v/s Storage Drive

• Think of a kitchen: The RAM is the countertop where you prepare ingredients — it’s fast and temporary.
• The storage drive is like the pantry or fridge where you store food for later.

RAM v/s Storage Drive

Feature	Short-Term Storage	Long-Term Storage
Speed	Fast (e.g., RAM)	Slower (e.g., Hard Drive, SSD)
Volatility	Volatile (data lost when powered off)	Non-volatile (data retained)
Capacity	Limited (typically GBs)	Larger (TBs or more)
Use Cases	Temporary data, active processes	Permanent data, file storage

Cloud (Remote) storage

• Data stored on remote servers via internet
• Examples: Google Drive, Dropbox, iCloud
• Pros: accessibility, backup, size and scalability
• Cons: internet dependency, privacy concerns

Differences between local and cloud (remote) storage

Local v/s Cloud : Quick assessment

• Open your machine’s file explorer (or Finder on Mac) and see if you can distinguish between any local and cloud (remote) storage locations.

What is a File?

• Typically, anything you would like to store long-term will be in a file.

• File: A collection of data (stored as sequence of bytes)

• Could be a document, image, video, or program

• A file has a name and an extension.

File Extensions

• File extensions help identify the file type and associated programs.

• File extensions are suffixes following a file name (.txt, .jpg, .py, .ipynb, .pdf, etc.)

• Metadata: size, type, modified date, etc.

• Softwares can only open and edit particular file types that they are designed for. e.g. Microsoft Excel won’t be able to open your .ipynb files.

• Try opening an image file (.png,.jpg, etc.) with any text editor (e.g. Notepad, TextEdit, etc.)

Folder (also called directory)

• Container to store files and subfolders

• Hierarchical structure

• Why do I need folders? Why can’t I have everything in my Downloads folder?

  • Organization: Folders help keep files organized and easy to find.
  • Clutter: Without folders, the Downloads folder would become cluttered and chaotic.
  • Context: Folders provide context for the files within them (e.g., work projects, personal files).
  • Navigation: Folders make it easier to navigate and locate files on your computer.

• Do folders need extensions?

• Please follow the mini module: https://teachbooks.io/files-and-folders

Why need computer languages?

• Computers only understand binary (0s and 1s)

• Languages translate human ideas into machine-readable commands.

• Examples: Python, Java, C, HTML.

Machine Code:

• Pure 0s and 1s, directly executed by CPU.

• Extremely fast, but almost impossible for humans to read/write.

• Example: To write 39 you would write 100111.

Assembly Language:

• Low-level symbolic language, one step above machine code.

• Uses short mnemonics instead of raw binary (e.g., MOV, ADD).

• Needs an assembler to convert to machine code.

High-Level Languages:

• Python, Java, C, JavaScript.

• Easier to read/write, closer to human language.

• Need compiler or interpreter to run.

Low-level (LL) v/s High-level (HL) languages

• LL are closer to machine code, while HL are closer to human language.

• HL are generally easier to learn and use, making them more accessible for beginners, but …

• … HL will not offer the same level of performance and efficiency as LL

• LL are great for system programming, embedded systems, and performance-critical applications.

• Note: Not a binary separation, but rather a spectrum of abstraction levels. For example, Python (highest), C (middle), and Assembly Language (lowest).

Why have so many programming languages?

• Tools in a toolbox: hammer ≠ screwdriver; each solves a different problem.

• Different languages for different goals:

  • Performance-critical tasks → C, C++

  • Web development → JavaScript, HTML/CSS

  • Data analysis/science → Python, R

  • Mobile apps → Java/Kotlin (Android), Swift (iOS)

• Trade-offs:

  • Ease of use vs execution speed

  • Flexibility vs strict rules

Print Hello world! in Assembly

section .data
    hello:     db 'Hello world!',10    ; 'Hello world!' plus a linefeed character
    helloLen:  equ $-hello             ; Length of the 'Hello world!' string

section .text
    global _start

_start:
    mov eax,4            ; The system call for write (sys_write)
    mov ebx,1            ; File descriptor 1 - standard output
    mov ecx,hello        ; Put the offset of hello in ecx
    mov edx,helloLen     ; helloLen is a constant, so we don't need to say
                         ;  mov edx,[helloLen] to get it's actual value
    int 80h              ; Call the kernel
    mov eax,1            ; The system call for exit (sys_exit)
    mov ebx,0            ; Exit with return code of 0 (no error)
    int 80h;

Print Hello world! in C and Python

C

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    return 0;
}

Python

print("Hello world!")

Graphical User Interfaces (GUIs)

• Windows File Explorer or Mac Finder are Graphical User Interfaces (GUIs).
• GUIs allow users to interact with the computer using visual (graphical) elements like windows, icons, and buttons.
• They make it easier for users to navigate the file system and manage files without needing to type commands.
• But they can be limiting when you want more control over the system.

Opening files

• If you’re in Windows File Explorer or Mac Finder, simply double clicking on a file will open it in the default application.

• Like we discussed before, a file extension tells your computer which application to use to open it.

• But what if we have files that contain code (i.e. scripts)? e.g. .py files.

• Double-clicking scripts will open them for editing, not for executing them (or running them).

• Enter the terminal…

What is the terminal?

• Also called command line interface (CLI) - as opposed to GUI
• A text-based interface for interacting with the computer / alternative to GUI (point and click)
• Users type commands instead of using graphical buttons.
• More details of why a terminal is needed is provided in the slides of the lecture “Python in a Terminal”.

CLI v/s GUI

File & Folder Practice

• Using your computer’s file explorer (GUI), in Documents, create a folder with your name and the course code as a suffix.

• Inside it, create 2 text files with .txt extension. Rename one with a .py extension. (For Windows users, you can create directly through File Explorer. For Mac users, do it via a text editor (e.g. TextEdit or VSCode), renaming can be done through Finder.)

• Copy the hello.py file that you created during the “Python in a Terminal” lecture and paste it in this folder.

File Types

• Change the file with .txt extension to .jpg → try to open. What happens?

Terminal Navigation

• Use cd to go into your folder.

• List contents with ls (or dir on some Windows machines).

Run a Script

• Use python hello.py to run your script from the terminal.

• Go one level higher in the directory structure using cd ..

• Now run the command python hello.py to run your script from the terminal. What happens?

• How can you fix this and get the script running again?