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HTTP (HyperText Transfer Protocol)

the set of rules used for transferring data between a client (like your browser) and a server on the web.

• Sends requests for web content

• Receives responses from servers

• Works with URLs and web pages

• HTTPS = HTTP + encryption for security

Used in the client-server model to access websites!

protocol

• A protocol ensures reliable communication between devices.

• Examples include:
  

  • HTTP (HyperText Transfer Protocol)

  • TCP/IP (Transmission Control Protocol / Internet Protocol)

  • DNS (Domain Name System)

HTTP

HTTP is one of the protocols you must understand for AP CSP, especially in the “Internet” unit.

Here’s what you need to know:

✅ Basics:

• HTTP is used for transferring web pages and other content on the web.

• When you type a URL into your browser, it uses HTTP to request the web page from a server.

✅ Key Concepts:

• HTTP is a request-response protocol:
  

  • Your computer (the client) sends an HTTP request.

  • The server responds with the requested content (like an HTML page, image, etc.).

✅ Important Terms:

• GET request: asks for data (e.g., loading a webpage).

• POST request: sends data to a server (e.g., submitting a form).

• HTTP is not secure by itself (it doesn’t encrypt data) — that’s why we now often use HTTPS (secure HTTP).

ISP - internet service provider

• What it is: A company that gives you access to the internet (like Comcast, Verizon, or AT&T).

• Think of it like: The road your data travels on to get to the internet.

• ISPs assign your device an IP address and connect you to other networks.

• What it is: A company that gives you access to the internet (like Comcast, Verizon, or AT&T).

• Think of it like: The road your data travels on to get to the internet.

• ISPs assign your device an IP address and connect you to other networks.

TCP (Transmission Control Protocol)

Breaks data into packets, ensures all arrive and are put back in order. Can recover lost packets.

IP (Internet Protocol)

Addresses and routes each packet to the correct destination

DNS (Domain Name System)

translates human-readable domain names (like google.com) into IP addresses that computers use to locate each other.

• Like a phonebook for the internet

• Lets you use easy names instead of IPs (like 142.250.64.78)

The World Wide Web (WWW)

a collection of web pages and content that can be accessed using the internet and a web browser.

• Uses HTTP to share information

• It’s not the internet itself — just one way to use it

the internet

The Internet is a global network of networks that connects computers around the world.

• Allows data to travel between devices

• Supports services like the web, email, and file sharing

Router

A router is a device that forwards data between different networks.

• Directs internet traffic to the right location

• Found in homes, schools, businesses

• Think: traffic controller for data

Bandwidth

Bandwidth is the maximum amount of data that can be sent over a network in a given time.

• Measured in bits per second (bps)

• More bandwidth = faster data transfer

Domain

A domain is the human-readable name of a website (like example.com).

• It’s mapped to an IP address using DNS

• Makes websites easier to remember

Computer Network

A computer network is a group of connected devices that can share data and resources.

• Can be small (home Wi-Fi) or large (the internet)

• Uses protocols like TCP/IP

Computing device

A computing device is any machine that can process and send data. A physical device that can run a program

• Examples: phones, laptops, routers

• Connect to networks to exchange info

Open Access

Definition: Information or content that is freely available to the public, usually online, without paywalls or restrictions, but still copyrighted.

• Common in: Academic research, journals, and educational resources.

• Example: An academic article published under an open access license — you can read it for free, but you can’t repost or remix it without permission unless the license allows it.

✅ You can access it freely, but you don’t own it.

Open Domain

Definition: Content or information that is not owned by anyone and is free to use, modify, or distribute without restriction. No copyright.

• Often called public domain.

• Common in: Very old works (like Shakespeare), or things the creator deliberately released without rights.

• Example: The U.S. Constitution, Beethoven’s symphonies, or images released into the public domain.

✅ You can use it however you want, even for commercial purposes.

Free Access

Definition: Content you can view for free, but it might still be restricted in how you can use it.

• Difference from Open Access: Free access might be temporary or limited — you can read or watch it, but you don’t have rights to reuse or redistribute it.

• Example: A news article you can read without paying, or a free YouTube video that you can’t legally download or remix.

✅ You can see it, but usage is limited.

Proprietary

Owned by a person/company. You need permission or a license to use it. Microsoft Word format (.docx), Apple’s iOS Can limit innovation, sharing, or compatibility.

Decidable Problems

A problem that an algorithm can solve correctly every time and in a finite amount of time. Is a number even? Is a string a palindrome? These are fully solvable.

Non-Proprietary

Open to everyone. Not owned or controlled. Often part of open standards. HTML, JPEG, MP3, TCP/IP Encourages universal access, easier collaboration, interoperability.

Heuristic

A strategy to find a good enough or approximate solution when a perfect solution is too slow or impossible. Finding a good route on a map (Google Maps), facial recognition Computers use these to solve complex problems faster, but not always perfectly.

Undecidable Problems

A problem that no algorithm can solve for all inputs. Ever. “Will this program run forever or stop?” (Halting Problem) Some problems just can’t be solved with an algorithm.

Overflow Error

• Definition: Happens when a value is too big for the computer to store in the available number of bits.

• Example: A variable can only store numbers up to 255 (8 bits), but you try to store 300. The computer “overflows” and wraps around to a lower number (e.g., 300 → 44).

Logic Error

• Definition: The program runs, but the output is wrong because the logic or algorithm is flawed.

• Example: You want to calculate the average of two numbers:

average = num1 + num2 / 2

This actually divides only num2 by 2. Correct logic should be:

average = (num1 + num2) / 2

Syntax Error

• Definition: The code doesn’t follow the rules of the programming language, so it won’t run at all.

• Example:

if x = 5:

This causes a syntax error. The correct syntax is:

if x == 5:

Runtime Error

Definition: The code runs at first, but something goes wrong while it’s running.

• Example:

print(10 / 0)

This causes a runtime error because dividing by zero is not allowed.

Rounding Error

Definition: Happens with floating-point numbers when exact decimal values can’t be represented in binary.

• Example:

print(0.1 + 0.2)

This might output 0.30000000000000004 instead of 0.3.

parallel computing

• Definition: Multiple processors or cores work at the same time on different parts of a problem to solve it faster.

• Example: Sorting a large list by splitting it into smaller parts and sorting each part simultaneously on different cores.

distributed computing

• Definition: Multiple computers (often in different locations) work together by communicating over a network to solve a problem.

• Example: A website uses multiple servers around the world to handle thousands of user requests simultaneously.

sequential computing

• Definition: The program runs instructions one after another, step by step, without overlap.

• Example: A program that adds numbers one by one in a loop, finishing each addition before moving to the next.

Linear Runtime (O(n))

• Definition: The time it takes to run the program grows directly proportional to the size of the input.

• Example: A loop that goes through each item once.

Exponential Runtime (O(2^n))

Definition: The runtime doubles (or more) with each additional input element, growing much faster than linear.

• Example: Checking all subsets of a set (like the powerset).

Logarithmic Runtime (O(log n))

• Definition: The time it takes grows slowly, increasing by a constant amount every time the input size doubles.

• Example: Binary search in a sorted list — you cut the search space in half each step.

binary search

Only works on sorted lists.

• Repeatedly divides the search range in half:

1. Check the middle item.

2. If it’s what you want → done!

3. If it’s too big → search the left half.

4. If it’s too small → search the right half.

• Very efficient: takes ~log₂(n) steps instead of n.

• Example:

Looking for 7 in [1, 3, 5, 7, 9, 11]

→ Middle is 5 → 7 > 5 → search right → find 7

exponential search

Also for sorted lists, especially useful for very large lists.

• First, it rapidly increases the range (1, 2, 4, 8…) to find a rough section where the value might be.

• Then it uses binary search in that section.

• Faster than binary search if the item is near the beginning.

Linear/Sequential Search

You should know:

• It checks each element one by one.

• It works on unsorted data.

• It’s simple but can be inefficient for large lists.

crowdsourcing

Crowdsourcing is the practice of obtaining input, ideas, services, or data from a large group of people—often from an online community.

Key Points for AP CSP:

• Involves collaboration through the internet or other digital platforms.

• Allows problems to be solved faster and often more creatively.

• Can be used for collecting large amounts of data, solving complex tasks, or funding projects.

Examples:

• Wikipedia: Created and maintained by volunteers around the world.

• Duolingo translations: Used to crowdsource translations of texts.

• GoFundMe or Kickstarter: Crowdsourcing for financial contributions.

• Foldit: A game where users help scientists by folding proteins to solve biomedical problems.

citizen science

Definition: Citizen science is scientific research conducted, in whole or in part, by amateur or nonprofessional scientists—often in collaboration with professional scientists.

Key Points for AP CSP:

• Involves the general public in data collection and analysis.

• Uses technology to make science more accessible and participatory.

• Relies on computational tools to process and analyze the massive amount of data gathered.

Examples:

• eBird: Bird watchers submit sightings to help track bird populations.

• Zooniverse: Volunteers help classify galaxies, count penguins, or transcribe historical documents.

• Globe at Night: People report light pollution observations to contribute to research.

creative commons lisence

In AP Computer Science Principles (AP CSP), the Creative Commons License is defined as:

A public copyright license that enables the free distribution and use of a creator’s work, as long as the user follows the license conditions.

HTTP cookies

An HTTP cookie is a small piece of data that a website stores on a user’s computer to remember information about the user across sessions.