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Digital Information

Analogue Data vs Digital Data

Analog

Digital

Differences between

—

Pros for digital data

Wider Application
More Accurate Measurements
Easier to read

How Computers represent Digital Data?

Method: binary bits.

A bit stores data either 0 or 1, can represent 2 different status.

- Some Samples -

—

Decimal System vs Binary System

Capacities:

for Decimal, n digits can represent 10ⁿ different values.
for Binary, n digits can represent 2ⁿ different values.

Converting between Binary and Decimal via code

def switch_to_binary(ten_digit):
    ten_digit = int(ten_digit)
    digit_length = 1
    binary_digit={}
    while True:
        if int(ten_digit)<2**digit_length:
            break
        digit_length += 1
    output = ""
    for i in range(1,digit_length+1):
        position = digit_length+1-i
        result = ten_digit//2**position
        binary_digit[f"{position}"] = result
        ten_digit = ten_digit - result*(2**position)
        output = f"{output}{result}"
    output = f"{output}{ten_digit}"
    return output
print("\033c")
while True:
    try:
        ten = input("Insert Number : ")
        fin_result = switch_to_binary(ten)
        print(f" > Output:\n  - The binary result for {ten} is {fin_result}.\n\n")
    except KeyboardInterrupt:
        import sys
        sys.exit("\033cUser Keyboard Interrupt")

Place and Value

—

Limitations of Storing Numbers

for binary data of n bits, value of data should be within 2ⁿ-1.

Error related: Overflow :

Overflow might occur when value exceeds the limit according to the bits to store the value.

Example: 17 in 4-bit computer will be recorded as 1, so 8+9=1 might occured in case of Overflow.

Error related: Round Off Errors :

Round off errors occur due to computers will automatically round an infinite number to the nearest floating point number.

Example: 0.1+0.1 = 0.20000000001 might occured in case of Round Off Errors.

Storing Text in Binary

All types of audio,video,image,emoticons,texts,programs…etc can all be stored as bits.

Types of Compressions

Lossy Compression:

Lossy Compression lost parts of the data PERMANANTLY.

Example: 4K video -> 1080p video ; 8K image -> 4K image ; 192k audio -> 80k audio etc.
Usage scenes: In case we don’t require all the data when we use the file, ex. post wechat moments.

Lossless Compression:

Files compressed using Lossless Compression can be fully restored to its ORIGINAL content.

Example: Zip,7z format, RLE Compression etc.

Usage scenes: In case we want to recover the data later. ex. storing design files.

The Internet

The Internet is a global and open network.

A computer network is any group of interconnected computing devices capable of sending or receiving data.

The Internet is world’s largest computer network

⚠️ Not same with World Wide Web: The World Wide Web is system of organizing information that’s accessible through the internet.

Computer Network Topology

Note: Two computers cannot communicate with each other when they are not connected to the same computer network, which DOESN’T mean requires direct connection.

Metadata: Data that stores the destination and route of the data package. Will NOT contain contents of message content, etc.

Internet Speed

Speed is the combination of bandwidth and Latency. Even if the bandwidth is high, Internet speed will still be limited by latency.

Licences and Ethics

Creative Commons License

Creative Commons License allows the author to manage whether the content is allowed to be copied/used.

Online Data Security

Cyber Attacks

Phishing Attack: Trick for private data by making a webpage with similar/same layout and asking user to enter their passcode, address, etc.

Examples: a email for passcode resets, usually linking to a page with a field for you to enter your information.
Prevention Methods: Contact the organization to confirm; Check the website domain. etc.

Rogue Access Points: The access points installed on the network without the admin’s permission.

How that’s riskful: Your data can be viewed and modified by the actual manipulator of the rougue access points.

Computer Malware: Malicious Software that is unknowingly installed on a computer.

Types of malware: Trojan Horse, viruses, worm, keylogging software
Purpose and effects: Steal Data, adware advertisements popups, Encrypts your data and block access to applications, demanding the user to pay a ransom, utilizing computer’s resources to mine for cryptocurrency.
Keylogging Software(Important): record keyboard events and upload the logs elsewhere.

Protection of malware

Firewall: A system manipulating ingoing and outgoing network traffic and determines what to allow.

Anti-virus Software: Recognizes the virus codes by comparising it with the virus data base.

Algorithms

Sorting Algorithms

Python Code

num = [45, 23, 6, 19, 38]

def bubbleSort(num):
    for i in range(1, len(num)):
        for j in range(0, len(num)-i):
            if num[j] > num[j+1]:
                temp = num[j]
                num[j] = num[j+1]
                num[j+1] = temp
    return num


def selectionSort(num):
    for i in range(len(num)-1):
        minIndex = i
        for j in range(i+1, len(num)):
            if num[j] < num[minIndex]:
                minIndex = j
        if i != minIndex:
            temp = num[i]
            num[i] = num[minIndex]
            num[minIndex] = temp
    return num

def insertionSort(num):
    for i in range(len(num)):
        preIndex = i - 1
        current = num[i]
        while preIndex >= 0 and num[preIndex] > current:
            num[preIndex + 1] = num[preIndex]
            preIndex -= 1
        num[preIndex + 1] = current
    return num

Unit Conversion

Difference between ipv4 and ipv6

ipv6 support 2¹²⁸ different IP addresses, significantly more than ipv4 which has 2³²

Amount of Data

1 Byte = 8 bit
1 KB(KiloByte) = 1,024 Bytes
1 MB(MegaByte) = 1,024 KB = 1,024² Bytes
1 GB(GigaByte) = 1,024 MB = 1,024² KB = 1,024³ Bytes
1 TB(TeraByte) = 1,024 GB = 1,024² MB = 1,024³ KB = 1,024⁴ Bytes
1 PB(PetaByte) = 1,024 TB = 1,024² GB = 1,024³ MB = 1,024⁴ KB = 1,024⁵ Bytes

Internet Speed

1 B/s(Byte per Second) = 8 bps(Bit per Second)

Question answer logic

When see “Effect of Limiting Bandwidth” – Find network speed variables (in Bits(Bytes) per second)

When see “Citizen Science Project” – Find choice requires user to upload/contribute data.

When see “no-rights-reserved Creative Commons License” – Find choices indicates sharing.

When see “Symmetric Encryption” – “Same passkey” “Should be kept secret”

When see “Public Key Encryption” – “Is safe” “Not the same passkey to en- and de- ”

When see “Digital Certificate” – Find choice indicates “Validate/verify ownership of package”

When see “Multifactor Authentication” – Find options contained at least 2 of following: Password, Keyword, Biometric Authentication, Time Sensitive Verification Code. etc.

When see “parallel computing pros” – “Faster” “Suitable for a large amount of data”

When see “parallel computing cons” – “No use when next step require output of current step as input”

When see “Keylogging” – Find option contain “record your keyboard actions”

When see “Phishing” – Find option contain “trick” “send a fake email/message”

When see “Privacy” – Find option contain “unauthorized user / users not in friend list”

When see “Increase Digital Divide” – Find option indicates “Require more to be online”

When see “Decrease DIgital Divide” – Find option indicates “Provide more opportunities to be online”

When see “Collaborate pros” – Find option indicates this is more efficient and could combine ideas.

When see “Collaborate cons” – Find option indicates require managing

When see “crowdsourcing” – Find option indicates user to upload/contribute some data.

When see “FTP/IP” – Find option indicates this protocal allows different devices communicate with each other.

When see “Difference between ipv4 and ipv6” – Find option with “Allow more user to access internet”

When see “Weak Password” – Find option with “Guess/try a large amount of attempts.”

When determine whether is Phishing – Consider: 1. Not from authority organizations. 2. Request username/passwd/user information. etc. 3. Domain name not match

State: Developed. Latest Update: 04-22 2024

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