computer science

why is binary used by computers?

digital circuits have two states → on (1) + off (0)

state the uses of binary

numbers, text, sound, graphics

what does the acronym MSB represent?

most significant bit

in terms of sign-magnitude & two’s-complement, what do the circuits 0 and 1 indicate?

0 = positive

1 = negative

define overflow

when result > max bits

define arithmetic shift right

same as logical yet the sign bit is kept for signed values

state reasons as of why hexadecimal is better use than binary

easier to read (1 hex = 4 binary digits)

what does the acronym ASCII represent?

American Standard Code for Information Intercharge

define extended ASCII

supports over 1 million characters (up to 32 bits) → includes (emojis, global scripts)

define bitmap

image made by pixels, each stored in binary

higher resolution = more detail, larger file size

define color depth + state an example

number of bits per pixel

eg; 1-bit = 2 colors

explain sound representation

sound = analogue → needs to be digitised as computers only understand binary

digitising sound = sampling → measuring the amplitude of a sound wave at regular intervals

what’s the sample rate measured in? + state an example

hertz (Hz)

eg; 44,000 Hz → 44,000 samples per second

how does a higher sample rate impact sound?

smoother + more accurate sound

what happens if the sampling frequency is low?

lower quality sound & loss of detail

what happens if the sampling frequency is high?

better sound quality & larger file size

what does sample resolution refer to in sound?

number of bits used to store each sample

what impact does low resolution have on images/sound?

fewer colors / sound levels → poorer quality

what limits the quality & precision of digital data?

number of bits available to store it

state the importance of compression

• reduces file size

• speeds up downloads/uploads

• saves storage space

differentiate between lossless & lossy compression

lossless → no data lost

lossy → data is lost

state example files of both lossless & lossy compression

lossless → ZIP, PNG

lossy → JPEG, MP3, MP4

what are both lossless & lossy compression good for?

lossless → best for text, code, archives

lossy → photos, audio, videos

state the function of run-length encoding (RLE) + state an example

replaces sequences of repeated data with a count + value

eg; AAAABBBCCDAA → 4A3BC1D2A

state the function of encryption

scrambles data, enabling only authorized people to read it

what’s encryption used to protect?

• personal data

• financial information

• confidential files

what happens if no encryption is available?

data sent over the internet can be intercepted/read by unauthorized access

explain the pigpen cipher

a symbol-based substitution cipher where each letter is replaced with a symbol based on a grid

what is the caesar cipher?

a substitution cipher that shifts letters a fixed number of positions in the alphabet

explain the vigenere cipher

polyalphabetic; uses a keyboard to shift each letter differently

explain the rail fence cipher

transposition cipher changing the order of letters

define the input-process-output model

simple model used to describe how computers/systems work

explain the input-process-output model

input → data from user/environment

process → instructions carried out

output → result shown to user

storage → data saved to memory/files

state the different computational models

sequential, parallel, multi-agent

explain what happens in the sequential model

(1) tasks are carried out one after another

(2) each process must complete before the next begins

explain what happens in the parallel model

tasks are carried out at the same time on multiple processors/cores

used for speeding up large tasks

explain what happens in multi-agent model

(1) a system made of multiple independent agents interacting

(2) each agent follows simple rules, but their combined behavior creates complex results

state all hardware components

CPU, main memory, secondary storage, input/output devices

state the function of the CPU

executes instructions

state the function of the main memory

temporarily stores data & programs in use

state the function of the secondary storage

permanently stores files & programs

differentiate between the functions of input & output devices

input devices → send data to computer

output devices → shows results to user

how do the hardware components work together?

CPU + RAM → output

files → loaded from secondary storage → RAM → CPU processes → output

differentiate between RAM & ROM

RAM → volatile, holds data/programs in use

ROM → non-volatile, stores startup instructions

state the function of cache

volatile, very fast memory near CPU; stores frequent instructions

state the function of the virtual memory

volatile, hard drive space used when RAM is full

what’s a stored program?

program where instructions are stored in memory & fetched one at a time for execution

what does the Von Neumann Architecture state?

data/programs share the same memory/buses

explain the fetch-decode-execute cycle

fetch → instructions from memory

decode → in control unit

execute → in ALU

state all CPU components

CU, ALU, registers, clock, buses

state the function of the CU (control unit)

manages instructions & data flow

state the function of the ALU

performs calculations & logic

state the function of the registers

small storage for immediate data

state the function of the clock

controls timing of instructions

state the three different types of buses

address bus → memory location

data bus → actual data

control bus → control signals

state the factors affecting the CPU performance

• clock speed

• cores

• cache size/type

how does the clock speed impact the CPU performance?

more cycles per second = faster

how do the cores impact the CPU performance?

more cores = more instructions processed at once

how does the cache size/speed impact the CPU performance?

cache size → bigger cache = faster access to frequent data

cache speed → L1 (fastest , smallest) → L2 → L3 (slower , larger)

state the different types of physical data storage

magnetic, optical, solid state

state the features & an example of the magnetic storage type

features → moving parts, large capacity, cheap

eg; hard disk drive (HDD)

state the features & an example of the optical storage type

features → laser reads pits/lands

eg; CD, DVD, Blu-ray

state the features & an example of the solid state storage type

features → no moving parts, fast, durable

eg; SSD, USB flash drive

state the function of the cloud storage + provide features

saves data on remote servers via the internet

features → accessible anywhere, scalable storage, requires internet

state some contemporary examples

USB sticks, external SSD’s, cloud platforms

define embedded systems + provide examples

computers built into another device to control it

eg; washing machines, microwaves

state the features of embedded systems

• designed for specific tasks

• small & low power

state the function of logic gates

used in circuits/programs to make decisions

state & describe the basic logic gates

AND → true only if both inputs are true

OR → true if either input is true

NOT → reverses input (true → false, false → true)

state the use of writing logic statments from problems

AND → when both conditions must be true

OR → when either condition is ok

NOT → to reverse a condition

define operating systems (OS)

softwares that manage computer hardware & software, acting as bridges between the user & hardware

state the main functions of operating systems

file/process/hardware management & user interface

define utility software

software performing specific maintenance tasks to maintain a system’s efficiency/security

state the key utilities of utility software

• file conversion

• compression

• defragmentation

• backup

• antimalware

state the different types of anti-malware

antivirus → blocks viruses

anti-spyware → detects spying programs

define simulation + provide examples

imitates real-world processes for testing without risk or cost

used to test safely, reduce cost, predict outcomes
eg; flight simulators, business models

differentiate between system & application software

system software → controls/runs the computer (eg; drivers)

application software → helps users do tasks (eg; games)

differentiate between high & low-level languages

high-level language → code close to human language (java)

low-level language → closer to machine code (assembly)

state the features + uses of both high & low-level languages

high-level languages →

features → easier to learn, portable

used for → general software development

low-level languages →

features → fast, hardware-specific

used for → embedded systems

state the importance of translators

high-level languages/assembly must be translated since computers only understand machine code

state the different types of translators

assembler, compiler, interpreter

explain the assembler

converts each assembly instruction to binary

used for → assembly into machine code

pros → fast, direct hardware control

cons → non-portable, harder to debug

explain the compiler

translates all code at once before running

used for → high-level into machine code

pros → fast execution

cons → takes time to compile

explain the interpreter

translates line-by-line at runtime

used for → high-level languages

pros → easy to test

cons → slower execution

state the purpose of connecting computers in a network

• share resources

• communication

• centralized management

• easier backups & file access

differentiate between LAN, WAN & PAN

LAN (local area network) → cover small areas (homes, schools)

WAN (wide area network) → covers large areas (internet, banking networks)

PAN (personal area network) → very small areas (phones, laptops)

different between client-servers & peer-to-peer models

client-servers → servers that provide services requested by clients

peer-to-peer → devices share data directly, equal roles

differentiate between the pros & cons of both wired & wireless connectivity

wired (ethernet) → fast, stable, secure yet less portable

wireless (Wi-Fi) → flexible yet slow

what are network speeds measured in?

bits per second (bps)

state the common measurement units

mbps = megabits/sec (1 million bps)

gbps = gigabits/sec (1 billion bps)

define protocols

rules for communication between devices

state all the different types of protocols

• ethernet

• Wi-Fi

• TCP/IP

• HTTP

• HTTPS

• FTP

• POP3

• IMAP

• SMTP

differentiate between ethernet & Wi-Fi

ethernet → wired data transfer

Wi-Fi → wireless data transfer

state the purpose of the TCP/IP

sends/routes all data over internet

state the purpose of HTTP/HTTPS

access web pages (HTTPS = securer version)

state the purpose of FTP

transfers files between computers

state the purpose of POP3

downloads emails, deletes from servers

state the purpose of IMAP

reads emails, keeps on servers

state the purpose of SMTP

sends emails to servers

what’s included with the data sent in packets?

• data

• destination address

• error-checking bits