Computer Science
Paper 1
1.1 Systems Architecture
1.2 Memory and Storage
1.3 Computer Networks, connections and protocols
1.4 Network Security
1.5 Systems Software
1.1.1
1.1.2
1.1.3
1.2.1
1.2.2
1.2.3
1.2.4
1.2.5
1.3.1
1.3.2
1.4.1
1.4.2
1.5.1 Operating Systems
1.5.2 Utility System Software
Architecture of the CPU
What is the CPU?
What is the FDE cycle?
CPU stands for processing unit
also known as the brains of the computer - the CPU processes data and controls hardware (hard drive, input / output devices)
The FDE cycle is a process the CPU goes through when processing instructions
Stands for Fetch - Decode - Execute
Fetch - First instruction is loaded from Main Memory into CPU
Decode = Decodes instructions
Execute = Instruction is carried out
Cache = Stores temporary storage
Memory Management unit = The ss hardware that handles virtual memory and operations involving cache
CPU clock = Measures the number of cycles that the CPU executes per second
Control unit = controls how data moves around the CPU, controls input and output
Registers = a kind of temporary storage
Hyperthreading = Where the CPU will divide up its physical cores
Bus = carries data to its designated location
ALU unit = Stands for Arithmetic and Logic - handles maths instructions
Von Neumann Architecture
Von Neumann created the concept for a modern computer (Stored program computer)
Stored Program computers use 5 special registers for processing
Program Counter = used to locate where the next instruction needs to go in order for it to be executed correctly by the CPU
Memory Address Register - Updated by the Program Counter to hold the location of the next instruction that has to be fetched from RAM - then this information is then taken to RAM by the address bus
Memory Data Register = Instructions from main memory are stored in the MDR before being moved to the correct register in order to be processed
Current instruction register = where the current instruction being processed is being held and decoded
Accumulator (ACC) = Temporarily stores data while calculations are being performed by the ALU
CPU Performance
Core = Another name for a processing unit - CPU's will often typically have more than one processing unit and each unit will be called a core - they contain ALU's, CU's and Registers
Clock = The clock will measure how many instructions the CPU is able to take out per second - often it ticks over 3 billion times (3ghz), this means 3 billion instructions have been processed
Cache = a small amount of temporary memory that stores instructions likely to be reused again by the CPU in the near future
Overclocking = When a CPU is ran at a higher speed than intended by manufacturers - allowing more instructions to be processed
Embedded systems
Vehicles
Digital Watches
GPS Systems
Fitness Trackers
Central heating
Memory
Used to store data in a computer system - can be either Temporary or Permanent
Memory is split up into 2 categories - Main memory (can be directly accessed by CPU) and Secondary storage (Non volatile memory outside of the CPU)
RAM (Random access memory)
ROM (Read only memory)
Flash Memory
Virtual Memory
Volatile Memory = Memory that is lost when a computer turns off / loses power
Disk Thrashing
Storage
Magnetic Storage
Optical Storage
Solid State storage
Units of Storage
A bit - the smallest possible size of unit (4 digits)
A byte is 8 bits
A kilobyte is 1024 bytes
A megabyte is 1024 kilobytes
A gigabyte is 1024 megabytes
a Terabyte is 1024 gigabytes
Data storage
Data can be stored in Binary, Characters (letters), images and sound.
Metadata is data about data
Typically will tell you about how many bits are in the photo, the image width, the resolution and the
Compression is where bits in a file are reduced in order to make the file size smaller to save space on a device
Lossy Compression
Lossless compression
Lossless compression will allow for the file size to be reduced while withstanding the same quality as the original file before compression
Lossy compression will permanently delete data from the file and therefore the quality of the file will be reduced
Networks and topologies
Types of networks
LAN's
Local area networks typically only cover a small geographical area such as a school or a small office building
WAN's
Wide area networks cover large geographical areas such as a town or a country.
The internet is considered a WAN
Connect users by connecting multiple LAN's in different geographical locations
click to edit
Common Protocols
TCP
IP
HTTP
HTTPS|
FTP
POP
IMAP
Post office protocol
file transfer protocol
hypertext transfer protocol secured
Internet protocol
Transmission control protocol
Hypertext transfer protocol
internet message access protocol
Encryption
A process that scrambles readable text so it can only be read by the person who has a decryption key
Networking
Advantages
Userscan sharefiles
users can share connections with other devices
Users can access their files from any device on the network
servers can control security, back up data and complete software updates
click to edit
click to edit
Disadvantages
Increased security reasks
Malware and viruses can spread quickly between computers
If a server crashes, the computers will not work
Networking is a group of devices that are connected to eachother
Paper 2
2.1 Algorithms
2.2 Programming Techniques
2.3 Produce Robust Programs
2.5 Programming languages and integrated development environments
2.4 Boolean Logic
2.1.1 Computational Thinking
2.1.2 Designing, creating, refining algorithms
2.1.3 Searching and sorting algorithms
Abstraction
Decomposition
Algorithmic Thinking
Abstraction involves filtering out the information we dont need in order to be able to concentrate on the information that we do need.
An example of this would be ; A drawing of a metro map that only has important landscapes and stops mapped out.
click to edit
An algorithm is a set of steps that is followed to carry out an instruction
Algorithms can be designed using pseudocode an flow diagrams
click to edit
click to edit
Algorithms are starting points
Breaking down a problem
click to edit