Topic 1: The characteristics of contemporary processors, input, output and storage devices Flashcards
What are the 2 Architectures of the Computer
Von Neumann Architecture
Harvard Architecture
What is Von Neumann Architecture
Has one control unit, ALU, registers and memory unit with a shared memory and data bus used for data and instructions.
What is Harvard Architecture
Has separate memories for instructions and data. It is more commonly used in embedded processors
Compare Harvard and Von Neumann Architectures
- Von Neumann Architecture is cheaper to develop as the control unit is simpler and allows programs to be optimised in size.
- Harvard Architecture allows data and instructions can be fetched in parallel and both memories can be different sizes.
What is Contemporary Processing
- Combines Harvard and Von Neumann architecture
- Von Neumann is used when working with data and instructions in main memory
- Harvard is used when working with cache.
- Has a separate instruction and data cache.
What is RAM
Random Access Memory
* Volatile
* Holds data and programs which are currently in use
* High access speeds
* Very expensive per gigabyte
What is ROM
Read Only Memory
* Non-volatile (Cannot be modified)
* Used to store fixed instructions such as the computer start up routine
What is a Multi-core System
Multi-core CPUs have many cores which complete separate fetch-execute cycles independently.
What are Parallel Systems
Parallel systems can carry out multiple instructions simultaneously using a single core using techniques like pipelining.
Steps of the Fetch stage of FDE Cycle
o Address copied from the PC to the MAR.
o Data bus copies the instruction from that location to the MDR
o At the same time, the contents of the PC increase by 1
o The value is them copied from the MDR to the CIR
Steps of Decode stage of the FDE cycle
Contents of the CIR are split into operand and opcode
Steps of Execute stage of the FDE cycle
The opcode is executed on the operand
What is the Opcode
The type of instruction and the hardware to execute it
What is Operand
The address where the operation is performed
Name the 5 registers:
- PC (Program Counter)
- ACC (Accumulator)
- MAR (Memory Address Register)
- MDR (Memory Data Register)
- CIR (Current Instruction Register)
Name the 3 buses
- Data bus
- Address bus
- Control bus
What is the PC
Stores the address of the next instruction to be executed
What’s the ACC
Stores the results of calculations
What’s the MAR
Holds the address in memory that that is to be written to or read from
What’s the MDR
Holds data which has been read or needs to be written
What’s the CIR
Stores the current instruction, split into operand and opcode
What are Buses
- Parallel wires connecting two or more CPU components together
- The number of wires determine the width
- The System bus contains the data bus, control bus and address bus
What is the ALU
Arithmetic Logic Unit
Carries out arithmetic and logical operations
What is the CU
Control Unit
Directs operations inside the processor
What are registers
Small, fast memory cells used to temporarily store data
What is Flash Storage
- Fast and compact
- Logic gates store an electrical charge
- High represents a binary 1
- Low represents a binary 0
- Information is stored in blocks which are combined to form pages
- More expensive
- Limited lifespan
What are SSD
Solid State Drives
* Light and portable
* No moving parts
* More resistant to damage from movement than hard disk drives
* High data transfer rates
* Smaller capacity than hard disk drives
What is Virtual Storage
- A method of storing information remotely.
- Allows multiple computers to access data over a network or The Internet.
- Includes cloud storage and network accessible storage.
- Becoming more popular as network and Internet speeds increase.
- Relies on a network connection for access to data.
- Limited by network speed.
What is Virtual storage limited by
Network Speed
What Is Magnetic Storage
- Two magnetic states represent binary
o Polarised sectors represent 1
o Unpolarised sectors represent 0 - Can be damaged by strong magnets
Features of Hard Disk Drives
- High capacity
- Magnetic platters rotate at high speeds beneath a read/write head
- Multiple platters are stacked to maximise storage capacity
- Moving parts can become damaged
Features of Magnetic Tape
- An older storage medium
- Tape is round onto reels within a cartridge
- The tape drive spins the reels to move the tape across a reader
Features of Floppy Disks
- A thin magnetic disk in a plastic case.
- Small and portable
- Typical storage capacity of 1MB
What’s an Input device
Input devices are used to send data to the computer, such as a keyboard, mouse or sensor.
What’s and Output Device
Output devices allow the computer to send information out, such as a speaker or screen.
What is RISC
Reduced Instruction Set Computers
* Small instruction set
* One instruction is one line of machine code
* Used in personal computers
What is CISC
Complex Instruction Set Computers
* Large instruction set
* Instructions built into hardware
* Used in microcontrollers and embedded systems
* Compiler has less work to do
* Less RAM is needed to store the code
How does Optical Storage work
- Use lasers to read and write to a disk.
- Sectors of the disc are written in a spiral.
o Pits scatters light representing 0
o Lands reflects light representing 1
Disadvantages of Optical Storage
- Small and light so very portable
- Easily scratched
- Not very fast
Features of a CD
Compact disk
Commonly used for audio but can store any data type
Stores relatively little information
Features of a DVD
Digital Versatile Disk
Higher storage capacity than CDs
Often used to store videos
Features of Blu-ray
More than 5x as much storage as DVDs
Used to store HD films
What is Pipelining
- Allows three instructions to be processed through the fetch, decode and execute cycle at the same time.
- Data is stored in a buffer close to the CPU until required.
- Whilst one instruction is being executed, another can be decoded and another fetched.
- Reduces the amount of CPU idle time.
What’s a GPU
Graphics Processing Unit
* Had multiple processors working in parallel.
* Efficiently completes repetitive tasks.
* Used for image processing and machine learning.
* A co-processor (a secondary processor which supports the activities of the primary processor)
3 Factors that affect CPU performance
- Clock Speed
- Number of Cores
- Amount and Type of Cache Memory
What is Clock Speed
- Determined by the system clock
- All activities begin on a clock pulse
- Each operation starts when the clock changes from 0 to 1
- The clock speed is the number of clock cycles which can be completed in a second.
- Faster clock speed = better performance
What is Number of Cores
- Each core is an independent processor which executes its own fetch-execute cycle
- CPUs with several cores can complete more than one fetch-execute cycle at the same time
- Some applications can only use one core.
- More cores = better performance
What is the Amount and Type of Cache Memory
- Cache memory is fast memory built into the CPU
- Instructions are held in cache allowing them to be accessed quickly if needed.
- As cache fills up, unused instructions are overwritten.
- More cache = better performance
- Cache can be Level 1, 2, or 3
- Level 1 is the fastest but smallest
- Level 3 is the slowest but largest
