Computers π» | Computer Architecture | 3.1 Flashcards
What does CPU stand for?
Central Processing Unit
Define CPU
The part of a computer that is responsible for the execution or processing of all the instructions and data in a computer
Define microprocessor
A type of integrated circuit on a single chip.
What is Von Neumann architecture?
A form of computer architecture developed that introduced the idea of a βstored programβ, allowing computer memories to store programs as well as data
What are the three components of a CPU?
- Units
- Registers
- Buses
What are the units in a CPU?
Arithmetic Logic Unit (ALU) and Control Unit (CU)
What are the registers in a CPU?
- Program Counter (PC)
- Memory Address Register (MAR)
- Memory Data Register (MDR)
- Current Instruction Register (CIR)
- Accumulator (ACC)
What are the three buses in a CPU?
Address bus, data bus, control bus
What is the function of the ALU?
It allows the required arithmetic and logical operations to be carried while a program is being run.
What is the function of the control unit?
It ensures synchronisation of data flow and program instructions throughout a computer.
It also decodes instructions.
What is the purpose of the CIR?
Stores the current instruction being decoded and executed
Current Instruction Register
What is the purpose of the ACC?
Used when carrying out ALU calculations to store data temporarily during calculations
Accumulator
What is the purpose of the MAR?
Stores the address of the memory location currently being read from or written to
Memory Address Register
What is the purpose of the MDR?
Stores data which has just been read from memory or data which is about to be written to memory
Memory Data Register
What is the purpose of the PC (Program Counter)?
Stores the address where the next instruction to be read can be found
Each partition of memory contains β¦
An address and its contents
What are registers?
A part of the CPU that temporarily stores data for different reasons
What is a system bus?
A connection between major components in a computer that can carry data, addresses, or control signals
Define address bus
The system bus that carries the addresses throughout the computer system
Define data bus
The system bus that allows data to be carried from CPU to memory (and vice versa), or to and from I/O decvices
Define control bus
The system bus that carries signals from control unit to all other computer components
Which part of the CPU is responsible for decoding instructions?
The CU
Which data buses are unidirectional, and which are bidirectional?
Unidirectional: address bus
Bidirectional: data bus and control bus
What is the bus width?
The number of bits in a system bus
How does bus width impact address buses?
The wider the bus, the more memories that can be simultaneously addressed
How does bus width impact data buses?
The wider the bus, the larger the word length that can be transferred (word - group of bits which can be regarded as a single unit). The larger the word length the better the performance.
How does bus width impact control buses?
There is no need to widen the bus width of a control bus as it only is used to carry around control signals
What is the purpose of the system clock?
It produces timing signals on the control bus to ensure synchronisation takes place
What does IAS stand for?
Immediate Access Store
Define IAS
Memory that holds all data and programs neded to be accessed by the control unit (the RAM)
Define Fetch-Decode-Execute
A cycle in which instructions and data are fetched from memory, decoded, and finally executed
How is an instruction fetched?
fetch-execute cycle
- The address of the instruction, held in PC is sent using address bus to MAR
- Using the data bus, the next instruction is fetched from the memory address stored in the MAR, and stored in the MDR
- Contents of the MDR are copied to the CIR
- PC is incremented so that the next instruction can be processed
*PC = Program Counter
What does CIR stand for?
Current Instruction Register
Define increment
Increase by one
Why should an instruction be decoded?
fetch-execute cycle
The instruction is decoded so it can be interpreted in the next (execute) part of the cycle
How is an instruction executed?
fetch-execute cycle
- The CPU passes the decoded instruction as a set of control signals to the appropriate components within the computer system
- Allows each instruction to be carried out in its logical sequence
What is the clock cycle?
The vibrational frequency of the system clock which sends out pulses along the control bus
In what units is clock speed measured?
GHz
How does clock speed affect computer performance?
Potentially, a higher clock speed can lead to a better performance but there are dangers such as overclocking
Define overclocking
Changing the clock speed of a system clock to a value higher than the factory/reccomended settings
What are the possible dangers of overclocking?
- Executing instructions outside design limits can lead to very unsynchronised operations, making the computer frequently crash an unstable
- Overclocking can lead to serious overheating of the CPU leading to unreliable performance
Define cache
A temporary memory using static RAM to hold frequently used data/instructions by the CPU thereby increasing CPU performance
Why is cache memory faster than RAM?
- It uses Static RAM
- The memory is located within the CPU itself, so has faster access times
How does cache size impact performance?
The larger the cache memory size, the better the CPU performance
Define core
A unit on a CPU made up of an ALU, control unit, and registers. A CPU may contain a number of cores.
How can number of cores impact performance?
- Using more cores alleviates the need to continually increase clock speeds
- However doubling the number of cores doesnβt necessarily double computer performance as it will take more time for the CPU to communicate with each core
Define instruction set
The complete set of machine code instructions used on a particular microprocessor : a limited ammount of opcodes that can be used
Define opcode
Part of a machine code instruction that identifies what action the CPU has to perform on data / operand
Define operand
Part of a machine code instruction that identifies what data is to be used
Why is the instruction set limited?
There is a limited number of opcodes that can be used
What is the difference between the instruction set and programming code?
Instruction sets: The low level language instructions that instruct the CPU
Program code: The higher level language instructions that require interpreters or compilters to convert the code into the instruction set understood by a computer
Define embedded system
A combination of hardware an software which is designed to carry out a specific set of functions
What are the three things an embedded system can be based on?
Microcontrollers, microprocessors, or System on Chips (SoC)
What does a microcontroller contain in an embedded system?
- A CPU
- Some RAM
- Some ROM
- Other peripherals
- All on one chip
Together, carries out specific task
What does a microcontroller contain in an embedded system?
- A CPU
- Some RAM
- Some ROM
- Other peripherals
- All on one chip
Together, carries out specific task
What does a microprocessor contain in an embedded system?
- Integraded circuit with only a CPU on the chip
- No RAM, ROM, or peripherals - those have to be added
What does an SoC contain in an embedded system?
- May have a microcontroller as one of its components
- Almost always includes CPU, I/O ports, and secondary storage on one microchip
What is the difference between a programmable and non-programmable embedded system?
- A Non-programmable device had to be replaced if it requires a software update
- A programmable device can be updated by connecting it to a computer, or by updates from the internet
What are the benefits of devices being controlled via embedded systems?
- Small in size; easy to fit into devices
- Low cost compared to other systems
- Dedicated to one task; allows for simple interfaces
- Consume little power
- Can be remotely controlled
- Very fast reaction to changing input
What are the drawbacks of devices being controlled using embedded systems?
- Difficult to upgrade some
- Troubleshooting faults in the device becomes specialist task
- Interface can be confusing
- If it has internet access, open to hackes and viruses
- Devices are often thrown away rather than repair; very wasteful
How do most embedded systems work?
An operator inputs data manually from a UI, or data is automatically input by a sensor - and the output is connected to related components
What embedded systems are found in motor vehichles?
- GPS system
- In-car entertainment system
- Aribags
- Fuel injection system
- ABS breaking
- Traction control
What embedded systems are found in vending machines?
- Input pad
- Sensors to show position of gates
- Coin counter
- Temperature sensor to maintain environment
- Display showing prices
- Actuators to control motors that dispense items
What embedded systems are found in washing machines?
- Keypad to select wash cycle
- Dial to control cooking duration
- Dial to control temperature
What embedded systems are found in lighting systems?
- System allowing for remote control from phone
- Device checking time of day or day of week
- Sensor checking whether room is occupied
- Sensor checking brightness of natural light
What embedded systems are found in lighting systems?
- System allowing for remote control from phone
- Device checking time of day or day of week
- Sensor checking whether room is occupied
- Sensor checking brightness of natural light
What embedded systems are found in security systems?
- Keypad interface
- Temperature sensor
- Pressure sensor
- Acoustic sensor
