ARCHITECTURE Flashcards
State the basic internal components of a computer system.
- CPU
- Input/output devices
- Storage
What is the role of the processor?
The part of the computer which processes data by executing program instructions in the form of machine code which the processor is designed to handle based on a specific processor instruction set.
Describe the role of the main memory.
Memory that can be directly accessed by the processor
Outline the function of the address bus.
- Uni-directional bus
- carries the address of the memory location that data needs to be retrieved from or written to
- From processor to main memory and I/O controllers
- width of bus refers to number of bits that can be used to form the address of a memory location in main memory
What is the function of the data bus?
- Bi-directional bus
- Carries data between the internal components of the system allowing values to be written or read
- width of bus refers to number of bits that can be transferred in one operation
- if width is the same as the computer word then retrieving data from a single memory address can be done in one operation
Describe the function of the control bus.
- used to send control signals which manage and orchestrate the operations of the computer system
- these signals can include: clock signal, memory write/read and bus request
Outline the role of the I/O controllers.
- The I/O controller acts as an interface between a peripheral device and the processor of the computer
- Peripherals cannot be directly connected to the processor as they work in different ways, speeds and with different signals
Define device drivers.
Software which interacts directly with I/O controller that must be installed in order to communicate with a peripheral
Briefly outline what a system bus is.
The system bus is a set of parallel connections that allow internal components to communicate with each other and exchange data.
Define a word.
the amount of data in terms of bits a CPU’s internal data registers can hold and process at one time
Define the stored program concept.
Machine code instructions are loaded into main memory to be executed by the processor.
These instructions are fetched one at a time and executed by the processor immediately in a sequential order.
What are the features of von Neumann Architecture? (+ drawbacks and uses)
- Uses same address bus and data bus for instructions and data
- von Neumann architecture allows for the instructions and data to be saved in the same memory
- can be exploited by hackers who could disguise instructions (malware) as data that the processor may execute unknowingly when attempting to read the data
- Commonly used in general-purpose computers as it enables a more flexible use of the main memory, which allows the processor to run a variety of programs
Describe the features of Harvard architecture.
- separate memory units and buses for instructions and data, which means that both memories can be accessed simultaneously (improves processor performance)
- each memory can be adapted to meet the needs of a particular system
- Used in embedded systems, the instruction memory can be implemented as a read-only memory (ROM), which protects the programs from accidental or deliberate changes by hacking
- Used in embedded systems where speed of operation is crucial and minimal storage is available e.g. washing machines, traffic lights
Arithmetic logic unit (ALU)
A component within the processor which is responsible for performing arithmetic calculations and logical operations.
Control unit
- responsible for directing the operations of all the other components of the processor
- uses and sends control signals to read data, decodes instructions by splitting them into opcode and operand, organised sequence of micro-operations to execute instruction
Clock
- generates regular clock pulses by emitting a signal that continuously oscillates between a low and a high state
- The clock signal is used to synchronise the operations of the processor components.
General-purpose registers
- temporarily store and access the results of operations
- keep the results of the intermediate calculations that are produced as part of a larger computation
Program counter
Holds the address of the next instruction to be executed by the processor
Memory Address register
Temporarily holds the address of the memory location that the processor needs to access, either to read from or write to.
Memory Data/Buffer register
Temporarily holds the data that are read from or written to the main memory.
Current instruction register
Holds the current instruction that the processor is executing
Status register
- Used to store information about the result of the last instruction that the ALU executed.
- Each bit within the status register acts as a flag to indicate if an error or exception has occurred within the process
Accumulator
Stores the result of any calculation processed by the ALU
Describe the steps of the fetch-decode-execute cycle.
FETCH
1. The memory location address is transferred from the program counter to the MAR
2. The program counter is incremented by 1
3. Memory read signal sent across control bus to main memory
4. Data/instructions from memory location is placed on data bus and stored in MBR
5. Instruction transferred from MBR to CIR
DECODE
6. Instruction is decoded in control unit by splitting into opcode and operand
7. Additional data is fetched from memory and passed to registers
EXECUTE
8. Instruction is executed by the ALU
9. GP registers store intermediate values of calculations
10. The final result is stored in the accumulator