Systems Architecture Flashcards
What is the stored program concept?
The idea of a memory unit storing data or programs.
Therefore, more versatile as a singular machine could store different programs for different tasks.
This concept allowed for the creation of general purpose machines.
What does the Von Neumann architecture consist of?
A processor.
A memory unit that communicates with processor.
Connections (buses) for I/O devices.
Secondary storage saving/backing up data.
What does the processor do?
Executes program instructions to process data.
Handles main memory and I/O operations.
How does the processor access program instructions and data? Hint (TFD)
The instructions and data are transferred from secondary to main memory.
They can then be fetched, decoded and executed/processed.
Data can also be provided by I/O devices via I/O controllers.
What is cache memory?
Fast access M that stores most frequently used data/instructions.
It is located on the processor.
What is main memory?
Stores data/instructions while they are being processed. (RAM/ROM)
What are I/O controllers?
Devices that help with communications between peripheral devices and the control unit.
What are buses?
Connections that transfer data and signals between components in a computer.
What is the address bus?
Either reads or writes data to a memory location.
Is undirectional, one way connection from P to M and I/O C.
Allows the processor to establish a connection with an addressable ‘unit’, whether its a memory location or I/O controller.
What is the data bus?
Data is transferred to and from the P, M and I/O C.
It is bi-directional, it allows two-way connection between internal components of the system.
What is the control bus?
Sends control signals to manage and orchestrate operations in a computer system.
Including exchanging status signals between components of the computer system, and transmitting clock signals required for the coordination of operations.
It is also bi-directional.
What determines how much data can be transferred along the data bus or address bus?
The width of the bus (no. parallel lines).
If width is n bits then 2ⁿ bits can be transferred at a time.
What can the control bus be used for? Hint (RASS)
Request communication between units.
Acknowledge a request.
Specify the data type being transferred via the other buses.
Sync the communication between components using the clock pulses.
What are some examples of control signals? Hint (RWRGBIC)
M read: Puts data from a M location onto the data bus.
M write: Stores data from the data bus to a M location.
Bus request: Signifies a component needs access to a bus.
Bus grant: Signifies component is informed it can use a bus.
Bus busy: Signifies bus is not available (in use)
Interrupt request: Signifies an error has occurred an requires attention of CPU.
Clock signals: C bus supplies components with clock pulses.
What is the ALU?
It’s responsible for all arithmetic calculations and logic operations.
What is the control unit?
Organises the sequence in which program instructions are executed and decodes them.
It controls communications within the computer with control signals.
What tasks does the control unit carry out? Hint (RW-D-O-A)
Uses C signals to enable data to be read and written to main M.
Decodes instructions to know what needs to be done (ALU, storing etc.)
Organises micro-operations in order for the instruction to carry out.
Uses C signals to determine which ALU operation will carry out.
What does the clock do?
Synchronises the operation of the processors components.
Each operation carried out takes a number of clock “cycles”.
How does the clock do its job?
Generating regular pulses that emit a signal that oscillates between a low (0) and high (1) state.
What is a rising and falling edge (clock)?
Rising edge - changing from a low (0) to a high (1) state.
Falling edge - changing from a high (1) to a low (0) state.
How is one clock cycle found?
The time taken between two sequential rising edges is called the clock period and it corresponds to one clock cycle.
How is the clock speed calculated?
Clock speed (Hz) = 1 / clock period (s)
What does a program being ‘ready’ mean (CPU)?
The program instructions have been translated into machine code.
The program instructions have been loaded (from secondary storage) into the main M (RAM).
Describes what happens in the fetch part of the fetch-execute cycle.
Contents of the PC are copied to the MAR. MAR copies address to address bus.
C unit instructs a M read operation so that M location is transferred to the P. The instruction is then transferred and saved to the MDR via the data bus.
Contents of MDR are copied to CIR.
What happens in the decode part of the fetch-execute cycle?
C unit splits instruction in CIR into operand and opcode to determine the type of instruction to be carried out.
What does the “memory read” control function do?
Puts data from a M location onto the data bus.
What does the “memory write” control function do?
Stores data from the data bus to a M location.
What does the “bus request” control function do?
Signifies a component needs access to a bus.
What does the “bus grant” control function do?
Signifies component is informed it can use a bus.
What does the “bus busy” control function do?
Signifies bus is not available (in use)
What does the “interrupt request” control function do?
Signifies an error has occurred that requires attention of CPU.
How does a compiler work?
It takes the source code as a whole and translates it into machine code.
This machine code can then be run at any time.
How does an interpreter work?
It translates one line of code at a time and then executes it.
It does not produce an executable file.
What are advantages of using an interpreter?
Errors are found quickly as the interpreter halts at an erroneous line.
Minimal storage: lines are not stored after translation.
What are disadvantages of using an interpreter?
Interpreted programs run slower.
The program has to be interpreted every time to be run.
They do not produce an executable file that can be distributed.
What are advantages of a compiler?
Compiled programs run quickly as they are already translated.
Provides an executable file.
What are disadvantages of a compiler?
They don’t find errors.
There must be available memory to hold the data.
The program must all be recompiled if a change is made.
How does having more cache memory improve performance?
More instructions can be stored in cache memory.
This increases the probability of a cache hit.
Fewer fetches from main memory.
What are advantages of Harvard architecture?
Reduces bottleneck of data buses as instruction and data can be accessed simultaneously.
Instruction memory can be made exclusively ROM to prevent the program being hacked.
What is the role of interrupts?
To suspend the currently executing program.
So that a device that requires the attention of the processor can be serviced.
Why must the contents of registers be saved before servicing an interrupt?
So that the currently running task can be returned to.
As the interrupt will clear register values.
