A-Level CS

Cards (272)

  • How does the CPU access the main memory in a computer system? When a program needs to access the main memory, the CPU sends a control signal down the control bus to indicate that it needs to read the memory. Then, it sends the memory address it wishes to access down the address bus. The main memory can then reply by sending the requested data back to the CPU along the data bus.
  • What are the components of a computer architecture? The components of a computer architecture include the processor (CPU), main memory, I/O controller, system bus, and data/address/control buses.
  • What are the different types of buses in the system bus? In the system bus, there are three types of buses: the data bus, the control bus, and the address bus.
  • What is the purpose of the system bus? The system bus is a pathway composed of three separate buses that connect the processor, main memory, and I/O devices.
  • What is the purpose of I/O controllers in a computer system? I/O controllers act as an interface between the CPU and peripheral devices. They translate the signals from the device into the format required by the processor. I/O controllers are connected to their respective I/O ports, where the peripherals are connected to the computer.
  • What is the main memory in a computer system and how does it communicate with the CPU? The main memory is a data store that can be directly accessed by the CPU. It is used to store program instructions and data. The main memory communicates with the CPU using the System Bus.
  • What is the role of the processor in a computer system? The processor, also known as the CPU (Central Processing Unit), is the brain of the computer system. It executes programs and supervises the operation of the rest of the system.
  • What is the need for I/O Controllers? If peripheral devices were connected directly to the CPU, the CPU would have to be redesigned every time a new type of device was connected. Additionally, different voltages are required for different devices, and these might not match those required for the processor. Finally, peripheral devices work much slower than the processor, so the I/O Controllers act as a buffer between devices and prevent the CPU from being slowed down.
  • What is the purpose of the motherboard? The motherboard is where the key components of the computer system are housed.
  • What is the purpose of control bus? The Control Bus is a bi-direction bus which is used to carry control signals, such as clock signals and interrupt requests.
  • What is the address bus? The Address Bus is a uni-directional bus which is used to carry address signals from the CPU to the main memory and I/O devices.
  • What is the purpose of the data bus? The Data Bus is a bi-directional bus which is used to transfer data and instructions.
  • What is the purpose of the RAM? The RAM can be read from or written to, and it is volatile. It stores the code to run the operating system and the programs that run on your computer.
  • What is the purpose of the ROM? The ROM can only be read from, and it is non-volatile. It tends to store the core software instructions.
  • Name one other device controllor which may be found in a typical microcomputer. Floppy disc, hard disc.
  • Why does the address bus only carry addresses in one direction? Address only goes from the processor to device controllers / main memory, regardless of whether the data is to be read from or written to that location.
  • What is the use of the Clock Signal? To synchronise operations.
  • What is the purpose of the Interrupt Request? Indicates that an interrupt is pending / transmission error.
  • What is the stored program concept? The stored program concept is where the program instructions are stored in main memory, then fetched, decoded and executed by the processor. Programs can be moved in and out of the main memory.
  • What is the Von Neumann Architecture? The Von Neumann Architecture is based on shared memory space for instructions and data, with the procesor following a linear fetch, decode and execute cycle.
  • Where is the Von Neumann architecture used? It is used in General Purpose Machines.
  • What is the Harvard Architecture? The Harvard Architecture is based on storing instructions and data in seperate memory units, each with its on bus. This allows for reading and writing data to be completed at the same time as fetching an instruction.
  • Where is Harvard Architecture used? Embedded systems
  • What are the advantages of Von Neumann Architecture? There is a high level of flexibility, as the memory is shared between instructions and data so the level assigned to each can fluctuate depending on task.
  • What are the disadvantages of Von Neumann Architecture compared to Harvard Architecture? Speed is limited when compared to Harvard, due to Von Neumann architecture having only one memory location and set of buses It is less secure, because data can be executed as code.
  • What are the advantages of Harvard Architecture when compared to Von Neumann Architecture? Two sets of memory and buses mean instructions and data can be fetched simultaneously - reducing delays waiting for memory fetches. Additionally, it avoids the possibility of data being executed as code making it harder to hack.
  • What are the disadvantges of Harvard Architecture when compared to Von Neumann Architecture? There is limited flexibility as there is only a certain amount of memory that can be used for data and a certain amount for instructions.
  • What is the purpose of the Control Unit? The Control Unit coordinates all actvities of the CPU, such as directing the flow of data between the CPU and other devices and sending memory read/write requests to main memory on the control bus.
  • What is the purpose of the Clock? The Clock is the electronic unit that synchronises related components by generating pulses at a constant rate.
  • What is the Clock Speed? The Clock Speed is the frequency at which the internal clock generates pulses.
  • What is the purpose of the Arithmetic Logic Unit? The Arithmetic Logic Unit performs arithmetic and logical operations on data.
  • What is the purpose of General Purpose Registers? General Purpose Registers are tiny areas of extremely fast memory located in the processor. The more general purpose registers a CPU has, the faster it may work.
  • What is the purpose of the Program Counter? The Program Counter is a dedicated register that holds the address of the next instruction to be executed.
  • What is the purpose of the Memory Address Register? The Memory Address Register is a dedicated register that holds the address of the memory location from which data or an instruction is to be fetched or to which data is to be written.
  • What is the purpose of the Memory Buffer Register? The Memory Buffer Register is a dedicated register that is used to temporarily store the data which is read from or written to memory.
  • What is the purpose of the Current Instruction Register? The Current Instruction Register is a dedicated register that holds the current instruction being executed.
  • What is the purpose of the Status Register? The Status Register is a dedicated register that contains information about the state of the processor.
  • What is the opcode of an instruction? The opcode of an instruction defines the basic machine operation.
  • What is the operand of an instruction? The operand defines what we need to do the operation to, it can either contain the data to perform the operation on, or the memory address where that data can be found.
  • What is the process of Fetching in the Fetch-Decode-Execute Cycle? 1. When an instruction is fetched, the PC contain the address of the instruction. 2. This address is then copied into the MAR. 3. Then, the address is sent along the address bus to the main memory, where it will wait to receive a signal from the control bus. 4. The control unit sends a memory read signal on the control bus. 5. The content from that memory address can now be sent along the data bus, and is then copied onto the MBR. 6. The PC is incremented ready for the next instruction, and copied into the CIR.