4.1 ProcessorFundamentals.CPU_architecture incompl Flashcards
What is the Von Neumann architecture?
A computer architecture introduced in the 1940s that introduced the concept of the stored program.
What does the Arithmetic Logic Unit (ALU) do?
It performs all arithmetic and logical operations within the processor.
What is the role of the Control Unit (CU)?
It ensures the synchronisation of data flow and programs throughout the computer by sending control signals along the control bus.
What is the purpose of the system clock?
It produces timing signals on the control bus to ensure synchronisation in the computer system.
What is the Immediate Access Store (IAS)?
A memory component that holds all data and programs needed to be accessed by the control unit.
What is an accumulator in a CPU?
A temporary general-purpose register that stores numerical values during operations.
What is a register?
A temporary storage component in the processor that holds data or instructions as part of the fetch-execute cycle.
What is a status register?
A register used during arithmetic or logical operations to store information about the result, such as flags.
What is a flag in a CPU?
A flag indicates the status of a bit, e.g., N = 1 indicates the result of an addition gives a negative value.
What is the address bus?
A bus that carries addresses throughout the computer system.
What is the data bus?
A bus that allows data to be carried from the processor to memory (and vice versa) or to and from input/output devices.
What is the control bus?
A bus that carries signals from the control unit to all other computer components.
What does unidirectional mean in relation to buses?
It describes a bus where bits can travel in one direction only.
What does bidirectional mean in relation to buses?
It describes a bus where bits can travel in both directions.
What is a word in computing?
A group bits used by a computer to represent a single unit.
What is a clock cycle?
The vibrational frequency of the clock, measured in GHz, which sends out pulses along the control bus.
What is overclocking?
Changing the clock speed of a system clock to a value higher than the factory/recommended setting.
What does BIOS stand for?
basic input/output system
What is cache memory?
A high-speed auxiliary memory that allows for fast data transfer and retrieval.
What is a core in a CPU?
A unit made up of an ALU, control unit, and registers that is part of the CPU.
What is a dual core CPU?
A CPU containing two cores.
What is a quad core CPU?
A CPU containing four cores
What is a port in computing?
An external connection that allows a computer to communicate with peripheral devices.
What is a USB?
Universal Serial Bus, a type of port used to connect devices to a computer.
What is asynchronous serial data transmission?
A method where a single wire transmits bits one after the other, with the sender using its own clock.
What is HDMI?
High-Definition Multimedia Interface, a type of port used to connect devices to a computer, supporting high-definition signals.
What is VGA?
Video Graphics Array, a type of port used to connect devices to a computer, based on older analogue technology.
What is HDCP?
High-Bandwidth Digital Copy Protection , a part of HDMI technology that reduces the risk of piracy.
What is the fetch-execute cycle?
A cycle where instructions and data are fetched from memory, decoded, and then executed.
What is the program counter (PC)?
A register that stores the address of the instruction currently being executed or the address of the next instruction to be read.
What is the Current Instruction Register (CIR)?
A register that contains the instruction currently being executed or decoded.
What is Register Transfer Notation (RTN)?
A shorthand notation used to represent the movement of data and instructions in a processor.
What is an interrupt?
A signal sent from a device or software to the processor requesting its attention.
What is interrupt priority?
A system where interrupts are given priority levels to determine which should be serviced first.
What is an Interrupt Service Routine (ISR)?
Software that handles interrupt requests, such as sending “printer out of paper” notifications to the CPU.
What was a limitation of early computers before the Von Neumann model?
Early computers could not store programs or data, requiring significant human intervention to operate.
Who developed the concept of the stored program computer and when?
John Von Neumann in the mid-1940s
What are the main features of the Von Neumann architecture?
- Central processing unit (CPU or processor)
- Processor able to access memory directly
- Computer memories that store both programs and data
- Stored programs made up of sequentially executable instructions
What are the main components of the processor?
- Arithmetic logic unit (ALU)
- Control unit (CU)
- System clock
- Immediate access store (IAS)
What does the arithmetic logic unit (ALU) do?
It performs required arithmetic or logic operations during program execution.
Can a computer have more than one ALU? What operations do they perform?
It can. one ALU may perform fixed-point operations and another floating-point operations.
How are multiplication and division performed in the ALU?
Through sequences of addition, subtraction, and left/right shifting operations.
What is the accumulator (ACC)?
A temporary register used during ALU calculations.
What role does the control unit (CU) play in the CPU?
It reads instructions from memory, interprets them, and generates signals along the control bus for other components. It ensures synchronisation of data flow and program instructions
What is the purpose of the system clock in a computer?
To produce timing signals on the control bus to ensure synchronisation of operations. Computer crashes if it does not function.
What does the Immediate Access Store (IAS) do?
Holds data and programs temporarily that the processor needs to access.
Why is data stored temporarily in IAS instead of backing store?
Read/write operations with IAS are much faster than with backing store.
What is another name for the IAS?
Primary memory or RAM
What are the two types of registers in the Von Neumann system?
General purpose and special purpose registers
What is the function of general purpose registers?
They hold data frequently used by the CPU and can be directly accessed by programmers. Example: accumulator
What are special purpose registers used for?
They have specific functions within the CPU and hold the program state.
What is the purpose of the Index Register (IX)?
It is used for index addressing operations, especially in assembly code.
What is the function of the Memory Data Register (MDR), also known as the Memory Buffer Register (MBR)?
It stores data that has just been read from memory or is about to be written to memory.
What is the Status Register (SR) used for?
It contains bits (flags) that indicate conditions during arithmetic or logic operations.
What does the Memory Address Register (MAR) do?
It stores the address of the memory location currently being read from or written to.
Name the four flags in a Status Register.
- Carry flag (C)
- Negative flag (N)
- Overflow flag (V)
- Zero flag (Z)
What does the Carry Flag (C) indicate?
A carry has occurred after an addition operation.
When is the Negative Flag (N) set to 1?
When the result of a calculation is negative.
What does the Overflow Flag (V) represent?
An arithmetic operation has resulted in an overflow.
What does the Zero Flag (Z) indicate?
The result of an arithmetic or logic operation is zero.
What do the flags indicate in this example operation: 01110111 + 00111000 = 10101111?
N = 1 (negative result, incorrect for positive numbers)
V = 1 (overflow occurred)
C = 0
Z = 0
What do the flags indicate in this example operation: 10001000 + 11000111 = 101001111?
N = 0 (non-negative result, correct for negatives)
V = 1 (overflow occurred)
C = 1 (carry generated)
Z = 0
Name some other possible flags besides the main four in the course.
Parity flag, interrupt flag, half-carry flag.
What is the role of system buses in a computer?
System buses are used for parallel transmission of data, with each wire transmitting one bit at a time.
Name three buses in the Von Neumann architecture.
Address bus, data bus, control bus.
What is the purpose of the address bus?
It carries addresses throughout the computer system and is unidirectional.
Why is the width of the address bus important?
A wider bus allows more memory locations to be addressed at any given time.
How many memory locations can a 16-bit address bus access?
2¹⁶ or 65,536 memory locations.
What is the function of the data bus?
It is bidirectional and carries data, which can be addresses, instructions, or numerical values, between the CPU, memory, and input/output devices.
How does the width of the data bus affect computer performance?
A wider data bus allows larger word lengths to be transported, improving performance.
What is the purpose of the control bus?
It is bidirectional and carries control signals from the control unit to other computer components.
How does the system clock contribute to computer operations?
It produces timing signals to synchronise all operations in the computer.
What is the impact of increasing clock speed on computer performance?
It increases processing speed but may not necessarily improve overall performance due to other limiting factors.
What are the risks of overclocking a CPU?
- Execution of instructions outside design limits, causing unsynchronised operations.
- Frequent crashes and instability.
- Overheating, leading to unreliable performance.
What is cache memory, and how does it improve processor performance?
Cache memory is high-speed SRAM that stores frequently used instructions and data for faster access compared to main memory.
Why is SRAM used in cache memory instead of DRAM?
SRAM does not require refreshing and has faster access times.
How does the use of multiple cores in a CPU affect performance?
Multiple cores improve performance by dividing tasks, but communication between cores reduces the potential performance gain.
What is the difference between dual-core and quad-core CPUs in terms of performance?
- Dual-core CPUs have one channel, and communication between cores reduces performance slightly.
- Quad-core CPUs have six channels, requiring more communication and significantly reducing potential performance.
What are the factors that influence computer performance?
- Width of address and data buses
- Clock speed
- Cache memory usage
- Number of CPU cores
How does increasing bus width affect computer performance?
It increases the system’s performance and speed by allowing more data and memory locations to be addressed.
What are the key methods to improve a computer’s performance?
- Increasing bus width
- Increasing clock speed
- Using multi-core CPUs
- Employing cache memory
What is the primary function of computer ports?
To connect input and output devices to a computer, with the interaction controlled by the control unit.
What is USB, and why is it significant?
The Universal Serial Bus (USB) is an asynchronous serial data transmission method that has become the standard for transferring data between computers and devices.
How does a USB port detect and recognise a connected device?
- A small change in voltage on the data wires signals the presence of a device.
- The computer automatically recognises the device and loads the appropriate driver.
- If no driver is available, the user is prompted to download the required software.
What are the advantages of the USB system?
- Automatic detection and driver installation for connected devices.
- Connectors are unidirectional, preventing incorrect connections.
- It is the industry standard with extensive support.
- Supports multiple data transmission rates.
- Newer USB standards are backward compatible.
What are the limitations of the USB system?
- Limited transmission rate (less than 500 megabits per second).
- Maximum cable length is about five metres.
- Older USB standards (e.g., 1.1) may lose support in the future.
What is the purpose of an HDMI port?
To output high-definition audio and video signals from a computer to an HDMI-enabled device.
Why was HDMI introduced, and what did it replace?
HDMI was introduced as a digital replacement for the older analogue Video Graphics Array (VGA) system.
What features of modern HD televisions make VGA technology obsolete?
- Widescreen format (16:9 aspect ratio).
- Higher pixel density (e.g., 1920 × 1080).
- Faster refresh rates (e.g., 120Hz).
- Wider range of colours (up to 4 million variations).
How does HDMI support the requirements of modern HD televisions?
By providing increased bandwidth (around 10 gigabits per second) for transmitting high-quality sound and visual data.
How does HDMI offer piracy protection?
HDMI uses High-Bandwidth Digital Copy Protection (HDCP), which employs authentication protocols to ensure secure data transmission between devices.
What is HDCP, and how does it work?
HDCP (High-Bandwidth Digital Copy Protection) is an authentication protocol that checks the key of a connected device (e.g., an HD television) to enable secure handshaking before transmitting data.
What is VGA, and when was it introduced?
Video Graphics Array (VGA) is an analogue technology introduced in the late 1980s, supporting a resolution of 640 × 480 pixels and a refresh rate of up to 60Hz with 16 colours.
What are the advantages of VGA?
- Simpler technology with only one standard.
- Easy to split the signal and connect multiple devices.
- Secure connection.
What are the disadvantages of VGA?
- Outdated analogue technology.
- Prone to bending pins during connection.
- Requires high-grade cables to avoid signal distortion.
What are the advantages of HDMI?
- Supports modern digital systems with fast data transfer.
- Improved security against piracy.
- Current standard for televisions and monitors.
What are the disadvantages of HDMI?
- Fragile connections that can break easily.
- Limited cable length for maintaining signal quality.
- Five different cable/connection standards exist.
What is the fetch-execute cycle in a processor?
It is the process where the CPU fetches, decodes, and executes instructions from memory.
Describe the fetch phase of the fetch-execute cycle.
- The PC provides the address of the next instruction.
- The address is copied to the Memory Address Register (MAR) via the address bus.
- The instruction at the MAR address is copied to the Memory Data Register (MDR).
- The MDR content is transferred to the Current Instruction Register (CIR).
- The PC increments by 1 to point to the next instruction.
Describe the execute phase of the fetch-execute cycle.
- The decoded instruction in the CIR generates control signals.
- Signals are sent via the control bus to the appropriate system components.
- The instruction is executed in its logical sequence.
What happens after an instruction is executed in the fetch-execute cycle?
The system checks for any interrupts. If none are present, the cycle restarts. If an interrupt is detected, it is serviced before restarting the cycle.
How does the fetch-execute cycle use system buses?
Address Bus: Transfers the memory address from the PC to the MAR.
Data Bus: Transfers data and instructions to and from memory.
Control Bus: Sends signals to components for instruction execution.
Fetch-decode-execute cycle in Register Transfer Notation RTN:
MAR ← [PC] contents of PC copied into MAR PC ← [PC] + 1 PC is incremented by 1 MDR ← [[MAR]] data stored at address shown in MAR is copied into MDR CIR ←[MDR] contents of MDR copied into CIR
Why are double brackets used in MDR ← [[MAR]] in RTN?
Double brackets indicate that the data stored at the address shown in MAR (not the MAR contents itself) is being copied into MDR.
What does the RTN instruction MAR ← [PC] mean?
The contents of the Program Counter (PC) are copied into the Memory Address Register (MAR).
What does the RTN instruction PC ← [PC] + 1 mean?
The Program Counter (PC) is incremented by 1.
What does the RTN instruction MDR ← [[MAR]] mean?
The data stored at the address shown in the Memory Address Register (MAR) is copied into the Memory Data Register (MDR).
What does the RTN instruction CIR ← [MDR] mean?
The contents of the Memory Data Register (MDR) are copied into the Current Instruction Register (CIR).
What is the difference between abstract and concrete RTN?
- Abstract RTN is a generic notation that applies to any system.
- Concrete RTN is specific to a particular machine, such as a RISC computer.
What is an example of concrete RTN for a RISC computer?
instruction_interpretation := (¬Run/Start → Run ← 1; instruction _interpretation): Run → (CIR ← M[PC]:PC ← PC + 4; instruction _ execution)
What is the function of the interrupt register in the fetch-execute cycle?
The interrupt register detects and records interrupts by changing one of its bits.
How does the CPU check for interrupts during the fetch-execute cycle?
The CPU checks the interrupt register bit by bit at the next fetch-execute cycle.
What happens if the CPU detects an interrupt in the interrupt register?
- The CPU decides whether to service or ignore the interrupt based on its priority.
- If serviced, the CPU stops its current task and stores the contents of its registers.
What is an Interrupt Service Routine (ISR)?
The ISR is a program that handles interrupts by executing appropriate actions when an interrupt occurs.
What happens after an interrupt is fully serviced?
- The interrupt register is reset.
- The contents of the registers are restored.
- The CPU resumes its previous task.
What is an interrupt in computing?
An interrupt is a signal sent from a device or software to the processor, causing it to temporarily stop its current task and service the interrupt.
What are five common causes of interrupts?
- A timing signal
- Input/output processes (e.g., disk drive ready for data)
- A hardware fault (e.g., printer paper jam)
- User interaction (e.g., pressing <CTRL><ALT><BREAK>)</BREAK></ALT></CTRL>
- A software error (e.g., missing .exe file or division by zero)
How does a processor respond when it receives an interrupt?
The processor either continues its current task or stops to service the device/program that generated the interrupt, depending on the interrupt’s priority.
What is the importance of interrupt priority?
The computer must identify the interrupt type and establish its priority to determine whether it should be serviced immediately or deferred.
How do interrupts allow multitasking?
Interrupts enable computers to handle multiple tasks simultaneously, such as downloading a file while playing music.
What happens to the current task when an interrupt occurs?
The current task’s status, including the contents of the program counter and registers, is saved before servicing the interrupt.
What is an Interrupt Service Routine (ISR)?
The ISR is the process executed to handle an interrupt by loading the start address into the program counter and executing necessary actions.
What happens after an interrupt has been serviced?
The processor reinstates the saved status of the interrupted task by retrieving the saved register contents, allowing it to resume execution from where it left off.
