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CAP 2 - Processor Operation and RISC/CISC Processors

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71 Questions

What are the five basic parts of a processor as illustrated in the von Neumann machine?

Memory, Arithmetic Logic Unit, Program Control Unit, Input Equipment, Output Equipment

Which phase involves write back to memory and is usually slower than the other phases in instruction execution?

Memory Access Phase

What is the main differentiation in terms of instruction set architectures classes?

Internal Storage Type

In which storage type are both instructions and operands stored in memory following a specific abstract data type?

Stack Storage Type

Which special register is involved in instructions when using the accumulator storage type?

ACC register

What types of instructions and operands are implicitly on the top of stack in the stack storage type?

ALU operands

Which of the following statements about the accumulator architecture code and the GPR (register-memory) architecture code is correct?

The GPR architecture code has 31.5% fewer memory accesses compared to the accumulator architecture code.

Why are instructions with very different execution times or very different numbers of phases not suitable for a production line (pipeline)?

They can cause pipeline stalls, reducing overall performance.

What is the main advantage of using a Reduced Instruction Set Computer (RISC) architecture over a Complex Instruction Set Computer (CISC) architecture?

Simplified control logic and faster execution times.

In the context of a GPR (register-memory) architecture, what is the purpose of the control unit?

To generate control signals that coordinate the execution of instructions.

What is the main drawback of a single-cycle datapath processor design?

Lower performance compared to pipelined processor designs.

Which component of a processor is responsible for fetching instructions from memory and providing them to the control unit?

Instruction Fetch Unit

Which of the following is NOT one of the five basic parts of a processor with accumulator architecture?

Program status word (PSW)

What is the primary function of the control unit in a processor with accumulator architecture?

To fetch and decode instructions from memory

Which of the following is NOT a class of instruction set architectures (ISAs) mentioned in the text?

Very long instruction word (VLIW)

In the microprogram representation for the processor with accumulator architecture, what is the purpose of the instruction labeled '#15 Jump'?

To load the program counter with the address stored in the data register

What is the purpose of the instruction labeled '#16 Jump if positive' in the microprogram representation?

To jump to the address stored in the data register if the accumulator value is positive

Which of the following instructions is NOT present in the microprogram representation for the processor with accumulator architecture?

Shift

What are the five phases involved in the execution of an instruction in a processor?

Operation code fetch, operation code decode, operands fetch, effective instruction execution, results store

Explain the main difference between the stack and accumulator storage types in instruction set architectures.

In stack storage type, both instructions and operands are stored in memory following the stack data type, while in accumulator storage type, instructions involve a special register (ACC register) and sometimes memory.

Why does the phase involving memory access, such as writing back to memory, impact program performance significantly?

It can be 10 times slower than other phases, affecting the overall execution speed of the program.

What is the primary differentiation factor among instruction set architectures classes?

The internal storage type in a processor.

What is the main advantage of using a Reduced Instruction Set Computer (RISC) architecture over a Complex Instruction Set Computer (CISC) architecture?

RISC architectures are typically more efficient, faster, and easier to optimize due to their simpler instruction set.

Why is a single-cycle datapath processor design considered a drawback in modern processors?

It limits the processor's performance scalability and efficiency due to executing all instructions in a single clock cycle.

Explain why instructions with very different execution times or very different numbers of phases are not suitable for a production line (pipeline) in processor design.

Instructions with very different execution times or very different numbers of phases are not suitable for a production line (pipeline) because they can cause imbalances and bottlenecks in the pipeline. Pipelines work best when all instructions have similar execution times and number of phases, allowing for efficient parallel processing. Differences in these factors can lead to some instructions taking much longer to complete, stalling the pipeline and reducing overall performance.

Describe the main purpose of the control unit in a processor with a GPR (register-memory) architecture.

In a processor with a GPR (register-memory) architecture, the primary function of the control unit is to manage the flow of instructions and data between the various components of the processor. This includes fetching instructions from memory, decoding them, and then orchestrating the appropriate data transfers and arithmetic/logical operations to execute those instructions. The control unit ensures the correct registers are accessed, memory locations are read/written, and that the overall execution of instructions proceeds in the proper sequence.

What is the main differentiation in terms of instruction set architectures (ISAs) classes, and how does this impact processor design?

The main differentiation in ISA classes is between RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures. RISC ISAs typically have a smaller, simpler set of instructions that can be executed in a single clock cycle, while CISC ISAs have a larger, more complex set of instructions that may take multiple clock cycles to execute. This difference in instruction complexity impacts processor design, as RISC processors can be designed with simpler, more efficient pipelines, while CISC processors require more complex control logic and microarchitectures to handle the varied instruction set.

Explain the purpose of the microprogram and the role of the '#15 Jump' and '#16 Jump if positive' instructions in the microprogram representation for a processor with an accumulator architecture.

In a processor with an accumulator architecture, the microprogram represents the low-level control sequence that executes each instruction. The '#15 Jump' instruction is used to transfer control to a different part of the microprogram, allowing the processor to execute a different sequence of microoperations for a given instruction. The '#16 Jump if positive' instruction is a conditional jump that checks the sign of a value (e.g., the accumulator) and transfers control to a different part of the microprogram based on the result. These jump instructions provide the necessary control flow within the microprogram to execute the various instructions in the instruction set.

Contrast the accumulator architecture code and the GPR (register-memory) architecture code in terms of the number of instructions, memory accesses, and the overall efficiency of the two approaches.

The accumulator architecture code in Listing 2.8 has 19 instructions and performs 38 memory accesses (19 fetches and 19 operand fetches), while the GPR (register-memory) architecture code in Listing 2.9 has 15 instructions and performs 26 memory accesses (15 fetches and 11 operand fetches). This represents a 31.5% reduction in memory accesses for the GPR architecture compared to the accumulator architecture. The GPR architecture is more efficient because it can perform more operations using the registers, reducing the need for memory accesses. The fewer instructions and memory accesses in the GPR code also suggest a more compact and optimized implementation compared to the accumulator architecture.

Explain the main drawback of a single-cycle datapath processor design and how it compares to a more advanced pipelined design.

The main drawback of a single-cycle datapath processor design is that it requires all instructions to complete in a single clock cycle, regardless of their complexity. This means that the processor must be designed to accommodate the longest-running instruction, which can lead to inefficient use of the processor's resources and slower overall performance. In contrast, a pipelined design divides the execution of instructions into multiple stages, allowing different instructions to be processed concurrently. This enables the processor to achieve a higher throughput and better utilize its resources, as each stage can be optimized for the specific tasks it needs to perform. However, pipelining also introduces additional complexity in terms of hazard detection and resolution, which must be carefully managed to ensure correct program execution.

Explain the key differences between the stack and load-store classes of instruction set architectures (ISAs) in terms of memory access instructions.

The stack class has push and pop instructions for memory access, while the load-store class has separate load and store instructions for memory access.

Describe the purpose and connections of the key components in the processor with accumulator architecture illustrated in Figure 2.2.

The accumulator (ACC) register is connected to the ALU as its implicit operand. There is also a data register (DR), address register (AR), program counter (PC), and instruction register (IR). The control unit coordinates the operation of these components.

Explain the purpose of the instructions labeled '#15 Jump' and '#16 Jump if positive' in the microprogram representation for the processor with accumulator architecture shown in Figure 2.3.

The '#15 Jump' instruction causes the program counter (PC) to be loaded with the address value stored in the data register (DR), allowing for an unconditional jump. The '#16 Jump if positive' instruction checks if the value in the accumulator (ACC) is positive, and if so, loads the PC with the address in DR to perform a conditional jump.

What is the main advantage of using a Reduced Instruction Set Computer (RISC) architecture over a Complex Instruction Set Computer (CISC) architecture? Provide a specific example to illustrate your answer.

The main advantage of RISC over CISC is simpler instructions that can be executed more quickly. For example, in a RISC architecture, memory access is done via separate load and store instructions, rather than complex instructions like 'load effective address' in CISC that require multiple cycles.

In the context of a general-purpose register (GPR) architecture like MIPS, what is the role of the control unit? Describe two key responsibilities it has during instruction execution.

The control unit in a GPR architecture is responsible for coordinating the datapath components to implement each instruction. Two key responsibilities are: 1) Generating control signals to enable reading/writing of registers and memories, and 2) Determining the next instruction address (e.g. for branches).

What is the main drawback of a single-cycle datapath processor design? Explain how pipelining can help overcome this limitation.

The main drawback is that every instruction, regardless of complexity, must be completed in one cycle, limiting performance. Pipelining overcomes this by breaking instruction execution into stages that can be overlapped, allowing a new instruction to begin each cycle.

The arithmetic logic unit (ALU) operands are explicitly stored on the top of the stack in the stack storage type.

False

The main differentiation in terms of instruction set architectures classes is the internal storage type used in the processor.

True

The phases involving memory access, such as writing data back to memory, are typically faster than the other phases in instruction execution.

False

The control unit in a processor with a general-purpose register (GPR) architecture is responsible for fetching instructions from memory and providing them to the datapath.

True

Reduced Instruction Set Computer (RISC) architectures have a more complex instruction set compared to Complex Instruction Set Computer (CISC) architectures.

False

Instructions with very different execution times or very different numbers of phases are suitable for a production line (pipeline) in processor design.

False

The accumulator register in a processor with accumulator architecture is connected to the ALU as an explicit operand.

False

In the processor with accumulator architecture, the microprogram representation includes an instruction for division.

False

The instruction labeled '#21 Stop' in the microprogram for the processor with accumulator architecture indicates a halt to the processor.

True

In the processor with accumulator architecture, the data register (DR) is never written to memory.

False

The processor with accumulator architecture uses separate instructions for accessing memory compared to the stack storage type.

True

The instruction labeled '#5 Addition' in the microprogram for the processor with accumulator architecture involves subtracting two values before storing the result in memory.

False

The control unit is responsible for fetching instructions from memory and providing them to the processor's datapath.

False

The main advantage of using a RISC architecture over a CISC architecture is that RISC instructions have very different execution times and numbers of phases.

False

In a processor with accumulator architecture, the accumulator register is not one of the five basic parts of the processor.

True

The purpose of the '#15 Jump' and '#16 Jump if positive' instructions in the microprogram representation for the processor with accumulator architecture is to control the flow of execution within the microprogram.

True

The main drawback of a single-cycle datapath processor design is that it can achieve higher performance than a pipelined design.

False

In a GPR (register-memory) architecture, the control unit is responsible for fetching instructions from memory and providing them to the datapath, as well as controlling the execution of the instructions.

True

The five basic parts of a processor include memory, arithmetic logic unit, program ______ unit, input equipment, and output equipment.

control

The ______ unit is responsible for fetching instructions from memory and providing them to the datapath in a GPR (register-memory) architecture.

control

The main differentiation in terms of instruction set architectures classes is the internal ______ type used in the processor.

storage

In the ______ storage type, both instructions and operands are stored in memory following an abstract data type.

stack

The main advantage of using a Reduced Instruction Set Computer (RISC) architecture over a Complex Instruction Set Computer (CISC) architecture is that RISC instructions have very ______ execution times and numbers of phases.

different

The main ______ of a single-cycle datapath processor design is that it can achieve lower performance compared to a pipelined design.

drawback

The ______ register is connected to the ALU as its implicit operand in the processor with accumulator architecture.

accumulator

In the processor with accumulator architecture, the ______ is one of the five basic parts of the processor.

data register

The control unit in a processor with a general-purpose register (GPR) architecture is responsible for ______ instructions from memory and providing them to the datapath.

fetching

The main differentiation in terms of instruction set architectures classes is the internal ______ type used in the processor.

storage

The instruction labeled '______ Jump if positive' in the microprogram representation for the processor with accumulator architecture checks if the accumulator is positive.

#16

The main advantage of using a Reduced Instruction Set Computer (RISC) architecture over a Complex Instruction Set Computer (CISC) architecture is ______.

simplicity

The ______ register in a processor with accumulator architecture is connected to the ALU as an explicit operand.

accumulator

The ______ is responsible for fetching instructions from memory and providing them to the processor's datapath.

control unit

The main drawback of a ______ datapath processor design is that it can achieve lower performance than a pipelined design.

single-cycle

Instructions with very different execution times or very different number of ______ are not suitable for a production line, i.e., a pipeline.

phases

The main advantage of using a ______ architecture over a CISC architecture is that RISC instructions have similar execution times and numbers of phases.

RISC

Study Notes

Processor Operation

  • The processor operation involves the five basic parts: memory, arithmetic logic unit (ALU), program control unit, input equipment, and output equipment.
  • The instruction set architecture defines the processor's instructions, which leads to the design of control and data paths.

Instruction Execution Phases

  • The execution of an instruction can be split into different phases:
    • Operation code fetch
    • Operation code decode
    • Operands fetch
    • Effective instruction execution
    • Results store
  • Phases involving memory access can be 10 times slower than the other phases, impacting program performance.

Instruction Set Architectures Classes

  • The internal storage type in a processor differentiates instruction set architectures into classes:
    • Stack storage type
      • Instructions and operands are stored in memory following the abstract data type
      • ALU operands are implicitly on the top of the stack (TOS)
    • Accumulator storage type
      • Instructions involve the accumulator (ACC) register and sometimes the memory

Processor Architecture

  • The accumulator (ACC) register is connected to the ALU as its implicit operand
  • Other registers include:
    • Data register (DR)
    • Address register (AR)
    • Program counter (PC)
    • Instruction register (IR)

Microprogram

  • A microprogram represents the processor architecture
  • It defines the control unit and the data paths
  • Examples of microprograms include:
    • Load
    • Store
    • Addition
    • Subtraction
    • Multiplication
    • Jump
    • Jump if positive
    • Stop

Instruction Set Architecture Approaches

  • Instructions can be designed with small differences in execution time and phases to suit a production line (pipeline)
  • Examples of instruction set architectures include:
    • RISC (Reduced Instruction Set Computing)
    • CISC (Complex Instruction Set Computing)

Code Examples

  • Listing 2.8: Code for accumulator architecture
    • 19 instructions
    • 19 fetches
    • 38 memory accesses
  • Listing 2.9: Code for GPR (register-memory) architecture
    • 15 instructions
    • 15 fetches
    • 26 memory accesses (31.5% less than accumulator version)

Explore the intricacies of processor operation in Chapter 2, focusing on RISC and CISC processors. Learn about the five basic parts of a processor, the instruction set architecture, and the design of control and data paths.

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