Processor Types and Specifications

2020-02

Which of the following is/are TRUE regarding the Von Neumann architecture?

Single Instruction, Multiple Data (SIMD)
Single Program, Multiple Data (SPMD)
Single Instruction Stream, Single Data Stream (SISD)
Multiple Instruction, Multiple Data (MIMD)
Multiple Instruction, Single Data (MISD)

Solution

The correct option regarding the Von Neumann architecture is (c) Single Instruction Stream, Single Data Stream (SISD).

The Von Neumann architecture is a foundational computer architecture where both data and instructions are stored in the same memory space. This architecture is characterized by a single processing unit that executes instructions sequentially, one at a time, and processes data from a single stream. This aligns with the definition of SISD (Single Instruction, Single Data) in Flynn's Taxonomy, which categorizes computer architectures based on their instruction and data streams.

SISD (Single Instruction, Single Data):

This describes a uniprocessor machine that executes a single instruction on a single data stream sequentially, which is the core principle of the Von Neumann architecture.

SIMD (Single Instruction, Multiple Data):

This involves executing the same instruction on multiple data streams simultaneously, often found in parallel computing systems.

First microprocessor with SIMD: Intel i860 (1989)^[1]
First widely adopted SIMD in consumer CPUs: Intel Pentium MMX (1997)

SPMD (Single Program, Multiple Data):

This is a parallel programming model where multiple processors execute the same program on different parts of the data, but potentially with different control flow.

MIMD (Multiple Instruction, Multiple Data):

This is a parallel programming model where multiple processors execute different instructions on different parts of the data, potentially with different control flow.

Definition

MIMD means that multiple processors (or cores) can execute different instructions on different data at the same time.
Each processor can run its own program independently of the others.

How it differs from SIMD

Feature	SIMD (Single Instruction, Multiple Data)	MIMD (Multiple Instruction, Multiple Data
Instructions	Single instruction applied to all data	Different instructions on different data
Processors	Work in lockstep	Work independently
Flexibility	Less flexible, good for repetitive tasks like vector operations	Very flexible, good for general-purpose parallel tasks
Example	GPU graphics processing	Multi-core CPU running different programs

Key Characteristics

Each processor has its own control unit and local memory (sometimes shared memory in some systems).
Can execute completely independent tasks in parallel.
Suitable for complex systems like supercomputers or multi-core servers.

Examples

Multi-core CPUs running multiple applications simultaneously.
Distributed computing systems where each node processes a different task (like web servers in a cluster).
Modern supercomputers like IBM Blue Gene or Cray systems.

MISD (Multiple Instruction, Single Data):

This is a type of parallel computer where multiple processors execute different instructions on different data streams simultaneously, representing a higher level of parallelism.

2021-08

Which of the following is/are logical component(s) of a CPU?

Control Unit
Power Unit
Arithmetic and Logic Unit
Main Memory
BIOS

Solution

The logical components of a CPU are the Control Unit (CU) and the Arithmetic and Logic Unit (ALU).

Control Unit (CU):

This component controls and coordinates the operations of the CPU, including fetching instructions, decoding them, and managing the flow of data.

Power Unit:

No, the CPU doesn’t have a “power unit.” Power comes from the power supply (PSU), which is separate hardware.

Arithmetic and Logic Unit (ALU):

This component performs arithmetic and logical operations on the data, such as addition, subtraction, multiplication, and division.

Main Memory (MMU):

Not part of the CPU itself. It’s a separate component connected to the CPU.

BIOS (Basic Input/Output System)

Stored in ROM on the motherboard, not inside the CPU. It initializes hardware and starts the operating system.

Therefore, the correct options are (a) and (c).

2022-11

Which of the following is/are TRUE regarding the Microprocessor in modern computers?

Also known as the Central Processing Unit (CPU).
Microprocessor is a non-programmable, single purpose device.
Initially the microprocessors store instructions in a concurrent manner in memory.
It is the unit which performs all the calculations in a computer system.
Instructions in a microprocessor are fetched from the Arithmetic and Logic Unit (ALU).

Solution

(a) Also known as the Central Processing Unit (CPU).

This statement is TRUE. Modern CPUs are implemented on integrated circuit microprocessors, and the terms are often used interchangeably in the context of personal computers.

(b) Microprocessor is a non-programmable, single purpose device.

This statement is FALSE. Microprocessors are multipurpose, programmable devices designed to execute various instructions and perform diverse tasks.

(c) Initially the microprocessors store instructions in a concurrent manner in memory.

This statement is FALSE. Instructions are typically fetched sequentially from memory, though modern processors employ techniques like pipelining and caching to improve performance, which can give the appearance of concurrency.

(d) It is the unit which performs all the calculations in a computer system.

This statement is FALSE. While the microprocessor (specifically the ALU within it) performs the arithmetic and logical calculations, other components like GPUs also handle specialized calculations, especially in modern systems.

(e) Instructions in a microprocessor are fetched from the Arithmetic and Logic Unit (ALU).

This statement is FALSE. Instructions are fetched from memory (e.g., RAM) and then processed by the microprocessor's control unit, which then directs the ALU to perform operations based on those instructions.

Therefore, the only true statement is (a).

2023-10

What is the clock frequency of a CPU that is having a clock cycle time of 4 nano seconds in a 500MHz frequency?

250MHz
500MHz
0.25MHz
0.5MHz
2.5MHz

To determine the clock frequency of a CPU, we use the relationship between frequency and clock cycle time:

Problem: What is the clock frequency of a CPU that is having a clock cycle time of 4 nanoseconds?

Solution

Understand the relationship:

. Clock frequency (\(f\)) is the reciprocal of the clock cycle time (\(T\)). This can be expressed as: \(f=\frac{1}{T}\).

Convert units:

The given clock cycle time is 4 nanoseconds (ns).

Calculate the frequency:

Substitute the converted time into the formula: \(f=\frac{1}{4\times 10^{-9}\text{s}}=0.25\times 10^{9}\text{Hz}\).

Convert to MHz:

Since \(1\text{MHz}=10^{6}\text{Hz}\), convert the frequency to MHz: \(0.25\times 10^{9}\text{ Hz}=0.25\times 10^{3}\text{ MHz}=250\text{ MHz}\).

Answer: The clock frequency of the CPU is 250 MHz.

Therefore, the correct option is (a) 250MHz.

2023-14

Which of the following is/are considered as a responsibility of Program Counter in the CPU?

Coordinates and manages the execution of instructions, control data flow between different CPU components, and ensures the proper sequencing of operations in accordance with the program's instructions.
Holds the current instruction being executed, allowing the CPU to decode and execute it.
Performs arithmetic operations and logical operations on data, enabling the CPU to carry out mathematical calculations and make logical decisions.
Provides high-speed access to frequently used data and instructions, reducing the time it takes to fetch data from main memory.
Keeps track of the memory address of the next instruction to be fetched and executed, ensuring the sequential execution of program instructions.

The responsibility of the Program Counter (PC) in the CPU is to keep track of the memory address of the next instruction to be fetched and executed, ensuring the sequential execution of program instructions. Therefore, (e) is the correct option.

Here's why other options are incorrect:

(a) This describes the function of the Control Unit (CU), not the Program Counter.
(b) This describes the function of the Instruction Register (IR), which holds the instruction currently being executed after it's fetched from memory.
(c) This describes the function of the Arithmetic Logic Unit (ALU), which performs calculations and logical operations.
(d) This describes the function of the Cache memory, which provides fast access to frequently used data and instructions.

2023-29

Which of the following statements describes a responsibility of the Fetch phase of the Fetch-Decode-Execute cycle within a program's execution?

Determines the operands involved in the instruction, including their locations and addressing modes.
Go to the main memory and bring the instruction found at the address in the Memory Address Register, placing this instruction in the Instruction Register.
Performs the actual operation specified by the OPCODE of the instruction.
Control signals are generated based on the opcode and operands, preparing the CPU for the execution phase.
Copy the contents of the Program Counter to the Memory Address Register.

Solution

The correct statement describing a responsibility of the Fetch phase of the Fetch-Decode-Execute cycle is (b) Go to the main memory and bring the instruction found at the address in the Memory Address Register, placing this instruction in the Instruction Register.

Explanation:

The Fetch phase is the first stage of the Fetch-Decode-Execute cycle in a CPU. Its primary responsibility is to retrieve the next instruction from memory.

Program Counter (PC): The PC holds the address of the next instruction to be fetched.
Memory Address Register (MAR): The address from the PC is copied to the MAR.
Main Memory: The CPU then uses the address in the MAR to access the main memory and retrieve the instruction located at that address.
Instruction Register (IR): The fetched instruction is then placed into the Instruction Register (IR) for subsequent decoding.

The other options describe responsibilities of different phases:

(a) Determines the operands involved in the instruction, including their locations and addressing modes: This describes part of the Decode phase, where the instruction is interpreted.
(c) Performs the actual operation specified by the OPCODE of the instruction: This describes the Execute phase, where the operation is carried out.
(d) Control signals are generated based on the opcode and operands, preparing the CPU for the execution phase: This also relates to the Decode phase and the preparation for execution.
(e) Copy the contents of the Program Counter to the Memory Address Register: While this is a step within the fetch phase, it's not the complete description of the responsibility, which involves retrieving the instruction from memory and placing it in the IR.

for more info vist: Computer Organization | Different Instruction Cycles

2024-10

Which of the following is/are NOT (a) component(s) of a CPU?

Control Unit
Program Counter
Main Memory
System Clock
ALU

Solution

The component that is NOT part of a CPU is (c) Main Memory, (d) System Clock.

Explanation:

The Central Processing Unit (CPU) is the "brain" of a computer, responsible for executing instructions and performing calculations. It consists of several key components:

Control Unit (CU): This unit manages and coordinates the operations of the CPU, fetching instructions from memory, decoding them, and directing other components to execute them.
Arithmetic Logic Unit (ALU): The ALU performs all arithmetic operations (like addition, subtraction) and logical operations (like comparisons).
Registers: These are small, high-speed storage locations within the CPU that hold data and instructions temporarily during processing. The Program Counter is a specific type of register that stores the memory address of the next instruction to be executed.

Main Memory (RAM):On the other hand, it is a separate component of the computer system, external to the CPU. It serves as a larger, slower storage area where the CPU can temporarily store data and programs that are actively being used. While the CPU frequently interacts with main memory to fetch instructions and data, it is not considered a component of the CPU itself.

System Clock: This component generates timing signals that synchronise all operations within the CPU and other computer components. The system clock is a separate unit from the CPU. It is an electronic device, typically a crystal oscillator, located on the computer's motherboard.

How it works ⏰

The system clock generates a steady stream of electronic pulses, acting as the main metronome for the entire computer system. These pulses are used to synchronize the operations of all components on the motherboard, including the CPU, RAM, and various buses.
The CPU has its own internal clock, often referred to as the CPU clock or processor clock, which is derived from and is a multiple of the system clock's frequency. This allows the CPU to execute instructions at a much higher rate than the system clock itself. For example, a system clock might run at 100 MHz, while a modern CPU multiplies this signal to achieve a clock speed in the gigahertz (GHz) range.

System Clock vs. CPU Clock

System Clock: This clock, also known as the base clock or front-side bus (FSB) clock (though less common in modern architectures), sets the fundamental timing for the motherboard. It's the reference signal that synchronizes all other components.
CPU Clock:This is the speed at which the CPU processes instructions. It is determined by multiplying the system clock speed by a clock multiplier. This multiplier is set by the CPU and motherboard to achieve the advertised processor speed.

2024-14

Which of the following techniques can improve CPU throughput

Increasing the clock speed of the CPU.
Increasing the number of cycles per instruction.
Increasing the CPU clock cycle time.
Reducing the number of cycles per instruction.
Reducing the CPU clock cycle time.

Explanation:

CPU throughput, or performance, is generally improved by increasing the rate at which the CPU can execute instructions. This can be achieved through:

Increasing the clock speed of the CPU: Clock speed, measured in Hertz (e.g., GHz), determines how many cycles the CPU can perform per second. A higher clock speed means more cycles per second, leading to faster instruction execution and thus improved throughput.
Reducing the CPU clock cycle time: Clock cycle time is the inverse of clock speed. If the clock cycle time is reduced, it means the clock speed is increased, allowing the CPU to complete more cycles and execute instructions faster, thereby improving throughput.
Reducing the number of cycles per instruction (CPI): While not explicitly listed as a primary answer, reducing the average number of clock cycles required to execute each instruction also directly improves CPU performance and throughput. This is achieved through architectural improvements and efficient instruction set design.

Let's look at why the other options are incorrect:

Increasing the number of cycles per instruction: This would mean each instruction takes longer to execute, thus decreasing throughput.
Increasing the CPU clock cycle time: This is the opposite of reducing the clock cycle time, meaning the clock speed is decreased, which would reduce throughput.

References

S. Mueller, Upgrading and Repairing PCs, 22nd ed., Indianapolis, IN, USA: Que Publishing, 2015, p. 113.