Computer Architecture and Time-Slicing

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Questions and Answers

What does time-slicing allow a computer to achieve?

Executing one program continuously without interruptions.

Limiting CPU usage to only one program at a time.

Running multiple programs only on separate CPU cores.

Running multiple programs virtually simultaneously on a single CPU. (correct)

In the context of time-slicing, what is meant by 'subtasks'?

Independent processes that do not interact with each other.

Tasks that are executed simultaneously on multiple CPU cores.

Complete programs that run in isolation without any order.

Divided segments of a program that can be processed in a time slice. (correct)

How does a CPU handle two programs when they are given time slices in turn?

By alternating between the programs for short time intervals. (correct)

By allowing one program to finish before starting the other.

By executing both programs in parallel on a single core.

By assigning a static amount of time to each program.

What would happen if a higher priority program is running alongside a lower priority program during time-slicing?

The higher priority program may receive more frequent time slices. Signup and view all the answers

Which of the following best describes the structure of subtasks in both independent processes?

Subtasks are labeled sequentially and must follow a strict order. Signup and view all the answers

What is one limitation of increasing clock speed in a processor?

Increased power dissipation Signup and view all the answers

Which method does NOT contribute to increasing computational speed in a processor?

Adding more memory Signup and view all the answers

What does instruction pipelining achieve in a CPU?

Allows simultaneous execution of multiple instructions Signup and view all the answers

What role does an operating system play in a concurrent system?

It enables multiple tasks to run concurrently Signup and view all the answers

How does time-slicing contribute to CPU efficiency?

By allowing multiple tasks to share CPU time Signup and view all the answers

What is the benefit of using multiple processors in a concurrent system?

Allows faster completion of tasks by parallel processing Signup and view all the answers

What capability does autonomous peripheral operation provide to a CPU?

Improved handling of external data delays Signup and view all the answers

Which statement best describes a concurrent system?

It gives the illusion of simultaneous task execution. Signup and view all the answers

What is a consequence of increasing the clock frequency in CPUs?

Increased power dissipation Signup and view all the answers

What formula represents the relationship of dynamic power dissipation in a switching logic gate?

Pav = fclk C Vdd² Signup and view all the answers

Which strategy does NOT help in reducing dynamic power consumption in CPUs?

Increasing supply voltage Signup and view all the answers

What limit affects the ability to continually increase clock speed in CPUs?

Power dissipation limits Signup and view all the answers

What is a benefit of operating a CPU at the lowest possible voltage?

Decreased power consumption Signup and view all the answers

How are CPUs generally designed to process data?

Synchronous operation Signup and view all the answers

What do features like instruction pipelining and multiple CPUs aim to achieve?

Increase CPU efficiency Signup and view all the answers

Which mechanism can be used to reduce power consumption in microcontrollers according to the content?

Clock-gating Signup and view all the answers

What characteristic of a CPU running without an operating system defines it as a ‘bare metal’ system?

It executes instructions in a strict sequence. Signup and view all the answers

In the context of interleaved processing, what does 'totally ordered tasks' refer to?

Program instructions that always occur in the same order for fixed data. Signup and view all the answers

How do interleaved processing and parallel processing differ?

Interleaved processing executes tasks in a strict sequence, parallel processing executes them simultaneously. Signup and view all the answers

What role do machine code branch instructions play in a bare metal system?

They enable the CPU to skip parts of the instruction list. Signup and view all the answers

In interleaved processing, what happens to tasks from two different programs?

Fixed numbers of lines are executed alternately from each program. Signup and view all the answers

What is a key consideration when trying to make an algorithm run faster?

The order of execution of higher level programming instructions. Signup and view all the answers

What dictates the execution order of instructions in a totally ordered set?

The input data provided. Signup and view all the answers

What form of processing allows two programs to be executed in conjunction without an operating system?

Interleaved Processing. Signup and view all the answers

What is a thread in the context of parallel multithreading?

A section of code that can be run concurrently within a program. Signup and view all the answers

In time-slice multi-threading, what is necessary for the CPU to manage multiple threads?

An operating system layer to track CPU states. Signup and view all the answers

Why must data associated with a process be shared among threads?

Threads cannot access the main CPU memory directly. Signup and view all the answers

What is a potential issue that arises from shared data in multi-threading?

Data corruption or inconsistent state. Signup and view all the answers

What distinguishes parallel multithreading from time-slice multi-threading?

Parallel can run threads concurrently on separate cores; time-slice cannot. Signup and view all the answers

What does the operating system do in a time-slice multi-threading scenario?

Switches the CPU's state between different threads. Signup and view all the answers

What is an essential part of dealing with data sharing between threads?

Establishing a common data access point for threads. Signup and view all the answers

Why can a single core CPU only run one thread at a time in a time-slice system?

It can only execute one machine code instruction at a time. Signup and view all the answers

What is a characteristic of cooperative multitasking?

Tasks decide when to yield control of the CPU. Signup and view all the answers

What is the purpose of yielding in cooperative multitasking?

To give other tasks a chance to run. Signup and view all the answers

Which of the following is a disadvantage of cooperative multitasking?

It can cause delays if a task waits for resources. Signup and view all the answers

In a time-sliced concurrent system, what is the main challenge faced by the operating system?

Finding CPU time for multiple threads to run. Signup and view all the answers

Why might cooperative multitasking lead to an unresponsive system?

Tasks may not yield control in a timely manner. Signup and view all the answers

How is cooperative multitasking implemented in C++11?

By calling std::this_thread::yield(). Signup and view all the answers

What is the main responsibility of the cooperative scheduler in a cooperative multitasking system?

To wait for a process to yield the CPU. Signup and view all the answers

Which threading strategy allows a programmer to view their process as the only one running?

Pre-emptive multitasking. Signup and view all the answers

Study Notes

Concurrent Systems - Week 1

Background: Examples of concurrent systems include PC, cruise control, and air traffic control. Concurrent systems are needed for speed or to facilitate many simultaneous processes.
WK1 (Task10) Autonomous Peripherals: Efficient CPU use in microcontrollers relies on peripheral logic (e.g., UART, Timer) that can operate simultaneously with the CPU. Bit banging is a less efficient method of communication. DMA (Direct Memory Access) is a fast method where peripherals communicate with memory directly, without CPU intervention. Sleep modes are used in battery-powered devices to conserve energy.
WK1 (Task1) Faster Processing: Four key ways to increase computational speed: increasing CPU clock speed, using CPU features (instruction pipelining, autonomous peripherals), using multiple CPUs, and using time-slicing (task interleaving). Clock speed increases heat and power consumption, with limitations on miniaturization and quantum tunnelling.
Time-slicing: Multiple tasks can run on a single CPU core which makes it appear to run simultaneously through time-slicing. Algorithms can be ordered, partially, or unordered. The order of execution does not always affect the outcome.

Concurrent Systems - Week 2

WK2 (Task2) Processes & Threads: A computer program consists of machine code (binary), initial data and metadata for the compiler. A program on disk is a program. Copy the program to memory to run, it is known as a process, and each program can have one or more threads. Multiple threads may share resources. The process context block stores information about the process and its threads. The thread context has information about the CPU instructions. Processes run concurrently. Multi-threading handles CPU time-slicing between threads. Hyperthreading gives one CPU core two virtual cores.

Concurrent Systems - Week 3

Wk3 Cooperative and pre-emptive multitasking:
- Cooperative multitasking: The tasks themselves control when they relinquish ownership of the CPU.
- Pre-emptive multitasking OS: The OS scheduler controls when a task gives up the CPU.
- Event-driven programming: A mechanism where tasks are triggered by events/hardware changes, useful in GUI programs. This reduces the overhead of thread context switching.
- OS implementations:
  - Containers: A lightweight approach to virtualization, with multiple isolated processes running,
  - Virtual Machines (VMs): A virtualized operating system running on another OS to keep processes separate.
- CPU states and privileged access: Operating systems use privileged modes to restrict access to hardware resources.

Concurrent Systems - Week 4

WK4 Thread Programming:
- Creating Threads: Using the std::thread library in C++11.
- Passing Arguments: Passing data to a thread function .
- Thread Termination: Using detach() or join() to terminate threads.
- Thread Synchronization: Managing threads which access shared resources.
  - Atomicity: ensure operations on shared data are indivisible.
  - Mutexes, Condition Variables, Semaphores, Barriers: Primitives for safe access to shared data, efficiently synchronizing threads.
Revisiting Amdahl's Law: The performance gain from parallel processing is limited by the portion of the algorithm that cannot be parallelized.

Concurrent Systems - Week 5

Retrieving results from a thread: Using std::promise and std::future to communicate results between threads.
Implementing inter-thread concurrency: Solutions to race conditions, deadlock, livelock, and resource starvation.
- Atomic instructions: Operations that are indivisible to ensure data integrity.
- Mutexes: A mutual exclusion lock for controlling access to shared variables.
- Condition Variables: Wait for a condition to become true.
- Counting Semaphores: Limiting the access to the shared resource.
Synchronisation Barriers: Implementing points for different tasks to wait or coordinate.

Concurrent Systems - Week 7

Inter-process Communication (IPC):
- Shared Memory: One or more processes share a common memory space.
- Sockets: Point-to-point communication, primarily over a network.
- Pipes: A unidirectional communication channel between processes
- Named Pipes: Allows communications between processes, even on different computers
- Channels: An umbrella term for methods that offer a direct pathway for data exchanges between processes.
- Message Queues: Data is temporarily stored for synchronization
- Publish/subscribe: Used for communication between multiple processes, one publisher, many subscribers.
Temporal behavior:
- Synchronous: Processes wait for each other in a predictable order
- Asynchronous: Processes run independently

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Description

This quiz explores key concepts related to computer architecture and time-slicing, including CPU handling of multiple tasks, the structure of subtasks, and the impact of clock speed. Test your understanding of how operating systems manage concurrent systems and the efficiency gains from different processing methods.