OS CPU

the operating system works closely with?

processor, processes, and threads

Processor

executes instructions

Thread

performs a sequence of instructions within a process

allows multiple tasks to make progress during overlapping periods

Concurrency

A processor

also known as the Central Processing Unit (CPU), is the hardware component that executes instructions from computer programs.

Why the Processor Is Important

Without a processor, software programs cannot execute instructions. Applications such as browsers, games, operating systems, and office software all depend on processor resources

instruction cycle.

The CPU generally processes instructions through

Fetch

The processor retrieves an instruction from memory.

Decode

The processor determines what the instruction means and what operation must be performed

Execute

The processor performs the required operation.

Store

The result is stored in a register or memory.

Arithmetic Logic Unit

performs arithmetic and logical operations

Control Unit (CU)

coordinates the activities of the processor

Registers

are very small and very fast storage locations inside the processor

Program Counter (PC)

Contains the address of the next instruction.

Instruction Register (IR)

Contains the instruction currently being processed.

General-Purpose Registers

Store temporary data used during computation

Registers

are faster than ordinary RAM because they are located directly within the processor

Cache memory

is high-speed memory used to store frequently accessed data and instructions.

Common cache levels include

L1 Cache

⦁ Very fast

⦁ Small capacity

⦁ Closest to the CPU core

L2 Cache

⦁ Larger than L1

⦁ Slightly slower

L3 Cache

⦁ Larger than L1 and L2

⦁ Often shared among CPU

If frequently used information is already in cache, the CPU can access it faster instead of retrieving it from slower main memory.

Cache Is Important

CPU core

is an individual processing unit within a processor

Clock speed

indicates how quickly a processor's clock operates.

quad-core

processor has four processing cores

This allows multiple threads to potentially execute simultaneously.

More CPU cores

Having BLANK does not automatically make every program faster. The software must be designed to take advantage of multiple cores.

⦁ MHz – megahertz

⦁ GHz – gigahertz

Clock speed is commonly measured in:

process

is a program that is currently executing

Process Control Block (PCB).

The operating system maintains information about processes through a structure commonly

When the operating system switches between processes, it needs to save and restore information about each process. The PCB helps the operating system manage this information

Why PCB Is Important

New

The process is being created.

Ready

The process is waiting for CPU time.

Running

The process is currently being executed by the CPU.

Waiting/Blocked

The process is waiting for an event or resource.

Terminated

The process has finished execution.

Basic Flow

New

↓

Ready

↓

Running

↓

Terminated

thread

is the smallest unit of execution that can be scheduled by an operating system

Why Threads Are Used

allow an application to perform different activities without requiring a separate process for every activity

single-threaded process

has one thread of execution.

multithreaded process

contains multiple threads.

Responsiveness

The application can continue responding while another thread performs a background task.

Resource Sharing

Threads within the same process can share memory and resources.

Economy

Creating threads generally requires fewer resources than creating separate processes.

Scalability

Multithreaded applications can take advantage of multiple CPU cores.

Complexity

Programs become more difficult to design and debug.

Deadlocks

Threads may become permanently blocked.

Race Conditions

Threads may interfere with shared data.

Synchronization Overhead

Locks and other synchronization mechanisms can reduce performance if used excessively.

User-level threads

are managed by a user-level thread library or runtime environment

Advantages of User-level threads

⦁ Fast thread management

⦁ Lower overhead

⦁ Flexible implementation

disadvantages of User-level threads

⦁ Limited kernel awareness

⦁ Blocking behavior can be problematic in some models

⦁ Parallel execution depends on the underlying threading model

Kernel-level threads

are managed directly by the operating system kernel.

The operating system can schedule individual threads.

Advantages Kernel-Level Threads

⦁ Better support for multicore systems

⦁ Individual threads can be scheduled

⦁ A blocked thread does not necessarily block other threads

Disadvantages Kernel-level threads

⦁ More operating-system overhead

⦁ Thread management can be more expensive

Concurrency

to manage multiple tasks during overlapping periods of time.

Concurrency does not necessarily mean that tasks execute at exactly the same moment

Parallelism

means executing multiple tasks at the same time using multiple processing resources.