What is a Process in an Operating System?
Summary
TLDRThis lecture delves into the concept of a process in operating systems, explaining its role as a unit of work and its lifecycle through various states such as new, ready, running, waiting, and terminated. It highlights the importance of the operating system in managing processes, the function of the scheduler in process execution, and the concept of preemptive multitasking with time slices for CPU usage. The lecture also touches on the trade-offs between responsiveness and performance in different system types and introduces the process control block that stores essential information about each process.
Takeaways
- 💻 The operating system (OS) acts as the first software layer on top of the hardware, managing applications and system resources.
- 🔧 The OS is responsible for task management, which includes executing programs on the CPU, either by user initiation or the OS itself.
- 📝 A program must be compiled into an executable format like a .jar or .exe file before it can be run on the CPU.
- 🚀 When an executable file is launched, the OS creates a process object in memory, which it manages throughout its lifecycle.
- 🔑 A process is defined as an instance of a program loaded into memory, representing a unit of work in the OS.
- 🌀 A process has various states, starting with 'new', transitioning to 'ready', and then to 'running', 'waiting', and finally 'terminated'.
- ⏱️ The scheduler is a dedicated OS component that selects processes to run on the CPU, implementing preemption to manage CPU time among processes.
- 🔄 Preemptive multitasking allows the CPU to execute parts of different processes in intervals, preventing any single process from monopolizing the CPU.
- 📊 The number of CPU cores affects the system's throughput; more cores allow more processes to run in parallel.
- 🕒 The time limit for CPU usage by a process is known as a time slice, which is crucial for balancing process execution and system responsiveness.
- 🔄 Context switching is the process of changing the currently running process on the CPU, which can impact performance if frequent.
- 🗂️ The process control block (PCB) stores vital information about a process, including its state, ID, privileges, scheduling info, and memory allocation.
Q & A
What is the role of the operating system in a computer's architecture?
-The operating system acts as the first software layer on top of the hardware, managing the CPU, memory, and devices. It is responsible for task management, security, performance, and other responsibilities, serving as an interface between the hardware and the applications layer.
What is a process in the context of an operating system?
-A process is an instance of a program loaded into memory or a unit of work in an operating system. It is an object stored in memory that contains information about the execution of a particular program and is managed by the operating system.
How does a program become executable on the CPU?
-A program, which is initially a text file with instructions, needs to be compiled into an executable binary file, such as a .jar or .exe file, which can then be launched by the operating system to create a process object in memory.
What is the initial state of a process when it is created?
-When a process is created, its initial state is 'new'. It then transitions to the 'ready' state when it is prepared to be run on the CPU.
What is the role of the scheduler in an operating system?
-The scheduler is a dedicated component of the operating system responsible for selecting processes in the ready state and placing them onto the CPU for execution, based on a well-defined algorithm.
What is preemption in the context of process execution?
-Preemption is the behavior where the operating system moves a running process back to the ready state to allow other processes to use the CPU. This ensures that the CPU is shared among multiple processes.
What is the purpose of the waiting state in a process's lifecycle?
-The waiting state is when a process needs to wait for some external resources, such as data received over the network. During this state, the process is not executing on the CPU but is waiting for the required resources to become available.
How does having multiple CPU cores affect the system's throughput?
-Having multiple CPU cores allows the system to handle multiple processes in parallel, effectively tripling the throughput if there are three cores, as each core can execute a process simultaneously.
What is preemptive multitasking and why is it important?
-Preemptive multitasking is a mechanism where the CPU executes small parts of different processes at different times, rather than running a single process for a long duration. This ensures that the system remains responsive and can handle multiple tasks concurrently.
What is a time slice in the context of process execution?
-A time slice is the specific time limit during which a process is allowed to use the CPU. This value, typically around 100 milliseconds on Linux, is dynamically adjusted by the operating system to manage the execution of processes.
What is a context switch and why is it significant?
-A context switch is the operation of changing the process that is currently running on the CPU with another process. It is significant because it allows for multitasking and efficient CPU usage, but it can also impact performance due to the overhead involved in saving and loading the state of processes.
What information is typically stored in a process control block?
-A process control block contains the current state of the process, a unique ID, privileges specifying resource access, a pointer to the next instruction, CPU register data, scheduling information like priority, virtual memory allocation, a pointer to the parent process, and information about file descriptors used by the process.
Outlines
🖥️ Understanding Processes and Task Management in Operating Systems
This paragraph introduces the concept of a process in an operating system, explaining its role within the computer's architecture. It describes the operating system as a complex component that manages tasks, which are programs to be executed on the CPU. The process lifecycle is detailed, starting from the creation of an executable binary file from a program, through the various states a process goes through, such as new, ready, running, waiting, and terminated. The paragraph also explains the role of the scheduler in managing process execution and the concept of preemption, which allows the operating system to manage CPU time among multiple processes. The example of a single CPU core handling multiple processes illustrates the process lifecycle and the impact of having multiple CPU cores on system throughput.
🕒 Preemptive Multitasking and Process Scheduling
This paragraph delves into the specifics of preemptive multitasking, explaining how it prevents system unresponsiveness by assigning a time limit, known as a time slice, for each process's CPU usage. It contrasts the needs of user-oriented operating systems, which prioritize responsiveness, with server-side systems that favor performance and may allow longer-running processes. The paragraph also discusses the importance of the type of workload in determining the appropriate level of multitasking. It introduces the concept of a context switch, which is the operation of changing the process being run on the CPU, and hints at potential performance issues related to this operation. Lastly, it outlines the information stored in a process control block, which includes the process's state, ID, privileges, pointers, scheduling information, virtual memory allocation, and file descriptors, noting that the exact content may vary by operating system.
Mindmap
Keywords
💡Process
💡Operating System
💡CPU
💡Task Management
💡Executable
💡Scheduler
💡Process State
💡Preemption
💡Context Switch
💡Process Control Block
💡Time Slice
Highlights
A process is defined as an instance of a program loaded into memory, serving as a unit of work in an operating system.
The operating system is responsible for task management, including the execution of programs on the CPU.
A program must be compiled into an executable binary file before it can be executed on the CPU.
The operating system creates a process object in memory when a binary file is launched for execution.
A process is initially in a 'new' state and transitions to 'ready' when it's prepared to run on the CPU.
The scheduler is a dedicated component of the operating system that selects processes to run on the CPU.
Preemption is the behavior where the operating system moves a running process back to the ready state to allow other processes to use the CPU.
A process can enter a 'waiting' state if it requires external resources, such as data over a network.
The process lifecycle includes states such as new, ready, running, waiting, and terminated.
Having multiple CPU cores allows for parallel processing, increasing system throughput.
Preemptive multitasking ensures that no single process monopolizes the CPU, allowing for a responsive system.
The time limit for CPU usage by a process is known as the time slice, which is typically 100 milliseconds on Linux.
Context switch is the operation of changing the process currently running on the CPU with another.
Process information is stored in a data structure called the process control block, which can vary by operating system.
The process control block contains details such as the process state, unique ID, privileges, and scheduling information.
Different types of systems, like user-oriented or server-side, have different scheduling priorities due to their specific needs.
The lecture provides a comprehensive overview of processes in the context of an operating system, highlighting their lifecycle and management.
Transcripts
all right so in this first lecture we're
going to see what actually is a process
in an operating system
so first if we take a look on the
conceptual architecture of a computer we
know that at the bottom we got the
hardware which contains the cpu the
memory and devices like peripherals and
other external components
on top of that we got the first software
layer in a computer which is the
operating system
and based on that we got the
applications layer which contains all
the applications managed by the user
the operating system is a very complex
component with lots of responsibilities
like security performance and many
others
but probably one of the most important
ones is task management and by task i'm
referring to any program that should be
executed on the cpu which is launched by
the user or by the operating system
itself
so let's see in more detail how this
works
let's say we have a program which is
just a text file with instructions
stored on the local disk
to be able to run it on the cpu we need
to compile it to get an executable
binary file which can be a jar an exe or
any other executable format
that is also stored on the local disk
now when we launch the binary file into
the execution
the operating system will create a
process object that is stored into the
memory in that case
from now on the process will be
completely managed by the operating
system
so if we have to define a process we can
say that a process is an instance of a
program loaded into memory
or more generically a process is a unit
of work in an operating system
keep in mind that a process is not an
active entity it's just an object stored
in memory that contains information
about the execution of a particular
program
a process always has a state when you
create a process its initial state will
be new
when the process is able to be run on
the cpu it will immediately transition
to the ready state
the operating system has a dedicated
component called scheduler which is
responsible for selecting processes from
the ready state and placing them onto
the cpu in order to be executed
the process runs on the cpu for a while
and it can be moved to the ready state
by the operating system when it decides
to let other processes to use the cpu
this behavior is called preemption and
we'll take a closer look on how it works
further in this lecture
a running process can also be moved into
the waiting state if it needs to wait
for some external resources like for
some data that needs to be received over
the network for example
and finally when the process does not
have any other instructions to be
executed it will move to the terminated
state
now let's assume that we have one cpu
core and we got three processes launched
by the user and we want to see how those
processes move through those states
usually if the system has enough
capacity the processes will move
directly to the ready state
the scheduler picks one process based on
a well-defined algorithm and moves it
into the running state
it picks only one process because there
is only one cpu core available
the chosen process runs for a while on
the cpu and then it needs access to some
external resource which may take some
time so it gets moved into the waiting
state
as soon as the cpu is free the scheduler
immediately takes another process and
moves it into the running state
the waiting process receives the data
from the external component and moves
into the ready state ready to be picked
by the scheduler again
the currently running process is
preempted by the operating system
because its time slice has elapsed
and the workflow continues until all the
instructions of the processes are
executed and they move to the terminated
state
this workflow is actually called the
process lifecycle
now if you have three cpu cores for
example we will be able to handle three
processes in parallel which triples the
throughput of the entire system
now let's take a look on what preemption
really is
let's imagine we have a single cpu core
and we have a process that is called
clock which is responsible for simply
printing the current time on the screen
if that process is the only one that is
running on the cpu the system will
become unresponsive because there are
other processes that need to use the cpu
like your browser or the ui components
of the operating system
so to solve that issue each process is
assigned a particular time limit during
which it's able to use a cpu
in that way the cpu will execute small
parts of a process at different times
rather than executing the same process
for a large amount of time leaving space
for other processes to be executed
this mechanism is called preemptive
multitasking and it should always be
preceded with a trade-off in mind
because operating systems that are user
oriented like windows mac os ubuntu and
others need to be responsive so
processes related to ui components are
likely to be scheduled more on the cpu
by leveraging the preemptive
multitasking
on the other hand server-side systems
like windows server or ubuntu server
usually need performance rather than
responsiveness so their scheduler will
likely favor long-running processes
so basically you should have in mind the
type of the workload you're currently
running to see if too much multitasking
can become a problem
now regarding the time limit for which
processes should execute on the cpu
it actually has a name it's called time
slice
and its value is usually 100
milliseconds on linux but it's
dynamically adjusted by the operating
system anyway so you can't really tell
which value it has at any given time
when the process being run on the cpu is
changed with another one
this operation is called context switch
and we'll see in the next lectures why
this operation could become a problem in
terms of performance
now the last important aspect that we
need to know about the process is the
actual information that is stores we
just saw previously that a process lives
in the memory but what it actually
contains
well first it needs to contain the
current state that it has running
waiting terminated or any other state a
unique id which is just a number to
identify the process
some privileges that specify on which
resources the process has access to
a pointer to the next extraction that
needs to be executed
the data that was stored in the cpu
registers when the process was switched
off the cpu
some information related to the
scheduling process like priority for
example
information related to the virtual
memory currently allocated by the
process
a pointer to the parent process and some
information related to which file
descriptors are being used
this data structure is called process
control block
and its content can slightly vary
depending on the operating system
so that's pretty much all you need to
know about the process in the context of
multithreading
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