CONCURRENCY IS NOT WHAT YOU THINK

Summary

This video script explores the concept of concurrency in computing, which allows multiple processes to run simultaneously on a single CPU. It traces the evolution from mainframes to personal computers, explaining how early operating systems enabled multitasking. The script delves into CPU operation, detailing how processes are managed through queues and scheduling. It contrasts cooperative and preemptive scheduling, highlighting the importance of hardware support for effective multitasking. The video concludes by discussing the role of multi-core systems in enhancing parallelism and the future of complex computing concepts.

Takeaways

• 💡 Multitasking has been possible since the era of single-core CPUs, challenging the misconception that it's solely a feature of multicore systems.
• 🏛️ Early mainframe computers were massive, expensive, and limited in number, leading to the development of multitasking to maximize their usage.
• 🔄 The process of running a program in early computers involved multiple steps, including loading compilers and assemblers, which was time-consuming and inefficient.
• 👥 The advent of time-sharing operating systems like Multics allowed multiple users to connect to a single computer, improving resource utilization.
• 🔄 The concept of concurrency was pivotal in allowing the execution of multiple processes by interleaving them, giving the illusion of simultaneous execution.
• 🖥️ Personal computers initially could only run one program at a time, but with the influence of systems like Unix, they evolved to support multitasking.
• 🤖 CPUs handle instructions in a cycle of fetch, decode, and execute, with jump instructions allowing for non-linear execution paths.
• 🕒 Operating systems manage process execution through a scheduler, which assigns CPU time to processes in a queue, ensuring fairness in resource allocation.
• ⏰ Preemptive scheduling, enabled by hardware timers, prevents any single process from monopolizing CPU resources, enhancing system security and responsiveness.
• 🔩 Multi-core systems enhance processing power by allowing true parallelism, but concurrency remains essential for efficient resource management when there are more processes than cores.

Q & A

What is the main focus of the video script?

The main focus of the video script is to explain the fundamentals of concurrency, a technique that allows computers to run multiple processes simultaneously, even with a single CPU.

How did early computers manage to run multiple programs despite having a single processor?

Early computers managed to run multiple programs by breaking down programs into smaller segments and interleaving them so that the CPU could execute them in an alternate order, creating the illusion of multitasking.

What is the significance of the invention of transistors in the context of the script?

The invention of transistors allowed mainframes to become smaller and more affordable, which eventually led to the development of personal computers and the need for multitasking capabilities.

Why were early computers designed to be used by one user at a time?

Early computers were designed for single-user use due to their high cost and limited availability. They were massive and expensive, making it impractical for multiple users to access them simultaneously.

What is the role of an operating system in managing multiple processes on a single CPU?

An operating system manages multiple processes by using a scheduler to allocate CPU time to each process, ensuring that each process gets a fair share of processing time and that the CPU is never idle.

What is the difference between cooperative scheduling and preemptive scheduling as explained in the script?

Cooperative scheduling relies on processes voluntarily giving up control of the CPU, whereas preemptive scheduling uses hardware timers to forcibly take control of the CPU from processes that do not relinquish it in a timely manner.

Why was the development of multi-core systems significant for multitasking?

Multi-core systems allow for true parallelism and simultaneous execution of multiple processes, as each core can handle a separate process, reducing the need for context switching and improving overall performance.

How does the CPU handle instructions as described in the script?

The CPU handles instructions through a cycle of fetch, decode, and execute. It uses special registers like the instruction register and the address register to manage the flow of instructions.

What is the purpose of a hardware timer in the context of process scheduling?

A hardware timer is used to implement preemptive scheduling by setting a time limit for a process's CPU usage. Once the timer expires, it triggers an interruption, forcing the process to relinquish control of the CPU.

What is the role of interruptions in the interaction between user programs and the operating system?

Interruptions serve as signals to the CPU, allowing user programs to request services from the operating system, such as file operations or memory allocation, and to regain control of the CPU when necessary.

Why did personal computers initially struggle with multitasking?

Personal computers initially struggled with multitasking because they were designed for single-tasking and lacked the hardware and software mechanisms to efficiently manage multiple processes simultaneously.

Outlines

00:00

💻 The Evolution of Computer Multitasking

This paragraph introduces the concept of multitasking in computers, challenging the common belief that multicore systems are the only solution for running multiple programs simultaneously. It highlights that even single-core computers have been capable of multitasking since the days of early computing systems like the Commodore Amiga and Apple Macintosh. The paragraph sets the stage for an exploration of concurrency, a technique that allows multiple processes to run at the same time on a single CPU. It also touches on the history of mainframe computers, their evolution, and the challenges faced in the early days of computing, such as the complexity of programming and the high costs associated with computer operation and maintenance.

05:00

🔄 The Mechanism of Task Switching

This section delves into how task switching is achieved in operating systems. It explains that while computers execute instructions sequentially, they can be broken down into smaller segments and interleaved to create the illusion of simultaneous execution. The paragraph introduces the concept of time-sharing operating systems, like Multics, which was one of the first to implement this technique. It also discusses the transition of computers from mainframes to personal computers and how the latter initially could not multitask but eventually adopted concurrency techniques to allow a single user to run multiple programs at once. The explanation includes a brief overview of CPU registers and the process of fetching, decoding, and executing instructions, which is fundamental to understanding how task switching is managed by the operating system.

10:01

🕒 CPU Scheduling and Process Management

This paragraph focuses on the inner workings of CPU scheduling and process management within an operating system. It describes the process queue managed by the scheduler and the dispatcher, which selects processes for execution when the CPU is available. The paragraph explains how the operating system regains control of the CPU through interruptions, which are signals that pause the current task and allow the operating system to handle essential tasks, such as I/O operations. It also introduces the concept of cooperative scheduling, where processes voluntarily relinquish control, and preemptive scheduling, which uses a hardware timer to ensure the operating system can regain control even if a process does not release the CPU voluntarily. The paragraph emphasizes the importance of hardware support for implementing preemptive scheduling and touches on the historical use of these scheduling methods in operating systems like Windows and Multics.

15:03

🚀 Multi-core Systems and True Parallelism

The final paragraph discusses the advent of multi-core systems and their impact on multitasking and concurrency. It explains that while rapid process switching can create the illusion of simultaneous execution, the increasing number of processes can lead to lag. To address this, both software and hardware solutions have been developed. On the software side, more complex schedulers can manage processes more efficiently, while hardware solutions, such as increasing CPU speed or adding multiple processing units to a chip, enable true parallelism and simultaneous execution. The paragraph concludes with a distinction between concurrency and parallelism, emphasizing that concurrency deals with managing many tasks at once, whereas parallelism is about executing many tasks at once. It also encourages viewers to explore more complex concepts like scheduling, threads, and race conditions in future episodes.

Keywords

💡Concurrency

Concurrency refers to the ability of a system to handle multiple tasks or processes simultaneously. In the context of the video, concurrency is a fundamental concept that allows computers to run multiple processes at the same time, even with a single CPU. It's crucial for efficient multitasking and is exemplified by early operating systems like Multics, which managed multiple user processes.

💡CPU (Central Processing Unit)

The CPU is the primary component of a computer that performs most of the processing inside the computer. The video explains how CPUs handle instructions through a cycle of fetch, decode, and execute, which is fundamental to understanding how concurrency is managed. The CPU's role in executing instructions is central to the discussion of how multitasking is achieved.

💡Multicore Systems

Multicore systems are computer processors that have two or more independent processing units called cores. The video discusses how multicore systems enhance performance by allowing true parallelism and simultaneous execution of multiple processes, which is an advancement over single-core systems that rely on rapid context switching to create the illusion of multitasking.

💡Operating System

An operating system is the software that manages computer hardware and software resources and provides common services for computer programs. The video highlights the role of operating systems in managing access to the CPU and other hardware, enabling multitasking and concurrency by scheduling processes and handling interruptions.

💡Multitasking

Multitasking is the ability of a system to switch between multiple tasks or processes, giving the appearance that they are running simultaneously. The video explains how early computers managed multitasking through techniques like time-sharing, where the CPU rapidly switched between tasks to create the illusion of simultaneous execution.

💡Compiler

A compiler is a program that translates code written in a high-level programming language into machine code that a computer's processor can execute. The video script mentions compilers in the context of early computing, where programmers had to load compilers onto the computer to convert source code into executable machine code.

💡Assemble

To assemble in the context of computing refers to the process of converting assembly language into machine code. The video script describes how, after the compiler translated source code into assembly language, an assembler was needed to further convert this into machine code that the CPU could execute.

💡Interruptions

Interruptions in computing are signals sent to the CPU to temporarily pause its current task and switch to a different task. The video explains how interruptions are used by programs to request services from the operating system, such as IO operations, and how they allow the operating system to regain control of the CPU for scheduling and other tasks.

💡Process

A process is an instance of a program in execution. The video discusses how the operating system manages processes, including how it schedules them for execution on the CPU and how processes interact with the operating system through interruptions and other mechanisms.

💡Scheduling

Scheduling in the context of operating systems refers to the method by which the operating system allocates CPU time to processes. The video touches on different scheduling methods, including cooperative and preemptive scheduling, and how they affect the ability of the operating system to manage multiple processes efficiently.

💡Preemptive Scheduling

Preemptive scheduling is a method where the operating system can forcibly take control of the CPU from a running process to allocate it to another process. The video explains how preemptive scheduling, supported by hardware timers, prevents any single process from monopolizing the CPU and enhances the security and efficiency of multitasking.

Highlights

Multicore systems are not the only way computers can run multiple programs simultaneously; concurrency allows it even with a single CPU.

Multitasking has been possible since the days of single-CPU computers, as seen in the Commodore Amiga and Apple Macintosh from the mid-80s.

Early mainframe computers were massive, expensive, and limited in access, leading to the development of time-sharing systems.

The evolution of computers from mainframes to personal computers saw a shift from multi-user to single-user systems.

Operating systems like MultiCS and Unix enabled multitasking by interleaving program segments for execution.

Modern personal computers have adopted multitasking capabilities, allowing a single user to run multiple programs at once.

CPUs handle instructions through a cycle of fetch, decode, and execute, which is fundamental to understanding multitasking.

The CPU's address register is crucial for the operating system to switch between different processes.

Interruptions are a hardware-level signal that allows the operating system to regain control of the CPU for essential tasks.

Cooperative scheduling, where processes voluntarily relinquish control, can lead to security risks if a process enters an infinite loop.

Preemptive scheduling, which relies on hardware timers, ensures that the operating system can regain control even if a process is uncooperative.

Multi-core systems allow for true parallelism by distributing processes across multiple processing units.

Concurrency is about managing many tasks at once, while parallelism is about executing many tasks simultaneously.

The video promises future episodes exploring more complex concepts like scheduling, threads, and race conditions.

The sponsor, Brilliant, offers interactive learning experiences to enhance problem-solving skills in computer science.

The video concludes by emphasizing the importance of understanding concurrency and parallelism for grasping more advanced computer science topics.

Transcripts

have you ever wondered how your computer

is able to run thousands of programs at

the same time you are probably thinking

about multicore systems which is not

unexpected given the recent Push by CPU

manufacturers suggesting that more cores

means better performance what some

people ignore is that multitasking has

been around since those days when

computers had a single CPU today we are

going to learn the fundamentals about

concurrency a technique that lets

computers run multiple processes

simultaneously even if they're equipped

with just one

CPU hi friends my name is George and

this is core

dumped this video is sponsored by

brilliant more about them

later back in the mid 80s computers like

the Commodore Amiga and Apple Macintosh

already could run multiple programs at

once despite having only one processor

so how did they do it to understand we

need to go back further in computer

history as is well known early computers

were very primitive these monsters also

known as mainframes were massive

machines that filled entire rooms they

were so expensive that only governments

big companies and some universities

could afford them and considering that

these things were top technology in the

entire world not even these wealthy

entities could afford many of them not

to mention the operation and maintaining

costs I mean just imagine having one of

these things for each accountant in your

company or each researcher in a

university access to computers was very

limited back then often requiring

appointments scheduled weeks in

advance mostly due to the invention of

transistors eventually main frames

became smaller though still pricey but

efforts were not only focused on

shrinking the size but also on boosting

processing speed although computers were

becoming faster operating them was still

complicated if you have no idea what I'm

talking about let me give you an

example to run a program written in some

programming language Fortran for

instance the computer couldn't just take

the source code and execute it as we do

with languages like python in modern

days before the compiler needed to be

loaded onto the computer at that time it

was common to store programs in magnetic

tapes so it was the programmer's

responsibility to mount this tape and

wait for the compiler to be loaded in

main

memory only when the compiler was ready

to run the programmer would input the

source code to be translated to Assembly

Language which still couldn't be

executed by the computer because it

needed to be compiled again down to

machine code by another program called

an assembler so temporarily it was

necessary to store the assembly output

whether on tapes punched cards or other

storage methods of the time the

procedure required mounting another tape

with the assembler requiring the

programmer to wait once

again once loaded the assembler would

take the compiler output and translate

it into machine code that the computer

can run only then the program could be

executed

as you can see a significant amount of

setup time could be involved in the

running of a single program and if

something went wrong it might have meant

starting all over

again this setup time was a real problem

while tapes were being mounted or the

programmer was typing commands the CPU

sat idle but even though it was doing

nothing other programmers still couldn't

use it because computers were designed

to be used by one user at a time and

remember in the early days few computers

were available as they cost Millions

thus computer time was extremely

valuable and owners wanted their

computers to be used as much as possible

to get as much as they could from their

Investments this is when early operating

systems were born the rest of this story

deserves its own video what's pertinent

for us right now is that researchers

eventually conceive the notion of

enabling multiple users to connect to a

single computer simultaneously but with

the operating system arbitrating access

to the

hardware under this approach each user

accessed the computer through some type

of input and output device such as a

teletype writer or a dumb terminal by

the late '70s dumb terminals were the

preferred IO device don't let this thing

confuse you it might seem like a vintage

computer but it is just a screen with a

keyboard used to send commands to the

computer and display the

output when these things were

disconnected from the computer they were

completely useless hence the interesting

name the story of terminals is kind of

fascinating as an interesting fact this

is why that little program you use to do

something on your computer by writing

commands is called a

terminal this Arrangement enabled the

computer to execute one user's programs

While others were either loading theirs

or awaiting user

input but what if multiple users were

ready to run their programs

simultaneously well in that situation

things get more complicated as the

computer disposes of one Processing Unit

users would have to share it somehow

remember that a program is just a

sequence of instructions for the

computer's CPU to execute one by

one if multiple programs are ready for

execution the straightforward approach

would be to execute them

sequentially however even though the CPU

would always be utilized here users

would have to wait a long time to start

seeing results from their

programs to address this problem

programs can be broken down into smaller

segments and interleaved so that the CPU

can execute them in an alternate

order now you might think that this

makes no sense since everything is still

being executed sequentially but keep in

mind that computers even early ones were

thousands of times faster than humans at

performing calculations so these tiny

fractions of a program would ideally be

executed very fast so fast that we as

persons would be under the illusion that

all programs are being executed at the

same

time

this kind of operating system received a

special name multic was one of the first

time sharing operating systems of all

time later in the late '70s early 80s

computers started arriving on the Home

Market as they were intended to be used

by one user at a time they got the name

personal computers which somehow remains

until

today however when personal computers

first came into play they were designed

to run one program at a time and were

uncapable of

multitasking but multics which inspired

the creation of Unix had been around for

quite a while at that point since

concurrency was already a known

technique it didn't take too much time

until PC manufacturers started shipping

personal computers capable of

multitasking instead of using

concurrency to allow multiple users to

use the same computer at the same time

it was used to allow a single user

running multiple programs at the same

time if you know a bit about how

computers run in instructions you

probably understand that we can't just

divide programs and mix them together in

this animation I'm not saying programs

are actually divided and loaded into

memory like that instead it demonstrates

the sequence of processes being carried

out how this is achieved is exactly what

we'll discuss next but before getting

into it we need to understand how CPUs

handle instructions which is exactly

what I'm going to show you after a quick

message from our sponsor brilliant if

you're following this channel it's

probably because here here we don't just

talk we explain concepts with intuitive

animations which make the learning

process enjoyable traditional studying

sometimes can feel like endless reading

with no real engagement but with

brilliant learning isn't just about

reading text it's about diving in and

interacting with the

courses this can help you a lot if you

want to become a better Problem Solver

which is what distinguishes good from

average

developers you can find all kinds of

computer science related courses like

the latest course on how large language

models work work where you can get

Hands-On with real language models learn

the fundamentals about this technology

that is currently changing the world

learn why the training data is important

and even learn how to tune an llm by

yourself to generate different kind of

output you can get for free 30 days of

brilliant premium and a lifetime 20%

discount when subscribing by accessing

brilliant.org cord dumped or using the

link in the description

below and now back to the video inside

the CPU there are special registers like

the instruction register and the address

register the address register holds the

memory location of the next instruction

the CPU will

execute when the CPU is ready for the

next instruction it fetches this value

and copy it to the instruction register

the CPU then decodes this to know what

to do next an addition a subtraction a

copy operation whatever after the

instruction is executed the address

register value increases pointing to the

next instruction

this is basically how CPUs go through

instructions step by step repeating this

cycle fetch decode and

execute there are also jump instructions

they change the address register value

making the CPU jump to a specific

instruction instead of the next one in

line This is key for dealing with

conditions and Loops in

programs

because of this programs don't have to

be literally split and mixed instead

they're loaded normally and the

operating system makes the CPU switch

between them by changing the address

register value our concern right now is

when is the operating system itself

executed because remember the operating

system is also software it needs the CPU

to do its

job when a program starts running it's

labeled as a process the operating

system system employs a specific data

type to store the details of each

running process these processes are

lined up in a queue which is overseen by

a special part of the operating system

known as auler when the CPU becomes

available another component called the

dispatcher steps in it selects the

topmost element from the queue reads the

process information and configures the

address register so that the CPU can

access that process in memory keep in

mind that I'm omitting a lot of

information here this is actually way

more complicated and I'm only only

telling you what's necessary for this

video but don't worry because a

dedicated video about CPU scheduling is

already planned okay but we still

haven't answered the question how does

the operating system manage to run

itself to do all of this

work when we write programs we don't

explicitly code instructions to give the

CPU back to the operating system right

well that's what we might

think in practice programs depend on the

operating system to perform essential

tasks when we use functions to open a

file read and write to it or things like

requesting memory we are interacting

with the operating system these

interactions occur through interruptions

at the hardware level interruptions act

as signals to the CPU when an

interruption occurs the CPU pauses its

current task saves its state by taking a

snapshot saving it in memory and

immediately jumps to a predefined

location in memory where the interrupt

service routine associated with that

specific Interruption resides this

routine is somewhere in the memory

region allocated to the operating system

itself programs use interruptions

extensively especially for Io operations

as only the operating system kernel can

handle interactions with

Hardware this is how the operating

system regains control of the CPU now

that the address register is pointing to

the operating system code the operating

system can use the CPU not only to

handle the interruption but to attend

other tasks including scheduling

processes

since IO operations often take time the

process that initiated the interruption

is temporarily placed back in the queue

while waiting for the hardware response

but before the process's captured state

is stored within the process

information then the dispatcher selects

another process from the queue and sets

the CPU to execute

it now this process can utilize the CPU

until at some point it needs some sort

of IO operation requiring giving control

back to the operating

system this cycle repeats continuously

until it's the turn of our process

again when the process is taken from the

queue its state is read and restored in

the CPU jumping to the correct location

in the user program to resume exactly

where it left

off and this is the process that allows

the operating system to alternate CPU

usage among multiple

processes but there is a huge problem

with this approach

once the CPU is allocated to a process

it retains control until the process

voluntarily releases either by

terminating or entering a waiting state

by invoking the operating

system consider an infinite Loop

scenario if there are no interruptions

inside the loop the CPU will endlessly

execute those instructions if a process

intentionally or unintentionally avoids

making interruptions the operating

system will never regain

control in modern modern times this

poses a serious security risk as

malicious programs can exploit this

vulnerability to monopolize CPU

resources preventing other programs from

accessing

them this scheduling method reliant on

process cooperation is known as

Cooperative scheduling or non-preemptive

scheduling unfortunately there's no

software fix for this issue so Hardware

intervention is

necessary to prevent any user program

from completely taking over the CPU a

hardware timer is deployed its function

is straightforward a time limit is set

and it begins counting down once the

time expires the timer triggers an

interruption the timer is typically

implemented within the CPU itself so

before allocating the CPU to any process

the operating system dispatcher uses a

privileged instruction to set and start

the

timer while processes can still

relinquish the CPU by triggering

interruptions if a process takes too

long to do so the timer ensures that the

operating system will eventually regain

control this mechanism known as

preemptive scheduling offers increased

security however an operating system can

only implement it if the hardware

supports

it if you look at the history of Home

Computing you'll find out that Windows

used Cooperative scheduling up until

version 3 from Windows 95 and subsequent

versions Windows has been used using

preemptive

scheduling interestingly enough multic

was designed to support preemptive

scheduling right from the start this is

particularly fascinating given that

we're discussing systems developed back

in the

1960s and finally what's the deal with

multi-core

systems well it's simple rapidly

switching between processes can create

the illusion of simultaneous execution

but as the number of running processes

increases the time it takes for each

process to regain C puu access also

increases leading to noticeable

lag to address this there are both

software and Hardware Solutions on the

software side a more complex scheduler

can help manage processes more

efficiently we will discuss this in a

future episode as for Hardware Solutions

one option is to increase the CPU speed

allowing processes to regain CPU time

faster however this approach has its

limits due to physical

constraints the Breakthrough came with

the addition of multiple processing

units to the same chip creating

multi-core systems with multiple cores

the Schuler can allocate different

processors to different programs

enabling true parallelism and

simultaneous

execution despite this there can still

be more processes than cores requiring

concurrency to efficiently distribute

processing resources among numerous

processes in multi-core

systems and just for reaching this part

of the video I'll leave you with this

beautiful phrase concurrency is about

dealing with lots of things that at once

but parallelism is about doing lots of

things at once and this is all you need

to understand this topic now you are

ready for more complex Concepts like

scheduling threads and race conditions

which we will explore in future episodes

this video has been quite lengthy but I

hope you found it enjoyable if you did

please hit the like button that would

help me a lot and if you want to learn

more don't let the AI voice scare you I

really try to produce quality content so

consider subscribing and following me on

other platforms