43. EDEXCEL GCSE (1CP2) Operating systems - Part 1

Summary

This video explores key concepts of operating systems, focusing on multitasking, scheduling, and memory management. It explains how an operating system allows multiple programs to appear as if they are running simultaneously through task-switching and scheduling algorithms. Memory management is discussed, highlighting how programs are loaded into RAM, and how virtual memory helps when RAM is full. The video also touches on device drivers, explaining how they translate operating system commands into hardware-specific instructions for devices like printers.

Takeaways

• 🖥️ Multitasking allows multiple programs to appear as if they are running simultaneously by quickly switching between them using time slices.
• ⏲️ The processor allocates a small amount of time to each process, cycling through them rapidly so that users don't notice the task switching.
• 📋 Scheduling algorithms are used by the operating system to manage task switching and keep the CPU efficiently executing processes.
• 💾 Memory management is a crucial function of the operating system, ensuring that programs are placed in RAM and utilizing virtual memory when RAM is full.
• 📉 Over time, memory can become fragmented as different programs are loaded and closed, requiring the operating system to manage these fragments.
• 📀 Virtual memory is a technique where the operating system swaps inactive programs to the hard disk when the RAM is full, giving the illusion of more memory.
• 🔌 Device drivers are used by the operating system to translate general instructions into specific commands that hardware devices, like printers, can understand.
• 🖨️ Different types of printers use varied technologies (inkjet, laser, plotter) to produce similar outputs, but they all rely on drivers to function properly.
• 💡 The operating system manages interactions between the user and hardware through device drivers, ensuring consistent and reliable functionality.
• 📊 The operating system is responsible for ensuring that multitasking, memory management, and hardware communication happen seamlessly.

Q & A

What is multitasking in the context of an operating system?

Multitasking is when the processor allocates small time slices to multiple programs, cycling between them rapidly. This makes it appear as if all programs are running simultaneously, though in reality, only one program executes at a time in any given moment.

How does the processor switch between tasks in a multitasking environment?

The processor allocates a small amount of time to each task, known as a time slice, and switches between them so quickly that the user perceives all tasks as running simultaneously.

What is the role of scheduling algorithms in an operating system?

Scheduling algorithms manage how the operating system allocates time slices to different tasks. When a task enters the CPU, it either completes and exits or its time expires, moving it back to the ready state until it can resume.

What happens when a program's time slice is exhausted but the task is incomplete?

When a program's time slice is exhausted, but the task is not complete, the process is moved back into the ready state, where it waits for its next opportunity to run.

What is the purpose of virtual memory in modern computers?

Virtual memory allows the operating system to move instructions that are not immediately needed from RAM to the hard disk, freeing up RAM for other tasks. This creates the illusion of having more memory than is physically available.

How does the operating system manage memory fragmentation?

The operating system manages fragmented memory by fitting new programs into available memory blocks without rearranging the existing ones, as moving them would be resource-intensive.

Why is hard disk space cheaper than RAM, and how does this impact memory management?

Hard disk space is cheaper than RAM on a per-byte basis, which is why operating systems use virtual memory, allowing less critical data to be stored on the hard disk when RAM is full.

What is the purpose of a device driver in an operating system?

A device driver translates the general instructions from the operating system into specific commands that a particular piece of hardware, such as a printer, can understand, allowing it to perform its tasks correctly.

What are some examples of multitasking activities in a typical computer environment?

Examples of multitasking include using a word processor while browsing the web, playing music, running antivirus software, updating the system clock, and the operating system performing background maintenance.

What happens when a program is closed in terms of memory management?

When a program is closed, its memory space is not immediately erased, but it is marked as free and available for reuse by the operating system for new programs.

Outlines

00:00

💻 Understanding Multitasking, Scheduling, and Memory in Operating Systems

In this segment, Craig introduces the concepts of multitasking, scheduling, and virtual memory in operating systems. He explains that while multiple programs seem to run simultaneously, the processor allocates small time slices to each, rapidly cycling between tasks. This illusion of parallelism is achieved through multitasking, where programs like a word processor, web browser, music player, antivirus, and system clock appear to operate concurrently. Scheduling algorithms manage this process, determining how programs enter the CPU, execute, and either complete or return to a ready queue. This careful task management allows smooth multitasking. Craig also touches on how memory management involves allocating RAM to different programs without rearranging existing data, leading to memory fragmentation.

05:05

💾 Virtual Memory and Device Drivers in Modern Computers

Craig dives into the concept of virtual memory and how it enables computers to handle more programs than the available RAM can hold. When RAM is full, inactive program instructions are transferred to the hard disk, creating virtual memory and giving the appearance of more RAM than physically exists. He also highlights the role of device drivers, which allow different hardware components, such as printers, to communicate with the operating system. Craig explains that although different printers (inkjet, laser, plotter) use varying technologies, device drivers translate the operating system’s instructions to ensure uniform output across these devices.

Keywords

💡Multitasking

Multitasking refers to the ability of an operating system to handle multiple programs or tasks simultaneously by rapidly switching between them. In the video, it is described through the example of a word processor, web browser, music player, and antivirus all appearing to run at once, though in reality, each task is allocated a small time slice in quick succession. This process is so fast that the user perceives it as if everything is running concurrently.

💡Scheduling

Scheduling is the process used by the operating system to manage the order in which programs are executed by the CPU. The video explains that when multiple tasks are running, the CPU uses scheduling algorithms to decide which task gets to run, for how long, and in what sequence. Programs either finish execution or are put back into a 'ready' state if they need more time or are blocked by a higher priority task.

💡Virtual Memory

Virtual memory is a technique where a portion of the hard disk is used as if it were additional RAM. The video explains that when the RAM is full, less critical programs or parts of programs are moved from RAM to the hard disk to free up space. When those programs are needed again, they are swapped back into RAM, creating the impression that the computer has more memory than it actually has.

💡RAM

RAM (Random Access Memory) is a type of volatile memory that temporarily stores data for programs that are currently running. The video mentions how programs are loaded from the hard disk into RAM, and when the RAM is full, virtual memory is used. The operating system carefully manages this space to ensure multitasking can occur smoothly.

💡Time Slice

A time slice is the small amount of time allocated to a task by the CPU during multitasking. The video uses this term to explain how the processor switches between different programs, like a word processor and a web browser, giving each a brief moment to execute before moving to the next. This fast switching creates the illusion of concurrent execution.

💡Ready State

The ready state refers to when a process is waiting for its turn to execute in the CPU. According to the video, after a task's time slice expires or it is blocked, it moves back to the ready state, where it waits for another opportunity to run. The ready state is essential in the scheduling process for managing multitasking.

💡Fragmentation

Fragmentation occurs when memory is broken into scattered free spaces due to the allocation and deallocation of programs. The video illustrates this through an example where different programs occupy different-sized blocks of memory. When some are closed, their spaces are freed, but new programs must fit around the remaining ones, making memory usage less efficient over time.

💡Device Driver

A device driver is software that allows the operating system to communicate with hardware devices. The video explains this using the example of printers, where different technologies like inkjet, laser, or plotter printers require different instructions to print the same document. The device driver translates the operating system’s commands into specific actions the hardware can understand.

💡Hard Disk

The hard disk is a non-volatile storage device used to store data permanently. In the video, it is mentioned as the location from which programs are loaded into RAM. The hard disk is also used in virtual memory when the RAM is full, serving as an overflow space for temporarily storing inactive program data.

💡CPU

The CPU (Central Processing Unit) is the core component of a computer that executes instructions and processes data. In the video, it is central to multitasking, as it allocates time slices to different programs and switches between them using scheduling algorithms. The CPU also interacts with both RAM and virtual memory to run programs efficiently.

Highlights

Introduction to multitasking, scheduling, and virtual memory.

Multitasking allows the processor to cycle between programs, giving the illusion of simultaneous execution.

Example of multitasking: running a word processor, web browser, music player, antivirus, and clock concurrently.

Multitasking occurs through time slices, where the processor allocates time to each task quickly.

Scheduling algorithms determine how tasks are swapped in and out of the CPU.

Scheduling algorithms ensure tasks either complete or return to the ready state if not finished or blocked.

Memory management is handled by the operating system, which allocates RAM for programs.

Example of memory management: loading a program into RAM, closing it, and how memory is marked free.

Over time, memory becomes fragmented as multiple programs are loaded and closed.

Virtual memory is used when RAM is full, allowing programs to swap data to the hard disk.

Virtual memory creates the impression of having more RAM by temporarily moving less-needed instructions to the hard disk.

Device drivers translate operating system instructions into commands that specific hardware, like printers, can understand.

Different printers (inkjet, laser, plotter) use different technologies but need the same document output, managed through device drivers.

Operating systems manage multitasking, memory, and hardware communication through core functions such as scheduling, virtual memory, and device drivers.

Summary of multitasking, scheduling, memory management, and the importance of device drivers in system operations.

Transcripts

- [Craig] In this video, we look at some of the features of an operating system in a little bit more detail.

(uplifting piano jingle)

So let's start by looking at three interrelated concepts;

multitasking and the use of scheduling and virtual memory.

So when you have more than one program open and running at the same time,

the processor allocates a small amount of time to each process and cycles between them.

As this happens so quickly, it appears as if multiple programs are executing simultaneously.

So let's look at a typical example.

Here we have a word processor that's had a document open,

but that's not the only program that our computer has open.

Perhaps you're also doing some research on the web using your web browser.

Perhaps as you're working,

you're also listening to some music that's being played by a media player in the background.

You might well also have antivirus software

that's preventing viruses from coming down from the internet and infecting your computer.

The clock is also updating in the corner of your screen,

and the operating system itself is engaging in a number of maintenance tasks

in the background as you're using the computer.

So it appears that all these applications are running at the same time, but they're not.

The word processor has a small time slice,

and then it's passed to the web browser, that has a small time slice,

that's passed to the music player, that has a small time slice,

then to the antivirus, then to the clock,

and then back to the word processor again.

But your computer executes these instructions so quickly that, as a user,

you don't really notice that it's actually switching tasks.

This is what we call multitasking.

Now this process of swapping tasks and programs in and out of memory in the CPU

is handled by the operating system using what is known as scheduling algorithms.

Essentially, a new process enters and gets placed in a ready queue.

They execute or run in the CPU until either

they're complete, in which case they leave the CPU,

or the time allotted to them has expired but they're not yet complete, so they move back into the ready state.

Or they're blocked by some other more important process or task but are still not yet completed,

so they're moved back into the ready state.

It is these scheduling algorithms that allow computers to perform multitasking.

There are many different scheduling algorithms that can be used, and we've listed a few below.

The actual details of how each of these various scheduling algorithms works is beyond the scope of GCSE

but is something you will study at A Level.

Now in order to manage multitasking,

the operating system also has to manage the memory very carefully.

So when a program is loaded from the hard disk,

it's put into a specific place in the RAM, decided by the operating system.

Here in this illustration,

we can see two orange squares representing the size of a program that's just been loaded into the RAM.

Another smaller program gets loaded, represented by the purple square.

The user now may choose to close the first program.

So here we can see the orange squares have disappeared.

Now in reality, nothing is really erased from memory,

but the illustration shows that those memory locations are no longer being used by that application,

and so they are essentially marked as free and available for reuse.

The user may then choose to open a third program, represented here by the green squares.

This third program is bigger than the previous two,

but you'll notice because the second purple program is taking up a space in memory already,

it's not simply shifted around because that would be very slow and intensive.

It stays where it is, and the green program fits around it.

So over time, the memory becomes fragmented,

and the operating system has to manage these fragments of programs across the entire memory.

When programs and data are being fetched and executed by the CPU, they are stored in RAM.

However, this assumes that the memory is large enough to hold all the programs being executed.

In modern computers, it's common to have more than one program open at once.

However, you can store significantly more programs on the hard disk compared to RAM

because byte for byte, hard disk space is much cheaper than RAM.

When you turn your computer on, the bootstrap program will load the operating system from the disk into RAM.

When you use a computer, every time you double-click an icon to load a program,

it transferred those instructions into RAM.

But what happens when you run out of RAM?

As instructions are fetched one at a time,

that means that some of the instructions are not likely to be fetched in the near future.

Therefore, one solution is to transfer instructions that are not being used to a space on the hard disk,

and this is known as virtual memory.

When these instructions are needed again,

a different program can be swapped out of RAM to virtual memory

to make room for the instructions that are now needed.

This gives the impression that a computer has more memory than it actually has.

In addition to this, when you save or load a program or when you interact with the operating system,

when you use your keyboard or mouse, or if you print a piece of work or display something on the screen,

the computer has to be able to output to all of these various devices.

If we think about printers specifically,

although the document you want to print will be the same

and you expect it to look the same no matter what type of printer you're actually printing it to,

the technology behind each printer can vary wildly.

If you've got an inkjet printer,

it's spraying droplets of ink onto the page.

If you've got a laser printer,

then it's magnetising areas of the page and using toner to fuse to the page

in order to produce the output.

And the plotter is going to use a pen to draw across the page.

So there are three very different technologies to produce what could essentially be exactly the same output.

And therefore, a device driver is needed to translate the operating system instructions to print

into a series of instructions that that particular piece of hardware is going to understand.

And this is the purpose of a device driver.

So on the screen are some notes regarding multitasking and scheduling.

Pause the video and take some notes.

And here is a summary of memory management, virtual memory and device drivers.

Again, pause the video and take some notes.

(uplifting piano jingle)