INTRODUCTION

Android succeeded in making smartphones useful, everyday tools that anyone could use. It has millions of applications that users can install - most of them free. It allows people to easily connect to the internet and allows people from across the world to access the internet from their homes. Smartphones also replace many devices including phones, digital cameras, alarms, music players and even computers. Finally, it works with a larger number of different devices, many of which are affordable. Thanks to a combination of these factors, Android was installed on 85% of all smartphones in 2018 and 42% of all computers (including desktop computers, notebooks and servers). In contrast, the iOS operating systems (used by iPhone) work on a very small number of expensive devices.

In this chapter, you will learn more about system software, including operating systems like Android. The chapter will start by looking at operating systems in greater detail, before looking at a few of the different processing techniques that is, memory systems software. The chapter will then look at how application instructions are converted into a language your CPU can understand, before ending with a look at virtual memory and virtualisation.

Let’s refresh your memory on software and operating systems by reading the Software in a nutshell section.

SOFTWARE IN A NUTSHELL

Software refers to digital items made up of 1s and 0s that tell your computer what to do. There are many different types of software, including applications, games and utilities. However, the focus of this chapter will be on a category of software called system software, which is responsible for managing your computer. It does this in several important ways, including:

• translating the instructions from your software to a language your hardware can understand
• sending these instructions to the correct hardware
• receiving information from the hardware (such as button presses on a keyboard) and sending it to the software
• allowing different applications to communicate with each other
• making sure all the hardware and software on your computer are working correctly.

The most important type of system software is the operating system, which controls your hardware and software, provides a user interface for users to interact with, and manages the resources of the computer.

The operating system has thousands of small tasks that it processes to ensure your computer continues to run smoothly. These tasks can be summarised as:

• managing and interpreting the signals sent and received by your hardware
• understanding and communicating with different hardware devices using drivers
• managing a computer’s memory and storage
• monitoring your hardware’s performance
• providing an interface for users to interact with the computer
• allowing the computer’s hardware to interact with its software
• allowing computers to connect and communicate over a network.

In Grade 10 you learned that there are three main types of operating systems: stand-alone operating systems, network operating systems and embedded operating systems.

Stand-alone operating systems can work directly on computers (or smartphones, like Android) and make sure that the tasks of the operating system are completed. Almost all home computers, office computers and smartphones use stand-alone operating systems.

Network or server operating systems are operating systems that are not designed to be used on their own, but rather to help other computers on a network. These operating systems form the backbone of the world’s largest network: the internet. Finally, embedded operating systems are operating systems designed to be used on a single device with a very specific purpose (such as a SmartTV or video camera).

UNIT
2.1 Types of operating systems

Operating systems play a critical role in many different areas of a computer’s functioning, including the computer’s:

• hardware
• software
• processes
• storage
• memory
• networks

In this unit, you will look at the three operating systems (stand-alone, network and embedded) you already know in more detail.

Table 2.1: Comparison between various operating systems

2.2.1Fill In the missing words in the crossword puzzle below.

UNIT
2.2 Compilers and interpreters

Programming languages have been designed so that humans can read and write it more easily.

Most modern programming languages value the importance of programming code that is simple, easy to read and easy to use.

Unfortunately, because programs are made up of lines of code, they are often not as simple to read or understand as you might want them to be. Programs in a modern programming language are still much, much easier to understand than machine code. Machine code refers to the instructions delivered directly to your CPU and is written in binary (or hexadecimal) and gives instructions. This might include references to memory addresses, logical operations or any other instruction for your CPU to complete.

Your CPU can only understand interpreted or compiled code. In this unit you will learn about interpreters and compilers and see how they differ.

INTERPRETER

In computer terms, the programming interpreter reads the first line of the code, interprets it into machine code and sends it to the CPU to be processed. It then interprets the next line and sends that to the CPU, and so on. By interpreting the program line by line, the program can immediately start running. However, since every line needs to be interpreted before it can run, the program will often run a bit more slowly than a compiled program. The source code is interpreted as the program is run, the interpreter (and interpreted language) must be installed on the same computer that the program is running. An example of an interpreted language is JavaScript.

COMPILER

In contrast to an interpreter, the compiler takes the entire source code and translates it into machine code. This translated code is saved as an executable file on the computer that can be opened on any computer without requiring the computer to have a compiler. Examples of compiled languages include BASIC, C++, Delphi and Java.

The following table summarises the main differences between interpreters and compilers.

Table 2.2: Summary of the main differences between interpreters and compilers

Follow the QR link in the margin to watch an old but very simple video explaining the difference between compilers and interpreters.

UNIT
2.3 Overview of processing techniques

On very old operating systems, you could only load one program into the computer’s memory at a time. This means you could only run one program at a time! When this program was not doing anything, the CPU would also not be doing anything. Today, most people would not be happy with a computer that could only run one task at time; they want to be able to multitask!

On a computer, multitasking allows you to run multiple tasks (also called processes or applications) at the same time. For example, you may want to listen to music while browsing the internet on your computer. More than this, you want your computer to continue running all its background services like checking for emails, updating applications and managing your network at the same time.

Example 2.3.1 How many processes are you running?

On Windows 10, you can see a list of all these tasks running in the background by opening the Task Manager. To open the Task Manager.

• Open your Start Menu and enter the words “task manager”.
• Open the Task Manager desktop application that is found.

You can also open the Task Manager by pressing the CTRL-SHIFT-ESC hotkey on your keyboard. Once opened, you will see a list of every process running on your computer. On most Windows 10 computers, there will be more than 50 applications and processes running at any time.

So how can a single CPU complete various tasks for dozens of different processes at the same time? The CPU completes tasks using the following techniques:

• multitasking
• multiprocessing
• multithreading.

Let’s look at each of these processing techniques.

MULTITASKING

Figure 2.5 shows an example of the Windows Task Manager application. As the image shows, only 3% of the CPU is being used. This means that there are times when the CPU is idle and waiting to receive new instructions.

Rather than waiting for a single program to send new instructions, processor multitasking allows the operating system to send instructions from different processes to a single processor. If the instructions are sent and completed quickly enough, the processor can complete all the instructions from multiple applications without causing any of the applications to slow down. In this way, you can run multiple applications (or processes) on one processor seemingly at the same time.

MULTIPROCESSING

Where both multitasking and multiprocessing use the same processor to quickly swap between different tasks or threads, multiprocessing uses multiple processors to complete tasks. Today, many CPUs (including smartphone CPUs) are made up of more than one processor (called a core). Each core is then able to complete program instructions on its own.

Technically, a CPU with four cores should be able to complete four times as many instructions as the same CPU with only one core. However, in practice this is not always the case. For example, in most applications the instructions need to be executed one after the other. When this is the case, it does not make sense for one core to complete the first instructions while another core completes the last instructions.

Multi-core processors therefore allow you to process multiple threads or multiple processes more quickly but may not improve the performance on any single process.

Example 2.3.2 How are the processors being used?

The Task Manager can also show how each of the processors is being used. To see the processor utilisation:

• Open the Task Manager and go to the Performance tab.
• Right click on the graph and hover over the Change graph to option.
• Select the Logical processors option.

The graph should change from a single graph to a few smaller graphs with each graph showing the utilisation of one of the processors. The Ryzen 5 1600X CPU has twelve logical processors, so the figure below shows how much each of these processors has been used over the last 60 seconds.

MULTITHREADING

Where multitasking allows your computer to complete the instructions for different processes by quickly switching between them, multithreading completes the instructions for multiple different tasks inside the same program (called threads) by quickly switching between them. Instructions from the same program are divided into multiple threads. Each thread can be run independently and executed when the CPU has time available between tasks.

Imagine that you are browsing the internet and decide to download a large file. If a program could only run one task at a time, you would have to stop browsing the internet while your browser downloads this file, and you would only be able to continue browsing the internet once the download has completed.

Fortunately, multithreading allows your computer to split this task into separate threads, with one thread managing the downloads while another thread manages your browsing. Your CPU can then quickly swap between these threads, so that both your downloads and your browsing continue without interruption.

Example 2.3.3 How many threads are you running?

The Task Manager not only shows the number of processes open on your computer, but also the number of threads running. To see the number of threads:

• Open the Task Manager
• Click on the Performance tab at the top of the Task Manager
• Select the CPU graph from the panel on the left

In the main window you will see a graph showing how much of the CPU’s total capacity has been used over the last 60 seconds. Right underneath that is a lot of numbers, including the number of processes (211 in Figure 2.6) and threads (2 723 in Figure 2.6). Based on the figure, there are therefore roughly 13 threads open for each process.

The following table highlights the differences between multiple threads and multiple processes.

UNIT
2.4 Virtual machines and virtualisation

Virtualisation is the act of creating a virtual device. Each virtual device acts as a node and is allocated its own virtual hardware, CPU, RAM and storage space.

These virtual machines behave in the same way as a real computer. For a virtual machine to be created, the host machine has to be capable of hosting a virtual machine. A virtual machine must have its own operating system and its own applications installed. The different virtual machines also do not have access to the host computer or any of the other virtual machines.

USES OF VIRTUAL MACHINES

The following list gives some of the most popular reasons for using virtual machines:

• Virtual machines allow users to install operating systems. If you wanted to test out an open source operating system like Ubuntu, then a virtual machine allows you to do so without interferring with your computer.
• Virtual machines can be used to install an application that might contain a virus. Testing it on a virtual machine will allow you to see if the application contains a virus. If it does, you can simply delete the entire virtual machine.
• The image of the virtual harddrive can be used to back up your computer, or to transfer all your data to a new computer.
• Virtual machines enable mobile developers to develop applications for different versions of Android and iOS without having to own hundreds of different devices.

If you want to see how to create your own virtual machine, you can follow the QR code in the margin.

Discuss the following in groups