Memory unit. The computer will have memory that can hold both data and also the program processing that data. In modern computers this memory is ram.

Input – Output. This architecture allows for the idea that a person needs to interact with the machine. Whatever values that are passed to and forth are stored once again in some internal registers.

The arrows between components, i.e. the connection between the CPU and the memory are known as a bus. This connection implies that information should flow between various parts of the computer. In a modern computer built to the Von Neumann architecture, information passes back and forth along a 'bus'. There are buses to identify locations in memory - an 'address bus'. And there are buses to allow the flow of data and program instructions - a 'data bus'.

Types of memory. A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts called cells. Each location or cell has a unique address which varies from zero to memory size minus one. For example if computer has 64k words, then this memory unit has 64 * 1024=65536 memory locations. The address of these locations varies from 0 to 65535.There are two main categories of memories:

• primary memory (internal) that temporarily memorises data while programs are running.

• secondary memory (auxiliary) that stores information over the long term, including after the

computer is turned off.

The main characteristics of a memory are:

Capacity, representing the global volume of information (in bits) that the memory can store

Access time, corresponding to the time interval between the read/write request and the

availability of the data

Cycle time, representing the minimum time interval between two successive accesses

Through put, which defines the volume of information exchanged per unit of time, expressed in bits per second

Non-volatility, which characterises the ability of a memory to store data when it is not being supplied with electricity

The ideal memory has a large capacity with restricted access time and cycle time, a high throughput and is non-volatile. However, fast memories are also the most expensive. This is why memories that use different technologies are used in a computer, interfaced with each other and organized hierarchically. The fastest memories are located in small numbers close to the processor. Auxiliary memories, which are not as fast, are used to store information permanently.  Primary memory is mainly used by CPU, so it is termed as primary memory. It is also called main memory. Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed reside in main memory. It is divided into two subcategories RAM and ROM.

Random access memory, generally called RAM is the system's main memory, i.e. it is a space that allows you to temporarily store data when a program is running. Unlike data storage on an auxiliary memory such as a hard drive, RAM is volatile, meaning that it only stores data as long as it supplied with electricity. Thus, each time the computer is turned off, all the data in the memory are irremediably erased. 

Read-only memory, called ROM, is a type of memory that allows you to keep the information contained on it even when the memory is no longer receiving electricity. Basically, this type of memory only has read-only access. However, it is possible to save information in some types of ROM memory. 

Secondary memory. This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing data/information permanently. CPU directly does not access these memories instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory, and then CPU can access it. For example : Magnetic tapes, Magnetic disks(Hard disk, Floppy disk), Optical disks(CD-ROM, DVD, etc) .

Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed.

Number system. Number system is a writing system for expressing numbers, it is way to represent any number with a certain set of symbols called digits. The total number of digits used in a number system is called its base of number system or radix. Number systems can be categorized into two groups: positional and non-positional systems.

Non-positional called the number system, in which the value of numbers does not depend on its place (position) in a record number. An example no positional number system can serve as a Roman. For example, to record the number one use the letter I, two and three look like a set of characters II, III, but for the record number of five selected new symbol V, six - VI, ten - introduced the character X, one hundred - with a thousand – M.

Positional number system is the system in which the value of the digit depends on its place (position) in a record number. Positional number system is familiar to us in everyday life it is decimal system, in which the value (weight) numbers depends on its position in the record number. The Decimal Number System consists of ten digits from 0 to 9. These digits can be used to represent any numeric value. The base of decimal number system is 10. It is the most widely used number system. The value represented by individual digit depends on weight and position of the digit.

All notations used in computer science (binary, octal, hexadecimal) are positional.

The binary number system (base 2).

Almost all modern computers are digital computers, which means that they can recognize only two distinct electronic states of electrical charge. For simplicity, these states are identified as 0 and 1, or equivalently, false and true, or off and on. This means that each digit can have only two possible values. These values are 0 and 1. Binary digits are called bits. System consists of two digits 0 and 1. Its base is 2.

What is a computer? A computer is an electronic device that manipulates information, or data. It has the ability to store, retrieve, and process data. You may already know that you can use a computer to type documents, send email, play games, and browse the Web. You can also use it to edit or create spreadsheets, presentations, and even videos.

Hardware vs. software. Before we talk about different types of computers, let's talk about two things all computers have in common: hardware and software.

• Hardware is any part of your computer that has a physical structure, such as the keyboard or mouse. It also includes all of the computer's internal parts.

• Software is any set of instructions that tells the hardware what to do and how to do it. Examples of software include web browsers, games, and word processors.

Everything you do on your computer will rely on both hardware and software. For example, right now you may be viewing this lesson in a web browser (software) and using your mouse (hardware) to click from page to page. As you learn about different types of computers, ask yourself about the differences in their hardware. As you progress through this tutorial, you'll see that different types of computers also often use different types of software.

What are the different types of computers? When most people hear the word computer, they think of a personal computer such as a desktop or laptop. However, computers come in many shapes and sizes, and they perform many different functions in our daily lives. When you withdraw cash from an ATM, scan groceries at the store, or use a calculator, you're using a type of computer.

Desktop computers. Many people use desktop computers at work, home, and school. Desktop computers are designed to be placed on a desk, and they're typically made up of a few different parts, including the computer case, monitor, keyboard, and mouse.

Laptop computers. The second type of computer you may be familiar with is a laptop computer, commonly called a laptop. Laptops are battery-powered computers that are more portable than desktops, allowing you to use them almost anywhere.

Tablet computers. Tablet computers—or tablets—are handheld computers that are even more portable than laptops. Instead of a keyboard and mouse, tablets use a touch-sensitive screen for typing and navigation. The iPad is an example of a tablet.

Servers. A server is a computer that serves up information to other computers on a network. For example, whenever you use the Internet, you're looking at something that's stored on a server. Many businesses also use local file servers to store and share files internally.

Other types of computers. Many of today's electronics are basically specialized computers, though we don't always think of them that way. Here are a few common examples.

• Smartphones: Many cell phones can do a lot of things computers can do, including browsing the Internet and playing games. They are often called smartphones.

• Wearables: Wearable technology is a general term for a group of devices-including fitness trackers and smartwatches-that are designed to be worn throughout the day. These device sare often called wearables forshort.

• Game consoles: A game console is a specialized type of computer that is used for playing video games on your TV.

• TVs: Many TVs now include applications-or apps-that let you access various types of online content. For example, you can stream video from the Internet directly onto your TV.

PCs and Macs. Personal computers come in two main styles: PC and Mac. Both are fully functional, but they have a different look and feel, and many people prefer one or the other.

PCs. This type of computer began with the original IBM PC that was introduced in 1981. Other companies began creating similar computers, which were called IBM PC Compatible (often shortened to PC). Today, this is the most common type of personal computer, and it typically includes the Microsoft Windows operating system.

Macs. The Macintosh computer was introduced in 1984, and it was the first widely sold personal computer with a graphical user interface, or GUI (pronounced gooey). All Macs are made by one company (Apple), and they almost always use the Mac OSX operating system.

What is a laptop computer? A laptop is a personal computer that can be easily moved and used in a variety of locations. Most laptops are designed to have all of the functionality of a desktop computer, which means they can generally run the same software and open the same types of files. However, laptops also tend to be more expensive than comparable desktop computers.

How is a laptop different from a desktop? Because laptops are designed for portability, there are some important differences between them and desktop computers. A laptop has an all-in-one design, with a built-in monitor, keyboard, touchpad (which replaces the mouse), and speakers. This means it is fully functional, even when no peripherals are connected. A laptop is also quicker to set up, and there are fewer cables to get in the way.

You'll also have to the option to connect a regular mouse, larger monitor, and other peripherals. This basically turns your laptop into a desktop computer, with one main difference: You can easily disconnect the peripherals and take the laptop with you wherever you go.

Here are the main differences you can expect with a laptop.

• Touchpad: A touchpad—also called a trackpad—is a touch-sensitive pad that lets you control the pointer by making a drawing motion with your finger.

• Battery: Every laptop has a battery, which allows you to use the laptop when it's not plugged in. Whenever you plug in the laptop, the battery recharges. Another benefit of having a battery is that it can provide backup power to the laptop if the power goes out.

• AC adapter: A laptop usually has a specialized power cable called an AC adapter, which is designed to be used with that specific type of laptop.

• Ports: Most laptops have the same types of ports found on desktop computers (such as USB), although they usually have fewer ports to save space. However, some ports may be different, and you may need an adapter in order to use them.

• Price: Generally speaking, laptops tend to be more expensive than a desktop computer with the same internal components. While you may find that some basic laptops cost less than desktop computers, these are usually much less powerful machines.

Inside a computer. Have you ever looked inside a computer case, or seen pictures of the inside of one? The small parts may look complicated, but the inside of a computer case isn't really all that mysterious. This lesson will help you master some of the basic terminology and understand a bit more about what goes on inside a computer.

Motherboard. The motherboard is the computer's main circuit board. It's a thin plate that holds the CPU, memory, connectors for the hard drive and optical drives, expansion cards to control the video and audio, and connections to your computer's ports (such as USB ports). The motherboard connects directly or indirectly to every part of the computer.

CPU/processor. The central processing unit (CPU), also called a processor, is located inside the computer case on the motherboard. It is sometimes called the brain of the computer, and its job is to carry out commands. Whenever you press a key, click the mouse, or start an application, you're sending instructions to the CPU.

The CPU is usually a two-inch ceramic square with a silicon chip located inside. The chip is usually about the size of a thumbnail. The CPU fits into the motherboard's CPU socket, which is covered by the heat sink, an object that absorbs heat from the CPU.

A processor's speed is measured in megahertz (MHz), or millions of instructions per second; and gigahertz (GHz), or billions of instructions per second. A faster processor can execute instructions more quickly. However, the actual speed of the computer depends on the speed of many different components—not just the processor.

RAM (random access memory). RAM is your system's short-term memory. Whenever your computer performs calculations, it temporarily stores the data in the RAM until it is needed. This short-term memory disappears when the computer is turned off. If you're working on a document, spreadsheet, or other type of file, you'll need to save it to avoid losing it. When you save a file, the data is written to the hard drive, which acts as long-term storage.

RAM is measured in megabytes (MB) or gigabytes (GB). The more RAM you have, the more things your computer can do at the same time. If you don't have enough RAM, you may notice that your computer is sluggish when you have several programs open. Because of this, many people add extra RAM to their computers to improve performance.

Hard drive. The hard drive is where your software, documents, and other files are stored. The hard drive is long-term storage, which means the data is still saved even if you turn the computer off or unplug it.

When you run a program or open a file, the computer copies some of the data from the hard drive onto the RAM. When you save a file, the data is copied back to the hard drive. The faster the hard drive, the faster your computer can start up and load programs.

Power supply unit. The power supply unit in a computer converts the power from the wall outlet to the type of power needed by the computer. It sends power through cables to the motherboard and other components.

If you decide to open the computer case and take a look, make sure to unplug the computer first. Before touching the inside of the computer, you should touch a grounded metal object—or a metal part of the computer casing—to discharge any static buildup. Static electricity can be transmitted through the computer circuits, which can seriously damage your machine.

Expansion cards. Most computers have expansion slots on the motherboard that allow you to add various types of expansion cards. These are sometimes called PCI (peripheral component interconnect) cards. You may never need to add any PCI cards because most motherboards have built-in video, sound, network, and other capabilities.

However, if you want to boost the performance of your computer or update the capabilities of an older computer, you can always add one or more cards. Below are some of the most common types of expansion cards.

Video card. The video card is responsible for what you see on the monitor. Most computers have a GPU (graphics processing unit) built into the motherboard instead of having a separate video card. If you like playing graphics-intensive games, you can add a faster video card to one of the expansion slots to get better performance.

Sound card. The sound card—also called an audio card—is responsible for what you hear in the speakers or headphones. Most motherboards have integrated sound, but you can upgrade to a dedicated sound card for higher-quality sound.

Network card. The network card allows your computer to communicate over a network and access the Internet. It can either connect with an Ethernet cable or through a wireless connection (often called Wi-Fi). Many motherboards have built-in network connections, and a network card can also be added to an expansion slot.

Bluetooth card (or adapter). Bluetooth is a technology for wireless communication over short distances. It's often used in computers to communicate with wireless keyboards, mice, and printers. It's commonly built into the motherboard or included in a wireless network card. For computers that don't have Bluetooth, you can purchase a USB adapter, often called a dongle.

Getting to know your computer's OS. Now that you know the absolute basics of using a computer, it's time to learn more about your computer's operating system. We'll be talking about the two most common operating systems in this lesson: Microsoft Windows and Mac OSX.

Getting to know the interface. Both PCs and Macs use a graphical user interface (GUI), and they each have their own look and feel. The interactive below will introduce you to the Windows and Mac interfaces.

Click the buttons in the interactive below to learn more about the Windows interface. Click the buttons in the interactive below to learn more about the Mac OS X interface.

If you have difficulty seeing or hearing—or if you have trouble manipulating the mouse or keyboard—there are many settings that can help make your computer easier to use. To learn more, check out our lesson on Using Accessibility Features.

All about your computer's file system. No matter which operating system you use, your computer uses folders to organize all of the different files and applications it contains. Folder icons on your computer are designed to look like file folders full of documents or pictures.

Each operating system has its own file system, which helps you find your folders and files. If you have a Windows PC, you'll use the File Explorer (also known as Windows Explorer). If you have a Mac, you'll use Finder. Here, we'll talk about the basic functions that are common to all computer file systems.

To find out more about file systems on Macs, check out the lesson on Working with Files in our OSX Basics tutorial. To learn more about PC file systems, take a look at the Working with Files lesson in our Windows Basics tutorial.

Opening your computer's file system. Whether you're using a PC or a Mac, the file system icon will be in the bottom-left part of the screen. On a PC, the File Explorer icon looks like a folder, as in the image below. On a Mac, the Finder icon looks like a face on the Dock, as in the image below. In both operating systems, you can also open the file system by clicking a folder from your desktop.

Basic navigation. Whether you're using Windows Explorer or Finder, basic navigation will work the same way. If you see the file you want, you can double-click it with your mouse. Otherwise, you can use the Navigation pane on the left side of the window to select a different location.

Deleting files. OS X and Windows use a Trash can—or Recycle Bin—to prevent you from accidentally deleting files. When you delete a file, it is moved to the Trash can. If you change your mind, you can move the file back to its original location. If you want to permanently delete the file, you will need to empty the Trash or Recycle Bin. To do this, right-click the icon and select Empty.

Opening files and applications. Each application on your computer has a group of file types—or formats—it is able to open. When you double-click a file, your computer will automatically use the correct application to open it. In our example, we're opening a Microsoft Word document (Chicago Trip Details), which will open in Microsoft Word.

However, there may be times you may want to open an application directly, instead of just opening a file.

• To open an application in Windows, click the Start button, then select the desired application. If you don't see the one you want, you can click All Programs/All Apps to see a full list, or simply type the name of the application on your keyboard to search for it. In the example below, we're opening  Internet Explorer.

• To open an application on a Mac, click the application's icon on the Dock. If you don't see the one you want, click the Spotlight icon in the top-right corner of the screen, then type the name of the application on your keyboard to search for it. In the example below, we're opening  Safari.

Adjusting your computer's settings. When you start using a new computer, you may want to begin by adjusting the computer's settings. Adjusting your settings can range from simple tasks such as changing your desktop background to more advanced tasks like adjusting your security or keyboard settings.

• In Windows 10, click the Start button, then select Settings.

• In Windows 8.1 and earlier, click the Start button, then locate and select the Control Panel. Check out the Adjusting Your Settings lesson in our Windows Basics tutorial to learn more about the Control Panel.

• On a Mac, click the Apple icon, then select System Preferences. Check out our Adjusting Your Settings lesson in our OS X Basics tutorial to learn more about System Preferences.

Shutting down your computer. When you're done using your computer, it's important to shut it down properly.

• To shut down Windows, click the Start button, then select Shut down (in some versions, this may say Turn Off Computer or look like the power symbol).

• To shut down a Mac, click the Apple icon, then select Shut Down.

№3 LECTURE

• Software.

• OS.

• Types of software and target characteristics.

• Basic operating system concepts.

• The evolution of operating systems.

• Classification of operating systems, including for mobile devices.

• Classification of desktop applications.

What is an operating system? An operating system is the most important software that runs on a computer. It manages the computer's memory and processes, as well as all of its software and hardware. It also allows you to communicate with the computer without knowing how to speak the computer's language. Without an operating system, a сomputer is useless.

The operating system's job. Your computer's operating system (OS) manages all of the software and hardware on the computer. Most of the time, there are several different computer programs running at the same time, and they all need to access your computer's central processing unit (CPU), memory, and storage. The operating system coordinates all of this to make sure each program gets what it needs.

Types of operating systems. Operating systems usually come pre-loaded on any computer you buy. Most people use the operating system that comes with their computer, but it's possible to upgrade or even change operating systems. The three most common operating systems for personal computers are Microsoft Windows, Mac OS X, and Linux.

Modern operating systems use a graphical user interface, or GUI (pronounced gooey). A GUI lets you use your mouse to click icons, buttons, and menus, and everything is clearly displayed on the screen using a combination of graphics and text.

Each operating system's GUI has a different look and feel, so if you switch to a different operating system it may seem unfamiliar at first. However, modern operating systems are designed to be easy to use, and most of the basic principles are the same.

Microsoft Windows. Microsoft created the Windows operating system in the mid-1980s. Over the years, there have been many different versions of Windows, but the most recent ones areWindows 10 (released in 2015), Windows 8 (2012), Windows 7 (2009), and Windows Vista (2007). Windows comes pre-loaded on most new PCs, which helps to make it the most popular operating system in the world.

Check out our tutorials on Windows Basics and specific Windows versions for more information.

Mac OS X. Mac OS is a line of operating systems created by Apple. It comes preloaded on all new Macintosh computers, or Macs. All of the recent versions are known as OS X(pronounced O-S Ten), and the specific versions include El Capitan (released in 2015),Yosemite (2014), Mavericks (2013), Mountain Lion (2012), and Lion (2011).

According to Stat Counter Global Stats, Mac OS X users account for less than 10% of global operating systems – much lower than the percentage of Windows users (more than 80%). One reason for this is that Apple computers tend to be more expensive. However, many people do prefer the look and feel of Mac OS X over Windows.

Linux. Linux (pronounced LINN-ux) is a family of open-source operating systems, which means they can be modified and distributed by anyone around the world. This is different from proprietary software like Windows, which can only be modified by the company that owns it.

According to StatCounter Global Stats, Linux users account for less than 2% of global operating systems. However, most servers run Linux because it's relatively easy to customize.

To learn more about different distributions of Linux, visit the Ubuntu, Linux Mint, and Fedora websites, or refer to our Linux Mint Resources. For a more comprehensive list, you can visit MakeUseOf's list of The Best Linux Distributions.

Operating systems for mobile devices. The operating systems we've been talking about so far were designed to run on desktop and laptop computers. Mobile devices such as phones, tablet computers, and MP3 players are different from desktop and laptop computers, so they run operating systems that are designed specifically for mobile devices. Examples of mobile operating systems include Apple iOS and Google Android. In the screenshot below, you can see iOS running on an iPad.

Operating systems for mobile devices generally aren't as fully featured as those made for desktop and laptop computers, and they aren't able to run all of the same software. However, you can still do a lot of things with them, like watch movies, browse the Web, manage your calendar, and play games.

What is Windows? Windows is an operating system designed by Microsoft. The operating system is what allows you to use a computer. Windows comes preloaded on most new personal computers (PCs), which helps to make it the most popular operating system in the world.

Windows makes it possible to complete all kinds of everyday tasks on your computer—for example, you can use Windows to browse the Internet, check your email, edit digital photos, listen to music, play games, and do much more.

Windows is also used in many offices because it gives you access to productivity tools such as calendars, word processors, and spreadsheets.

Microsoft released the first version of Windows in the mid-1980s. There have been many versions of Windows since then, but the most recent ones include Windows 10 (released in 2015), Windows 8 (2012), Windows 7 (2009), Windows Vista (2007), and Windows XP (2001).

About this tutorial. This tutorial is designed to show you the absolute basics of using a Windows computer, including how to use the desktop, how to open different files and applications, and how to move and resize windows. The information in this tutorial will apply to more recent versions of Windows, including the ones mentioned above. However, once you've learned the basics, you may also want to review one of our version-specific Windows tutorials—just select the version of Windows that's installed on your computer:

• Windows 10

• Windows 8

• Windows 7

• Windows XP

Windows 8 vs. otherversions

While most versions of Windows are relatively similar, Windows 8 works very differently from other versions. However, if you have Windows 8 on your computer, you should now be able to upgrade to Windows 10, which is more similar to earlier versions, such as Windows 7. We highly recommend that you upgrade your computer to Windows 10 if you can—review our tutorial on Windows 10 to learn how.

However, we'll still point out any major differences between Windows 8 and other versions, which means you'll see some Windows 8-specific information from time to time. If your computer uses Windows 8, you'll want to review both this tutorial and our Windows 8 tutorial to learn more about the differences.

№ 4 LECTURE