Chapter 1 - Computer System PDF

Chapter 1 Computer System 1.1 Introduction to Computer System “A computer would deserve A computer is an electronic device that can be to be called intelligent if it progra...

Chapter 1 Computer System 1.1 Introduction to Computer System “A computer would deserve A computer is an electronic device that can be to be called intelligent if it programmed to accept data (input), process it and could deceive a human into generate result (output). A computer along with believing that it was human.” additional hardware and software together is called a –Alan Turing computer system. A computer system primarily comprises a central processing unit (CPU), memory, input/output devices and storage devices. All these components function together as a single unit to deliver the desired output. A computer system comes in various forms and sizes. It can vary from a high-end server to personal desktop, laptop, tablet computer, or a smartphone. Figure 1.1 shows the block diagram of a computer system. The directed lines represent the flow of data and signal between the components. Secondary Storage Devices Primary Memory In this chapter Input Control Unit Output »» Introduction to Device (CU) Device Computer System »» Evolution of Arithmetic Logic Computer Unit (ALU) »» Computer Memory Central Processing Unit (CPU) »» Data Transfer Figure 1.1: Components of a computer system between Memory and CPU 1.1.1 Central Processing Unit (CPU) »» Data and It is the electronic circuitry of a computer that carries Information out the actual processing and usually referred as the »» Microprocessors brain of the computer. It is commonly called processor »» Software also. Physically, a CPU can be placed on one or more »» Operating System microchips called integrated circuits (IC). The ICs comprise semiconductor materials. Rationalised 2023-24 Ch 1.indd 1 08-Apr-19 11:36:15 AM  2 Computer Science – Class xi The CPU is given instructions and data through programs. The CPU then fetches the program and data from the memory and performs arithmetic and logic Keyboard operations as per the given instructions and stores the result back to memory. While processing, the CPU stores the data as well as instructions in its local memory called registers. Mouse Registers are part of the CPU chip and they are limited in size and number. Different registers are used for storing data, instructions or intermediate results. Other than the registers, the CPU has two main Scanner components — Arithmetic Logic Unit (ALU) and Control Unit (CU). ALU performs all the arithmetic and logic operations that need to be done as per the instruction in a program. CU controls sequential instruction execution, Touch Screen interprets instructions and guides data flow through the computer’s memory, ALU and input or output devices. Figure 1.2: Input devices CPU is also popularly known as microprocessor. We will study more about it in section 1.5. 1.1.2 Input Devices The devices through which control signals are sent to a computer are termed as input devices. These devices convert the input data into a digital form that is acceptable by the computer system. Some examples of input devices include keyboard, mouse, scanner, touch screen, etc., as shown in Figure 1.2. Specially designed braille keyboards are also available to help the visually impaired for entering data into a computer. Besides, we Display monitor can now enter data through voice, for example, we can use Google voice search to search the web where we can input the search string through our voice. Data entered through input device is temporarily Speaker stored in the main memory (also called RAM) of the computer system. For permanent storage and future use, the data as well as instructions are stored permanently in additional storage locations called secondary memory. Printer 1.1.3 Output Devices The device that receives data from a computer system for display, physical production, etc., is called output 3D printer device. It converts digital information into human- understandable form. For example, monitor, projector, Figure 1.3: Output devices headphone, speaker, printer, etc. Some output devices Rationalised 2023-24 Ch 1.indd 2 08-Apr-19 11:36:15 AM  Computer System 3 are shown in Figure 1.3. A braille display monitor is useful for a visually challenged person to understand the textual output generated by computers. A printer is the most commonly used device to get output in physical (hardcopy) form. Three types of commonly used printers are inkjet, laserjet and dot matrix. Now-a-days, there is a new type of printer called 3D-printer, which is used to build physical A punched card is a piece of stiff paper that replica of a digital 3D design. These printers are being stores digital data in used in manufacturing industries to create prototypes the form of holes at of products. Their usage is also being explored in the predefined positions. medical field, particularly for developing body organs. 1.2 Evolution of Computer From the simple calculator to a modern day powerful data processor, computing devices have evolved in a relatively short span of time. The evolution of computing devices in shown through a timeline in Figure 1.4 EDVAC/ENIAC Pascaline John Von Neumann introduced Blaize Pascal invented a mechanical the concept of stored program calculator known as Pascal calculator computer which was capable of or Pascaline to do addition and storing data as well as program subtraction of two numbers directly in the memory. The EDVAC and and multiplication and division through then the ENIAC computers were repeated addition and subtraction. developed based on this concept. Tabulating Machine Integrated Circuit Herman Hollerith designed An Integrated Circuit (IC) is 1642 a tabulating machine for 1945 a silicon chip which contains summarising the data stored entire electronic circuit on a on the punched card. It is very small area. The size of computer drastically reduced step towards programming. because of ICs. 1890 1970 1834 1947 Analytic Engine Transistor Charles Babbage invented Vacuum tubes were analytical engine, a replaced by transistors developed at Bell Labs, 500 BC mechanical computing device 1937 for inputting, processing, using semiconductor storing and displaying the materials. output, which is considered to form the basis of modern computers. Abacus Turing Machine Computing is attributed to The Turing machine concept was a the invention of ABACUS general purpose programmable almost 3000 years ago. It machine that was capable of solving was a mechanical device any problem by executing the capable of doing simple program stored on the punched cards. arithmetic calculations only. Figure 1.4: Timeline showing key inventions in computing technology Rationalised 2023-24 Ch 1.indd 3 08-Apr-19 11:36:15 AM  4 Computer Science – Class xi The Von Neumann architecture is shown in Figure 1.5. It consists of a Central Processing Unit (CPU) for processing arithmetic and logical instructions, a memory to store data and programs, input and output devices and communication channels to send or receive the output data. Electronic Numerical Integrator and Computer (ENIAC) is the first binary programmable Figure 1.5: Von Neumann architecture for computer based on Von Neumann the computer architecture. During the 1970s, Large Scale Integration (LSI) of electronic circuits allowed integration of complete CPU on a single chip, called microprocessor. Moore’s Law predicted exponential growth in the number In 1965, Intel co- of transistors that could be assembled in a single founder Gordon Moore microchip. In 1980s, the processing power of computers introduced Moore’s increased exponentially by integrating around 3 million Law which predicted components on a small-sized chip termed as Very that the number of transistors on a chip Large Scale Integration (VLSI). Further advancement in would double every two technology has made it feasible to fabricate high density years while the costs of transistors and other components (approx 106 would be halved. components) on a single IC called Super Large Scale Integration (SLSI) as shown in Figure 1.6. IBM introduced its first personal computer (PC) for the home user in 1981 and Apple introduced Macintosh 10,000,000,000 Number of Transistors per Integrated Circuit 1,000,000,000 Core 2 DUO Core i7 100,000,000 Intel Microprocessors Pentium IV Pentium II Pentium III 10,000,000 Pentium 1,000,000 486 486 100,000 Invention of the 386 Transistor 286 10,000 8086 1,000 4004 100 Doubles every 2 years 10 1 1940 1950 1960 1970 1980 1990 2000 2010 2020 Figure 1.6: Exponential increase in number of transistors used in ICs over time Rationalised 2023-24 Ch 1.indd 4 08-Apr-19 11:36:15 AM  Computer System 5 machines in 1984. The popularity of the PC surged by the introduction of Graphical User Interface (GUI) based operating systems by Microsoft and others in place of computers with only command line interface, like UNIX or DOS. Around 1990s, the growth of World Wide Web (WWW) further accelerated mass usage of computers and thereafter computers have become an indispensable part of everyday life. Further, with the introduction of laptops, personal computing was made portable to a great extent. This was followed by smartphones, tablets and other personal digital assistants. These devices have leveraged the technological advancements in processor miniaturisation, faster memory, high speed data and connectivity mechanisms. The next wave of computing devices includes the wearable gadgets, such as smart watch, lenses, headbands, headphones, etc. Further, smart appliances are becoming a part of the Internet of Things (IoT), by leveraging the power of Artificial Intelligence (AI). 1.3 Computer Memory A computer system needs memory to store the data and instructions for processing. Whenever we talk about the ‘memory’ of a computer system, we usually talk about the main or primary memory. The secondary memory (also called storage device) is used to store data, instructions and results permanently for future use. 1.3.1 Units of Memory A computer system uses binary numbers to store and process data. The binary digits 0 and 1, which are the basic units of memory, are called bits. Further, these bits are grouped together to form words. A 4-bit word is called a Nibble. Examples of nibble are 1001, 1010, 0010, etc. A two nibble word, i.e., 8-bit word is called a byte, for example, 01000110, 01111100, 10000001, etc. Like any other standard unit, bytes are grouped together to make bigger chunks or units of memory. Table 1.1 shows different measurement units for digital data stored in storage devices. Rationalised 2023-24 Ch 1.indd 5 08-Apr-19 11:36:16 AM  6 Computer Science – Class xi Table 1.1 Measurement units for digital data Unit Description Unit Description KB (Kilobyte) 1 KB = 1024 Bytes PB (Petabyte) 1 PB = 1024 TB MB (Megabyte) 1 MB = 1024 KB EB (Exabyte) 1 EB = 1024 PB GB (Gigabyte) 1 GB = 1024 MB ZB (Zettabyte) 1 ZB = 1024 EB TB (Terabyte) 1 TB = 1024 GB YB (Yottabyte) 1 YB = 1024 ZB 1.3.2 Types of Memory Human beings memorise many things over a lifetime, and recall from memory to make a decision or some action. However, we do not rely on our memory completely, and we make notes and store important data and information using other media, such as notebook, manual, journal, document, etc. Similarly, computers have two types of memory   — primary and secondary. (A) Primary Memory Primary memory is an essential component of a computer system. Program and data are loaded into the primary memory before processing. The CPU interacts directly with the primary memory to perform read or write operation. It is of two types viz. (i) Random Access Memory (RAM) and (ii) Read Only Memory (ROM). RAM is volatile, i.e., as long as the power is supplied to the computer, it retains the data in it. But as soon as the power supply is turned off, all the contents of RAM are wiped out. It is used to store data temporarily while the computer is working. Whenever the computer is started or a software application is launched, the required program and data are loaded into RAM for processing. RAM is usually referred to as main memory and it is faster than the secondary memory or storage devices. On the other hand, ROM is non-volatile, which means its contents are not lost even when the power is turned off. It is used as a small but faster permanent storage for the contents which are rarely changed. For Think and Reflect example, the startup program (boot loader) that loads the operating system into primary memory, is stored Suppose there is a computer with RAM in ROM. but no secondary (B) Cache Memory storage. Can we install RAM is faster than secondary storage, but not as fast a software on that computer? as a computer processor. So, because of RAM, a CPU Rationalised 2023-24 Ch 1.indd 6 08-Apr-19 11:36:16 AM  Computer System 7 may have to slow down. To speed up the operations of the CPU, a very high speed memory is placed between the CPU and the primary memory known as cache. It stores the copies of the data from frequently accessed primary memory locations, thus, reducing the average time required to access data from primary memory. When the CPU needs some data, it first examines the cache. In case the requirement is met, it is read from the cache, otherwise the primary memory is accessed. (C) Secondary Memory Primary memory has limited storage capacity and Pen is either volatile (RAM) or read-only (ROM). Thus, a Drive computer system needs auxiliary or secondary memory to permanently store the data or instructions for future use. The secondary memory is non-volatile and has larger storage capacity than primary memory. It is slower and cheaper than the main memory. But, it CD/DVD cannot be accessed directly by the CPU. Contents of secondary storage need to be first brought into the main memory for the CPU to access. Examples of secondary memory devices include Hard Disk Drive (HDD), CD/ DVD, Memory Card, etc., as shown in Figure 1.7. However, these days, there are secondary storage devices like SSD which support very fast data transfer speed as compared to earlier HDDs. Also, data transfer between computers have become easier and simple due to the availability of small-sized and portable flash or pen drives. 1.4 Data Transfer between Memory and CPU Figure 1.7: Storage devices Data need to be transferred between the CPU and primary memory as well as between the primary and secondary memory. Data are transferred between different components of a computer system using physical wires called bus. For example, bus is used for data transfer between a USB port and hard disk or between a hard disk and main memory. Bus is of three types — (i) Data bus to transfer data between different components, (ii) Address bus to transfer addresses between CPU and main memory. The address of the memory location that the CPU wants to read or write from is specified in the address bus, Rationalised 2023-24 Ch 1.indd 7 08-Apr-19 11:36:16 AM  8 Computer Science – Class xi and (iii) Control bus to communicate control signals between different components of a computer. All these three buses collectively make the system bus, as shown in Figure 1.8. As the CPU interacts directly with main memory, any data entered from input device or the data to be accessed from hard disk needs to be placed in the main memory for further processing. Figure 1.8: Data transfer between components through The data is then transferred between system bus CPU and main memory using bus. The CPU places on the address bus, the address of the main memory location from which it wants to read data or to write data. While executing the instructions, the CPU specifies the read or write control signal through the control bus. As the CPU may require to read data from main memory or write data to main memory, a data bus is bidirectional. But the control bus and address bus are unidirectional. To write data into memory, the CPU places the data on the data bus, which is then written to the specific address provided through the address bus. In case of read operation, the CPU specifies the address, and the data is placed on the data bus by a dedicated hardware, called memory controller. The memory controller manages the flow of data into and out of the computer's main memory. 1.5 Microprocessors In earlier days, a computer's CPU used to occupy a large room or multiple cabinets. However, with advancement in technology, the physical size of CPU has reduced and it is now possible to place a CPU on a single microchip only. A processor (CPU) which is implemented on a single microchip is called microprocessor. Nowadays, almost all the CPUs are microprocessors. Hence, the terms are used synonymously for practical purpose. Microprocessor is a small-sized electronic component inside a computer that carries out various tasks involved in data processing as well as arithmetic and logical operations. These days, a microprocessor is built over an integrated circuit comprising millions of small components like resistors, transistors and diodes. Rationalised 2023-24 Ch 1.indd 8 08-Apr-19 11:36:16 AM  Computer System 9 Microprocessors have evolved over time in terms of their increased processing capability, decreasing physical size and reduced cost. Currently available microprocessors are capable of processing millions of instructions per millisecond. Table 1.2 lists different types of microprocessors along with their generation, time period, and underlying technology since their inception in early 1970s. Table 1.2 Generations of Microprocessor Generation Era Chip Word Maximum Clock Cores Example* type size memory size speed First 1971-73 LSI 4 / 8 1 KB 108 KHz- Single Intel 8080 bit 200 KHz Second 1974-78 LSI 8 bit 1 MB Upto 2 MHz Single Motorola 6800 Intel 8085 Third 1979-80 VLSI 16 bit 16 MB 4 MHz - 6 Single Intel 8086 MHz Fourth 1981-95 VLSI 32 bit 4 GB Upto 133 Single Intel 80386 MHz Motorola 68030 Fifth 1995 till SLSI 64 bit 64 GB 533 MHz - Multicore Pentium, date 34 GHz Celeron, Xeon *few prominent examples are included. 1.5.1 Microprocessor Specifications Microprocessors are classified on the basis of different features which include chip type, word size, memory size, clock speed, etc. These features are briefly explained below: (A) Word Size Word size is the maximum number of bits that a microprocessor can process at a time. Earlier, a word was of 8 bits, as it was the maximum limit at that time. At present, the minimum word size is 16 bits and maximum word size is 64 bits. (B) Memory Size Depending upon the word size, the size of RAM varies. Activity 1.1 Initially, RAM was very small (4MB) due to 4/8 bits word size. As word size increased to 64 bits, it has become The maximum memory feasible to use RAM of size upto 16 Exabytes (EB). size of microprocessors of different generations (C) Clock Speed are given at Table 1.2. Computers have an internal clock that generates pulses Represent each of the memory size in terms (signals) at regular intervals of time. Clock speed simply of power of 2. means the number of pulses generated per second by the Rationalised 2023-24 Ch 1.indd 9 08-Apr-19 11:36:16 AM  10 Computer Science – Class xi Activity 1.2 clock inside a computer. The clock speed indicates the speed at which the computer can execute instructions. Find out the clock speed of the microprocessor Earlier, it was measured in Hertz (Hz) and Kilohertz of your computer and (kHz). But with advancement in technology and chip compare with that of density, it is now measured in Gigahertz (GHz), i.e., your peers? billions of pulses per second. (D) Cores Core is a basic computation unit of the CPU. Earlier processors had only one computation unit, thereby capable of performing only one task at a time. With the advent of multicore processor, it has become possible for the computer to execute multiple tasks, thereby increasing the system’s performance. CPU with two, four, and eight cores is called dual-core, quad-core and octa-core processor, respectively. 1.5.2 Microcontrollers The microcontroller is a small computing device which has a CPU, a fixed amount of RAM, ROM and other peripherals all embedded on a single chip as compared to microprocessor that has only a CPU on the chip. The structure of a microcontroller is shown in Figure 1.9. Keyboard, mouse, washing machine, digital camera, pendrive, remote controller, microwave are few examples of microcontrollers. As these are designed for specific tasks only, hence their size as well as cost is reduced. Because of the very small size of the microcontroller, it is embedded in another device or system to perform a specific functionality. For Clock CPU Memory example, the microcontroller in a fully automatic washing machine is used to control the washing cycle Bus System without any human intervention. The cycle starts with the filling of water, after which the clothes are Input Output soaked and washed; thereafter the water is drained I/O-ports and the clothes are spin dry. The simple use of microcontroller has permitted repetitive execution Figure 1.9: Structure of of tedious tasks automatically without any human microcontroller intervention, thereby saving precious time. 1.6 Data and Information A computer is primarily for processing data. A computer system considers everything as data, be it instructions, pictures, songs, videos, documents, etc. Data can also be Rationalised 2023-24 Ch 1.indd 10 08-Apr-19 11:36:16 AM  Computer System 11 raw and unorganised facts that are processed to get meaningful information. So understanding the concept of data along with its different types is crucial to understand the overall functioning of a computer. Sometimes people use the terms data, information and knowledge interchangeably, which is incorrect. 1.6.1 Data and Its Types A computer system has many input devices, which provide it with raw data in the form of facts, concepts, instructions, etc., Internally everything is stored in binary form (0 and 1), but externally, data can be input to a computer in the text form consisting of English alphabets A–Z, a–z, numerals 0 – 9, and special symbols like @, #, etc. Data can be input in other languages too or it can be read from the files. The input data may be from different sources, hence it may be in different formats. For example, an image is a collection of Red, Green, Blue (RGB) pixels, a video is made up of frames, and a fee receipt is made of numeric and non-numeric characters. Primarily, there are three types of data. (A) Structured Data Data which follows a strict record structure and is easy to comprehend is called structured data. Such data with pre-specified tabular format may be stored in a data file to access in the future. Table 1.3 shows structured data related to monthly attendance of students maintained by the school. Table 1.3 Structured data: Monthly attendance records of students Roll No Name Month Attendance (in %) R1 Mohan May 95 R2 Sohan May 75 R3 Sheen May 92 R4 Geet May 82 R5 Anita May 97 R1 Mohan July 98 R2 Sohan July 65 R3 Sheen July 85 R4 Geet July 94 R5 Anita July 85 Rationalised 2023-24 Ch 1.indd 11 08-Apr-19 11:36:16 AM  12 Computer Science – Class xi It is clear that such data is organised in row/column Think and Reflect format and is easily understandable. Structured data Can you give some may be sorted in ascending or descending order. In the more examples of unstructured data? example, attendance data is sorted in increasing order on the column ‘month’. Other examples of structured data include sales transactions, online railway ticket bookings, ATM transactions, etc. (B) Unstructured Data Data which are not organised in a pre-defined record format is called unstructured data. Examples include audio and video files, graphics, text documents, social media posts, satellite images, etc. Figure 1.10 shows a report card with monthly attendance record details sent to parents. Such data are unstructured as they consist of textual contents as well as graphics, which do not follow a specific format. Attendance record for the month of July School Logo Attended: Guardian’s Signature Principal’s Signature Figure 1.10: Unstructured data: Monthly attendance record (C) Semi-structured Data Data which have no well-defined structure but maintains internal tags or markings to separate data elements are called semi-structured data. Examples include email document, HTML page, comma separated values (csv file), etc. Figure 1.11 shows an example of semi-structured data containing student’s month-wise attendance details. In this example, there is no specific format for each attendance Name: Mohan Month: July Class: XI Attendance: 98 Name: Sohan Month: July Class: XI Attendance: 65 record. Here, each data value Name: Sheen Month: July Class: XI Attendance: 85 is preceded by a tag (Name, Name: Geet Month: May Class: XI Attendance: 82 Name: Geet Month: July Class: XI Attendance: 94 Month, Class, Attendance) for Figure 1.11: Semi-structured data: Month-wise total the interpretation of the data attendance record maintained by the school value while processing. Rationalised 2023-24 Ch 1.indd 12 08-Apr-19 11:36:17 AM  Computer System 13 1.6.2 Data Capturing, Storage and Retrieval Activity 1.3 To process data, we need to first input or capture Visit some of the places the data. This is followed by its storage in a file or a like bank, automobile database so that it can be used in the future. Whenever showroom, shopping data is to be processed, it is first retrieved from the mall, tehsil office, etc., file or database so that we can perform further actions and find out 2 – 3 names of tools or instruments on it. used to capture data in (A) Data Capturing digital format. It involves the process of gathering data from different sources in the digital form. This capturing may vary from simple instruments like keyboard, barcode readers used at shopping outlets (Figure 1.12), comments or posts over social media, remote sensors on an earth orbiting satellite, etc. Sometimes, heterogeneity among data sources makes data capturing a complex task. Figure 1.12: Capturing (B) Data Storage data using barcode reader It is the process of storing the captured data for processing later. Now-a-days data is being produced at a very high rate, and therefore data storage has become a challenging task. However, the decrease in the cost of digital storage devices has helped in simplifying this task. There are numerous digital storage devices available in the market like as shown in Figure 1.7. Data keeps on increasing with time. Hence, the storage devices also require to be upgraded periodically. In large organisations, computers with larger and faster storage called data servers are deployed to store vast amount of data. Such dedicated computers help in processing data efficiently. However, the cost (both hardware and software) of setting up a data server as well as its maintenance is high, especially for small organisations and startups. (C) Data Retrieval It involves fetching data from the storage devices, for its processing as per the user requirement. As databases grow, the challenges involved in search and retrieval of the data in acceptable time, also increase. Minimising data access time is crucial for faster data processing. 1.6.3 Data Deletion and Recovery One of the biggest threats associated with digital data is its deletion. The storage devices can malfunction or crash down resulting in the deletion of data stored. Users can Rationalised 2023-24 Ch 1.indd 13 08-Apr-19 11:36:17 AM  14 Computer Science – Class xi Activity 1.4 accidentally erase data from storage devices, or a hacker or malware can delete the digital data intentionally. Explore possible ways of recovering deleted Deleting digitally stored data means changing the data or data from a details of data at bit level, which can be very time- corrupted device. consuming. Therefore, when any data is simply deleted, its address entry is marked as free, and that much space is shown as empty to the user, without actually deleting the data. In case data gets deleted accidentally or corrupted, there arises a need to recover the data. Recovery of the data is possible only if the contents or memory space marked as deleted have not been overwritten by some other data. Data recovery is a process of retrieving deleted, corrupted and lost data from secondary storage devices. There are usually two security concerns associated with data. One is its deletion by some unauthorised person or software. These concerns can be avoided by limiting access to the computer system and using passwords for user accounts and files, wherever possible. There is also an option of encrypting files to protect them from unwanted modification. The other concern is related to unwanted recovery of Activity 1.5 data by unauthorised user or software. Many a times, Create a test file and we discard our old, broken or malfunctioning storage then delete it using Shift+Delete from devices without taking care to delete data. We assume the keyboard. Now that the contents of deleted files are permanently recover the file using removed. However, if these storage devices fall into the the methods you have hands of mischief-mongers, they can easily recover explored in Activity 1.4. data from such devices; this poses a threat to data confidentiality. This concern can be mitigated by using proper tools to delete or shred data before disposing off any old or faulty storage device. 1.7 Software Till now, we have studied about the physical components or the hardware of the computer system. But the hardware is of no use on its own. Hardware needs to be operated by a set of instructions. These sets of instructions are referred to as software. It is that component of a computer system, which we cannot Rationalised 2023-24 Ch 1.indd 14 08-Apr-19 11:36:17 AM  Computer System 15 touch or view physically. It comprises the instructions and data to be processed using the computer hardware. The computer software and hardware complete any task together. The software comprises a set of instructions which on execution deliver the desired outcome. In other words, each software is written for some computational purpose. Some examples of software include operating systems like Ubuntu or Windows 7/10, word processing tool like LibreOffice or Microsoft Word, video player like VLC Player, photo editors like GIMP and LibreOffice draw. A document or image stored on the hard disk or pen drive is referred to as a soft-copy. Once printed, the Hardware refers to the physical components document or an image is called a hard-copy. of the computer system which can be seen and 1.7.1 Need of Software touched. For example, The sole purpose of a software is to make the computer RAM, keyboard, hardware useful and operational. A software knows how printer, monitor, CPU, etc. On the other hand, to make different hardware components of a computer software is a set of work and communicate with each other as well as with instructions and data the end-user. We cannot instruct the hardware of a that makes hardware computer directly. Software acts as an interface between functional to complete the desired task. human users and the hardware. Depending on the mode of interaction with hardware and functions to be performed, the software can be broadly classified into three categories viz. (i) System software, (ii) Programming tools and (iii) Application software. 1.7.2 System Software The software that provides the basic functionality to operate a computer by interacting directly with its constituent hardware is termed as system software. A system software knows how to operate and use different hardware components of a computer. It provides services directly to the end user, or to some other software. Examples of system software include operating systems, system utilities, device drivers, etc. (A) Operating System As the name implies, the operating system is a system software that operates the computer. An operating system is the most basic system software, without which other software cannot work. The operating system manages other application programs and provides Rationalised 2023-24 Ch 1.indd 15 08-Apr-19 11:36:17 AM  16 Computer Science – Class xi access and security to the users of the system. Some of the popular operating systems are Windows, Linux, Macintosh, Ubuntu, Fedora, Android, iOS, etc. (B) System Utilities Software used for maintenance and configuration of the computer system is called system utility. Some system utilities are shipped with the operating system for example disk defragmentation tool, formatting utility, system restore utility, etc. Another set of utilities are those which are not shipped with the operating system but are required to improve the performance of the system, for example, anti-virus software, disk cleaner tool, disk compression software, etc. (C) Device Drivers As the name signifies, the purpose of a device driver is to Activity 1.6 ensure proper functioning of a particular device. When Ask your teacher to it comes to the overall working of a computer system, help you locate any two device drivers installed the operating system does the work. But everyday new on your computer. devices and components are being added to a computer system. It is not possible for the operating system alone to operate all of the existing and new devices, where each device has diverse characteristics. The responsibility for overall control, operation and management of a particular device at the hardware level is delegated to its device driver. The device driver acts as an interface between the device and the operating system. It provides required services by hiding the details of operations performed at the hardware level of the device. Just like a language translator, a device driver acts as a mediator between the operating system and the attached device. The categorisation of software is shown in Figure 1.13. 1.7.3 Programming Tools In order to get some work done by the computer, we need to give instructions which are applied on the input data to get the desired outcome. Computer languages are developed Figure 1.13: Categorisation of software for writing these instructions. Rationalised 2023-24 Ch 1.indd 16 08-Apr-19 11:36:17 AM  Computer System 17 It is important to understand here that computers and Notes humans understand completely different languages. While humans are able to write programs in high-level language, computers understand machine language. There is a continuous need for conversion from high level to machine level language, for which translators are needed. Also, to write the instruction, code editors (e.g., IDLE in Python) are needed. We will briefly describe here the programming languages, language translators and program development tools. (A) Classification of Programming Languages It is very difficult for a human being to write instructions in the form of 1s and 0s. So different types of computer programming languages are developed to simplify the coding. Two major categories of computer programming languages are low-level languages and high-level languages. Low-level languages are machine dependent languages and include machine language and assembly language. Machine language uses 1s and 0s to write instructions which are directly understood and executed by the computer. But writing a code in machine language is difficult as one has to remember all operation codes and machine addresses. Also finding errors in the code written in machine language is difficult. To simplify the writing of code, assembly language was developed that allowed usage of English-like words and symbols instead of 1s and 0s. But one major drawback of writing a code in this language is that the code is computer specific, i.e., the code written for one type of CPU cannot be used for another type of CPU. High level languages are machine independent and are simpler to write code into. Instructions are using English like sentences and each high level language follows a set of rules, similar to natural languages. However, these languages are not directly understood by the computer. Hence, translators are needed to translate high-level language codes into machine language. Examples of high level language include C++, Java, Python, etc. (B) Language Translators As the computer can understand only machine language, a translator is needed to convert program written in assembly or high level language to machine Rationalised 2023-24 Ch 1.indd 17 08-Apr-19 11:36:17 AM  18 Computer Science – Class xi Code in high language. The program code written in assembly or level language high-level language is called source code. The source (Source Code) code is converted by a translator into the machine understandable form called object (machine) code as depicted in Figure 1.14. Language translater As we have different types of computer languages, different translators are needed to convert the source code to machine code. The three types of translators used in computing systems are assembler, compiler Code in machine language and interpreter. (Object Code) The translator used to convert the code written Figure 1.14: Translator to in assembly language to machine language is called convert source code into assembler. Each assembler can understand a specific object code microprocessor instruction set only and hence, the machine code is not portable. We also need translators to convert codes written in high level language (source code) to machine understandable form (machine code) for execution by the computer. Compiler converts the source code into machine code. If the code follows all syntactic rules of the language, then it is executed by the computer. Once translated, the compiler is not needed. An interpreter translates one line at a time instead of the whole program at one go. Interpreter takes one line, converts it into executable code if the line is syntactically correct, and then it repeats these steps for all lines in the source code. Hence, interpreter is always needed whenever a source code is to be executed. (C) Program Development Tools Whenever we decide to write a program, we need a text editor. An editor is a software that allows us to create a text file where we type instructions and store the file as the source code. Then an appropriate translator is used to get the object code for execution. In order to simplify the program development, there are software called Integrated Development Environment (IDE) consisting of text editor, building tools and debugger. A program can be typed, compiled and debugged from the IDE directly. Besides Python IDLE, Netbeans, Eclipse, Atom, Lazarus are few other examples of IDEs. Debugger, as the name implies, is the software to detect and correct errors in the source code. Rationalised 2023-24 Ch 1.indd 18 08-Apr-19 11:36:17 AM  Computer System 19 1.7.4 Application Software Activity 1.7 The system software provides the core functionality of With the help of your the computer system. However, different users need the teacher, install one computer system for different purposes depending upon application software in their requirements. Hence, a new category of software your computer. is needed to cater to different requirements of the end- users. This specific software that works on top of the system software is termed as application software. There are again two broad categories of application software — general purpose and customised application software. A computer system (A) General Purpose Software can work without The application software developed for generic application software, applications, to cater to a bigger audience in general but it cannot work are called general purpose software. Such ready-made without system application software can be used by end users as per software. For example, we can use a computer their requirements. For example, spreadsheet tool Calc even if no word of LibreOffice can be used by any computer user to do processing software calculation or to create account sheet. Adobe Photoshop, is installed, but if no GIMP, Mozilla web browser, iTunes, etc., fall in the operating system is category of general purpose software. installed, we cannot work on the computer. (B) Customised Software In other words, the use These are custom or tailor-made application software, of computer is possible that are developed to meet the requirements of a specific in the absence of application software. organisation or an individual. They are better suited to the needs of an individual or an organisation, considering that they are designed as per special requirements. Some examples of user-defined software include websites, school management software, accounting software, etc. It is similar to buying a piece of cloth and getting a tailor-made garment with the fitting, colour, and fabric of our choice. 1.7.5 Proprietary or Free and Open Source Software The developers of some application software provide Activity 1.8 their source code as well as the software freely to the With the help of your public, with an aim to develop and improve further with teacher, install one each other’s help. Such software is known as Free and free and open source Open Source Software (FOSS). For example, the source application software on code of operating system Ubuntu is freely accessible your computer. for anyone with the required knowledge to improve or add new functionality. More examples of FOSS include Python, Libreoffice, Openoffice, Mozilla Firefox, etc. Sometimes, software are freely available for use but Rationalised 2023-24 Ch 1.indd 19 21-May-19 4:32:01 PM  20 Computer Science – Class xi Think and Reflect source code may not be available. Such software are called freeware. Examples of freeware are Skype, Adobe When a computer is Reader, etc. When the software to be used has to be turned on, who brings the OS into RAM from purchased from the vendor who has the copyright of the the secondary storage? software, then it is a proprietary software. Examples of proprietary software include Microsoft Windows, Tally, Quickheal, etc. A software can be freeware or open source or proprietary software depending upon the terms and conditions of the person or group who has developed and released that software. 1.8 Operating System An operating system (OS) can be considered to be a resource manager which manages all the resources of a computer, i.e., its hardware including CPU, RAM, Disk, Network and other input-output devices. It also controls Types of User various application software and device drivers, manages Interface of system security and handles access by different users. Operating System It is the most important system software. Examples of popular OS are Windows, Linux, Android, Macintosh and so on. Command-based Interface The primary objectives of an operating system are two-fold. The first is to provide services for building and running application programs. When an application program needs to be run, it is the operating system Graphical User which loads that program into memory and allocates Interface it to the CPU for execution. When multiple application programs need to be run, the operating system decides the order of the execution. Touch-based The second objective of an operating system is to Interface provide an interface to the user through which the user can interact with the computer. A user interface is a software component which is a part of the operating system and whose job is to take commands or inputs Voice-based from a user for the operating system to process. Interface 1.8.1 OS User Interface There are different types of user interfaces each of which provides a different functionality. Some commonly used Gesture-based Interface interfaces are shown in Figure 1.15. (A) Command-based Interface Figure 1.15: Types of user Command-based interface requires a user to enter the interface of OS commands to perform different tasks like creating, Rationalised 2023-24 Ch 1.indd 20 08-Apr-19 11:36:17 AM  Computer System 21 opening, editing or deleting a file, etc. The user has to Notes remember the names of all such programs or specific commands which the operating system supports. The primary input device used by the user for command based interface is the keyboard. Command based interface is often less interactive and usually allows a user to run a single program at a time. Examples of operating systems with command-based interface include MS-DOS and Unix. (B) Graphical User Interface Graphical User Interface (GUI) lets users run programs or give instructions to the computer in the form of icons, menus and other visual options. Icons usually represent files and programs stored on the computer and windows represent running programs that the user has launched through the operating system. The input devices used to interact with the GUI commonly include the mouse and the keyboard. Examples of operating systems with GUI interfaces include Microsoft Windows, Ubuntu, Fedora and Macintosh, among others. (C) Touch-based Interface Today smartphones, tablets and PCs allow users to interact with the system simply using the touch input. Using the touchscreen, a user provides inputs to the operating system, which are interpreted by the OS as commands like opening an app, closing an app, dialing a number, scrolling across apps, etc. Examples of popular operating systems with touch- based interfaces are Android and iOS. Windows 8.1 and 10 also support touch-based interfaces on touchscreen devices. (D) Voice-based Interface Modern computers have been designed to address the needs of all types of users including people with special needs and people who want to interact with computers or smartphones while doing some other task. For users who cannot use the input devices like the mouse, keyboard, and touchscreens, modern operating systems provide other means of human-computer interaction. Users today can use voice-based commands to make a computer work in the desired way. Some operating Rationalised 2023-24 Ch 1.indd 21 08-Apr-19 11:36:17 AM  22 Computer Science – Class xi systems which provide voice-based control to users include iOS (Siri), Android (Google Now or “OK Google”), Microsoft Windows 10 (Cortana) and so on. (E) Gesture-based Interface Some smartphones based on Android and iOS as well as laptops let users interact with the devices using gestures like waving, tilting, eye motion and shaking. This technology is evolving faster and it has promising potential for application in gaming, medicine and other areas. 1.8.2 Functions of Operating System Now let us explore the important services and tasks that an operating system provides for managing the computer system. (A) Process Management While a computer system is operational, different tasks are running simultaneously. A program is intended to carry out various tasks. A task in execution is known Operating system is called resource manager as it as process. We can activate a system monitor program manages different resources that provides information about the processes being like main memory, CPU, I/O devices, so that each executed on a computer. In some systems it can be resource is used optimally activated using Ctrl+Alt+Delete. It is the responsibility and system performance does of operating system to manage these processes and get not deteriorate. multiple tasks completed in minimum time. As CPU is the main resource of computer system, its allocation among processes is the most important service of the operating system. Hence process management concerns the management of multiple processes, allocation of required resources, and exchange of information among processes. (B) Memory Management Primary or main memory of a computer system is usually limited. The main task of memory management is to give (allocate) and take (free) memory from running processes. Since there are multiple processes running at a time, there arises a need to dynamically (on-the-go) allocate and free memory to the processes. Operating system should do it without affecting other processes that are already residing in the memory and once the process is finished, it is again the responsibility of the operating system to take the memory space back for re- Rationalised 2023-24 Ch 1.indd 22 08-Apr-19 11:36:17 AM  Computer System 23 utilisation. Hence, memory management concerns with Notes management of main memory so that maximum memory is occupied or utilised by large number of processes while keeping track of each and every location within the memory as free or occupied. (C) File Management Data and programs are stored as files in the secondary storage of a computer system. File management involves the creation, updation, deletion and protection of these files in the secondary memory. Protection is a crucial function of an operating system, as multiple users can access and use a computer system. There must be a mechanism in place that will stop users from accessing files that belong to some other user and have not been shared with them. File management system manages secondary memory, while memory management system handles the main memory of a computer system. (D) Device Management A computer system has many I/O devices and hardware connected to it. Operating system manages these heterogeneous devices that are interdependent. The operating system interacts with the device driver and the related software for a particular device. The operating system must also provide the options for configuring a particular device, so that it may be used by an end user or some other device. Just like files, devices also need security measures and their access to different devices must be restricted by the operating system to the authorised users, software and other hardware only. Summary A computing device, also referred as computer, processes the input data as per given instructions to generate desired output. Computer system has four physical components viz. (i) CPU, (ii) Primary Memory, (iii) Input Device and (iv) Output Devices. They are referred to as hardware of computer. Computer system has two types of primary memories viz. (i) RAM, the volatile memory and (ii) ROM, the non-volatile memory. Rationalised 2023-24 Ch 1.indd 23 08-Apr-19 11:36:17 AM  24 Computer Science – Class xi Notes System bus is used to transfer data, addresses and control signals between components of the computer system. A microprocessor is a small-sized electronic component inside a computer that performs basic arithmetic and logical operations on data. Microcontroller is a small computing device which has a CPU, a fixed amount of RAM, ROM and other peripherals embedded on a single chip. Software is a set of instructions written to achieve the desired tasks and are mainly categorised as system software, programming tools and application software. Hardware of a computer cannot function on its own. It needs software to be operational or functional. Operating system is an interface between the user and the computer and supervises the working of computer system, i.e., it monitors and controls the hardware and software of the computer system. Exercise 1. Name the software required to make a computer functional. Write down its two primary services. 2. How does the computer understand a program written in high level language? 3. Why is the execution time of the machine code less than that of source code? 4. What is the need of RAM? How does it differ from ROM? 5. What is the need for secondary memory? 6. How do different components of the computer communicate with each other? 7. Draw the block diagram of a computer system. Briefly write about the functionality of each component. 8. What is the primary role of system bus? Why is data bus is bidirectional while address bus is unidirectional? 9. Differentiate between proprietary software and freeware software. Name two software for each type. Rationalised 2023-24 Ch 1.indd 24 08-Apr-19 11:36:17 AM  Computer System 25 10. Write the main difference between microcontroller Notes and microprocessor. Why do smart home appliances have a microcontroller instead of microprocessor embedded in them? 11. Mention the different types of data that you deal with while browsing the Internet. 12. Categorise the following data as structured, semi- structured and unstructured: Newspaper Cricket Match Score HTML Page Patient records in a hospital 13. Name the input or output device used to do the following: a) To output audio b) To enter textual data c) To make hard copy of a text file d) To display the data or information e) To enter audio-based command f) To build 3D models g) To assist a visually-impaired individual in entering data 14. Identify the category (system, application, programming tool) of the following software: a) Compiler b) Assembler c) Ubuntu d) Text editor Explore Yourself 1. Ask your teacher to help you locate any two device drivers installed on your computer. 2. Write any two system software and two application software installed on your computer. 3. Which microprocessor does your personal computer have? Which generation does it belong to? 4. What is the clock speed of your microprocessor? 5. Name any two devices in your school or home that have a microcontroller. Rationalised 2023-24 Ch 1.indd 25 08-Apr-19 11:36:18 AM  26 Computer Science – Class xi Notes 6. Check the size of RAM and HDD of a computer in your school. Make a table and write their size in Bytes, Kilobytes, Megabytes and Gigabytes. 7. List all secondary storage devices available at your school or home. 8. Which operating system is installed on your computer at home or school? Rationalised 2023-24 Ch 1.indd 26 08-Apr-19 11:36:18 AM