IC_Unit2- Basic Computer Architecture.pdf

103-IC Unit-2 SDJ International College UNIT-2: Basic Computer Architecture 2.1 Concepts of Address Bus and Data Bus 2.2 Concept of virtual memory and cache memory 2.3....

103-IC Unit-2 SDJ International College UNIT-2: Basic Computer Architecture 2.1 Concepts of Address Bus and Data Bus 2.2 Concept of virtual memory and cache memory 2.3. Hardware Components 2.3.1. Motherboard 2.3.2. Types of Processor (CPU and GPU) 2.3.3. Understanding processor speed 2.3.4. Memory – RAM(SRAM,DRAM, SDRAM), ROM, EPROM, EEPROM 2.3.5. Storage Devices – Hard Disk, CD, DVD, USB flash memory 2.4. Introduction to Software 2.4.1. Purpose and significance of Operating System 2.4.2. Concept of System Software and Application Software 2.1 Concepts of Address Bus and Data Bus There are three major components in a computer system. They are the Central Processing Unit (CPU), Memory and Input, Output devices. The CPU is the major unit that process data. Memory holds data required for processing. The input and output devices allow the users to communicate with the computer. The mechanism for each of the components to communicate with each other is the bus architecture. It is an electronic communication system, which carries information through electronic pathways called circuit lines. The system bus is divided into three types called address bus, data bus and control bus. The main difference between address bus and data bus is that the address bus helps to transfer memory addresses while the data bus helps to send and receive data. That is, the address bus is used to specify a physical address in the memory while the data bus is used to transmit data among components in both directions. Therefore, the address bus is unidirectional while the data bus is bidirectional. Address Bus The address bus helps to identify the particular location in the memory. Assume that the CPU needs to read data from memory. Then, the address bus helps to identify that specific location. Furthermore, each IO device has a unique ID, and it is the address of that component. The address bus helps to transfer memory addresses of data and IO. The width of the address bus determines the amount of memory the system can address. When there are ‘n’ address lines, it can directly address 2 n memory locations. For example, an 8085 microprocessor has address bus of 16 bits. Therefore, it can access 2 16 = 65536 different memory locations. Data Bus Data bus helps to transfer data between various components. It includes the related hardware components such as wires and optical fiber. The data bus consists of 8, 32, 64, etc. separate lines. The number of lines refers to the width of the data bus. This Prof. Ankita Sorathia Page 1 103-IC Unit-2 SDJ International College bus width helps to determine the data transferring rate. Therefore, the data bus width determines the system performance, but it is expensive to increase the number of lines. The other bus besides the address bus and data bus is the control bus. It is bidirectional and transmits control signals from one component to another. Point of difference Address Bus Data Bus 1. Definition It is a computer bus that is used to It is a computer bus that is specify the physical address of the used to transmit data memory. amongst the different connected components. 2.Directional Flow Unidirectional flow (from Bidirectional flow(from microprocessor to I/O devices or microprocessor to I/O microprocessor to memory). devices and memory or I/O devices and memory to microprocessor). 3. Transfer It helps to transfer memory address Helps to send and receive of the data or I/O. the data. 4. Bus width Its width determines the amount of Its width determin the data memory, a system can address. transfer rate. 2.2 Concepts 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 the computer, where data is to be processed and instructions Prof. Ankita Sorathia Page 2 103-IC Unit-2 SDJ International College 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 the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535. Memory is primarily of three types − 1) Cache Memory 2) Primary Memory/Main Memory 3) Secondary Memory 1) Cache Memory Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them. Advantages The advantages of cache memory are as follows −  Cache memory is faster than main memory.  It consumes less access time as compared to main memory.  It stores the program that can be executed within a short period of time.  It stores data for temporary use. Disadvantages The disadvantages of cache memory are as follows −  Cache memory has limited capacity.  It is very expensive. 2) Primary Memory (Main Memory) Primary memory holds only those data and instructions on which the computer is currently working. It has a 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 resides in the main memory. It is divided into two subcategories RAM and ROM. Characteristics of Main Memory  These are semiconductor memories.  It is known as the main memory.  Usually volatile memory.  Data is lost in case power is switched off.  It is the working memory of the computer.  Faster than secondary memories.  A computer cannot run without the primary memory. Prof. Ankita Sorathia Page 3 103-IC Unit-2 SDJ International College 3) Secondary Memory This type of memory is also known as external memory or non-volatile. It is slower than the 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. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc. Characteristics of Secondary Memory  These are magnetic and optical memories.  It is known as the backup memory.  It is a non-volatile memory.  Data is permanently stored even if power is switched off.  It is used for storage of data in a computer.  Computer may run without the secondary memory.  Slower than primary memories. What is virtual memory? Virtual memory is a memory management technique used by operating systems (OS). It allows a computer to temporarily increase the capacity of its main memory — RAM — by using secondary memory such as a hard drive or solid-state drive (SSD). Virtual memory utilizes hardware and software to manage how information is stored and retrieved from the hard drive. Virtual memory helps people do more on their computers without paying for more RAM capacity. While memory is much cheaper today than it used to be, RAM is still one of the most expensive types of memory How does virtual memory work? Whenever your computer stores something in RAM, that information is assigned a memory address — a reference to where the information is stored on the RAM chip. When your computer starts running low on RAM, the OS will start transferring data from the RAM to your hard drive. The OS sets up a paging file: A dedicated space on your hard drive for virtual memory. Data stored on a hard drive is always assigned a physical address — a reference to where the information is stored in the drive. The OS also maps physical addresses to virtual addresses as part of the virtual memory process. Virtual addresses look like RAM addresses. That way, when a program is running on your computer, it can seamlessly use RAM or virtual memory. When a program uses data stored in virtual memory, the OS knows how to find the data using the physical address. Advantages of Virtual Memory:  Virtual Memory allows the users to run more than one applications at once.  It enhances the degree of multiprogramming. Prof. Ankita Sorathia Page 4 103-IC Unit-2 SDJ International College  Virtual Memory is a logical unit of computer memory that increases the main memory capacity by storing or executing a large size program than the main memory.  It does not require any fixed limit on the degree of multiprogramming.  It increases the CPU.  It is required whenever the system does not have much space to store any big programs or files. Disadvantages of Virtual Memory:  Virtual Memory can slow the process of application in the system.  It may take more time to switch between the applications.  It reduces the stability of the system. Point of difference Cache Memory Virtual Memory 1. Definition Cache memory is a high speed of Virtual memory is a logical unit of computer memory that reduces the computer memory that increases access time of files or documents the capacity of main memory by from the main memory. storing or execute programs of larger size than the main memory in the computer system. 2. Memory unit Cache memory is defined as a Virtual memory is not defined as a memory unit in the computer memory unit in the computer system. system instead it is just a technique. 3. Speed It is a high speed memory as It is not high speed memory as compared to virtual memory. compared to cache memory. 4. Size Its size is very small as compared Its size is very large as compared to virtual memory. to cache memory. 5. Operation General stores frequently used data The virtual memory keeps those in the cache memory to reduce the data or programs that may not access time of files. completely be placed in the main memory. 6. Management Cache memory is controlled by the Whereas virtual memory is hardware of the system. controlled by the operating system. 7. Mapping It does not require a mapping It requires a mapping structure to structure to access the files in the map the virtual cache memory. address with the physical address. Prof. Ankita Sorathia Page 5 103-IC Unit-2 SDJ International College 2.3 Hardware Components 2.3.1. Motherboard  A motherboard is one of the most essential parts of a computer system.  It holds together many of the crucial components of a computer, including the central processing unit (CPU), memory and connectors for input and output devices.  The base of a motherboard consists of a very firm sheet of non-conductive material, typically some sort of rigid plastic.  Thin layers of copper or aluminum foil, referred to as traces, are printed onto this sheet. These traces are very narrow and form the circuits between the various components.  In addition to circuits, a motherboard contains a number of sockets and slots to connect the other components.  A CPU socket - the actual CPU is directly soldered onto the socket. Since high speed CPUs generate a lot of heat, there are heat sinks and mounting points for fans right next to the CPU socket.  A power connector to distribute power to the CPU and other components.  Slots for the system's main memory, typically in the form of DRAM chips.  A chip forms an interface between the CPU, the main memory and other components. On many types of motherboards, this is referred to as the Northbridge. This chip also contains a large heat sink.  A second chip controls the input and output (I/O) functions. It is not connected directly to the CPU but to the Northbridge. This I/O controller is referred to as the Southbridge. The Northbridge and Southbridge combined are referred to as the chipset.  Several connectors, which provide the physical interface between input and output devices and the motherboard. The Southbridge handles these connections. Prof. Ankita Sorathia Page 6 103-IC Unit-2 SDJ International College  Slots for one or more hard drives to store files. The most common types of connections are Integrated Drive Electronics (IDE) and Serial Advanced Technology Attachment (SATA).  A read-only memory (ROM) chip, which contains the firmware, or startup instructions for the computer system. This is also called the BIOS.  A slot for a video or graphics card. There are a number of different types of slots, including the Accelerated Graphics Port (AGP) and Peripheral Component Interconnect Express (PCIe).  Additional slots to connect hardware in the form of Peripheral Component Interconnect (PCI) slots. Features of Motherboard A motherboard comes with following features −  Motherboard varies greatly in supporting various types of components.  Motherboard supports a single type of CPU and few types of memories.  Video cards, hard disks, sound cards have to be compatible with the motherboard to function properly.  Motherboards, cases, and power supplies must be compatible to work properly together. Popular Manufacturers :: Following are the popular manufacturers of the motherboard.  Intel  ASUS  AOpen  ABIT  Biostar  Gigabyte  MSI 2.3.2. Types of Processor (CPU and GPU) The processor as the "brain" of the computer. The processor is a circuit that performs all of the calculations needed to run the computer. Modern computers often have more than one processor. For example, a gaming computer typically has both a central processing unit (CPU) and a graphics processing unit (GPU). The GPU takes some of the burdens off the CPU by processing any graphics that need to be rendered on the screen. Although most people think of PCs when they think of processors, other devices can have processors as well. A smartphone is a good example. Smartwatches, calculators, tablets, TVs, and even cars have processors, too. Prof. Ankita Sorathia Page 7 103-IC Unit-2 SDJ International College Central Processing Unit (CPU): CPU is known as brain for every ingrained system. CPU comprises the arithmetic logic unit (ALU) accustomed quickly to store the information and perform calculations and Control Unit (CU) for performing instruction sequencing as well as branching. CPU interacts with more computer components such as memory, input and output for performing instruction. Graphics Processing Unit (GPU): GPU is used to provide the images in computer games. GPU is faster than CPU’s speed and it emphasis on high throughput. It’s generally incorporated with electronic equipment for sharing RAM with electronic equipment that is nice for the foremost computing task. It contains more ALU units than CPU. Point of CPU GPU difference 1. Full form Central Processing Unit Graphics Processing Unit 2. Memory CPU needs more memory than GPU. GPU needs lesser memory than CPU. 3. Speed CPU’s speed is less than GPU. GPU’s speed is more than CPU. 4. Processing CPU is suitable for serial instruction GPU is suitable for parallel processing instruction processing 5. Latency CPU emphasis on low latency. GPU has no emphasis on low latency. 6. CPU doesn’t emphasis on high GPU emphasis on high throughput. Throughput throughput. 7. Job CPU quickly processes the tasks that GPU breaks the jobs into separate Processing requires interactivity. smaller tasks to process them simultaneously. 8. Interaction CPU interacts with more It’s generally incorporated with computer components electronic equipment for sharing such as memory, input and RAM with electronic equipment output for performing that is nice for the foremost instruction. computing task. 2.3.3. Understanding processor speed Most computer applications require that the computer system meets minimum requirements in order for the installation to run. One of those requirements is processor speed. Processor speed measures (in megahertz or gigahertz; MHz or GHz) the number of instructions per second the computer executes. The need for speed is most evident for schools that offer advanced computing classes including web design, animation and graphic design. The processor speed for Prof. Ankita Sorathia Page 8 103-IC Unit-2 SDJ International College schools that primarily utilize “normal” sized programs for word processing and introduction to computers, for example, would not require the speed to be as high. Why processor speed matters?  The more cycles that a computer's central processing unit is able to complete per second, the faster data is able to be processed.  The faster data can be processed, the faster the computer can complete a task.  This means that a computer with a fast processor speed can complete more tasks in the same amount of time than a computer with a slow processor, and that more applications can be running at the same time.  Some applications are processor-intensive, which means that they require a great deal of data to be processed in order to operate. What affects the processor speed?  Processor speed is impacted by several factors.  These include circuit size, die size, cache size, efficiency of the instruction set and manufacturing variables.  Smaller chips usually result in faster processor speeds because the data has less distance to travel, but smaller chips also result in greater heat generation, which needs to be managed. 2.3.4. Memory-RAM(SRAM,DRAM, SDRAM), ROM, EPROM, EEPROM Types of Computer Storage Devices Now we will discuss different types of storage devices available in the market. These storage devices have their own specification and use. Some of the commonly used storage devices are:  Primary Storage Devices  Magnetic Storage Devices  Flash memory Devices  Optical Storage Devices  Cloud and Virtual Storage 1. Primary Storage Devices  RAM: It stands for Random Access Memory. It is used to store information that is used immediately or we can say that it is a temporary memory. Computers bring the software installed on a hard disk to RAM to process it and to be used by the user. Once, the computer is turned off, the data is deleted. With the help of RAM, computers can perform multiple tasks like loading applications, browsing the web, editing a spreadsheet, experiencing the newest game, etc. It allows you to modify quickly among these tasks, remembering where you’re in one task once you switch to a different task. It is also used to load and run applications, like your spreadsheet program, answers commands, like all edits you made within the spreadsheet, or toggle between multiple programs, like once you left the spreadsheet to see the email. Memory is nearly always actively employed by your computer. It ranges from 1GB – 32GB/64GB Prof. Ankita Sorathia Page 9 103-IC Unit-2 SDJ International College depending upon the specifications. There are different types of RAM, and although they all serve the same purpose, the most common ones are :  SRAM: It stands for Static Random Access Memory. It consists of circuits that retain stored information as long as the power supply is on. It is also known as volatile memory. It is used to build Cache memory. The access time of SRAM is lower and it is much faster as compared to DRAM but in terms of cost, it is costly as compared to DRAM.  DRAM: It stands for Dynamic Random Access Memory. It is used to store binary bits in the form of electrical charges that are applied to capacitors. The access time of DRAM is slower as compared to SRAM but it is cheaper than SRAM and has a high packaging density.  SDRAM: It stands for Synchronous Dynamic Random Access Memory. It is faster than DRAM. It is widely used in computers and others. After SDRAM was introduced, the upgraded version of double data rate RAM, i.e., DDR1, DDR2, DDR3, and DDR4 was entered into the market and widely used in home/office desktops and laptops. SDRAM uses a feature called pipelining, which accepts new data before finishing processing previous data. A delay in data processing is called latency.  ROM: It stands for Read-Only Memory. The data written or stored in these devices are non- volatile, i.e, once the data is stored in the memory cannot be modified or deleted. The memory from which will only read but cannot write it. The information is stored permanently during manufacture only once. ROM stores instructions that are used to start a computer. This operation is referred to as bootstrap. It is also used in other electronic items like washers and microwaves. ROM chips can only store a few megabytes (MB) of data, which ranges between 4 and 8 MB per ROM chip. There are two types of ROM:  PROM: PROM is Programmable Read-Only Memory. These are ROMs that can be programmed. A special PROM programmer is employed to enter the program on the PROM. Once the chip has been programmed, information on the PROM can’t be altered. PROM is non-volatile, that is data is not lost when power is switched off.  EPROM: Another sort of memory is the Erasable Programmable Read-Only Memory. It is possible to erase the info which has been previously stored on an EPROM and write new data onto the chip.EPROM can be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. The user then can write new program on it.  EEPROM : EEPROM is Electrically erasable programmable read-only memory. Here, data can be erased without using ultraviolet light, with the use of just applying the electric field. It can be erased and re-programmed about ten thousand times. Both erasing and programming take about 4 to 10 ms (millisecond). In EEPROM, any location can be selectively erased and programmed. EEPROMs can be erased one byte at a time, rather than erasing the entire chip. Hence, the process of Re-programming is flexible but slow. Prof. Ankita Sorathia Page 10  103-IC Unit-2 SDJ International College 2.3.5. Storage Devices – Hard Disk, CD, DVD, USB flash memory 2. Magnetic Storage Devices :: Physically, a magnetic disk is a thin, circular plate/platter made of metal or plastic that is usually coated on both sides with a magnetizable recording material such as iron-oxide Data are recorded on the disk in the form of tiny invisible magnetized and non-magnetized spots (representing 1s and 0s) on the coated surfaces of the disk The disk is stored in a specially designed protective envelope or cartridge, or several of them are stacked together in a sealed, contamination-free container  Floppy Disk: Floppy Disk is also known as a floppy diskette. It is generally used on a personal computer to store data externally. A Floppy disk is made up of a plastic cartridge and secured with a protective case. Nowadays floppy disk is replaced by new and effective storage devices like USB, etc. The two types of floppy disks in use today are:  5¼-inch diskette, whose diameter is 5¼-inch. It is encased in a square, flexible vinyl jacket  3½-inch diskette, whose diameter is 3½-inch. It is encased in a square, hard plastic jacket Advantages of Floppy Disk:  Floppy plates are little and light weighted. Subsequently, can be divert where the client needs.  The plastic packaging assists with adding no further enclosing’s. This ensures that plates don’t get scratch coincidentally.  Regarding evaluating as well, floppy plates are generally cheap. Since the costs of them can’t be contrasted with the capacity mediums today. Disadvantages of Floppy Disk:  Floppy disks have a limited storage capacity as compared to Hard disks.  Floppy circles are comprised of plastic packaging which is extremely fragile.  Heat and attractive fields are known to influence the floppy circles, hence leaving the records on it to get undermined. Prof. Ankita Sorathia Page 11  103-IC Unit-2 SDJ International College  Hard Disk: HDD is an electro-mechanical storage device, which is an abbreviation of Hard Disk Drive. It uses magnetic storage for storing and retrieving the digital data.  It is a non-volatile storage device.  Hard Disk Drive is installed internally in our computer systems, which is connected directly to the disk controllers of the motherboard.  Hard Disk Drive is a storage device which stores the operation system (OS), installed software, and the other computer files.  HDD means the data is retained when our computer system is shut down. HDD is also called a fixed disk, hard disk, or hard drive. The HDD was introduced in the year 1956 by IBM.  The first personal computer contains a hard drive of less than 1 megabyte, while modern computers contain the hard drive of 1 terabyte.  The disk is divided into tracks.  Each track is further divided into sectors.  Though the outer tracks are bigger in size than the inner tracks but they contain the same number of sectors and have equal storage capacity.  This is because the storage density is high in sectors of the inner tracks where as the bits are sparsely arranged in sectors of the outer tracks.  Some space of every sector is used for formatting. Working of Hard Disks  Read-Write(R-W) head moves over the rotating hard disk.  It is this Read-Write head that performs all the read and write operations on the disk and hence, position of the R-W head is a major concern.  To perform a read or write operation on a memory location, we need to place the R-W head over that position.  Some important terms must be noted here: o Seek time – The time taken by the R-W head to reach the desired track from it’s current position. o Rotational latency – Time taken by the sector to come under the R-W head. o Data transfer time – Time taken to transfer the required amount of data. It depends upon the rotational speed. o Controller time – The processing time taken by the controller. o Average Access time – seek time + Average Rotational latency + data transfer time + controller time. Advantages of Hard Disk Drives:  One of the significant advantages of a Hard Disk drive is that its cost is low.  Another advantage of Hard Disk Drive is that it is readily available in the market. Prof. Ankita Sorathia Page 12 103-IC Unit-2 SDJ International College  Hard Disk Drives are faster than the optical disks.  The capacity for storing the data in HDDs are large. Disadvantages of Hard Disk Drives :  The speed of reading and writing in HDD is slower than the RAM.  HDDs are noisy.  Another disadvantage of HDD is energy inefficiency. HDDs consume more power.  The form factor of HDDs is heavier than the SSDs. Types of Hard Disks  Zip/Bernoulli Disks: Uses a single hard disk platter encased in a plastic cartridge Disk drives may be portable or fixed type Fixed type is part of the computer system, permanently connected to it Portable type can be carried to a computer system, connected to it for the duration of use, and then can be disconnected and taken away when the work is done Zip disks can be easily inserted/removed from a zip drive just as we insert/remove floppy disks in a floppy disk drive.  Disk packs: Uses multiple (two or more) hard disk platters mounted on a single central shaft. Disk drives have a separate read/write head for each usable disk surface (the upper surface of the top-most disk and the lower surface of the bottom most disk is not used) Disks are of removable/interchangeable type in the sense that they have to be mounted on the disk drive before they can be used, and can be removed and kept off-line when not in use  Winchester Disks: Uses multiple (two or more) hard disk platters mounted on a single central shaft Hard disk platters and the disk drive are sealed together in a contamination-free container and cannot be separated from each other. For the same number of disks, Winchester disks have larger storage capacity than disk packs because: “All the surfaces of all disks are used for data recording (storing) Point of difference HDD SSD 1. Full form HDD stands for Hard Disk Drive. SSD stands for Solid State Drive. 2. Read-write time The time for reading and writing The time for reading and writing the data in HDD is longer. the data in SSD is shorter. 3. Latency High. Low. 4. Operation support Hard Disk Drives Solid State Drives supports fewer supports the more operations. operations of Prof. Ankita Sorathia Page 13  103-IC Unit-2 SDJ International College input/output per second 5. Weight The weight of HDDs is heavy. Because the SSDs do not have a rotating disk and motor, the weight of these storage devices is light. 6. Data Transfer In the HDDs, the In the SSDs, the transfer of data is transfer of data is not sequential sequential 7. Noise Due to the mechanical movements, This storage device does not produce HDDs produce noise. noise. 8. Cost Cheaper. More expensive. 9. Physical size HDD are larger in size. SSD are more compact in terms of physical size. 10. Magnetic effect Magnet can harm or erase the data SSD are safe from magnetic effect. completely. 11. Heat generation More because of mechanical parts. Low because no such moving mechanical parts are there. 12. Power consumption More power consumption because of Less power consumption. moving mechanical parts. 13. Boot-up time The average boot-up time of OS is 30 The average boot-up time of OS is 10 to 40 seconds. to 13 seconds. 14. File opening speed The file opening speed of HDDs is The file opening speed of SSD is 30% slightly slower. faster than the HDD. 15. Vibration Due to the spinning of platters may As there are no moving parts, so there results in vibration is no vibration  Magnetic Card: It is a card in which data is stored by modifying or rearranging the magnetism of tiny iron-based magnetic particles present on the band of the card. It is also known as a swipe card. It is used like a passcode(to enter the house or hotel room), credit card, identity card, etc.  Tape Cassette: It is also known as a music cassette. It is a rectangular flat container in which the data is stored in an analog magnetic tape. It is generally used to store audio recordings.  SuperDisk: It is also called LS-240 and LS-120. It is introduced by Imation Corporation and it is popular with OEM computers. It can store data up to 240 MB. Prof. Ankita Sorathia Page 14 103-IC Unit-2 SDJ International College 3. Flash Memory Devices It is a cheaper and more portable storage device. It is the most commonly used device to store data because is more reliable and efficient as compared to other storage devices. Some of the commonly used flash memory devices are:  Pen Drive: It is also known as a USB flash drive that includes flash memory with an integrated USB interface. We can directly connect these devices to our computers and laptops and read/write data into them in a much faster and more efficient way. These devices are very portable. It ranges from 1GB to 256GB generally.  SSD: It stands for Solid State Drive, a mass storage device like HDD. It is more durable because it does not contain optical disks inside like hard disks. It needs less power as compared to hard disks, is lightweight, and has 10x faster read and writes speed as compared to hard disks. But, these are costly as well. While SSDs serve an equivalent function as hard drives, their internal components are much different. Unlike hard drives, SSDs don’t have any moving parts and thus they’re called solid-state drives. Instead of storing data on magnetic platters, SSDs store data using non-volatile storage. Since SSDs haven’t any moving parts, they do not need to “spin up”. It ranges from 150GB to a few more TB.  SD Card: It is known as a Secure Digital Card. It is generally used with electronic devices like phones, digital cameras, etc. to store larger data. It is portable and the size of the SD card is also small so that it can easily fit into electronic devices. It is available in different sizes like 2GB, 4GB, 8GB, etc.  Memory Card: It is generally used in digital cameras. printers, game consoles, etc. It is also used to store large amounts of data and is available in different sizes. To run a memory card on a computer you require a separate memory card reader.  Multimedia Card: It is also known as MMC. It is an integrated circuit that is generally used in-car radios, digital cameras, etc. It is an external device to store data/information. 4. Optical Storage Devices Optical Storage Devices is also secondary storage device. It is a removable storage device.  An optical disk stores data using laser light and is read using the same.  Laser light reads data on a spinning disk.  Due to this, optical disks are also known as laser disks or optical laser disks.  CD: It is known as Compact Disc. It contains tracks and sectors on its surface to store data. It is made up of polycarbonate plastic and is circular in shape. CD can store data up to 700MB. o CDs can store many types of data like audio, video, games, any documents, etc.  The data are scanned by a laser beam with a CD driver to visualize the data.  The only thing that is less in CD is storage capacity is very less compared to HDD or DVD and the read-write speed is also very less.  CD was invented in the year 1960 by the American physicist James Russell.  The compact disk (CD) was introduced by Philips and Sony in 1980 and released in 1982.  The standard diameter of a CD is 120mm and thickness is 1.2mm. Prof. Ankita Sorathia Page 15  103-IC Unit-2 SDJ International College Following are some optical storage devices:  CD-R (Compact Disc – Recordable):  This type of compact disc can be written only once and can not erased. You only have one chance to write or burn the data into the CD-R and the data can not be deleted and/or erased afterwards.  Its follows the WORM (Write Once Read Many) strategy.  The CD-R is the disc that you will use if you have audios, videos, or any other data that you want to store by burning or writing it in to the disc.  The data stored inside the CD-R is done by burning/writing process.  CD-ROM (Compact Disk - Read Only Memory):  This disks are read once, after read it is use as a ROM, that is cannot be updated later.  CD ROM on the other hand contained pre-pressed data that are usually software or games that can only be read alone.  The data stored in the CD ROM is done by pressing.  CD-RW (Compact Disc - ReWritable):  This type of compact disc can be written multiple times and can be erased also, like pendrive.  A CD-RW can be written, read, erased, and re-written. Advantages of CD:  Cost of CD is cheap.  It can be carried out easily. Its portable  It uses a laser to burn data into the disk, so that no noise in the data.  In that time, an entire software package can be stored on one CD, so its very reliable for the software industries in the days. Disadvantages of CD:  Easy to scratch on CD.  Storage capacity is lower than a hard drive or DVD, nowadays CD is not used at all.  Read-write speed is slower.  To burn CD we need software, so burning is not much easy as hard disk or pen drive.  DVD: It is known as Digital Versatile Disc. DVDs are circular flat optical discs used to store data. It comes in two different sizes one is 4.7GB single-layer discs and another one is 8.5GB double- layer discs. DVDs look like CDs but the storage capacity of DVDs is more than as compared to CDs. It is of two types:  DVD-R: It stands for Digital Versatile Disc read-only. In this type of DVD, once the data is written can not be erased. It is read-only. It is generally used to write movies, etc.  DVD-RW: It stands for Digital Versatile Disc Read Write. In this type of DVD, you can easily write or erase data multiple times. Advantages of DVD:  DVD’s are used to hold very large files several Gb.  DVD’s are portable.  DVD’s have five to ten time’s the capacity compared to CD.  Not at risk to magnetic fields and resistant to heat. Disadvantages of DVD:  Not fully supported by HDTV. Prof. Ankita Sorathia Page 16  103-IC Unit-2 SDJ International College  Incompatibility of discs and players.  There is no single standard of DVD.  Blu-ray Disc: It is just like CD and DVD but the storage capacity of blu ray is up to 25GB. To run a Blu-ray disc you need a separate Blu-ray reader. This Blu-ray technology is used to read a disc from a blue-violet laser due to which the information is stored in greater density with a longer wavelength. 5. Cloud and Virtual Storage Nowadays, secondary memory has been upgraded to virtual or cloud storage devices. We can store our files and other stuff in the cloud and the data is stored for as long as we pay for the cloud storage. There are many companies that provide cloud services largely Google, Amazon, Microsoft, etc. We can pay the rent for the amount of space we need and we get multiple benefits out of it. Though it is actually being stored in a physical device located in the data centers of the service provider, the user doesn’t interact with the physical device and its maintenance. For example, Amazon Web Services offers AWS S3 as a type of storage where users can store data virtually instead of being stored in physical hard drive devices. These sorts of innovations represent the frontier of where storage media goes. Characteristics of Computer Storage Devices  Data stored in the Memory can be changed or replaced in case of a requirement, because of the mobility of the storage devices.  Storage Devices validate that saved data can be replaced or deleted as per the requirements because the storage devices are easily readable, writeable, and rewritable.  Storage Devices are easy and convenient to access because they do not require much skill set to handle these resources.  The storage capacity of these devices is an extra advantage to the system.  Storage Devices have better performance and data can be easily transferred from one device to another. 2.4. Introduction to Software 2.4.1 Purpose and significance of Operating System The operating system (OS) acts as a manager for all the I/O device, memory, CPU, file storage resources and allocates them to specific programs and users, whenever necessary to perform a particular task. Therefore, the operating system is the resource manager that means it can manage the resources of a computer system internally. There are some of functionalities of Operating System given below. 1.) Program Execution The purpose of a computer systems is to allow the user to execute programs. So the operating systems provides an environment where the user can conveniently run programs. The user does not have to worry about the memory allocation or multitasking or anything. These things are taken care of by the operating systems. Running a program involves the allocating and deallocating memory, CPU scheduling in case of multiprocess. These functions cannot be given to the user-level programs. So user-level programs cannot help the user to run programs independently without the help from operating systems. 2.) I/O Operations Prof. Ankita Sorathia Page 17 103-IC Unit-2 SDJ International College Each program requires an input and produces output. This involves the use of I/O. The operating systems hides the user the details of underlying hardware for the I/O. All the user sees is that the I/O has been performed without any details. So the operating systems by providing I/O makes it convenient for the users to run programs. For efficiently and protection users cannot control I/O so this service cannot be provided by user-level programs. 3.)File System Manipulation The output of a program may need to be written into new files or input taken from some files. The operating systems provides this service. The user does not have to worry about secondary storage management. User gives a command for reading or writing to a file and sees his her task accomplished. Thus operating systems makes it easier for user programs to accomplished their task. This service involves secondary storage management. The speed of I/O that depends on secondary storage management is critical to the speed of many programs and hence I think it is best relegated to the operating systems to manage it than giving individual users the control of it. It is not difficult for the user-level programs to provide these services but for above mentioned reasons it is best if this service s left with operating system. 4.)Communications There are instances where processes need to communicate with each other to exchange information. It may be between processes running on the same computer or running on the different computers. By providing this service the operating system relieves the user of the worry of passing messages between processes. In case where the messages need to be passed to processes on the other computers through a network it can be done by the user programs. The user program may be customized to the specifics of the hardware through which the message transits and provides the service interface to the operating system. 5.) Error Detection An error is one part of the system may cause malfunctioning of the complete system. To avoid such a situation the operating system constantly monitors the system for detecting the errors. This relieves the user of the worry of errors propagating to various part of the system and causing malfunctioning. This service cannot allowed to be handled by user programs because it involves monitoring and in cases altering area of memory or deallocation of memory for a faulty process. Or may be relinquishing the CPU of a process that goes into an infinite loop. These tasks are too critical to be handed over to the user programs. A user program if given these privileges can interfere with the correct (normal) operation of the operating systems. 2.4.2. Concept of System Software and Application Software Software is a set of programs, which is designed to perform a well-defined function. A program is a sequence of instructions written to solve a particular problem. There are two types of software − Prof. Ankita Sorathia Page 18 103-IC Unit-2 SDJ International College  System Software  Application Software System Software: The system software is a collection of programs designed to operate, control, and extend the processing capabilities of the computer itself. System software is generally prepared by the computer manufacturers. These software products comprise of programs written in low-level languages, which interact with the hardware at a very basic level. System software serves as the interface between the hardware and the end users. Some examples of system software are Operating System, Compilers, Interpreter, Assemblers, etc. Here is a list of some of the most prominent features of a system software −  Close to the system  Fast in speed  Difficult to design  Difficult to understand  Less interactive  Smaller in size  Difficult to manipulate  Generally written in low-level language Application Software: Application software products are designed to satisfy a particular need of a particular environment. All software applications prepared in the computer lab can come under the category of Application software. Prof. Ankita Sorathia Page 19 103-IC Unit-2 SDJ International College Application software may consist of a single program, such as Microsoft's notepad for writing and editing a simple text. It may also consist of a collection of programs, often called a software package, which work together to accomplish a task, such as a spreadsheet package. Examples of Application software are the following −  Payroll Software  Student Record Software  Inventory Management Software  Income Tax Software  Railways Reservation Software  Microsoft Office Suite Software  Microsoft Word  Microsoft Excel Features of application software are as follows −  Close to the user  Easy to design  More interactive  Slow in speed  Generally written in high-level language  Easy to understand  Easy to manipulate and use  Bigger in size and requires large storage space Point of SystemSoftware Application Software difference 1. Definition System Software maintain the Application software is system resources and give the built for specific tasks. path for application software to run. 2. Language Low level languages are used to High level languages are used write the system software. to write the application software. 3. Purpose Its a general While its a specific purpose purpose software. software. 4. System Without system software, While without application running system can’t run. software system always runs. 5. Working System software runs when While application software system is turned on and stop runs as per the user’s when system is turned off. request. Prof. Ankita Sorathia Page 20 103-IC Unit-2 SDJ International College 6. System Software programming is Application software Programming complex than application software. programming is simpler as comparison to system software. 7. Examples Operating systems Notepad, Photoshop. Microsoft office, etc. Prof. Ankita Sorathia Page 21