ITT Course – Unit I

ITT Course – Unit I

Chapter 2Parts of Computer

The Institute of Chartered Accountants of India(Setup by an Act of Parliament)

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100 Hours ITT Course

Learning Objectives To understand the various functions of CPU To know the concept of Virtual Memory To discuss about Bus, add-on cards, motherboard, sound card

and expansion slots


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An Introduction

A computer is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware.


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Typical PC Hardware

Hardware of PC:-1. Monitor2. Motherboard3. CPU4. RAM Memory5. Expansion card6. Power supply7. CD-ROM Drive8. Hard Disk9. Keyboard10. Mouse

http://en.wikipedia.org/wiki/File:Personal_computer,_exploded_5.svg


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Common Computer Architecture

Computers come in different forms, but most of them have a common architecture.

• All computers have a CPU • All computers have some kind of data bus which lets them get

inputs or output things to the environment.

• All computers have some form of memory. These are usually chips (integrated circuits) which can hold information.

• Many computers have some kind of sensors, which lets them get input from their environment.

• Many computers have some kind of display device, which lets them show output. They may also have other peripheral devices connected.


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Basic Computer Components (at a glance…)

• Case (Computer Cabinet)o Power Supplyo Motherboard

Microprocessor Memory Drive Controllers

o Hard Disk Driveo CD-ROM Driveo Floppy Drive o DVD Drive

• Monitor • Keyboard• Mouse


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Case (Computer Cabinet)

There are two basic styles of cases the computer may come assembled in as follows:-• Tower Style Case • Desktop Style Case

Front ViewRear View


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Desktop Style Case

Desktop style is in the shape of a rectangular box, that sets flat on a desk. Usually the computer monitor is placed on top of it.


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Tower Style Case

• A tower case, looks similar to a tower and are placed off to the side of the keyboard and monitor.

• The tower case is the most popular style of desktop computer today.

• Tower cases comes in varied sizes as mini tower, mid tower and full tower.


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Computer Case Related Terminology

Pin - A part of a connector that extends outward to extend into and make contact with a socket. Referred to as the male side of a connector.

Socket - A part of a connector that contains an internal contact to receive the extended side (pin) of a connector. Referred to as the female side of a connector.

Jack - A receptacle where power of signal connectors may be plugged into. These are usually on the case of a computer or the motherboard and are made to receive plugs from devices such as keyboards.

Plug - The part that connects with the jack, which comes from a keyboard, mouse, monitor or other device. This is the side associated with a cable.

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Inside the Case (Computer Cabinet)


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SMPS

A SMPS (Switched-Mode Power Supply is an electronic PSU (Power Supply Unit) that incorporates a switching regulator in order to provide the required output voltage. It attempts to produce a smoothed, constant-voltage, output from a varying input voltage.


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Inside SMPS

Legend:A - bridge rectifier B - input filter capacitors C - transformer D - output filter coil E - output filter capacitors


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Motherboard

A motherboard is the central printed circuit board (PCB) in a modern computers, and holds many components of the system, while providing connectors for other peripherals. • A typical desktop computer

has its microprocessor, main memory, and other essential components on the motherboard.

• Components such as external storage, controllers for video display & sound, and peripheral

devices may be attached to the motherboard as plug-in cards or

via cables. “In modern computers it is increasingly common to integrate some of the above mentioned peripherals into the motherboard itself.”


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Components of A Motherboard

http://upload.wikimedia.org/wikipedia/commons/9/9d/Acer_E360_Socket_939_motherboard_by_Foxconn.svg


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Modern Motherboard Configuration• Sockets (or slots) in which one or more microprocessors are

installed.• Slots into which the system's main memory is installed. • A chipset which forms an interface between the CPU's front-side

bus, main memory, and peripheral buses.

• Non-volatile memory chips (usually Flash ROM in modern motherboards) containing the system's firmware or BIOS

• A clock generator which produces the system clock signal to synchronize the various components

• Slots for expansion cards (these interface to the system via the buses supported by the chipset)

• Power connectors flickers, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.

• logic and connectors to support commonly-used input devices, such as PS/2 connectors for a mouse and keyboard.

• Additional peripherals such as disk controllers and serial ports were provided as expansion cards.


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Role of Motherboard Organization of Devices: Everything is connected to the motherboard & the way that the motherboard is designed dictates how the entire computer is going to be organized.

Control of the Devices: Built-in to the motherboard is the chipset and BIOS program, which between them control the majority of data flow throughout the different computer systems.

System Communication: Almost all communication between the PC and its peripherals, other PCs, and, the user, goes through the motherboard.

Processor Support: The motherboard socket depicts which choice of processor can be used in the system.

Peripheral Support: The motherboards components determine what type of peripherals can be used in the PC. For example, you can not use AGP cards if you only have PCI slots.

System Performance: The motherboard is a major factor in your system's performance as it dictates which type of processors, memory, system buses, and hard disk interface speed the system can have via its connectors or BIOS settings.

Upgradeability: As motherboards are developed newer processors may not be compatible with the hardware as limitations of the circuitry built-in to the board itself will not allow them to run. As a result a user can look for any upgrades.


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Modern Motherboard (Block Diagram)

• Modern Motherboard supports many on-board peripheral functions as well as several expansion slots.

• It is now possible to include support for many peripherals on the motherboard by combining many functions on one PCB

• The physical size and total cost of

the system may be reduced & highly-integrated motherboards can be produced.

http://upload.wikimedia.org/wikipedia/commons/b/bd/Motherboard_diagram.svg




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Bus• A 'bus' is a set of wires or copper tracks that are built into the

motherboard. • A bus is a parallel data communication path over which information

is transferred a byte or word at a time.

• The buses contain logic that the CPU controls. • The items controlled are the transfer of data, instructions, and

commands between the functional areas of the computer: CPU, memory, and I/O.

• The direction of signal flow for the different buses may be unidirectional or bidirectional depending on the type of bus and type of computer.

Need for a Bus:-• The CPU needs to move information in and out of memory. • Data needs to move between the hard disk and the CPU. • Data needs to move between the graphics card and the CPU • Data needs to move between the CDROM / DVD and the CPU • External buses such as USB can transfer data in & out of computer.


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Types of Buses

All computers use three types of basic buses. The name of the bus is generally determined by the type of signal it is carrying or the method of operation. Following are the types of buses:-Data Bus: These buses carry data from one unit to other, it is a bi-directional bus i.e., the data can be carried in both directions. Address Bus: These buses carry address given by the CPU from one unit to another in the computer. Control Bus: These buses carry control signal from ALU to memory and from memory to ALU and then to the output unit.


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Data BusThe bidirectional data bus, sometimes called the memory bus, handles the transfer of all data and instructions between functional areas of the computer. The bidirectional data bus can only transmit in one direction at a time. The data bus is used to transfer instructions from memory to the CPU for execution. It carries data (operands) to and from the CPU and memory as required by instruction translation. The data bus is also used to transfer data between memory and the I/O section during input/output operations.

• A bus usually contains between 1 to 64 wires or more, the no. of wires equals the number of 'bits' that can be transferred in one clock cycle.

• An 8 bit bus has 8 wires - it can transfer 8 bits

in one go, with 1 bit on each wire. • A 16 bit bus can transfer 16 bits in one cycle -

1

bit per wire.


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Address BusThe address bus consists of all the signals necessary to define any of the possible memory address locations within the computer, or for modular memories any of the possible memory address locations within a module. An address is defined as a label, symbol, or other set of characters used to designate a location or register where information is stored. Before data or instructions can be written into or read from memory by the CPU or I/O sections, an address must be transmitted to memory over the address bus.

• The number of lines in the address bus determines the amount of memory that can be directly addressed as each line carries one bit of the address.

• A computer with a 32-bit address bus can directly address 4GB of physical memory, while one with 36 bits can address 64GB.


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Control Bus

The control bus is used by the CPU to direct and monitor the actions of the other functional areas of the computer. It is used to transmit a variety of individual signals (read, write, interrupt, acknowledge, etc.) necessary to control & coordinate the operations of the computer.


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Other Classification of Bus

• Buses can be parallel buses, which carry data words in parallel on multiple wires, or serial buses, which carry data in bit-serial form.

• Most computers have both internal and external buses. An internal bus connects all the internal components of a computer to the motherboard (and thus, the CPU and internal memory). These types of buses are also referred to as a local bus, because they are intended to connect to local devices, not to those in other machines or external to the computer. An external bus connects external peripherals to the motherboard.

Examples of internal computer buses : Parallel• ISA (Industry Standard Architecture)• Multibus for Industrial Systems

Serial• 1-Wire• PCI Express

Examples of external computer buses : Parallel• SCSI (Small Computer System

Interface)• ATA (Advanced Technology

Attachment)

Serial• USB (Universal Serial Bus)• Serial ATA


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Input – Output Ports / Interface

Input-output ports are material elements on the computer, allowing the system to communicate with exterior elements, in other words to exchange data, hence the name input-output interface.


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Serial Ports / Interface

• Serial ports (also called RS-232, after the name of the standard they refer to) represent the first interfaces to allow computers to exchange information with the "outside world".

• The term serial refers to data sent via a single wire: the bits are sent one after the other.

• A personal computer generally has between one and four serial ports.

Serial connectors generally have 9 or 25 pins and take the above form as DB9 & DB25 connectors respectively


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Parallel Ports / Interface

• Parallel data transmission involves sending data simultaneously on several channels (wires). The parallel ports on personal computers can be used to send 8 bits (one octet) simultaneously via 8 wires.

Parallel ports, like serial ports, are built into the mother board. DB25 connectors allow connection to an exterior element (e.g. a printer).


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CPU

• The Central Processing Unit (CPU) or processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions.

• It controls all internal and external devices, performs arithmetic and logic operations.

• It interprets and carries out,

or processes, instructions and data contained in the software.


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Explaining CPU (A Real Life Example)


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Arithmetic Logical Unit

• The arithmetic and logic unit (ALU) is the part where actual computations take place. It consists of circuits which perform arithmetic operations (e.g. addition, subtraction, multiplication, division) over data received from memory and capable to compare numbers.

• While performing these operations the ALU takes data from the temporary storage area inside the CPU named registers.


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Diagrammatic View of Arithmetic Logical Unit


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Registers

• Registers are a small amount of memory locations built into the CPU.

• Registers are a group of cells used for memory addressing, data manipulation and processing.

• Some of the registers are general purpose and some are reserved for certain functions.

• It is a high-speed memory which holds only data for immediate processing and

results of this processing. • If these results are not needed for the

next instruction, they are sent back to the main memory and registers are occupied by the new data used in the next instruction.


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Types of Registers

The System Registers are mainly used by operating systems and system development programs (e.g. compilers).

Basic Register Types(differentiated by CPU architecture)

Basic Register Types(differentiated by CPU architecture)

Basic Registers System Registers

Operating systems and application programs access Basic Registers via instructions in order to store code / data / state information, change / compare data and transfer / change program flow.


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Categories of Registers

User Accessible RegisterData Register

Address Register

Index Register

Stack Register

Conditional Register

General Purpose Register

Floating Point Register

Constant Register

Vector Register

Special Purpose Register

Control & Status Register

Program Counter

Instruction Register

Program Status Word

Model Specific Register


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Registers Categories (Explained)User-accessible Registers User-accessible registers are divided into data registers & address registers. Data registers are used to hold numeric values such as integer and floating-point values.Address registers hold addresses and are used by instructions that indirectly access memory. Index registers are used for a special kind of indirect addressing where an immediate constant (i.e. which is part of the instruction itself) is added to the contents of a register to form the address to the actual operand or data.Stack register can be used by some instructions to maintain a stack (data structure). Conditional registers hold truth values often used to determine whether some instruction should or should not be executed. General purpose registers can store both data and addresses, i.e., they are combined Data / Address registers. Floating point registers store floating point numbers in many architectures. Constant registers hold read-only values such as zero, one, or pi. Vector registers hold data for vector processing done by SIMD instructions (Single Instruction, Multiple Data). Special purpose registers hold program state; they usually include the program counter , stack pointer, and status register .Model-specific registers store data and settings related to the processor itself.Control and status registers has three types. Program counter, instruction registers,

Program status word.


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Facts about CPU• The Central Processing Unit (CPU) is the brain of the computer.• Modern CPU's are what are called 'integrated chips'. • The CPU is composed of thousands of transistors. • Each transistor is a set of inputs and outputs. When the inputs

receive electricity, the combined charge changes the state of the transistor internally and you get a result out the other side. This simple effect of the transistor is what makes it possible for the computer to count and perform logical operations, all of which we call processing.

• The CPU attaches directly to a CPU "socket" on the motherboard. The CPU is inserted into the socket pin-side-down and a small lever helps to secure the processor.

• After running, modern CPUs can get very hot. To help dissipate this heat, it is necessary to attach a heat sink and a small fan directly on top of the CPU.

• A CPU usually contains an execution core with two or more pipelines, a data and address bus, a dedicated arithmetic logic unit (ALU, also called the math co-processor), and in some cases special high-speed memory for caching program instructions from RAM.

• The CPU's in most PC's and servers are general purpose integrated chips composed of several smaller dedicated-purpose components which together create the processing capabilities of the modern computer.


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CPU Operation

The fundamental operation of most CPUs is to execute a sequence of stored instructions called a program. The program is represented by a series of numbers that are kept in some kind of computer memory. There are four steps that nearly all CPUs use in their operation: fetch, decode, execute, and writeback.

Step 1: The first step, fetch, involves retrieving an instruction from program memory. Step 2: the decode step, the instruction is broken up into parts that have significance to other portions of the CPU. Step 3: the execute step is performed during which the various portions of the CPU are connected so they can perform the desired operation. Step 4: The final step, writeback, simply "writes back" the results of the execute step to some form of memory.


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CPU Operation (Diagrammatic View)

Control unit ALU

Registers

Processing device

(1) Fetch

(2) Decode (3) Execute

(4) Store

Memory

I-time E-time


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CPU Components

• Execution Core • Data Bus • Address Bus • Math Co-processor • Instruction sets / Microcode • Multimedia extensions • Registers • Flags • Pipelining • Memory Controller • High-Speed Cache Memory


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Processor Manufacturer

American Micro Devices (AMD) Intel

IBM

Texas Instruments

Motorola

Cyrix

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Expansion Slots

An opening in a computer where a circuit board can be inserted to add new capabilities to the computer.

Expansion Slots are used for adding more memory, graphics capabilities, and support for special devices. The boards inserted into the expansion slots are called expansion boards, expansion cards , cards , add-ins , and add-ons.

The primary purpose of an expansion card is to provide or expand on features not offered by the motherboard.


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Fitting Expansion Card In A Slot


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Expansion Slot Standards

• PCI Express (Peripheral Component Interconnect Express) • AGP (Accelerated Graphics Port)• PCI (Peripheral Component Interconnect)• ISA (international Standard Architecture)


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Expansion Slot Standards

PCI a computer bus for attaching hardware devices in a computer. Typical PCI cards used in PCs include network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards and disk controllers. PCI Express is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP standards. PCI Express is used in consumer, server, and industrial applications, as a motherboard-level interconnect. AGP is a high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics. ISA is all but gone today Apart from specialized industrial use.


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Computer Data Storage

• Computer data storage, often called storage or memory, refers to computer components, devices, and recording media that retain digital data used for computing for some interval of time.

• Computer data storage provides one of the core functions of the modern computer, that of information retention.


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Storage Terminologies

• A digital computer represents data using the binary numeral system.

• Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 1 or 0.

• The most common unit of storage is the byte, equal to 8 bits.

1 Byte = 8 bits1 Kilobyte (KB) = 1024 bytes 1 Megabyte (MB) = 1024 KB 1 Gigabyte (GB) = 1024 MB1 Terabyte (TB) = 1024 GB


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Storage Hierarchy

Various forms of storage, divided according to their distance from the central processing unit. The fundamental components of a general-purpose computer are arithmetic and logic unit, control circuitry, storage space, and input/output devices.


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Computer MemoryComputer systems use memory to store data. Memory should not be confused with hard disk space. In general, memory is used for programs and data that are currently being used. Hard disks store data permanently.


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Primary Storage / Main Memory

• Main memory is a device that records data and programs within a computer.

• It is also called "Main storage unit“ or “Primary Storage”. • This memory is the only one which is directly accessible to the

CPU. • The CPU continuously reads instructions stored there and

executes them as required.

• It uses semiconductor elements to record electrically, which makes it possible to perform fast operation and to read and write directly from CPU.

• It cannot be used in large quantities because the price for each unit is high.


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Processor Register

• They are located inside the processor. • Each register typically holds a word of data (often 32 or 64 bits). • CPU instructions instruct the arithmetic and logic unit to perform

various calculations or other operations on this data. • Registers are technically among the fastest of all forms of

computer data storage.


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Processor Cache

• It is an intermediate stage between ultra-fast registers and much slower main memory.

• It's use increases performance of the computer. • Most actively used information in the main memory is just

duplicated in the cache memory, which is faster, but of much lesser capacity.


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Cache (Level 1)

• Caches are designed to alleviate this bottleneck by making the data used most often by the CPU instantly available.

• This is accomplished by building a small amount of memory, known as primary or level 1 cache, right into the CPU.

• Level 1 cache is very small, normally ranging between 2 kilobytes (KB) and 64 KB.


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Cache (Level 2)

• The secondary or level 2 cache typically resides on a memory card located near the CPU.

• The level 2 cache has a direct connection to the CPU. A dedicated integrated circuit on the motherboard, the L2 controller, regulates the use of the level 2 cache by the CPU. Depending on the CPU, the size

of the level 2 cache ranges from 256 KB to 2 megabytes (MB). • In most systems, data needed by the CPU is accessed from the

cache approximately 95 percent of the time, greatly reducing the overhead needed when the CPU has to wait for data from the main memory.


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RAM

• It stands for Random Access Memory.• It is small-sized, light, but quite expensive.• It is volatile (lose the information when not powered).

The topic will be discussed in detail in the coming section…


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Reading & Writing Memory

• Main memory is directly or indirectly connected to the CPU via a memory bus.

• It is actually comprised of two buses • an address bus and • a data bus.

• The CPU firstly sends a number through an address bus, a number called memory address, that indicates the desired location of data.

• Then it reads or writes the data itself using the data bus. • Additionally, a memory management unit (MMU) is a small device

between CPU and RAM recalculating the actual memory address, for example to provide an abstraction of virtual memory or other tasks.


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ROM

• It stands for Read Only Memory.• It is a non-volatile primary storage.• It containing a small startup program (BIOS) is used to bootstrap

the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it.

The topic will be discussed in detail in the coming section…


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Flash Memory• Flash memory is a kind of semiconductor-based, non-volatile,

rewritable computer memory; that is, it has many of the same characteristics as RAM, except that the data is not wiped out when the machine is turned off.

• Flash memory stores bits of data in memory cells, but the data remains saved even when electrical power is cut.

• Due to its higher speed, durability, and low energy consumption, flash memory is ideal for many applications, such as digital cameras, mobile phones, printers, PDAs, laptop computers, and mp3 players.


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Types of Memory Card

There are many competing, incompatible memory card formats, almost one for every manufacturer. Among these formats of memory cards, the most common are as follows:-

• Compact Flash • Secure Digital cards (called SD Card) • Memory Stick • SmartMedia • MMC (MultimediaCard) • xD picture card


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Secondary Storage• Secondary storage (or external memory) differs from primary

storage in that it is not directly accessible by the CPU. • The computer usually uses its input/output channels to access

secondary storage and transfers the desired data using intermediate area in primary storage.

• It is non-volatile i.e., secondary storage does not lose the data when the device is powered down.

• In modern computers, hard disk drives are usually used as secondary storage.

• The secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories, providing also additional information (called metadata) describing the owner of a certain file, the access time, the access permissions, and other information.

• Some examples of secondary storage technologies are optical storage CD, DVD, flash memory, floppy disks, magnetic tape, paper tape, punched cards, Zip drives.


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Tertiary Storage• Tertiary storage or tertiary memory, provides a third level of

storage.• Typically it involves a robotic mechanism which will mount (insert)

and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use.

• It is primarily used for archival of rarely accessed information since it is much slower than secondary storage.

• It is primarily useful for extraordinarily large data stores, accessed without human operators.

• Typical examples include tape libraries and optical jukeboxes.

Steps to read information from tertiary storage• When a computer needs to read information from the tertiary storage, it will first

consult a catalog database to determine which tape or disc contains the information.

• Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library.


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Off-line Storage• Off-line storage, also known as disconnected storage, is a

computer data storage on a medium or a device that is not under the control of a processing unit.

• The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected.

• It must be inserted or connected by a human operator before a computer can access it again.

• Unlike tertiary storage, it cannot be accessed without human interaction.

• In modern personal computers, most secondary and tertiary storage media are also used for off-line storage.

• Optical discs and flash memory devices are most popular, and to much lesser extent removable hard disk drives.

• In enterprise uses, magnetic tape is predominant. • Older examples are floppy disks, Zip disks, or punched cards.


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Advantages of Off-line Storage• Off-line storage is used to transfer information, since the detached

medium can be easily physically transported. • Additionally, in case a disaster, for example a fire, destroys the

original data, a medium in a remote location will be probably unaffected, enabling disaster recovery

• Off-line storage increases general information security, since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques.

• Also, if the information stored for archival purposes is accessed seldom or never, off-line storage is less expensive than tertiary storage.


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Fundamental Storage Technologies

Semiconductor• Semiconductor memory uses semiconductor-based integrated

circuits to store information. • A semiconductor memory chip may contain millions of tiny

transistors or capacitors. • Both volatile and non-volatile forms of semiconductor memory

exist. • In modern computers, primary storage almost exclusively consists

of dynamic volatile semiconductor memory or dynamic random access memory.

• A type of non-volatile semiconductor memory known as flash memory has steadily gained share as off-line storage for home computers.

• Non-volatile semiconductor memory is also used for secondary storage in various advanced electronic devices and specialized computers.


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Magnetic • Magnetic storage uses different patterns of magnetization on a

magnetically coated surface to store information. Magnetic storage is non-volatile.

• The information is accessed using one or more read/write heads which may contain one or more recording transducers.

• A read/write head only covers a part of the surface so that the head or medium or both must be moved relative to another in order to access data.

• In modern computers, magnetic storage will take these forms:Magnetic disk

Floppy disk, used for off-line storage Hard disk drive, used for secondary storage

Magnetic tape data storage, used for tertiary and off-line storage


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Optical• Optical storage, the typical Optical disc, stores information in

deformities on the surface of a circular disc and reads this information by illuminating the surface with a laser diode and observing the reflection.

• Optical disc storage is non-volatile. • The deformities may be permanent (read only media ), formed

once (write once media) or reversible (recordable or read/write media).

• The following forms are currently in common use:• CD, CD-ROM, DVD, BD-ROM: Read only storage, used for mass

distribution of digital information (music, video, computer programs) • CD-R, DVD-R, DVD+R BD-R: Write once storage, used for tertiary and

off-line storage • CD-RW, DVD-RW, DVD+RW, DVD-RAM, BD-RE: Slow write, fast read

storage, used for tertiary and off-line storage • Ultra Density Optical or UDO is similar in capacity to BD-R or BD-RE

and is slow write, fast read storage used for tertiary and off-line storage.


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Magneto-optical Disc Storage • Magneto-optical disc storage is optical disc storage where the

magnetic state on a ferromagnetic surface stores information. • The information is read optically and written by combining

magnetic and optical methods.

• Magneto-optical disc storage is non-volatile, sequential access, slow write, fast read storage used for tertiary and off-line storage.

3D optical data storage has also been proposed.


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Paper• Paper data storage, typically in the form of paper tape or punched

cards, has long been used to store information for automatic processing, particularly before general-purpose computers existed.

• Information was recorded by punching holes into the paper or cardboard medium and was read mechanically (or later optically) to determine whether a particular location on the medium was solid or contained a hole.

• A few technologies allow people to make marks on paper that are easily read by machine, these are widely used for tabulating votes

and grading standardized tests. • Barcodes made it possible for any object that was to be sold or

transported to have some computer readable information securely

attached to it.


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Robotic storage• Large quantities of individual magnetic tapes, and optical or magneto-optical

discs may be stored in robotic tertiary storage devices.

• In tape storage field they are known as tape libraries, and in optical storage field

optical jukeboxes, or optical disk libraries per analogy. • Smallest forms of either technology containing just one drive device are referred

to as autoloaders or autochangers.• Robotic-access storage devices may have a number of slots, each holding

individual media, and usually one or more picking robots that traverse the slots and load media to built-in drives.

• The arrangement of the slots and picking devices affects performance. Important characteristics of such storage are possible expansion options: adding slots, modules, drives, robots.

• Tape libraries may have from 10 to more than 100,000 slots, and provide terabytes or petabytes of near-line information.

• Optical jukeboxes are somewhat smaller solutions, up to 1,000 slots.• Robotic storage is used for backups, and for high-capacity archives in imaging,

medical, and video industries. • Hierarchical storage management is a most known archiving strategy of

automatically migrating long-unused files from fast hard disk storage to libraries or jukeboxes. If the files are needed, they are retrieved back to disk.


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Types of Memory

Nonvolatile memory does not lose its data when the system or device is turned off. A no. of types of memory fall into this category. The most familiar is ROM, but Flash memory storage devices such as CompactFlash or SmartMedia cards are also forms of nonvolatile memory.

Types of Computer Memory(general classification)

Types of Computer Memory(general classification)

Volatile Memory Non-Volatile Memory

Volatile memory loses any data as soon as the system is turned off; it requires constant power to remain viable. Most types of RAM fall into this category.


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Volatile vs. Non-Volatile MemoryMemory

types

RAM ROM

SRAM DRAM PROM EPROM

Volatile Non-volatile

Semiconductor

EEPROM


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RAM

• RAM stands for Random Access Memory.

• It is the main memory of a computer which is used to store all of the working information of the computer such as the operating system, user programs and data.

• RAM is volatile.


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Dynamic RAM and Static RAM

Dynamic RAM is the most common type of RAM used in computers. It is relatively easy to manufacture and so is cheap. However, DRAM contents must be continually refreshed. The process of refreshing the memory takes time and while the memory is being refreshed it cannot be read from or written to. This makes DRAM cheap but slow.

Static RAM is physically different to dynamic RAM as the memory contents do not have to be continually refreshed. This means that it can always be accessed and so SRAM is a faster type of memory. However the process of manufacturing the memory and the components used make it more expensive. For this reason SRAM is used in smaller quantities where fast memory is required, such as cache.


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SDRAM

SDRAM (Synchronous Dynamic Random Access Memory) has a synchronous interface, meaning that it waits for a clock signal before responding to control inputs and is therefore synchronized with the computer's system bus.

SDRAM is widely used in computers; from the original SDRAM further generations of DDR (or DDR1), and then DDR2 and DDR3 have entered the mass market, with DDR4 currently being designed and anticipated to be available in 2012.


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ROM

• ROM stands for Read Only Memory.

• Whereas RAM is volatile, ROM is non-volatile which is to say that the contents are not lost when power is removed.

• ROM chips come with instructions already burned into the chip. It is commonly used for computer BIOS chips.

• ROM is cheap in high quantities and is generally used for PC BIOSes.


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PROM• PROM stands for Programmable

Read Only Memory.• PROM chips do not lose their data

when power is removed but, unlike standard ROM chips, come without a program already installed.

• The programs for the PROM chips

can be 'burned' into them with a special piece of programming hardware. Once burned this way the contents are never lost but nor can they be altered.

• PROM chips are commonly used where engaging a chip foundry to manufacture a custom ROM chip would be too expensive.

• PROM is expensive and is used for low volume applications.


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EPROM

• EPROM stands for Erasable Programmable Read Only Memory.

• EPROM chips can be erased once

programmed, thus making them ideal for testing new applications where a ROM chip will be required.

• They can be easily recognized by the plastic 'window' on the top of the chip. This is used to erase the

contents of the chip by shining ultra-violet light onto it.

• EPROM is expensive but reusable and are used for testing.


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EEPROM• EPROM stands for Electrically

Erasable Programmable Read Only Memory.

• EEPROMs can be programmed & erased without using any special extra hardware with the help of a simple electrical current.

• EEPROMs need not be completely programmed at one time. Instead blocks

of data can be programmed individually.• As well as being used in modern

computers for updateable BIOSes, EEPROMs are typically used for USB drives, as well as for compact flash memory, Multimedia cards, SD cards, etc.

• EEPROM is cheap and is used for reprogrammable ROM applications like

Flash.


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Summary of Memory Characteristics


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Virtual Memory

• Virtual memory is a computer system technique which gives an application program the impression that it has contiguous working memory (an address space), while in fact it may be physically fragmented and may even overflow on to disk storage.

• Systems that use this technique make programming of large applications easier and use real physical memory (e.g. RAM) more efficiently than those without virtual memory.

• Virtual memory differs significantly from memory virtualization in that virtual memory allows resources to be virtualized as memory for a specific system, as opposed to a large pool of memory being virtualized as smaller pools for many different systems.

• All modern general-purpose computer operating systems use virtual memory techniques for ordinary applications, such as word processors, spreadsheets, multimedia players, accounting, etc.


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Example of Virtual Memory

Documents

ITT Course – Unit I