Transcript ITT Course – Unit I – Chapter 2 – Parts of Computer

ITT Course – Unit I
Chapter 2
Parts of Computer
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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. Monitor
2. Motherboard
3. CPU
4. RAM Memory
5. Expansion card
6. Power supply
7. CD-ROM Drive
8. Hard Disk
9. Keyboard
10. Mouse
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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 Supply
o Motherboard
 Microprocessor
 Memory
 Drive Controllers
o Hard Disk Drive
o CD-ROM Drive
o 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 View
Rear 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, constantvoltage, 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
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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.
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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 bidirectional 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 Bus
The 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 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.
The 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.
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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
Examples of external computer buses :
Parallel
• SCSI (Small Computer System Interface)
• ATA (Advanced Technology Attachment)
Serial
• 1-Wire
• PCI Express
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.
Input – Output
Ports / Interface
Serial Port
Parallel Port
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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
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.
The System Registers are
mainly used by operating
systems
and
system
development
programs
(e.g. compilers).
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Categories of Registers
Data Register
User Accessible Register
Conditional Register
Index Register
Address Register
Stack Register
General Purpose Register
Floating Point Register
Constant Register
Vector Register
Special Purpose Register
Program Counter
Model Specific Register
Instruction Register
Control & Status Register
Program Status Word
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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)
Processing device
Control unit
ALU
(2) Decode
I-time
(1) Fetch
(3) Execute
E-time
Registers
Memory
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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
Motorola
IBM
Texas Instruments
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.
The primary purpose
of an expansion card
is to provide or expand
on features not offered
by the motherboard.
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.
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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
1 Kilobyte (KB)
1 Megabyte (MB)
1 Gigabyte (GB)
1 Terabyte (TB)
=
=
=
=
=
8 bits
1024 bytes
1024 KB
1024 MB
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 Memory
Computer 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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The Institute of Chartered Accountants of India
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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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Fundamental Storage
Technologies
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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Fundamental Storage
Technologies
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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Fundamental Storage
Technologies
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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The Institute of Chartered Accountants of India
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Fundamental Storage
Technologies
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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Fundamental Storage
Technologies
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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The Institute of Chartered Accountants of India
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Types of Memory
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.
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.
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Volatile vs. Non-Volatile Memory
Semiconductor
Memory
types
Volatile
Non-volatile
RAM
SRAM
ROM
DRAM
PROM
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EPROM
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
Memory.
for
Read
Only
• 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
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