Digital computer Basics by, Er. Swapnil Kaware

“Computer Memory
Basics”
Simplified Concept By,
Er. Swapnil V. Kaware,
M.E. (Electronics & Telecommunication)
svkaware@yahoo.co.in
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Simplified concepts by Er. Swapnil V.
Kaware

What is digital computer?.
• A digital computer is machine that stores
data in a numerical format and performs
operations on that data using mathematical
manipulation.
• This type of computer typically includes some
sort of device to store information, some
method for input and output of data, and
components that allow mathematical
operations to be performed on stored data.
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What is digital computer?.
• It accepts digital data as input, then it processes it
according to the instructions stored in its memory,
and provides the results as an output.
• A digital computer, however, stores all data as
numbers and performs operations on that data
arithmetically.
• Most computers use binary numbers to store data, as
the ones and zeros that make up these numbers are
easily represented with simple on-off electrical
states.
Simplified concepts by Er. Swapnil V. Kaware 3

Block diagram of digital computer
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Inside view of CPU…….
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(1). Input
• This is the process of entering data and
programs into the computer system. The main
purpose behind the use of this device is, to
provide data to the processing unit.
• e.g. Keyboard, Mouse, Light Pen,
Optical/magnetic Scanner, Touch Screen,
• Microphone etc.
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(2). Control Unit (CU)
• The process of input, output, processing
and storage is performed under the
supervision of a unit called 'Control Unit'.
• It decides when to start receiving data,
when to stop it, where to store data, etc.
• It takes care of step -by-step processing of
all operations in side the computer.
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(2). Control Unit (CU)
• The Control Unit acts like the supervisor
• It extracts instructions from memory and
decodes and executes them, and sends
the necessary signals to the ALU to
perform the operation needed.
• The control unit determines the sequence
in which computer programs and
instructions are executed.
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Arithmetic Logic Unit (ALU)
• The major operations performed by the ALU
are addition, subtraction, multiplication,
division, logic and comparison.
• The actual processing of the data and
instruction are performed by Arithmetic Logical
Unit.
• Data is transferred to ALU from storage unit
when required.
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CPU
• The ALU and the CU of a computer system are jointly
known as the central processing unit (CPU).
• The main purpose behind the use of this device is, to
control all the activities/processes happening inside
the microprocessor system.
• The CPU (Central Processing Unit) performs most of
the calculations which enable a computer to function,
and is sometimes referred to as the "brain" of the
computer.
• It is usually cooled by a heat sink and fan.
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Memory Unit
• The main purpose behind the use of this device is, to
store the data & Instructions for future purpose.
• The process of saving data and instructions
permanently is known as storage.
• The term primary memory is used for the information
in physical systems which function at high-speed.
Eg. RAM.
• The term secondary memory, for program and data
storage which are slow to access but offer higher
memory capacity. Eg ROM.
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Output
This is the process of producing results from
the data for getting useful information.
The main purpose behind the use of this
device is, to show data transferred from
processing unit.
Examples of output units: Screen, printers,
plotters, Monitor, Speakers etc.
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SOFTWARE
• It is the set of rules/instructions who instructs computer
about what to do, how to do and when to do.
• In order to perform any task, we have to give a set of
instructions in a particular sequence to the computer.
• These sets of instructions are called Programs.
• A software refers to a set of programs that makes the
hardware perform a particular set of tasks in particular
order.
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Hardware
• Computer hardware is the collection of physical
elements that constitutes a computer system.
• Computer hardware refers to the physical parts
or components of a computer such as
the monitor, mouse, keyboard, computer data
storage, hard drive disk (HDD), system unit
(graphic cards, sound cards, memory,
motherboard and chips), etc.
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Firmware
• Firmware is a software program or set of instructions
programmed on a hardware device.
• It provides the necessary instructions for how the device
communicates with the other computer hardware.
• Firmware is typically stored in the flash ROM of a hardware
device.
• Firmware can be thought of as semi-permanent since it
remains the same unless it is updated by a firmware updater.
• Firmware is held in non-volatile memory devices such
as ROM, EPROM, or flash memory.
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• Bit - Smallest unit of computer
memory.
• Byte - 8 bit = 1 byte
• Kilobyte - 1024 byte = 1 Kb
• Megabyte - 1024 kb = 1 Mb
• Gigabyte - 1024 mb = 1 Gb
• Terabyte - 1024 gb = 1 Tb
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Classification of Memory
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RAM
• Commonly known as Random Access Memory, or
just RAM.
• It holds instructions and data needed for
programs that are currently running.
• Contents of RAM are lost when power is turned
off.
• Hence RAM is usually a volatile type of memory
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RAM
• The storage of data and instructions inside the primary
storage i.e. RAM is temporary.
• Data and instructions can be read and modified.
• An example is as follows: A mobile phone has 128 kB or
256 kB of RAM to hold the stack and temporary
variables of the programs, operating system, and data.
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ROM
• It is also called as Read Only Memory
(ROM).
• The storage of program and data in the
ROM is permanent.
• It can be readable but cannot be
changable by the user/programmer.
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ROM
• Contents of ROM are not lost even when
power is turned off.
• Hence ROM is a Non-volatile type memory.
• Hence ROM is used to store as a permanent
data.
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SRAM
• Retains contents as long as power is maintained
• The word “static” refers that the memory retains its
contents as long as the power is supplied so that’s
why we can say this is volatile in nature.
• SRAM does not need to be refreshed periodically
• SRAM is faster but more expensive.
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SRAM
• It is faster with a typical assess time of
nanoseconds.
• SRAM can have an access time as low as 10
nanoseconds.
• FAST SRAM can be found in most CPU's, on
graphic/video cards, and on credit-card memory
cards.
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SRAM
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DRAM
• Must be constantly refreshed.
• Used for most PC memory because of size and cost.
• It also contains data only when electricity is available.
• DRAM needs to refreshed periodically due to this,
this RAM works slower.
• Mainly general PC uses this RAM because it is much
cheaper than SRAM and requires less space.
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DRAM
• Typically has access times of 50 to 70
nanoseconds (ns).
• it is what makes up the bulk of the system
memory in most systems.
• DRAM consists of micro capacitors, while
SRAM consists of off/on switches.
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DRAM
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PROM
• It is allso known as Programmable ROM
(Programmable Read Only Memory).
• It is possible for you to store your program in
PROM chip.
• Once the programmes are written it cannot be
changed and remain intact even if power is
switched off.
• Programs or instructions written in PROM or
ROM cannot be erased or changed.
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PROM
• Known as “programmable Read Only memory”.
• In this when the data is stored then we have no right to
change or alter any data to it.
• In this the data is written by Manufacturer company, even
you can also purchase blank PROM chip but it can be
programmed by special tool such as PROM programmers.
• In general PC’s mainly PROM is used because we don’t
have to alter any data to it
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PROM
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EPROM
It is also known as Erasable ROM.
The word “erasable” means we can change or
erase the data.
In this we can change the data with the help of
ultra violet rays.
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EPROM
• Reprogramming requires up to 20 minutes of high-intensity
UV light exposure.
• i.e. Once programmed, an EPROM can be erased
with the help of ultraviolet light.
• EPROM is less expensive.
• All data locations gets erased.
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EPROM
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EEPROM
• It is also known as “Electrically Erasable
Programmable ROM”.
• It is also called EAROM (Electrically Alterable
ROM) and NOVRAM (Non-Volatile RAM).
• The word refers “erasable” means we can
change or erase the data.
• The inside values/data can be stored and
erased electronically.
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EEPROM
• It Can change individual bytes without erasing the
entire chip.
• Selective/Particular data locations gets erased..
• EEPROM can be erased one byte at anytime by
using voltage between 20 to 25 volts for 10ms.
• It is more expensive.
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EEPROM
Most computers use it to hold up their startup instructions
Also used in many mobiles, smart phones, digital cameras
and PDA, camera, MP3 player, etc.
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Flash Memory
• Flash memory is an electronic non-volatile
computer storage medium that can be
electrically erased and reprogrammed.
• A flash memory functions as the ROM.
• Most computers use it to hold up their startup
instructions
• Used in Cellular phones, Digital cameras, Digital
music recorders, smart phones, digital cameras and
PDA, etc.
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Flash Memory
• There are two main types of flash memory.
1. NAND,
2. NOR,
• NAND type flash memory may be written and
read in blocks.
• NOR type flash allows a single machine
word(byte) to be written to an erased
locaFon or read independently.
• It requires equires low power.
• It is used in portable equipments.
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Flash Memory
• Following are the flash memory applications,
(i). It is used during the program run to save
nonvolatile data and results, for examples, a
picture in a digital camera, voice mail.
(ii). It is used to store storing SMS, MMS messages
in a mobile phone, phone book, address book.
(iii). It is used to store voice compressed form in a
voice recorder.
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Flash Memory
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Have a Nice
Day
Ahead!!!!!
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Kaware

Digital computer Basics by, Er. Swapnil Kaware

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