Computer memory and types of memory.pptx

Computer
Memory system
Prepared by
Shyama Barna Bhattacharjee

What will we learn from
today’s class?
• Computer memory system
• Types
• Characteristics of different memories
• What are the uses of different memories
• Real life example of that memory’s
implementation.

What is Memory?
The computer memory holds the data and
instructions needed to process raw data and
produce output. It is the same as a human mind,
where data, information, and instructions are
stored. It is a data storage device or a data
storage component where instructions for
processing data are kept along with the data
that has to be processed. Both the input and the
output can be held here.

How does computer memory work?
A program is loaded from secondary memory to primary memory when it
is opened. There are several types of memory and storage, for
example, a program being moved from a solid-state drive (SSD) to
RAM (Random Access Memory). The opened software will be able to
communicate with the computer's processor at a faster rate because
primary storage is accessed more quickly. The main or primary
memory can be accessed quickly from storage locations such as
temporary memory slots.
Data in memory is only saved temporarily since memory is volatile.
Data saved in volatile memory will be erased immediately whenever a
computer is turned off. A file is transported to secondary memory
for permanently storage when it is saved.
There are numerous kinds of memory present in a computer. Depending
on the primary memory utilized, it will perform differently, but
semiconductor-based memory is typically connected with memory.
Integrated circuits utilizing metal-oxide-semiconductor (MOS)
transistors based on silicon will be used to make semiconductor
memory.

Functions of Computer Memory
• Data Storage: The primary role of computer memory is to keep data. This includes the
OS, software packages, and user-generated documents. The hierarchical arrangement
guarantees that the most regularly accessed data is stored in the fastest, smallest sort of
memory.
• Program Execution: When software is launched, it's loaded into RAM for execution. The
CPU fetches commands and facts from RAM, and the quicker cache memory, when
possible, performs the critical computations. The rate and overall performance of this
approach impact the overall performance of the PC.
• Temporary Storage: Memory is used for brief storage of records throughout ongoing
operations. For example, at the same time as you edit a document, the adjustments are
quickly saved in RAM until you save the file. This temporary storage is crucial for
seamless individual considerations.
• Caching: Cache memory performs a pivotal function in caching regularly accessed
information. By preserving a copy of these records near the CPU, cache memory reduces
the time needed to retrieve information, enhancing the overall speed of the system.
• Virtual Memory: Operating structures use a concept known as virtual memory to simulate
larger RAM capacities than are physically available. This includes the use of a part of
RAM. While virtual memory allows the execution of larger applications, it's slower than
physical RAM.

Memory Hierarchy
Computer memory
system
Secondary
memory/Non-
volatile
memory/Auxilary
memory
Register Cache memory
Primary
memory/
Volatile
memory/Main
memory.
Exception :
ROM non-
volatile
Registers are the fastest
and smallest figure of
memory, residing inside
the CPU (Central
Processing Unit). They
keep the fact that the
CPU is actively used or
manipulated. Registers
provide the fastest
feasible way to get entry
to stored data. However,
their limited capacity
means they're capable
of saving a small
amount of data.
Cache memory is
the mediator
between registers
and RAM. It's
quicker than RAM
but larger than
registers. The CPU
uses cache
memory to save
often-accessed
data and
instructions,
decreasing the
time it takes to
fetch data from the

Memory Hierarchy
(continuing….)
Increased in
capacity , size&
access time

Is it memory or storage ??
While "memory" and "storage" are often used
interchangeably, they actually have notable
differences. Simply said, storage is
secondary memory, while memory is primary
or main memory. Storage refers to where
long-term data is stored, whereas memory
refers to where short-term data is stored.

Register Memory
Register memory is the smallest and
fastest memory in a computer. It is not a
part of the main memory and is located in
the CPU in the form of registers, which
are the smallest data holding elements. A
register temporarily holds frequently used
data, instructions, and memory address
that are to be used by CPU. They hold
instructions that are currently processed
by the CPU. All data is required to pass
through registers before it can be
processed. So, they are used by CPU to
process the data entered by the users.
Registers hold a small amount of data
around 32 bits to 64 bits. The speed of a
CPU depends on the number and size (no. of
bits) of registers that are built into the
CPU. Registers can be of different types
based on their uses. Some of the widely
used Registers include Accumulator or AC,

Types of Registers
•Data Register: It is a 16-bit register, which is used to store operands (variables)
to be operated by the processor. It temporarily stores data, which is being
transmitted to or received from a peripheral device.
•Program Counter (PC): It holds the address of the memory location of the next
instruction, which is to be fetched after the current instruction is completed. So, it
is used to maintain the path of execution of the different programs and thus
executes the programs one by one, when the previous instruction gets completed.
•Instructor Register: It is a 16-bit register. It stores the instruction which is
fetched from the main memory. So, it is used to hold instruction codes, which are
to be executed. The Control Unit takes instruction from Instructor Register, then
decodes and executes it.
•Accumulator Register: It is a 16-bit register, which is used to store the results
produced by the system. For example, the results generated by CPU after the
processing are stored in the AC register.
•Address Register: It is a 12-bit register that stores the address of a memory
location where instructions or data is stored in the memory.
•I/O Address Register: Its job is to specify the address of a particular I/O device.
•I/O Buffer Register: Its job is to exchange the data between an I/O module and
the CPU.

Cache memory
It is used to synchronize with high-speed CPU and
to improve its performance. Cache memory can only
be accessed by CPU. It can be a reserved part of the
main memory or a storage device outside the CPU. It
holds the data and programs which are frequently
used by the CPU. So, it makes sure that the data is
instantly available for CPU whenever the CPU needs
this data. In other words, if the CPU finds the
required data or instructions in the cache memory, it
doesn't need to access the primary memory (RAM).
Thus, by acting as a buffer between RAM and CPU,
it speeds up the system performance. There are
three levels of chache memory , such as L1,L2,L3 .
They act as different types of chache memory. The
L1 cache further has two types of caches: Instruction
cache, which stores instructions required by the

Types of computer memory
(Primary memory/Volatile
memory/Main memory):
• RAM: The term refers to the fact that the processor can directly access any storage location. Random Access
Memory, or RAM, is a piece of hardware that serves as the internal memory of the CPU. It is often found on a on
the motherboard of a computer. When the computer is turned on, it enables the CPU to store programs,
information, and result of the program. Also, it is a computer's read-write memory, which means data can be
added to it as well as read from it.
• Dynamic RAM: A type of random-access memory that is used in computing systems (primarily PCs) is called
dynamic random-access memory (DRAM). The data or program code required for a computer processor to
operate is often stored in DRAM, which is a kind of semiconductor memory. Each piece of data is stored in
DRAM in its own passive electrical component, which is located inside an integrated circuit board. Each
electrical component has two value states, known as 0 and 1, in one bit.
• Static RAM: As long as SRAM receives power, it keeps data bits in its memory. It does not need to be refreshed
on a regular basis, in contrast to DRAM, which stores bits in cells made up of a capacitor and a transistor.
• Double Data Rate SDRAM: Theoretically, DDR SRAM can increase the memory clock speed to at least 200
MHz. It is an SDRAM.
• Double Data Rate 4 Synchronous Dynamic RAM: DDR4 RAM is the successor to its preceding DDR2 and
DDR3 iterations. It is a kind of DRAM that contains a high-bandwidth interface. Higher module density and lower
voltage requirements are both possible with DDR4 RAM. It enables dual in-line memory modules (DIMMS) up to
64 GB; Also, higher data rate transfer speeds are paired with it.
• Rambus Dynamic RAM: A memory component called DRDRAM made a guarantee to transport up to 1.6 billion
bytes per second. The RAM controller subsystem consists of RAM, a bus connecting RAM to the
microprocessor, and computer-using devices that make up the subsystem.

Types of computer memory (Primary
memory/exception :Non-Volatile
memory/Main memory):
• Read-only memory: ROM is often only read from and not written to,
which is a type of computer storage. It is nonvolatile in nature, which
means it stores data permanently. The programming code is stored in the
ROM that enables a computer system to boot up or regenerate every time
when it is turned on.
• Programmable ROM: PROM is ROM that a user can modify only once.
Using a unique device known as a PROM programmer enables a user to
customize a microcode program.
• Erasable PROM: EPROM is a type of computer memory that can be
erased and re-used. It is programmable read-only memory PROM.
• Electrically erasable PROM: A user-modifiable ROM called
an EEPROM can be repeatedly wiped and reprogrammed with the help of
an using electrical voltage that is higher than usual. Unlike EPROM chips,
EEPROMs can be changed without being taken out of the computer.
However, an EEPROM chip must be completely deleted and
reprogrammed, not just some parts of it.

Some Ram brands
• Corsair –US based company
• G.SKILL- Taiwan based company
• Kingston-US based company
• Crucial- Micron technology –US
• Samsung- South Korean company

Secondary memory/Non-volatile
memory/Auxilary memory
Used to store large volume of data on a
permanent basis.

Sequential-access Storage
Devices
 Suitable for sequential processing applications
where most, if not all, of the data records need to
be processed one after another
 Magnetic tape is a typical example of such a
storage device

Magnetic Tape
 Physically, the tape medium is a plastic ribbon, whichis usually ½ inch or
¼ inch wide and 50 to 2400 feet long
 Plastic ribbon is coated with a magnetizable recordingmaterial such as
iron-oxide or chromium dioxide
 Data are recorded on the tape in the form of tinyinvisible
magnetized and non-magnetized spots (representing 1s and 0s) on
its coated surface
 Tape ribbon is stored in reels or a small cartridge orcassette
 Storage capacity of a tape = Data recording
density x Length
 Data recording density is the amount of data that can be stored on a given
length of tape. It is measured in bytes per inch (bpi)
 Tape density varies from 800 bpi in older systems to 77,000 bpi in some of the
modern systems

Magnetic Tape - Storage
Organization 1

Magnetic Tape - Storage
Organization 2

Advantage of Magnetic tape
 Storage capacity is virtually unlimited because as many tapes as required can
be used for storing very largedata sets
 Cost per bit of storage is very low for magnetic tapes.
 Tapes can be erased and reused many times
 Tape reels and cartridges are compact and light inweight
 Easy to handle and store.
 Very large amount of data can be stored in a small storage space
 Compact size and light weight
 Magnetic tape reels and cartridges are also easilyportable from one
place to another
 Often used for transferring data and programs fromone computer to
another that are not linked together

Disadvantages of Magnetic Tape
 Due to their sequential access nature, they are not suitable for storage of those
data that frequently require to be accessed randomly
 Must be stored in a dust-free environment because specks of dust can cause
tape-reading errors
 Must be stored in an environment with properly controlled temperature and
humidity levels
 Tape ribbon may get twisted due to warping, resultingin loss of stored data
 Should be properly labeled so that some useful data stored on a particular tape
is not erased by mistake

Magnetic Disk
 Commonly used direct-access secondary storage device.
 Physically, a magnetic disk is a thin, circular plate/platter made of metal or
plastic that is usually coated on both sides with a magnetizable recording
material such as iron-oxide
 Data are recorded on the disk in the form of tiny invisible magnetized and non-
magnetized spots(representing 1s and 0s) on the coated surfaces of the disk
 The disk is stored in a specially designed protective envelope or cartridge, or
several of them are stacked together in a sealed, contamination-free container

Magnetic Disk – Storage
Organization Illustrates the
Concept of Sectors

Magnetic disk –access time.
 Disk access time is the interval between the instant a computer makes a request for
transfer of data from a disk system to the primary storage and the instant this
operation is completed
 Disk access time depends on the following three parameters:
– Seek Time: It is the time required to position the read/write head over the
desired track, as soon as a read/write command is received by the disk unit
– Latency: It is the time required to spin the desired sector under the read/write
head, once theread/write head is positioned on the desired track
– Transfer Rate: It is the rate at which data are read/written to the disk, once
the read/write head is positioned over the desired sector
 As the transfer rate is negligible as compared to seektime and latency,
• Average access time
• = Average seek time + Average latency

Floppy Disk
 Round, flat piece of flexible plastic disks coated withmagnetic oxide
 So called because they are made of flexible plasticplates which can bend
 Also known as floppies or diskettes
 Plastic disk is encased in a square plastic or vinyl jacketcover that gives
handling protection to the disk surface

The hard disk is also known as a hard drive. It is a rigid magnetic
disc that stores data permanently, as it is a non-volatile storage
device. The hard disk is located within a drive unit on the
computer's motherboard and comprises one or more platters
packed in an air-sealed casing. The data is written on the platters
by moving a magnetic head over the platters as they spin. The
data stored on a computer's hard drive generally includes the
operating system, installed software, and the user's files and
programs, including pictures, music, videos, text documents, etc.
Hard Disk:

Solid-state Drive:
SSD (Solid State Drive) is also a non-volatile storage medium
that is used to hold and access data. Unlike a hard drive, it does
not have moving components, so it offers many advantages over
SSD, such as faster access time, noiseless operation, less power
consumption, and more.

Optical Disk
 Consists of a circular disk, which is coated with a thin metal or some other
material that is highly reflective
 Laser beam technology is used for recording/readingof data on the disk
 Also known as laser disk / optical laser disk, due to the use of laser beam
technology
 Proved to be a promising random access medium for high capacity secondary
storage because it can store extremely large amounts of data in a limited space

Types of Optical Disk
• CD-ROM
 Stands for Compact Disk-Read Only Memory
 Packaged as shiny, silver color metal disk of 5¼
inch (12cm) diameter, having a storage capacity
of about 650 Megabytes
 Disks come pre-recorded and the information
stored on them cannot be altered
 Pre-stamped (pre-recorded) by their suppliers,
by aprocess called mastering

Digital Video / Versatile Disk (DVD)
•
•
 Looks same as CD-ROM but has capacity of 4.7 GB or 8.5 GB
 Designed primarily to store and distribute movies
 Can be used for storage of large data
Types of DVDs:
• DVD-ROM (Read-Only): These types of DVDs come with media already recorded on them, such as movie dvds. As the name
suggests, data on these discs cannot be erased or added, so these discs are known as a read-only or non-writable DVD.
• DVD-R (Writable): It allows you to record or write information to the DVD. However, you can write information only once as it
becomes a read-only DVD once it is full.
• DVD-RW (Rewritable or Erasable): This type of discs can be erased, written, or recorded multiple times.

WORM Disk / CD-Recordable (CD-R)
 Stands for Write Once Read Many. Data can be written only once on them, but
can be read many times
 Same as CD-ROM and has same storage capacity
 Allow users to create their own CD-ROM disks by using a CD-recordable (CD-R)
drive that can be attached toa computer as a regular peripheral device
 Data to be recorded can be written on its surface in multiple recording sessions
CD-Read/Write (CD-RW)
Can be erased and written afresh

Memory Storage Devices
• Flash Drive (Pen Drive)
 Relatively new secondary storage device based on flash memory, enabling
easy transport of data from one computer to another
 Compact device of the size of a pen, comes in various shapes and stylish
designs and may have different added features
 Plug-and-play device that simply plugs into a USB (Universal Serial Bus) port
of a computer, treated asremovable drive

Memory Storage Devices
• Memory Card (SD/MMC)
SD Card stands for Secure Digital Card. It is most often used in
portable and mobile devices such as smartphones and digital
cameras. You can remove it from your device and see the things
stored in it using a computer with a card reader.
There are many memory chips inside the SD card that store the data;
it does not have moving parts. SD cards are not created equal, so
they may differ from each other in terms of speed, physical sizes,
and capacity. For example, standard SD cards, mini SD cards, and
micro SD cards.

Mass Storage Devices
• these are storage systems having several trillions of bytes of data storage capacity
 The three commonly used types are:
Disk array, which uses a set of magnetic disks
Automated tape library, which uses a set ofmagnetic tapes
CD-ROM Jukebox, which uses a set of CD-ROMs

Disk Array
 Set of hard disks and hard disk drives with a controller mounted in a single box,
forming a singlelarge storage unit
 It is commonly known as a RAID (Redundant Arrayof Inexpensive Disks)
 As a secondary storage device, provides enhanced storage capacity, enhanced
performance, andenhanced reliability
 Enhanced storage capacity is achieved by usingmultiple
disks
 Enhanced performance is achieved by using paralleldata transfer technique from
multiple disks
 Enhanced reliability is achieved by using techniquessuch as mirroring or striping
 In mirroring, the system makes exact copies of fileson two hard disks
 In striping, a file is partitioned into smaller parts anddifferent parts of the file are
stored on different disks

Automated Tape Library
 Set of magnetic tapes and magnetic tape drives with a controller mounted in
a single box, forming asingle large storage unit
 Large tape library can accommodate up to several hundred high capacity
magnetic tapes bringing the storage capacity of the storage unit to several
terabytes
 Typically used for data archiving and as on-line data backup devices for
automated backup in large computer centers

CD-ROM Jukebox
 Set of CD-ROMs and CD-ROM drives with a controller mounted in a single
box, forming a single large storage unit
 Large CD-ROM jukebox can accommodate up to several hundred CD-ROM
disks bringing the storage capacity of the storage unit to several terabytes
 Used for archiving read-only data in such applications as on-line museums,
on-line digital libraries, on-line encyclopedia, etc

Memory Units
A memory unit is a fundamental part of a computer machine that
performs a vital function for storing and retrieving information and
instructions. Memory units have distinct purposes, including
primary and secondary memories.
Functions of Memory Units:
Data Storage:
Data Retrieval:
Data Processing:
Multitasking:
System Performance:

Computer memory and types of memory.pptx

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