STORAGE FUNDAMENTALSUNIT-3

COMPUTER SYSTEM COMPONENTS

Central Processing Unit

OutputDevices

CacheMemory

Primary Storage

SecondaryStorageDevices

ControlUnit ALU

SpecialPurposeProcessors

Output Devices

InputDevices

Short Review

Communication Devices

Primary storage Volatile Temporary

STORAGE Secondary

storage Nonvolatile Permanent

Secondary storage characteristics Media Capacity Storage devices Access speed

RAMROMRead-Only-Memory

Random-Access-Memory

RAM or Random Access Memory “Waiting room” for computer’s CPU. Holds instructions for processing data,

processed data, and raw data. Data stored in RAM can be modified . RAM

is a volatile storage . Data will lose after switching off the computer. 

Ram is measured by: Capacity (in Megabytes or Gigabytes) Speed (in Nanoseconds)

MEMORY (RAM) Amount of RAM installed will determine.

Which software applications will run (efficiently)?How many software applications can be open simultaneously (multitasking ability)?

RAM upgrades are cost-effective and easy to install.

All software applications will have RAM specifications listed on their packaging.

Many applications list both a minimum and a recommended amount of RAM necessary to run the software.

 E.g. DDRam, DDR-2 Ram 

There is a type of memory that stores data without electrical current; it is the ROM (Read Only Memory) or is sometimes called non-volatile memory as it is not erased when the system is switched off.

Data stored in ROM cannot be modified. ROM works slower than the RAM memory. ROM is a non-volatile storage . Data remains

unchanged even after switching off the computer.  E.g. EPROM, EEPROM

Secondary storage is computer memory that is not directly accessible to the CPU of a computer, requiring the use of computer's input/output channels.

It is used to store data that is NOT in active use.

It is usually slower than primary storage but it always has higher storage capacity. It is non-volatile.

Data remains unchanged even after switching off the computer. 

Magnetic Storage

stores data by magnetizing microscopic particles on

the disk surface.

Examples: floppy disk, hard disk, tape

Optical Storagedata is read using laser light

and is possible to see data through a high

powered microscope.Examples CD and DVD

Secondary Storage Devices

Floppy Disks Diskettes or floppies Capacity 1.4MB 3½ inch disk Labeled 2HD data can be saved on

both sides Portable storage media Floppy disk drives (FDD)

Parts of a Floppy Shutter slide - metal component that

opens when disk is inserted in the drive. Labels - applied to external surface to

identify contents. Write-protect notch - when open,

prevents data to be written to the disk. Protects the disk from accidentally writing

over it.

Traditional Floppy Diskette

Hard Disks Use thicker, metallic platters for

storage

Faster than a floppy disketteSpeed is measured in rotations or revolutions per minute (rpm)

Large capacity

Sensitive instruments

Types of Hard Disk There are three different types of hard disks;

internal hard disk hard disk cartridge hard disk pack

All disks use a file system (File Allocation Table) to keep track of the names and locations of files that reside on a storage medium.

Internal Hard Disk

Located inside system unit Known as a fixed disk Designated as the C drive Advantages over floppies

Access speed Capacity

Optical Disks

Are permanent storage media that use laser technology to store data.

Optical disks can be 3½ , 4¼ , 5¼ ,8, 12 and 14 inches.

Most common size is 4¾ and is stored in a jewel box.

Two common formats are:- CD - Compact Disk DVD - Digital Versatile Disk or Digital

Video Disk

Optical format From 650 MB to 1 GB capacity Rotation speeds vary Types

Read only: CD-ROM Write once: CD-R Rewriteable: CD-RW

Compact Disc

Compact Disc CD-ROMs

read only - cannot be written on or erased by the user.

used to distribute databases, reference and software.

Write once - CD-R can be written to once but can be read many times

(WORM). CD burners are used to write data onto the disk.

Rewritable - CD-RW erasable optical disk, write many times, read many

times. Disk surface is not permanently altered so can be

written to, erased and written again.

Digital Versatile Disc Digital Versatile Disk or Digital Video

Disk (DVD) Similar to CDs, but can store more data

[can store 4GB to 17GB of data] Types

Read only Write once Rewritable

Other Type of Secondary Storage Devices

USB Flash Drives They are flash memory data storage devices

integrated with a USB interface. They are typically small, lightweight, removable

and rewritable . Data capacity: 512MB, 1GB, 2GB, 4GB, etc.

Flash memory cards Widely used in notebook computers, Cell phones, etc. Used to record MP3 music files

Magnetic tapes External storage Provides sequential access

Information stored in sequence Slower than disks which provide direct access

Other Type of Secondary Storage Devices

TYPES OF ROM

PROM (Programmable Read only Memory): it uses fusible links that can be burned by using special PROM burning circuit. It can be programmed by the user using a PROM programmer.

EPROM (Erasable Programmable Read only Memory): the information stored in an EPROM can be erased by exposing the memory to ultraviolet light. 

EEPROM (Electrically Erasable Programmable Read only Memory): it is also same as EPROM but the erasing is done by electrical signals.

TYPES OF RAMSRAM (Static RAM): It uses flip flops for storage elements. In SRAM once data is written into memory location, the data stays unchanged unless some new data is entered into that location.

DRAM (Dynamic RAM): It uses capacitors as storage element. The dynamic RAM contents may change with time due to leakage of charge. So it is required to refresh the storage elements periodically. It consumes less power compare to SRAM.

Questions?