computer memory ,., .

MEMORY

Hard Drive – storage RAM – memory

Memory vs. Storage

Storage, also known as mass media or auxiliary storage, refers to the various media on which a computer system can store data.

Storage devices hold programs and data in units called files.

Memory is a temporary workplace where the computer transfers the contents of a file while it is being used.

CLASSIFICATION- BIG PICTURE

Primary

Secondary

Volatile

Registers

Cache (I, II, III)

RAM

SRAM

DRAM

SDRAM

EDRAMEDOFLASH RAM

Non-volatile

ROM

PROM

EPROM

EEPROM

Magnetic memoryTapeHD, Zip Disk

FDD

Optical Memory

CD-ROM, CD-R, CD-RWDVD-ROM, DVD-RDVD- RW

(Semiconductor – chip). Main Memory

(Devices)

2ns

5ms

Memory Types &

Storage Devices

Why Is Storage Necessary?

Storage devices:Retain data when the computer is turned off

Are cheaper than memory

Play an important role during startup

Are needed for output

Storage Devices

Storage devices are categorized by:The type of operations they perform

The method they use to access the information

The technology they use

Their location in the storage hierarchy

Their capacity and speed

Sequential vs. Random Access Storage

Sequential – Storage devices that read and write data in a serial (one after the other) fashion

Random-Access – Storage devices that read and write data without going through a sequence of locations

Tape Drive – sequential storage

Hard Disk – random-access storage

Floppy Disk Drive – random-access storage

Storage Technologies: Magnetic and Optical

Magnetic – Storage devices use disks or tapes that are coated with magnetically sensitive material

Optical – Storage devices that use laser beams to read patterns etched into plastic disks

Magnetic Storage Optical Storage – CD/DVD drive

The Storage Hierarchy The three levels of storage hierarchy are:

Online storage – Also called primary storage, it is made up of the storage devices that are actively available to the computer system. User action is not required.

Near-online storage – Also called secondary storage, it is not readily available to the computer system. The user performs an action, such as inserting a disk, to make it available.

Offline storage – Also called tertiary storage or archival storage, it is not readily available to the computer system. Devices such as tape backup units store data for archival purposes.

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Floppy Disk Hard Drive CD ROM / DVD

Capacity – 720 KB to 1.44 MB

Access Time – 100ms

Capacity – Up to 80 GB

Access Time – 6 to 12ms

Capacity – CD-ROM 650 MB; DVD 17 GB

Access Time – 80 to 800ms

Storage Capacity and Speed

A storage device’s performance is measured by: Capacity – The number of bytes of data that a device can

hold Access Time – The amount of time, in milliseconds (ms),

it takes the device to begin reading data

Platter

Read/Write head

Hard Disks

Hard disks are high-speed, high-capacity storage devices.

They contain metal disks called platters. They contain two or more stacked platters with

read/write heads for each side. Hard disks can be divided into partitions to enable

computers to work with more than one operating system.

Floppy and Zip Disks and Drives

A disk or diskette is a portable storage medium.

High-density floppy disks that are commonly used today store 1.44 MB of data.

Disks work with a disk drive. Zip disks store up to 750 MB of data and are

not downwardly compatible with floppy disks.

Zip DriveFloppy Drive

Floppy Disk

CD-ROM Discs and Drives CD-ROM stands for Compact

Disc-Read Only Memory. CD-ROM drives can not write

data to discs. They are capable of storing

650 MB of data. They are used for storing

operating systems, large application programs, and multimedia programs.

CD-R and CD-RW Discs and Recorders

CD-R Discs can be read

and written to Discs can only be

written to “once” CD-R drives are

capable of reading and writing data

CD-RW Discs can be read and

written to Discs are erasable Discs can be written

to many times CD-RW drives are

capable of reading, writing, and erasing data

DVD-ROM Discs and Drives

DVD stands for Digital Video Disc. DVD technology is similar to CD-

ROM technology. DVDs are capable of storing up to

17GB of data. The data transfer rate of DVD

drives is comparable to that of hard disk drives.

DVD-R and DVD-RW drives have the ability to read/write data.

Solid State Storage Devices

Solid state storage devices use nonvolatile memory chips to retain data.

They do not have moving parts. They are small, lightweight, reliable, and

portable.

Compact Flash Memory

Flash Memory

Smart Card

Micro Drive

Memory Stick

PC Card

Solid State Storage Devices