computer memory ,., .
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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.
Slide 22
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
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