memory, storing devices,
DESCRIPTION
TRANSCRIPT
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Backing StorageDevices
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Definition
• Backing storage devices are where you can store data permanently.
• This means that data is held when the computer is switched off and can be loaded onto a computer system when required.
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Device MediaApprox
CapacityAccess
Floppy Disk Drive Floppy Disk 1.44Mb Random
CD-ROM drive CD-ROM
700Mb RandomCD Rewriter
CD-R
CD-RW
USB Flash Drive Flash ROM 1 - 8Gb Random
DVD-ROM Drive DVD-ROM
4.7Gb - 16Gb RandomDVD Rewriter
DVD-R
DVD-RW
Hard Disk Drive Hard Disk up to 5Tb Random
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Computer memory
• Computers have two types of memory.
• These are:– Internal memory – Backing storage
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Internal memory
• Internal memory is used by the computer to store programs and data that are currently being used. e.g. RAM (Random Access Memory).
• Internal memory is volatile memory.• Also called emptied memory(i.e. its contents
are lost) when the computer is turned off.
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Internal memory…
• Internal memory can not hold all the data and programs that a computer might need.
• It only holds the data and programs that are in use at a particular moment in time
• It empties and refills itself as different programs and files are used.
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Internal memory…
• Internal memory can not hold all the data and programs that a computer might need.
• It only holds the data and programs that are in use at a particular moment in time
• It empties and refills itself as different programs and files are used.
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Backing storage
• Backing storage is a memory that is used to store data and programs that are needed to be used again and again.
• It is a non-volatile memory • e.g. Computer discs (floppy, hard, or CDs)
are often used as backing storage.
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Backing Storage device…• Hard Disks are the main internal backing store usually
found inside computers.
• The main benefit of hard drives is that they have a large storage capacity e.g.
• 500 gigabytes or more.
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External Backing Store Flash
• Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed.
• Developed from EEPROM (electrically erasable programmable read-only memory)
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External Backing Store Floppy disks
• Floppy disks are a common external backing store, however only store up to 1.44 Mb of data.
• Excellent for transferring small files of data from one machine to another and for backing up important small files stored on your hard disk.
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3.5 inch Floppy Disk
Disk inside plastic case Write Protect
Notch
Head Contact Area
Metal Hub
Positioning & Drive Hole
Centre Hole
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External Backing Store…
• CD-ROM (Compact Disk Read Only Memory) disks are optical disks that use the same technology as musical compact disks.
• They store up to 700 Mb of data and a laser beam is used to read the data off the disk.
• What can they be used for?
• As CD-ROMs are much bigger than floppy disks,
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Read Only Memory
• Read Only Memory is memory that is not lost when the computer is switched off.
• All computers have a small amount of ROM.• This is so that essential instructions can be
stored.
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Read Only Memory…
• Instructions stored in the ROM enable the computer to check the hardware and load the operating systems.
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Measuring computer memory
• A common system of measurement is used to measure computer memory.
• These are:– Bits– Bytes
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Bits
• Computers use electronic circuits to perform the tasks they are programmed to complete.
• These circuits can be in one of two states - ‘On’ or ‘Off’.
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Bits
• In computer programming, when a circuit is ‘On’ it is given the numerical value 1 in the binary system.
• In computer programming, when a circuit is ‘Off’ it is given the numerical value 0 in the binary system.
• Transistors are silicon chips can store these values (Binary Digits).
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Bytes• Bytes are units of computer memory.• A byte is made up from eight bits.• Each character (letter, number, or punctuation
mark) on a standard QWERTY keyboard is made up of eight bits.
• These codes are common to all computer systems and are known as the ASCII Code (American Standard Code for Information Interchange).
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Bytes
• The code for the letter ‘a’ is 97.• This is 01100001 in binary.
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Bytes
128 64 32 16 8 4 2 1
0 1 1 0 0 0 0 1
64 32 1
The binary number 97 is made as follows:
64 + 32 + 1
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Bytes• 1 kilobyte = 1,024 bytes (210).
• 1 megabyte =1,024 kilobytes =1,048,576 bytes (220)
• 1 gigabyte = 1,024 megabytes = 1,073,741,824 bytes (230).
• 1 terabyte = 1,024 gigabytes = 1,099,511,627,776 bytes
(240).
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Types of memory
• There are two main types of memory.
• These are:– RAM (Random Access Memory)– ROM (Read Only Memory)
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The End