Our Lady of the Rosary CollegeOur Lady of the Rosary College2006-2007 S.2 Computer Literacy2006-2007 S.2 Computer Literacy

Lesson 8Lesson 8Storage UnitStorage Unit

Mr. Ku Heung ChinMr. Ku Heung Chin

The unit of memoryThe unit of memory How does computer store the character ‘A’?How does computer store the character ‘A’? Computer can only ‘read’ binary digit (0 or 1).Computer can only ‘read’ binary digit (0 or 1). Computer will change a character into 8 binary digit,Computer will change a character into 8 binary digit, e.g. A:0100 0001e.g. A:0100 0001 The coding standard is ASCII.The coding standard is ASCII.

D0100 0100

C0100 0011

B0100 0010

A0100 0001

H0100 1000

G0100 0111

F0100 0110

E0100 0101

Bits and BytesBits and Bytes

Each binary digit is 1 bitEach binary digit is 1 bit How many bits in one character?How many bits in one character?

– Ans: 8 bitsAns: 8 bits Each character need 1 Each character need 1 ByteByte of memory. of memory. How many bits in 1 How many bits in 1 ByteByte??

– Ans: 8 bitsAns: 8 bits

KB / MB / GB / TBKB / MB / GB / TB

Unit Abbreviation Value

Byte B 8 bits = 1 byte

Kilobyte KB 210 = 1024 bytes

Megabyte MB 220 = 1024 KB (about 1 million bytes)

Gigabyte GB 230 = 1024 MB (about 1 billion bytes)

Terabyte TB 240 = 1024 GB (about 1 trillion bytes)

Main MemoryMain Memory

It stores data and instruction to be It stores data and instruction to be executed by the CPU.executed by the CPU.

RRandom andom AAccess ccess MMemory (RAM)emory (RAM) RRead ead OOnly nly MMemory (ROM)emory (ROM)

RAM vs ROMRAM vs ROMRAMRAM ROMROM

Data can be read Data can be read from and written to it.from and written to it.

Data can only read from it. Its Data can only read from it. Its contents cannot be overwritten.contents cannot be overwritten.

It is used to store It is used to store program and data.program and data.

It is used to store programs It is used to store programs designed by the manufacturer designed by the manufacturer that configure and control the that configure and control the basic operations of a computer. basic operations of a computer. (BIOS)(BIOS)

It is It is volatilevolatile

(content will be lost (content will be lost when power off )when power off )

It is It is non-volatilenon-volatile

(content will remain unchanged (content will remain unchanged when power off)when power off)

Secondary storageSecondary storage

Magnetic storage devicesMagnetic storage devices– Floppy disk driveFloppy disk drive– Hard diskHard disk

Optical storage devicesOptical storage devices– CD-ROMCD-ROM– CD-RWCD-RW– DVD-ROMDVD-ROM– DVD-RWDVD-RW

Floppy Disk DriveFloppy Disk Drive

Small capacity.(1.2MB / 1.44MB)Small capacity.(1.2MB / 1.44MB) Read/write speed is very slow.Read/write speed is very slow.

Hard DiskHard Disk High capacity (80 GB ~ 500 GB)High capacity (80 GB ~ 500 GB) Fastest processing speed.Fastest processing speed. http://http://www.youtube.com/watch?vwww.youtube.com/watch?v

=9eMWG3fwiEU&eurl=9eMWG3fwiEU&eurl

CD-ROM / CD-RWCD-ROM / CD-RW

CCompact ompact DDisc isc RRead-ead-OOnly nly MMemory.emory.– 650 MB ~ 800MB650 MB ~ 800MB– Can write only onceCan write only once

CCompact ompact DDisc isc RRe-e-WWritableritable– can re-write data for many timescan re-write data for many times

DVD / DVD-RWDVD / DVD-RW

DDigital igital VVersatile ersatile DDiscisc / / DDigital igital VVideo ideo DDiscisc – 4.7GB – 8.5GB4.7GB – 8.5GB

Main Memory vs Secondary StorageMain Memory vs Secondary Storage

Properties / States Main Memory Secondary Storage

Power is off Data disappear.(It is volatile)

Data is still present.(It is non-volatile)

Size (in MB) Small Large

Price (in MB) Costly Relatively cheap

Relatively easy to remove

No Yes

Other Storage DevicesOther Storage Devices

Memory CardsMemory Cards– Smart Media (SM)Smart Media (SM)– Compact Flash (CF)Compact Flash (CF)– Secure Digital Card (SD)Secure Digital Card (SD)– Memory Stick (MS)Memory Stick (MS)– xD-Picture Card (XD)xD-Picture Card (XD)

The EndThe EndThanks for coming!!Thanks for coming!!