1. Our Lady of the Rosary College 2006-2007 S.2 Computer Literacy Lesson 8 Storage Unit Mr. Ku Heung Chin

2. The unit of memory  How does computer store the character ‘ A ’ ?  Computer can only ‘ read ’ binary digit (0 or 1).  Computer will change a character into 8 binary digit,  e.g. A:0100 0001  The coding standard is ASCII. D0100 C0100 0011 B0100 0010 A0100 0001 H0100 1000 G0100 0111 F0100 0110 E0100 0101

3. Bits and Bytes  Each binary digit is 1 bit  How many bits in one character? –Ans: 8 bits  Each character need 1 Byte of memory.  How many bits in 1 Byte? –Ans: 8 bits

4. KB / MB / GB / TB UnitAbbreviationValue ByteB8 bits = 1 byte KilobyteKB2 10 = 1024 bytes MegabyteMB2 20 = 1024 KB (about 1 million bytes) GigabyteGB2 30 = 1024 MB (about 1 billion bytes) TerabyteTB2 40 = 1024 GB (about 1 trillion bytes)

5. Main Memory  It stores data and instruction to be executed by the CPU.  Random Access Memory (RAM)  Read Only Memory (ROM)

6. RAM vs ROM RAMROM Data can be read from and written to it. Data can only read from it. Its contents cannot be overwritten. It is used to store program and data. It is used to store programs designed by the manufacturer that configure and control the basic operations of a computer. (BIOS) It is volatile (content will be lost when power off ) It is non-volatile (content will remain unchanged when power off)

7. Secondary storage  Magnetic storage devices –Floppy disk drive –Hard disk  Optical storage devices –CD-ROM –CD-RW –DVD-ROM –DVD-RW

8. Floppy Disk Drive  Small capacity.(1.2MB / 1.44MB)  Read/write speed is very slow.

9. Hard Disk  High capacity (80 GB ~ 500 GB)  Fastest processing speed.  http://www.youtube.com/watch?v=9 eMWG3fwiEU&eurl http://www.youtube.com/watch?v=9 eMWG3fwiEU&eurl http://www.youtube.com/watch?v=9 eMWG3fwiEU&eurl

10. CD-ROM / CD-RW  Compact Disc Read-Only Memory. –650 MB ~ 800MB –Can write only once  Compact Disc Re-Writable –can re-write data for many times

11. DVD / DVD-RW  Digital Versatile Disc / Digital Video Disc –4.7GB – 8.5GB

12. Main Memory vs Secondary Storage Properties / StatesMain MemorySecondary Storage Power is offData disappear. (It is volatile) Data is still present. (It is non-volatile) Size (in MB)SmallLarge Price (in MB)CostlyRelatively cheap Relatively easy to remove NoYes

13. Other Storage Devices  Memory Cards –Smart Media (SM) –Compact Flash (CF) –Secure Digital Card (SD) –Memory Stick (MS) –xD-Picture Card (XD)

14. The End Thanks for coming!!