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Storage Devices
Introduction
• A storage device is a hardware device capable of storing information. There are two storage devices used in computers; a primary storage device such as computer RAM and a secondary storage device such as a computer hard disk drive.
Parts of a Computer
• Monitor• System Unit• Keyboard• Mouse
System Unit
• Central Processing Unit Holds the central processor It is the brain of the computer Processes data and instructions
• Consists of :- Hard Disk RAM ROM CD-ROM drive Floppy Disk drive
Storage Devices
• RAM• ROM• Thumb Drive• CD-ROM• DVD-ROM• Hard Disc• Floppy Disc
RAM
• Stand for Random Access Memory• Random access memory is volatile memory, meaning it loses its contents once power is cut. • When a computer shuts down properly, all data located in random access memory is committed
to permanent storage on the hard drive or flash drive. At the next boot-up, RAM begins to fill with programs automatically loaded at startup, and with files opened by the user.
USEAllows the computer to read data quickly to run applications.
TYPESTwo types:1. Static RAM2. Dynamic RAM
DEFINITIONA form of data storage that can be accessed randomly at any time, in order and from any physical location
ROM
• Stand for Read Only Memory• Read Only Memory is a non-volatile memory as it is not
erased when the system is switched off.
USEStores the program required to initially boot the computer
TYPES
Types of ROM:-1. PROM2. EPROM3. EEPROM
DEFINITIONA form of data storage that cannot be easily altered or reprogrammed.
RAM vs ROM
RAM ROMRandom Access Memory Read Only Memory
Stores information temporarily Stores information permanently
Data can be changed Information inside cannot be changed
Data is lost when PC is switched off
Data is safe when PC is switched off
CD-ROM
• Compact Disc Read Only Memory• It is a optical disk capable of storing
large amounts of data - up to 1 GB, most common size is 650MB
• Single CD-ROM has storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages
• Information stored cannot be changed
Advantages and Disadvantages
Advantages Disadvantages
Small and portable Fairly fragile, easy to snap or scratch
Very cheap to produce Smaller storage capacity than a hard drive or DVD
Most computers can read CDs. Slower to access than the hard disk
Fairly fast to access the data
Hard Disk
• It is the main, usually largest, data storage device in a computer
• Contains a number of metal platters which have been coated with a special magnetic material
• Also known as Magnetic Storage Device• Measured in Gigabytes, now it’s available
in Terabyte• Possible to have external hard disk which
can be plugged into the computer and used to back up your data
Advantages and Disadvantages
Advantages Disadvantages
Large storage capacity Far slower to access data than ROM and RAM chips
Stores and retrieves data much faster than a floppy disk
Can crash which stop the computer from working
Stored items are not lost when you switch off the computer
Regular crashes can damage the surface of the disk, leading to loss
data in that sector
Cheap on a cost per megabyte compared to other storage devices
It is fixed inside the computer and cannot easily be transferred to
another computer
Floppy Disk
• Oldest type of portable storage device
• It becomes obsolete• Can store up to 1.44 Mb of data -
equivalent to around 300 pages of A4 text
• Ideal storage for transferring small files
Advantages and Disadvantages
Advantages Disadvantages
Portable - small and lightweight Not very strong - easy to damage
Inexpensive Data can be erased if the disk comes into contact with a magnetic field
Useful for transferring small files Quite slow to access and retrieve data
Security tab to stop data from being written over
Can transport viruses from one machine to another
Can be used many times Small Storage capacity
Many new computers don’t have floppy disk drives
Flash Memory
• Typically Small, lightweight, removable and rewritable
• Consist of a small printed circuit board which is encased in plastic or metal casing
• Available from 1 Gb up to 16 Gb
Advantages and Disadvantages
Advantages Disadvantages
More compact, portable and cheap Can be easily be lost
Hold more data than floppy disk or even a CD
If handled roughly, it can be damaged
More reliable than floppy disk
Being developed with fashionable looking casing
BINARY CODE
Binary Codes
• A bit is a binary digit. It can only hold one of two values: 0 and 1
• Bits are usually assembled into group of eight to form a byte
• A byte contains enough information to store a single ASCII character
Units Used
Unit Equivalent1 bit A 1 or 0 (b)
4 bits 1 nybble (?)
8 bits 1 byte (B)
1 kilobyte (KB) 1,024 bytes
1 megabyte (MB) 1,048,576 bytes
1 gigabyte (GB) 1,073,741,824 bytes
1 terabyte (TB) 1,099,511,627,776 bytes
1 petabyte (PB) 1,125,899,906,842,624 bytes
Bit and byte
• 1 byte = 8 bits • Example:
Sekolah Menengah Rimba How many bytes are there: 22 bytes So, how many bits are there?
Answer: 176 bits To find the total bits, you need to multiply
the bytes with 8. Because 1 byte is equal to 8 bits.
ASCII
• Stand for American Standard Code for Information Interchange.
• It’s a 7 bit character code where every single bit represents a unique character.
• Why 7 bit? Because the minimum workable size is 1 byte, those 7 bits are
the low 7 bits of any byte. The most significant bit is 0. That means, in any ASCII file, you're wasting 1/8 of the bits. In
particular, the most significant bit of each byte is not being used.
• In the computer program, information is not being stored as characters. It is stored as ASCII codes. ASCII codes are stored as 1’s and 0’s.
• In fact, ASCII codes are basically binary codes.
ASCII to binary
ASCII ‘A’ ‘a’ ‘R’ ‘r’
Binary 0100 0001 0110 0001 0101 0010 0111 0010
Spare the jokes, when we enter a word example, “Computer”,it will program as:
0100001101101111011011010111000001110101011101000110010101110010
Now you try!!
• Find out how many bits and bytes in these sentence:-
Respectful, Responsible, Caring, Positive, Collaborative and Integrity is Sekolah Menengah Rimba’s School Values.
Answer: Bytes - 113 bytes, Bits - 113 * 8 = 904 bits