CHAPTER 1 : STORAGE DEVICE

What will you learn...

Identify the name of SD

SD Purposes

Characteristics of SD

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Storage Device

A storage device is used in the computers to store the data. Its provides one of the core functions of the modern computer. There is four main types of storage:

Primary Storage

Secondary Storage

Tertiary Storage

Off-Line Storage

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Primary Storage

Also known as MAIN MEMORY. Main memory is directly or indirectly connected to the central processing unit via a memory bus. The CPU continuously read instructions stored there and executes them as required. RAM, ROM and Cache are example of primary storage.

RAM

It is called Random Access Memory because any of the data in RAM can be accessed just as fast as any of the other data. Two types of RAM are RAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory).

  STATIC RAM

Faster

More expensive

More power consumption

does not need to be refreshed

DYNAMIC RAM

Slower

Less expensive

Less power consumption

needs to be refreshed thousands of times per second. 
 

 ROM

 This memory is used as the computer begins to boot up. Small programs called firmware are often stored in ROM chips on hardware devices (like a BIOS chip), and they contain instructions the computer can use in performing some of the most basic operations required to operate hardware devices. ROM memory cannot be easily or quickly over written or modified.

 CACHE

Cache is a high-speed access area that can be either a reserved section of main memory or a storage device. Most computers today come with L3 cache or L2 cache, while older computers included only L1cache.

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Secondary Storage

 

Secondary storage are not directly accessible by the CPU. Computer usually uses its input / output channels to access secondary storage.Computer usually transfers the desire data using intermediate area in primary storage. Example of secondary storage are hard disk..

 HARD DISK

 The hard disk drive is the main, and usually largest, data storage device in a computer

It can store any where from 160 gigabytes to 16 terabytes

A hard disk unit comes with a set rotation speed varying from 4500 to 7200 rpm

Disk access time is measured in Milli seconds

Internal Hard Disk 
Portability : NO

Price : LESS EXPENSIVE

Speed : FAST

Size : BIG

  

 External Hard Disk

Portability : YES

Price : MORE EXPENSIVE

Speed : SLOW

Size : SMALL

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Tertiary Storage

 

Typically tertiary storage involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device. It is a comprehensive computer storage system that is usually very slow. Primarily useful for extraordinary large data stores for example:

 Magnetic Tape

Magnetically coated strip of plastic on which data can be encoded

Less expensive but slower

Example : Cassette Tape

Optical Disk

Holds content in digital format

Read using laser assembly

Example : Blu-ray, CD, DVD

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Off-Line Storage

Also known as disconnected or removable storage. Storage that is NOT under the control of a processing unit. Must inserted or connected by a human operator before a computer can access it again. Example:

 Floppy Disk

A soft magnetic disk

Portable

Can store data up  to 1.44MB

Two common size: 5 ¼” and 3 ½”

ZIP Diskette

Developed by Iomega that function like standard floppy disk

Portable

Hold up to 100MB – 250MB

USB Flash Drive

A small, portable flash memory card that plugs into a computer's USB port

Functions as a portable hard drive

Can store data from 256MB to 4TB

 Memory Card

Commonly used in consumer electronic devices such as:

Camera

MP3 Player

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Storage Device Features 

 

Volatility

Volatile: Require constant power to maintain the stored information

Non Volatile: Keeps the data even when the current is off     

Accessibility

Refers to reading or writing data records

Random access: Any location in storage, any time

Sequential access: Accessing will be in a serial order

Mutability 
Allows information to be overwritten at any time

Three types:

Read Write, Read Only, Slow Write/Fast Read 

Addressability 
Location-addressable: Stored with numerical memory address

File-addressable: Stored with human-readable directory

Content-addressable: Stored based on the basis of contents

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Other Storage Devices

  

Punched Card

Early method of data storage

Also known as Hollerith Cards

Containing several punched holes that represents data   

 
Cloud Storage

 The storage of data online in the cloud

Data can be stored in and accessible from multiple distributed and connected resources

RAID

Redundant Array of Independent Disk

Allows us to store the same data redundantly in a balanced way to improve overall storage performance 

 - END OF CHAPTER -

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