Chapter 8 - Type of Storage

Storage is frequently used to mean the devices and data connected to the computer through input/output operations A Storage is any computing hardware that is used for storing, porting and extracting data files and objects. It can hold and store information both temporarily and permanently, and can be internal or external to a computer, server or any similar computing device.
Storage holds data,instructions,and information for future use.A storage medium is the physical material on which a computer keeps data,instruction,and information.

Capacity is the number of bytes a storage medium can hold.


A Storage device is the computer hardware that records and/or retrieves items to and from storage media. 

Reading  is the process of transferring items from a storage medium into memory. 
Writing  is the process of transferring items from memory to a storage medium. 

Access time measures by the amount of time it takes a storage device to locate an item on a storage medium and the time required to deliver an item from memory to the processor.


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Hard disks

A hard disk drive (sometimes abbreviated as HDD ) is a non-volatile memory hardware device that permanently stores and retrieves information.

A hard disk contains one or more inflexible,circular platters that use magnetic particles to store data,instructions, and information.
Hard disks can store data using longitudinal recording or perpendicular recording.
Characteristics of a hard disk include:
1.Capacity
2.Platters
3.Read/Write heads
4.Cylinders
5.Sectors and tracks
6.Revolutions per Minute
7.Transfer Rate
8.Access Time 

Formatting is the process of diving the disk into tracks and sectors so that the operating system can store and locate data and information on the disk.

How a Hard Disks Works

 

1st :  The circuit board controls the movement of the head actuator and a small motor.

2nd : Small motor will spins the platters while the computer is running.

3rd:  When software requests a disk access,the read/write heads determine the current or new location of the data.

4th : The head actuator positions the read/write head arms over the correct location on the platters to read or write the data.

 

How Disk Cache Works

 

1st : A special-purpose chip on the hard disk, called a controller,receives a request for data,instructions,or information from the processor.

2nd : The controller first checks disk cache for the requested item.

3rd : If the controller does not find the requested item in disk cache, it locates the requested item on the hard disk's platters.

4th : The controller transfers the requested item to the processor. 

RAID (Redundant array of independent disks) is a group of two or more integrated hard disks.

Network attached storage (NAS) device e is a server connected to a network with the sole purpose of providing storage.

External hard disk is a separate free-standing hard disk that connects to your computer with a cable or wirelessly.

Removable hard disk is a hard disk that you insert and remove from a drive.

Internal and external hard disks are available in miniature sizes(miniature hard disks).

Disk controller consists of a special-purpose chip and electronic circuits that control the transfer of data,instructions ,and information from a disk to and from the system bus and other components of the computer. SATA , EIDE, SCSI ,SAS.


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Flash Memory Storage

Flash memory chips are a type of solid-state media and contain no moving parts.
Solid state drives (SSD) have several advantages over magnetic hard disks

  1.Faster access time

  2.Faster transfer rates

  3.Last longer

  4.Generate less heat and consume less power

 

 Types of flash memory storage:
1_ Memory card- removable flash memory device that can be inserted and removed from a slot in computer, mobile devices and card reader/writer.
Example :
  1.Compact Flash (CF)
  2.Secure Digital (SD)
  3.Secure Digital High Capacity (SDHC)
  4.Micro SD
  5.Micro SDHC
  6.Picture Card ( GRAPHIC CARD ?? )
  7.Memory Stick
  8.Memory Stick Micro (M2)
 

2_ USB flash drive- plug into USB port on a computer or mobile device.

3_Express card module-removable device that fits in express card slot.

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Cloud Storage 

An Internet service that provides storage to computer users.Users subscribe to cloud storage for a variety of reasons:

1.Access files from any computer
2.Store large files instantaneously
3.Allow others to access their files
4.View time-critical data and images immediately
5.Store offsite backups
6.Provide data center functions
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Optical Discs

An Optical Disc consists of a flat, round, portable disc made of metal, plastic, and lacquer that is written and read by a laser.Typically store software, data, digital photos, movies, and music.
How a Laser Reads Data on an Optical Disc

1.A laser diode shines a light beam toward the disc.

2.If light strikes a pit, it scatters.If light strikes a land, it is reflected back toward the laser diode.

3.Reflected light is deflected to a light-sensing diode,which sends a digital signal of 1 to the computer.Absence of reflected light is read as a digital signal of 0.

 

Tape- magnetically coated ribbon of plastic capable of storing large amount of data and informations. Require tape drive to read and write data and information.

Magnetic stripe card- contains magnetic stripe that stores information.

Smart card- stores data on thin microprocessor embedded in the card.

Microfilm and microfiche- store microscopic images of documents on a roll or sheet film.

Enterprise storage- uses special hardware to store huge volume of data and information for large businesses.