disk drives types

A disk unit is the description used to describe the physical disk drive or its casing.

Disk Drive Types:

• Hard Drives
•  Floppy Drives

• CD-ROM 
• CD-R
• CD-RW

• DVD-ROM 
• DVD-R
• DVD+R
• DVD-RW

• Blue Ray
• Removable Drives

  

 HARD DRIVES

These are also called 'fixed disks' in ancient computerese because the storage media is mounted within the computer and not intended to be removed.

Hard drives consist of one or more metal platters stacked together on a single spindle. Multiple read/write heads (one for the top and bottom of each platter) float next to the surface of the drive. Hard Disk drive capacities are determined by the number of cylinders and blocks per cylinder a drive will support.

This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing Data/Information permanently.

CPU directly does not access these memories, instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory and then CPU can access it. For example, disk, CD-ROM, DVD, etc.

Characteristics of Secondary Memory :

• These are magnetic and optical memories.
• It is known as backup memory.
• It is non-volatile memory.
• Data is permanently stored even if power is switched off.
• It is used for storage of the data in the computer.
• Computer may run without secondary memory.
• Slower than primary memories.

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FLOPPY DRIVES

Named for the media disks that could be pulled out and that would 'flop' when carried. These disks are designed to allow users to store data to a disk, remove it and carry the data elsewhere. These typically come in one of two formats in the United States: 3.5" @1.44Mbytes and 5.25" at 1.22 Mbytes. There are a few proprietary types as well, such as Zip drives, DAT tapes etc.

 

CD-ROM

CD-ROM  Compact Disk Read Only Memory or CD-ROMs are shiny circular pieces of plastic with a hole in the middle. These look like audio compact disks and computer software and data are stored on them. They are read using a powerful (red) light-emitting diode (LED) that is sometimes called a 'laser' and thus the name 'laser disk'. Compact Disk media is made of pressed layers of plastic and can store about 640 MB of data. 

DVD-ROM

DVD is a digital optical disc storage format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than compact discs while having the same dimensions.

Pre-recorded DVDs are mass-produced using molding machines that physically stamp data onto the DVD. Such discs are known as DVD-ROM, because data can only be read and not written or erased. Blank recordable DVD discs (DVD-R and DVD+R) can be recorded once using a DVD recorder and then function as a DVD-ROM. Rewritable DVDs (DVD-RW, DVD+RW, and DVD-RAM) can be recorded and erased multiple times.

DVDs are used in DVD-Video consumer digital video format and in DVD-Audio consumer digital audio format, as well as for authoring AVCHD discs. DVDs containing other types of information may be referred to as DVD data discs.

Blu-Ray

The latest development in data storage and movie disks is Blu-Ray, so called because it uses a blue LED (sometimes called a laser, which is actually something entirely different) to read/write from the disk.

Blu-ray Disc (BD) is a digital optical disc data storage format designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Conventional (pre-BD-XL) Blu-ray Discs contain 25 GB per layer, with dual layer discs (50 GB) being the industry standard for feature-length video discs. Triple layer discs (100 GB) and quadruple layers (128 GB) are available for BD-XL re-writer drives.[3] The name Blu-ray Disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs. The major application of Blu-ray Discs is as a medium for video material such as feature films. Besides the hardware specifications, Blu-ray Disc is associated with a set of multimedia formats. Generally, these formats allow for the video and audio to be stored with greater definition than on DVD.

The format was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. Sony unveiled the first Blu-ray Disc prototypes in October 2000, and the first prototype player was released in April 2003 in Japan. Afterwards, it continued to be developed until its official release in June 2006. As of June 2008, more than 2,500 Blu-ray Disc titles were available in Australia and the United Kingdom, with 3,500 in the United States and Canada. In Japan, as of July 2010, more than 3,300 titles have been released

During the high definition optical disc format war, Blu-ray Disc competed with the HD DVD format. Toshiba, the main company that supported HD DVD, conceded in February 2008, releasing its own Blu-ray Disc player in late 2009. 

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REMOVEABLE DRIVES

These are drives where the drive itself can be removed or ported elsewhere. The media is usually not pulled out. Removable hard drives are a good example of these.

 

 DISK DRIVE CAPACITIES

DRIVE TYPE                                                   ACCESS METHOD     CAPACITY

Floppy Drive (3.5")                                          Rewriteable     Magnetic Media     1.44 MB

Hard Drive                                                         Rewriteable     Magnetic Media     Various

Zip Drive                                                            Rewriteable     Magnetic Media     Various

CD-ROM     Compact Disk                               Read-Only     Optical Media     ~640 MB

CD-R     CD Recordable                                    Write Once     Optical Media     ~640 MB

CD-RW     CD Rewriteable                               Rewriteable     Optical Media     ~640 MB

DVD     Digital Video Disk                                 Read-Only     Optical Media     ~4.7 GB

DVD-R/DVD+R

DVD Recordable                                                 Write Once     Optical Media     ~4.7 GB

DVD-RW     DVD Rewriteable                           Rewriteable     Optical Media     ~4.7 GB

DVD-R/DVD+R DL

DVD Recordable Dual Layer                              Write Once     Optical Media     ~4.7 GB

DVD-RW DL     DVD Dual Layer                       Rewriteable     Optical Media     ~8.5 GB

BD-ROM     Blu-ray                                             Read-Only      Optical Media     25 GB

BD-R     Blu-ray                                                    Write Once     Optical Media     25 GB

BD-RE     Blu-ray                                                  Rewriteable     Optical Media     25 GB

BD-R (DL)     Blu-ray Dual Layer                       Write Once     Optical Media     50 GB

BD-RE (DL)     Blu-ray Dual Layer                     Rewriteable     Optical Media     50 GB

Disk Drive Types

Disk Drive Types

Disk Drive Types