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Virtual drive

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"Virtual disc" redirects here. Not to be confused with Virtual disk image.

A virtual drive in computing is a device that to the operating system appears to be an ordinary physical disk drive, with disc images substituted for disc reading hardware through the use of software called a disk emulator. It may also be termed an electronic disk, RAM disk, emulated disk, e-disk, pseudo-drive, super drive, hyperdrive or memory disk.

A virtual drive may emulate any type of physical drive, such as a hard drive, tape drive, key drive, floppy drive, CD/DVD/BD/HD DVD or a network share among others. An emulated drive is typically created either in RAM for fast read/write access (known as a RAM disk), or on a hard drive. Typical uses of virtual drives include the mounting of disk images of CDs and DVDs, and the mounting of virtual hard disks for the purpose of on the fly disk encryption ("OTFE").

Some operating systems such as Linux[1] and Mac OS X[2] have virtual drive functionality built-in (see loop device), while others such as Microsoft Windows require additional software.

Virtual drives are typically read-only, being used to mount existing disk images which are not modifiable by the drive. However some software provides virtual CD/DVD drives which can produce new disk images; this type of virtual drive goes by a variety of names, including "virtual burner".

Backup

Disk images may be created to avoid wear-and-tear on a physical disk, such as a CD or DVD, with the disk image mounted in a virtual drive when needed. Similarly, disk images can provide a backup copy of physical disks, in case the original is damaged, lost or stolen.

Enhancement

Using disk images in a virtual drive allows users to shift data between technologies, for example from CD optical drive to hard disk drive. This may provide advantages such as speed and noise (hard disk drives are typically four or five times faster than optical drives,[3] and also quieter). In addition it may reduce power consumption, since it may allow just one device (a hard disk) to be used instead of two (hard disk plus optical drive).

Some audiophiles argue that music played from a hard drive is superior to the same music played directly from CD,[4][5] due for example to lower data error rates.

Virtual drives may also be used as part of emulation of an entire machine (a virtual machine).

Software distribution

After the spread of broadband, CD and DVD disk images became a common medium for Linux distributions.[1] Applications for Mac OS X are often delivered online as an Apple Disk Image containing a file system that includes the application, documentation for the application, and so on. Online data and bootable recovery CD images are provided for customers of certain commercial software companies.

Disk images may also be used to distribute software across a company network, or for portability (many CD/DVD images can be stored on a hard disk drive). Disk images may also be needed to transfer software to machines without a compatible physical disk drive.

Security

Virtual hard disks are most commonly used in on the fly disk encryption ("OTFE") software such as FreeOTFE and TrueCrypt, where an encrypted "image" of a disk is stored on the PC. When you enter the disk's password, the disk image is "mounted", and made available as a new drive letter on your PC. Files written to this virtual drive are written to the encrypted image, and never stored in cleartext.

The process of making such an encrypted disk available for use is called "mounting", the process of removing it is called "dismounting" or "unmounting".

Virtual burner

A virtual CD burner is a device driver that emulates a writable CD/DVD drive.[6] [7]This is effectively the opposite of the normal CD emulation tools, as rather than using an ISO image to simulate a full or burnt CD, it creates an ISO image (or potentially other formats, such as creating MP3 files) based on files burnt to a virtual device. It appears as another drive in the system with writing capabilities.

When information is written to the drive using standard image writing programs such as Nero or iTunes, it creates an ISO Image representation of the CD that would, under normal circumstances, be physically created. ISO images can be compressed into .CSO images.

A virtual CD burner can be used by any CD burning/writing software, and create an image which can be later mounted as a virtual drive. Most CD writing software does not provide CD burner capability, instead providing a manual option within the program such as "Create Disc Image" or "New ISO File".

See also

References

  1. ^ a b "Linux ISO Images". LinuxHelp.net. Retrieved 2007-03-23.
  2. ^ Although OS X's built-in DiskImageMounter software does not emulate a physical drive
  3. ^ pcguide.com - Access Time
  4. ^ AVguide - Blog - Do Hard-Disk Drives Sound Better than CD?
  5. ^ 6moons.com - industry features: An Evolving Scenario - Audiophiles embrace Hard Drives
  6. ^ Phantom Burner - Virtual Blu-ray/DVD/CD burner drive
  7. ^ Virtual CD - Virtual Blu-ray/DVD/CD burner drive
  8. ^ Tools used to maintain VHD images
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