External hard disk drive

From Wikipedia, the free encyclopedia

  (Redirected from External hard drive)
Jump to: navigation, search


An external hard disk drive is a type of hard disk drive which is externally connected to a computer. Modern entries into the market consist of standard SATA, IDE, or SCSI hard drives in portable disk enclosures with SCSI, USB, IEEE 1394 Firewire, eSATA client interfaces to connect to the host computer.

Contents

[edit] History

Apple Lisa with a top-mounted ProFile hard drive.
Main article: History of hard disk drives

The first commercial hard disks were large and cumbersome, were not stored within the computer itself, and therefore fit within the definition of an external hard disk. The hard disk platters were stored within protective covers or memory units, which sit outside. These hard disks soon evolved to be compact enough that the disks were able to be mounted into bays inside a computer. Early Apple Macintosh computers did not have easily accessible hard drive bays (or, in the case of the Mac Plus, any hard drive bay at all), so on those models, external SCSI disks such as the Apple ProFile were the only reasonable option. Early external drives were not as compact or portable as their modern descendents.[1] [2] [3]

By the end of the 20th century, internal drives became the system of choice for computers running Windows, while external hard drives remained popular for much longer on the Apple Macintosh and other professional workstations which offered external SCSI ports. Apple made such interfaces available by default from 1986 and 1998. The addition of USB and Firewire interfaces to standard personal computers led such drives to become commonplace in the PC market as well. These new interfaces supplanted the more complex and expensive SCSI interfaces, leading to standardization and cost reductions for external hard drives.

[edit] Structure and design

A Seagate Pocket hard drive with USB cable extended next to a 2 GB CompactFlash card. The model depicted has a 6 GB capacity.

The internal structure of external hard disk drives is similar to normal hard disk drives; in fact, they include a normal hard disk drive which is mounted on a disk enclosure. In a 2007 PC Magazine article comparing the top 10 external hard drives, they found the cost per gigabyte value varied between ~0.30-0.50 USD.[4] As external hard drives retain the platters and moving heads of traditional hard drives they are much less tolerant of physical shocks than flash-based technology.[5] Larger models often include full-sized 3.5" PATA or SATA desktop hard drives, are available in the same size ranges, and generally carry a similar cost. More pricey models, especially small USB-powered pocket hard drives, generally cost considerably more per gigabyte and are limited to the sizes available for smaller drives intended for laptop and embedded devices. Some achieve sizes little different from small MP3 players, built around CompactFlash microdrives.[6]

[edit] Compatibility

Modern external hard drives are compatible with all operating systems supporting the relevant interface standards they operate with, such as USB MSC or IEEE1394. These standards are supported by all major modern server and desktop operating systems and many embedded devices. Obsolete systems such as Windows 98 (original edition)[7], Windows NT (any version before Windows 2000) old versions of Linux (older than kernel 2.4), or Mac OS 8.5.1 or older do not support them out-of-the-box, but may depend on later updates or third party drivers.

[edit] References

  1. ^ "Five decades of disk drive industry firsts". disktrend. http://www.disktrend.com/5decades2.htm. Retrieved on 2008-01-10. 
  2. ^ "IBM 3340 direct access storage facility". IBM. http://www-03.ibm.com/ibm/history/exhibits/storage/storage_3340.html. Retrieved on 2008-01-10. 
  3. ^ "IBM 1301 disk storage unit". IBM. http://www-03.ibm.com/ibm/history/exhibits/storage/storage_1301.html. Retrieved on 2008-01-10. 
  4. ^ "Top 10 External Hard Drives". PC Magazine. 16 November 2007. http://www.pcworld.com/article/id,123728/article.html. Retrieved on 2007-12-29. 
  5. ^ "What makes a great external hard drive". http://www.storagesearch.com/olixir-art1.pdf. Retrieved on 2007-12-29. 
  6. ^ Pexagon Store-It 4GB Pocket Microdrive USB Storage Drive - Ritz Camera
  7. ^ http://www.querycat.com/faq/ecdfeb8a60e2616cb47e1546f7833093

[edit] See also

[edit] External links

Sister project Wikimedia Commons has media related to: External hard drive
Retrieved from "http://en.wikipedia.org/wiki/External_hard_disk_drive"
Personal tools