Friday, April 3, 2009

Computer External Storage


• Optical Drive
• Hard Drive
• Floppy Drive
• Network Attachment Storage (NAS)


• CD-R

Both technologies (CD-R and CD-RW) use a small laser in the drive to record.

New on the market are CD-Rs that burn reliably at up to 16X speed and discs that can hold up to 700MB of data, rather than the more common 650MB.

When buying media, make sure that you match the media speed to that of your drive. Trying to burn an 8X CD-R at 12X is a sure way to ruin a disc.

Most CD-RW drives come with both software to burn a CD-R and packet-writing software, which lets you use a CD-RW just the same way that you use a hard or floppy disk, dragging and dropping files to the disc.


• uses laser technology.
• It contains of text, graphic, video and sound.
• Read Only means that data cannot be erased or modified.
• For a computer to read the items on a CD-ROM, you must place it into a CD-ROM drive.
• A CD-ROM can hold up to 700 MB of data.
• CD-ROM drive speed influence the quality of display and it is measured by its data transfer rate, which is the time it takes the drive to transmit data from CD-ROM.


• Allows the user to read data on all format CD.
• Allows user to write on a compact disc using own computer.
• Data can be written on discs in stages.
• Stored data cannot be deleted. User must have CD-R software and also CD-R drive to use it.


• Allows the user to read data on all format CD.
• Allows the user to write on multiple times.
• To use it user must have CD-RW software and CD-RW drive.


• A high-capacity compact disc ranges 4.7 GB to 17 GB data. Suitable to store large items such as video.
• In order to read a DVD-ROM the user must have a DVD-ROM drive or DVD player.

• Finally, some DVD- ROMs are double-sided. The user must remove the DVD-ROM and turn it over to read the other side.
• Available in a variety of formats, one of which stores digital or audio data.


• Allows user write once on it and read it many times.
• Specifications (e.g)
• Capacity - 4.7GB
• Speeds (DVD) - 2x write/ 1x rewrite/ 6x read
• Speeds (CD) - 8x write/ 8x rewrite/ 24x read
• Interface - IEEE 1394
• Buffer Size - 2 MB
• Access Time - 180-200 ms
• Warranty - 1 Year

System Requirements:
For Windows Users
• 800 MHz processor or greater
• 128MB of RAM
• Built-in FireWire port

For Macintosh Users
• G4
• 128MB of RAM
• Built-in FireWire port


• Hard disks store the majority of information on today's modern computer.
• Can be stored and delete.
• The hard disk retains information stored on it, with or without power.
• Hard Drive capacity is measured in GigaBytes, or 1 million megabytes (MB).
• Hard Drives connect to the motherboard (or sometimes an expansion card) through one of two special interfaces:
1. Integrated Drive Electronics (IDE)
2. Small Computer Systems Interface (SCSI, pronounced "scuzzy").

How a hard disk works

• Most hard disks have multiple platters stacked on top of one another and each platter has two read/write heads, one for each side.
• The hard disk has arms that move the read/write heads to the proper location on the platter.
• The location of the read/write heads often is referring to by its cylinder. Cylinder is the location of a single track through all platters.
• While the computer is running, the platters in the hard disk rotate at a high rate of speed. Usually 5,400 to 7,200 revolutions per minute.
• Access time is from 5 to 7 milliseconds, can be increased with disk caching. Cache Disk is a portion of memory that the CPU uses to store frequently accessed items.


• Can be inserted and removed from a hard disk drive
• Advantages:
– Used to store larger files
– To do backup
– For data security issue, user can remove the hard disk and leaving no data on the computer for secret files.
• Networks, minicomputers and mainframe computers often use disk packs.
• Disk Packs is a collection of removable hard disks mounted in the same cabinet.

Maintaining data stored on a hard disk

• Hard disk came lasts somewhere between three and five years, although many last much longer with proper care.
• To prevent the loss of items stored on a hard disk, you should perform preventative maintenance such as defragmenting or scanning the disk for errors.
• Operating systems such as Windows XP provides many maintenance utilities.


• A floppy or diskette is a portable, inexpensive storage medium that consists of a thin, circular, flexible plastic disk enclosed in a square-shaped plastic shell.
• The term portable means the storage medium can be moved from one computer to another computer.
Floppy disk drive is a device that can read from and write to a floppy disk.


• Can store large files containing graphics, audio or video.
• To make a backup. Backup is a duplicate of an original file and can be used if the original is lost or damaged.
• SuperDisk™ drive with capacity 120MB is developed by Imation.
• Sony Electronics Inc. has developed HiFD™ (High Capacity FD) with capacity 200 MB.
• Zip® drive developed by Iomega Corporation, with capacity 250 MB.

Network Attachment Storage (NAS)

• Traditional methods of solving a problem of shortage of disc space (extension of a capacity of a server's disc subsystem or a purchase of a new server)
• The NAS technology was developed as an alternative to universal servers carrying a lot of functions (printing, applications, fax server, e-mail etc.).

• NAS servers implement only one function - a file server function, thus fulfilling it better, simpler and faster.
• Advantages of the NAS:
1. Easy installation and administration
2. Lower cost
3. Access restriction standards support
4. Universality for clients (one server can service MS, Novell, Mac, Unix clients)
5. Support for the most of backup copying programs
6. Possibility to access data in case a master server is out of order
7. Transmission of huge amount of information (multimedia, presentations etc.)

• Data Replication & Mirroring
• Email Archiving
• Hot Failover
• IP Based Storage


• An e-mail archive is a repository kept in a non-production environment to provide secure retention of messages for compliance and operational purposes.
• It is not good policy to treat backups made for disaster recovery as archives.
• It makes sense to establish the difference between archives and backups in everyone's mind and in day-to-day practice.
• Use backups to restore e-mails at users' request
• Keep backups for long periods of time
• To search tapes in response to an opponent's discovery request.
• On the other hand, backups used solely for business continuity and routinely overwritten at short intervals — say, 90 days or less — have a fighting chance to be excluded from legal discovery.


• Failover is a backup operational mode in which the functions of a system component (such as a processor, server, network, or database, for example) are assumed by secondary system components when the primary component becomes unavailable through either failure or scheduled down time.

• Used to make systems more fault-tolerant, failover is typically an integral part of mission-critical systems that must be constantly available.

• The procedure involves automatically offloading tasks to a standby system component.

• Failover can apply to any aspect of a system:

1. Personal computer : for example, failover might be a mechanism to protect against a failed processor

2. Network; failover can apply to any network component or system components, such as a connection path, storage device, or Web server.

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