Storage, Input & Devices and Files

Storage Devices

Auxiliary or Secondary storage devices can be broadly categorized into two categories, magnetic and optical.

Magnetic Devices.

Magnetic devices get their name from the way they read and write data to and from a medium. Magnetic storage medium use non-magnetic material for disk, (aluminum in the case of hard drives and mylar in the case of floppy disk and magnetic tape) and then that material is coated with tiny iron particles. The read/write heads, (which are small electro-magnets) polarize the tiny iron particles to either positive or negative magnetism. The read/write heads can sense which polarity the iron particles are and interprets positive as "1" and negative as "0".

Types of Magnetic Devices

Hard Drives -

Hard Drives, sometimes called hard disks or fixed disk have these attributes; very high capacity, very high speed, randomly accessed, readable and writable.

Floppy Disk -

Floppy disk have these attributes; very low capacity, very slow speed, randomly accessed, readable and writable.

Magnetic Tape -

Magnetic tape has these attributes; large capacity, speed is slow but different, sequentially accessed, readable and writable.

Optical Devices

Optical storage devices get their name from the way they read and write data to and from a medium. Optical devices write data, (not all optical devices can write data) by burning tiny pits into the medium. When reading the data a laser is reflected off the medium. If the laser light strikes a pit the light is defused and does not reflect back to a sensor and this is interpreted as a "0". If the laser light strikes a "land" ( a place that has not been pitted by the writing laser) it is reflected back to the sensor and this is interpreted as a "1". Because of the way optical devices read data they can read only one bit at a time. Hard drives do not have this limitation so optical devices will always be slower than hard drives. The data stored by optical devices is immune to electromagnetic interference and is general much more secure that data stored to a magnetic device.

Types of Optical Storage Devices

CD-ROM -

Compact Disk Read Only Memory - have these attributes; medium capacity, medium speed, randomly accessed, read only.

CD-R

Compact Disk wRitable - same as CD-ROM but a blank disk can be written to one time. The disk is then just like a CD-ROM disk

CD-RW

Compact Disk ReWritable - same as CD-ROM but special disks may be repeatedly overwritten.

Input & Output Devices

• Printers
• Monitors
• Ports

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Printers

Impact Printers

The attributes of a Daisy Wheel printer are; fair letter quality, slow, loud, no graphics, can do carbon copies.
The attributes of a Dot Matrix printer are; poor letter quality, slow, loud, can do graphics, can do carbon copies.

Non-impact Printers

The attributes of an ink jet printer are; good letter quality, faster, quieter, can do graphics and inexpensive color, inexpensive, can not do carbon copies.
The attributes of a laser printer are; excellent letter quality, fastest, quietest, most expensive, can do graphics, can not do carbon copies.

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Monitors

Four factors which effect the display of a monitor.

• Refresh Rate
• Resolution
• Dot Pitch
• Size

The dot pitch is the distance between the three dots in a pixel. It is measured in fractions of a millimeter. .28 is good.
Size is the diagonal measurement of the screen in inches. Most monitors are 15 or 17 inches.

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Ports

Serial ports move data along a single line. They can only move data one bit at a time.

USB (Universal Serial Bus) ports are very high speed types of serial ports.

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Files

The three character extension on file names is special. It distinguishes data files from program files and allows the computer to what type of file it is. Now some file extensions are four characters.

Also know about formatting a disk; the 4 things which are put on a disk when its formatted. Know the two ways of measuring the speed of a disk and anything else you maybe asked on a test. Ha Ha.

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