2. Storage Device
A device capable of storing data.
The term usually refers to mass storage
devices, such as disk and tape drives.
They may come in the form of
lite storage and mass storage.
magnetic media, optical media storage
permanent and changeable storage, etc.
3. Disk drive
A machine that reads data from and writes data onto a disk.
A disk drive rotates the disk very fast and has one or more heads
that read and write data.
There are different types of disk drives for different types of
disks. For example,
a hard disk drive (HDD) reads and writes hard disks,
a floppy drive (FDD) accesses floppy disks,
A magnetic disk drive reads magnetic disks and
an optical drive reads optical disks.
Disk drives can be either
internal (housed within the computer) or
external (housed in a separate box that connects to the
computer).
4. Magnetic Disks (Floppy)
A soft magnetic disk. It is called floppy because it flops if you wave it (at
least, the 5¼-inch variety does).
Unlike most hard disks, floppy disks (often called floppies or diskettes) are
portable, because you can remove them from a disk drive.
Disk drives for floppy disks are called floppy drives.
Floppies come in three basic sizes:
8-inch: The first floppy disk design, invented by IBM in the late 1960s and used in
the early 1970s as first a read-only format and then as a read-write format. The
typical desktop/laptop computer does not use the 8-inch floppy disk.
5¼-inch: The common size for PCs made before 1987 and the predecessor to the
8-inch floppy disk. This type of floppy is generally capable of storing between 100K
and 1.2MB (megabytes) of data. The most common sizes are 360K and 1.2MB.
3½-inch: Floppy is something of a misnomer for these disks, as they are encased
in a rigid envelope. Despite their small size, microfloppies have a larger storage
capacity than their cousins -- from 400K to 1.4MB of data. The most common sizes
for PCs are 720K (double-density and 1.44MB (high-density). Macintoshes support
disks of 400K, 800K, and 1.2MB.
What is Density: How tightly information is packed together on a storage
medium (tape or disk).
Floppy disks can be single-density, double-density, high-density, or extra-high-
density.
To use a double-density, high-density, or extra-high-density disk, you must have a
disk drive that supports the density level.
Double-density disk: A floppy disk that has twice the storage capacity of a
single-density floppy. Single-density disks are now obsolete. Double-density
5¼-inch disks for PCs can hold 360K of data. Double-density 3½-inch disks
can hold 720K.
High-density disk: A high-quality floppy disk capable of holding more data
than a double-density disk. High-density 5¼-inch disks for PCs can hold
1.2MB (megabytes) of data. High-density 3½-inch disks can store 1.44MB.
6. SuperDisk
A disk storage technology developed by Imation
Corporation that supports very high-density
diskettes.
The result is that a SuperDisk diskette can have
2,490 tracks, as opposed to the 160 tracks that
conventional 3.5-inch 1.44 MB diskettes use.
This higher density translates into 120 MB
capacity per diskette.
Unlike other removable disk storage solutions,
such as the Zip drive, SuperDisk is backward
compatible with older diskettes.
This means that you can use the same
SuperDisk drive to read and write to older 1.44
MB diskettes as well as the new 120 MB
SuperDisk diskettes.
7. Zip drive
A high-capacity floppy disk drive
developed by Iomega
Corporation.
Zip disks are slightly larger than
conventional floppy disks, and
about twice as thick.
They can hold 100 or 250 MB of
data.
Because they're relatively
inexpensive and durable, they
have become a popular media
for backing up hard disks and
for transporting large files.
8. Jaz Drive
A removable disk drive
developed by Iomega
Corporation.
The Jaz drive has a 12-ms
average seek time and a transfer
rate of 5.5 Mbps.
The removable cartridges hold
up to 2 GB of data.
The fast data rates and large
storage capacity make it a viable
alternative for backup storage as
well as everyday use.
It is not compatible with 1.44MB
Floppy disk drives.
9. USB Flash Drive
A small, portable flash memory card that plugs into a
computer’s USB port and functions as a portable
hard drive with more than 4GB of storage capacity.
USB flash drives are touted as being easy-to-use as
they are small enough to be carried in a pocket and
can plug into any computer with a USB drive.
USB flash drives have less storage capacity than an
external hard drive, but they are smaller and more
durable because they do not contain any internal
moving parts.
USB flash drives also are called pen drives, key
drives or simply USB drives.
10. Hard Disk and Hard Disk Drive
Hard Disk:
A magnetic disk on which you can store computer data. The term hard is
used to distinguish it from a soft or floppy disk.
A hard disk, for example, can store anywhere from 10 to more than 160
gigabytes.
Hard disk drive
The mechanism that reads and writes data on a hard disk. Hard disk
drives (HDDs) for PCs generally have seek times of about 12
milliseconds or less. Many disk drives improve their performance through
a technique called caching.
There are several interface standards for passing data between a hard
disk and a computer. The most common are IDE, SATA and SCSI.
Seek time
Refers to the time a program or device takes to locate a particular piece of
data. For disk drives, the terms seek time and access time are often used
interchangeably. Technically speaking, however, the access time is often
longer the seek time because it includes a brief latency period.
16. What is Inside a Hard Drive?
Following is a description of the common features of the hard drive and how
each part works in relation to the others.
The Platters: The platters are the actual disks inside the drive that store the
magnetized data. Traditionally platters are made of a light aluminum alloy and
coated with a magnetizable material such as a ferrite compound that is
applied in liquid form and spun evenly across the platter or thin metal film plating
that is applied to the platter through electroplating, the same way that chrome is
produced.
The magnetic layer on the platters has tiny domains of magnetization that are
oriented to store information that is transferred through the read/write heads.
Most drives have at least two platters and the larger the storage capacity of the
drive, the more platters there are.
Each platter is magnetized on each side, so a drive with 2 platters has 4 sides to
store data.
The Spindle and Spindle Motor
The platters in a drive are separated by disk spacers and are clamped to a
rotating spindle that turns all the platters in unison. The spindle motor is built
right into the spindle or mounted directly below it and spins the platters at a
constant set rate ranging from 3,600 to 7,200 RPM or higher in some special
types of HDD.
17. What is Inside a Hard Drive?
The Read/Write Heads
The read/write heads read data from and write data to the platters.
There is typically one head per platter side, and each head is attached to a single
actuator shaft so that all the heads move in unison.
When one head is over a track, all the other heads are at the same location over their
respective surfaces.
Typically, only one of the heads is active at a time, i.e., reading or writing data.
When not in use, the heads rest on the stationary platters, called the landing zone.
The Head Actuator
All the heads are attached to a single head actuator, or actuator arm, that moves the
heads around the platters.
Each pulse moved the actuator over the platters in predefined steps.
The platters, spindle, spindle motor, head actuator and the read/write heads are
all contained in a chamber called the head disk assembly (HDA).
Outside of the HDA is the logic board that controls the movements of the
internal parts and controls the movement of data into and out of the drive.
18. What is Inside a Hard Drive?
Tracks and Sector
Sectors are the smallest unit that can be accessed on a disk.
When a disk undergoes a low-level format, it is divided into tracks and sectors.
The tracks are concentric circles around the disk and the sectors are
segments within each circle. For example, a formatted disk might have 40
tracks, with each track divided into 10 sectors. The operating system and disk
drive keep tabs on where information is stored on the disk by noting its track and
sector number.
A sector that cannot be used due to a physical flaw on the disk is called a bad
sector.
It’s not unusual for a hard disk to leave the manufacturing process with a
damaged sector; however, this does not affect the overall performance of the
disk as the damaged space is considered unusable.
19. What is Inside a Hard Drive?
Cylinder:
For hard disks, each platter is divided into tracks, and a single
track location that cuts through all platters (and both sides of
each platter) is called a cylinder. Hard disks have many
thousands of cylinders.
Cluster
A group of disk sectors. The operating system assigns a
unique number to each cluster and then keeps track of files
according to which clusters they use.
Occasionally, the operating system marks a cluster as being
used even though it is not assigned to any file. This is called a
lost cluster. You can free up disk space by reassigning lost
clusters, but you should first make sure that the clusters do not,
in fact, contain valuable data. In DOS and Windows, you can find
lost clusters with the ScanDisk utility.
The size of each cluster depends on the disk's partition size.
22. Magnetic Tape
A magnetically coated strip of plastic on which data can be encoded.
Storing data on tapes is considerably cheaper than storing data on
disks.
Relatively permanent and holds large quantities of data
Access time slow
Tapes are sequential-access media. So, accessing data on tapes is
much slower than accessing data on disks.
Mainly used for backup, storage of infrequently-used data, transfer
medium between systems
Kept in spool and wound or rewound past read-write head
Once data under head, transfer rates comparable to disk
20-400GB typical storage
Common technologies are 4mm, 8mm, 19mm, LTO-2 , SDLT, DLT, DAT,
AIT, DDS
23. Optical Storage Media
A storage medium from which data is read and to which it is written by
lasers.
Optical disks can store much more data up to 6 gigabytes (6 billion
bytes)
There are three basic types of optical disks:
CD-ROM: Like audio CDs, CD-ROMs come with data already encoded onto
them. The data is permanent and can be read any number of times, but CD-
ROMs cannot be modified.
WORM: Stands for write-once, read -many. With a WORM disk drive, you
can write data onto a WORM disk, but only once. After that, the WORM disk
behaves just like a CD-ROM.
Erasable: Optical disks that can be erased and loaded with new data, just
like magnetic disks. These are often referred to as EO (erasable optical)
disks.
These three technologies are not compatible with one another; each
requires a different type of disk drive and disk. Even within one
category, there are many competing formats, although CD-ROMs are
relatively standardized.
24. Compact Disk (CD)
1982
Diameter of 12 cm
1.2 mm thick disc of
polycarbonate plastic
Closed Tracks
700 MB
Philips and Sony
DVDLaser Disk
27. Understanding CD Burner Speeds
when you go to buy a CD burner you will see some numbers that looks
like 12x2x24 (three numbers separated by the letter "x"), these
numbers indicate the drive speeds of the CD drive.
The "x" stands for the transfer of 0.15 MB of data per second, and
each number represents a different action that the CD drive can take.
A CD-R drive has two actions –
recording onto and
reading from compact discs.
A CD-RW drive has three actions –
recording,
rewriting (erasing and recording over) and
reading.
When looking at the drive speeds,
The first number ("12" in the above example) indicates the speed at which the
CD drive will record data onto a CD-R compact disc. So, in the above example,
the CD drive will record data at 12 times 0.15 MB/second.
The second number ("2" in the above example) indicates the speed at which the
CD drive will rewrite data onto a CD-RW compact disc. So in the above example,
the CD drive will rewrite data onto the compact disc at 2 times 0.15 MB/s.
Typically, the second number, the rewrite speed, is lower than the first number,
the write speed, because rewriting is a slower process than writing.
The last number ("24" in the above example) indicates the speed at which the
drive will read data from a compact disc. So in the above example, the CD drive
will read data from a compact disc at 24 times 0.15 MB/s.
