These Notes from the class of BS EDUCATION 1st Semester (Spring) Session 2023-2027 Teacher :Ch Naveed Afzal semester started in march 2023 and end in july 2023

1. Storage Devices
Storage devices, such as disk drives, store your documents (data files) and programs (executable files)
when they are not currently in use for processing. Unlike the contents of RAM, the data stored on
these devices does not vanish when power is turnedoff.
The major categories of storage devices are magnetic, solid state, and optical.
Random-Access Memory (RAM):
RAM is a form of primary storage, it is volatile. RAM takes the
form of integrated circuits (ICs) and it is used to temporarily store
data and allows quick access to this stored data. This data can be
accessed in any order.
Read-Only Memory (ROM):
ROM is a class of non-volatile storage device that is
programmed at the time of creation; it cannot be
reprogrammed at any later time. Data stored in ROM cannot be
modified; therefore, it is mainly used to store BIOS (Basic Input &
Output System) routine.
Hard Disk Drive
A hard disk drive contains disks made of metal and coated with a metal
oxide that can be magnetized. A tiny electromagnetic read/write head on
the end of a seek arm magnetizes tiny spots on the disk to store data.
Magnetic spots magnetized in one direction represent a one; spots
magnetized in the opposite direction represent a zero (OK, I simplified
things a little, but you get the idea). The same electromagnetic head can
later sense the magnetic fields of the spots as they pass underneath the
head, allowing the data to be read back from thedisk.
Hard drives are rated by their storage capacity, typically tens or hundreds of gigabytes. They are also
rated by how fast the disks spin (in rpm, rotations per minute), which is typically thousands of rpm.
Another way to rate a hard disk is by average access time (measured in milliseconds, ms), which
tells on average how long it would take the drive to retrieve any bit of data from the disk. Typical
seek times are around 6 ms.
The electronics that control the hard disk often incorporate some cache memory. The drive reads in
several sectors of data instead of just one—that way, if the CPU happens to request those next
sectors, the drive can send them immediately without having to wait for the disk to rotate back
around again.
A Hard Disk is divided into tracks and sectors; Data on this hard disk is positioned into these tracks and
sectors so they can be easily read by the heads and also to help reduce fragmentation on the hard disk.
The controller electronics for a hard drive may be IDE, or ATA, or SCSI, or something else.
Don’t worry about this detail here, but you do need to get the right kind to go into your computer if
you want to add additional drives. You can also plug additional hard drives externally into the USB
or Firewire ports of a computer, ifdesired.
Floppy Diskette
In a floppy diskette the disk is made of flexible mylar plastic coated with
metal oxide that can be magnetized. Floppy diskettes are 3.5" in size (older
style floppy diskettes for early PCs were5.25").
A shutter protects the disk surface from dirt and fingerprints; the
shutter slides out of the way when the disk is inserted into the drive so
that the read/write heads can reach the disk.
A small plastic slider can be slid to unblock a hole in the corner of the diskette to write-protect the

2. disk (so data can’t be accidentallyerased).
High-density floppy diskettes hold 1.44 MB. The access time is much slower than for a hard disk,
and they are somewhat unreliable. Many new computers don’t have a floppy drive, but you can
purchase an external drive to plug in if you needto.
Zip Disk
A Zip disk is similar in size to a floppy diskette, but thicker. It is basically a
“super floppy” but the higher construction tolerances and smaller
read/write heads allow the Zip disk to hold more data than a floppy. The
first Zip disks held 100 MB. Later Zip drives could read 250 MB Zips (in
addition to the old 100 MB disks). An even newer model Zip drive uses
750 MB disks.
Both Zip disk and floppy diskettes have the advantage of being removable media. Data stored on
these disks can be removed and taken to other locations. Both Zips and floppies can be
formatted for either the PC or the Macintosh (Macs can read both formats).
We had Zip drives in our previous PCs and Macs at UNM-LA, but our newer computers don't
use these, so you may never have to deal withthem.
Flash Drive
A USB Flash Drive is a portable solid state memory device that plugs into
a USB port on your computer. They have many other names (such as key
drive, pocket drive, thumb drive, pen drive). They have replaced floppy
diskettes and Zip disks at UNM-LA as our preferred means to carry files
around. They work on both Macs and PCs.
These small drives store data on flash memory microchips (a kind of
EEPROM). Flash memory can be erased and re-written a limited number
of times (typically many thousands of times). Some units have a write-
protect switch.The storage capacity varies, but anything from 16 MB to
over a gigabyte are available.
Flash Memory Cards
The same kind of flash memory used in the USB flash drives above are
is used in small memory cards (a Secure Data SD card, and a Compact
Flash card are shown on the right). These cards are are used by
PDAs, digital cameras, MP3 music players, and other digital devices.
You can attach a flash memory card reader to your computer to
read and write data to these cards as well. These memory cards (and
other types not
shown here) come in a variety of storage capacities from tens of megabytes to
over a gigabyte. CD-ROM
A CD-ROM (Compact Disc Read Only Memory) is an optical storage medium that can
hold about 670MB. “Optical” means that light is used to read the data from the
disk (it is not a magnetic medium). CD-ROMs are very cheap to produce in large
quantities, so most software is distributed on CD-ROMs.Data is stored on a CD-ROM as small pits in the
plastic of an inner layer, which is then aluminized and overcoated with another clear layer. A laser beam
inside the CD-ROM drive is bounced off the disk and the sequences of pits and not-pits (the reflectivity is
different) is converted into the ones and zeros of thedata.
CD-ROM drives are rated by speed, such as 32x, which means 32 times faster than
the first CD- ROM drives.
CD-R and CD-RW
CD-R (Compact Disc - Recordable) and CD-RW (Compact Disk - ReWritable) are CDs that can be
written to (if your computer has a CD-RWdrive).
The CD-R discs have a layer of dye that is changed by a higher power laser in the drive to record data
(the low power reading laser does not change the data). The CD-R can only have its data surface
changed ONCE at each spot (although you can write multiple sessions to one disk until it is full). After
that, it is read-only. CD-Rs can hold 700 MB ofdata.
The CD-RW discs contain a phase-change material that different power laser beams can read,
write, and erase, so these disks can be used many times (but must be erased before re-writing).
DVD
DVD-ROM discs (DVD = Digital Versatile Disc) are optical storage media similar to CD-
ROMs, but with a higher storage capacity. DVDs use smaller spots to record data, and the disks can be
dual-layer and double-sided, with each layer holding 4.7 GB of data (so a dual- layer/double-sided DVD
can hold 18 GB ofdata).

3. Like CDs, DVDs also have recordable variants, although there are still multiple formats (DVD-R and
DVD+R) competing for dominance. A single-layer DVD-R can hold 4.7 GB of data (Dual Layer discs
can hold twice asmuch).
DVD drive speeds are rated in terms of how many times faster that the original DVD dirves they are (a
6x DVD drive is 6 times faster)
Blu-ray Disc
Blu-ray (not Blue-ray) also known as Blu-ray Disc (BD), is the name of a new optical disc format jointly
developed by the Blu-ray Disc Association (BDA), a group of the world's leading consumer electronics,
personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi,
Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson). The format was developed to
enable recording, rewriting and playback of high-definition video (HD), as well as storing large
amounts of data. The format offers more than five times the storage capacity of traditional DVDs and
can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc. This extra capacity combined
with the use of advanced video and audio codecs will offer consumers an unprecedented HD experience.
While current optical disc technologies such as DVD, DVD±R, DVD±RW, and DVD-RAM rely on a red
laser to read and write data, the new format uses a blue-violet laser instead, hence the name Blu-ray.
Despite the different type of lasers used, Blu-ray products can easily be made backwards compatible
with CDs and DVDs through the use of a BD/DVD/CD compatible optical pickup unit. The benefit of
using a blue-violet laser (405nm) is that it has a shorter wavelength than a red laser (650nm), which
makes it possible to focus the laser spot with even greater precision. This allows data to be packed more
tightly and stored in less space, so it's possible to fit more data on the disc even though it's the same size
as a CD/DVD. This together with the change of numerical aperture to 0.85 is what enables Blu-ray
Discs to hold 25GB/50GB. Recent development by Pioneer has pushed the storage capacity to 500GB on
a single disc by using 20 layers.
A standard CD has a diameter of 12.0 cm, and a hole that is centered on the axis of symmetry and has a
diameter of 1.50 cm. The CDs thickness is 1.2 mm,CD 200 to 2400, dvd 1600 to 4000,bluray 10,000+