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Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  

Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…


Removable media is any type of mass storage device that you may use in one system and then physically remove from that system and use in another. Removable media has been a part of the personal PC from its first introduction back in 1980. Granted, back then the only removable media available were floppy disks, but the ability to easily move programs and data from one machine to another was quickly established as one of the strongest points of the personal computer. Over time, higher capacity removable media technologies were introduced. Some technologies—CDs, DVDs, and thumb drives, for example have become very common. Today’s highly inter-networked computers have reduced the need for removable media as a method of sharing programs and data, but removable media has so many other uses that this hasn’t slowed things down a bit. Removable media is the perfect tool for software distribution, data archiving, and system backup. 
In this chapter we will discuss the most common types of removable media. All removable media are broken down into these groups: 

  • Floppy drives  The traditional floppy drive 
  • Flash memory  From flash memory cards to USB thumb drives 
  • Optical media  Any shiny disc technology from CD-ROMs to DVDs 
  • External storage drives any hard drive or optical drive that connects to a PC via an external cable. 

Now we will demonstrate various removable devices & their usage in this segment. 

  • Floppy Drives

 These little disks, storing a whopping 1.44 MB of data per disk, have been part of PCs from the beginning. For decades, the PC industry has made one attempt after another to replace the floppy with some higher capacity removable media, only to keep falling back to the floppy disk. 

Floppy drive technology was well entrenched motherboard makers found it easy to add, all BIOS supported them, and they were almost al-ways the first boot device, so techs loved floppies when they helped boot a system. Now a days the floppy drive disappeared from PCs. 

  • Flash Memory 

Flash memory, the same flash memory that replaced CMOS technology for your system BIOS, found another home in PCs in the form of removable mass storage devices. Flash memory comes in two different families: USB thumb drives and memory cards. USB thumb drives are flash devices that contain a standard USB connection. Memory cards is a generic term for a number of different tiny cards that are used in cameras, PDAs, and other devices. Both of these families can manifest themselves as drives in Windows, but they usually perform different jobs. USB thumb drives have replaced virtually all other re-writable removable media as the way people transfer files or keep copies of important programs. Now let’s discuss various devices which comes under the FLASH MEMORY. 

USB Thumb Drives

Moving data between computers is always a pain, and even more so since digital photography and multimedia storage has littered hard drives with huge files that won’t fit on a single floppy disk. You simply plug one into any USB port and it will appear as a removable storage device in My Computer. After you plug the drive into a USB port, you can copy or move data to or from your hard disk and then unplug the unit and take it with you. You can read, write, and delete files directly from the drive. Because these are USB devices, they don’t need an external power source. The non-volatile flash memory is solid-state, so it’s shock resistant and is supposed to retain data safely for a decade. The latest systems enable you to boot to a thumb drive. With a boo-table thumb drive, you can replace both boo-table floppies and boo-table CDs with fast flash drives. Making a thumb drive boo-table is a bit of a challenge, so most of the classic boo-table utility CD makers have created USB versions that seek out your thumb drive and add an operating system with the utilities you wish to use. Most of these are simply versions of Linux-based live CDs. At this point, there’s no single magic USB thumb drive to recommend, as boo-table USB drives are still quite new and updated versions come out almost daily. USB thumb drive has variety of speeds depends on their variations. 

Flash Cards

Flash cards are the way people store data on small appliances. Every digital camera, virtually every PDA, and many cell phones come with slots for some type of memory card. Memory cards come in a number of different incompatible formats, so let’s start by making sure you know the more common ones. 

Smart Media

Smart Media came out as a competitor to CF cards and for a few years was quite popular in digital cameras. The introduction of SD media reduced Smart Media’s popularity, and no new devices use this media.

Secure Digital 

Secure Digital (SD) cards are arguably the most common flash media format today. About the size of a small postage stamp, you’ll see SD cards in just about any type of device that uses flash media. SD comes in two types: the original SD and SDIO. SD cards store only data. The more advanced SDIO (the “IO” denoting input/output rather than storage) cards also support devices such as GPS and cameras. SD cards also come in two tiny forms called Mini Secure Digital (Mini-SD) and Micro Secure Digital (Micro-SD) cards. They’re extremely popular in cellular phones that use flash memory, but see little use in other devices. 

XD Picture Card 

Extreme Digital (XD) Picture Cards are about half the size of an SD card. They’re almost exclusively used in digital cameras, although Olympus (the developer of the XD technology) produces a USB housing so you can use an XD Picture Card like any other USB flash memory drive. XD Picture Cards come in three flavors: original, Standard (Type M), and Hi-Speed (Type H). The Standard cards are faster than the original cards, which were only available for a short time; the Hi-speed cards are two to three times faster than the others and enable you to capture full-motion video (assuming the camera has that capability, naturally!).  

Card Readers

Whatever type of flash memory you use, your PC must have a card reader in order to access the data on the card directly. There are a number of inexpensive USB card readers available today and some PCs.  

Optical Media

CD- and DVD-media discs and drives come in a variety of flavors and formats, enabling you to back up data, record music, master a home video, and much, much more. Generically, we call them optical-media discs and the drives that support them optical drives. CD stands for compact disc, a medium that was originally designed more than 20 years ago as a replacement for vinyl records. The CD now reigns as the primary method of long-term storage for sound and data. The DVD (digital versatile disc) first eliminated VHS cassette tapes from the home movie market, but has also grown into a contender for backups and high-capacity storage. Optical media include a number of technologies with names such as CD-ROM, CD-R, CD-RW, DVD, DVD+RW, HD-DVD, and so on. Each of these technologies will be discussed in detail in this segment. 


The best way to understand the world of optical discs is to sort out the many types of technologies available, starting with the first, the compact disc. 

How CDs Work

CDs—the discs that you buy in music stores or may find in software boxes—store data via microscopic pits. CD producers use a power laser to burn these pits into a glass master CD.  

Once the CD producer creates a master, expensive machines create plastic copies using a very high-tolerance injection molding process. The copies are coated with a reflective metallic covering and then finished with lacquer for protection. 

CD readers (like the one in your car or the one in your PC) use a laser and mirrors to read the data from the CD. The metallic covering of the CD makes a highly reflective surface—the pits create interruptions in that surface, while the non-pitted spots, called lands. The laser picks up on the reflected pattern that the pits and lands create, and the CD drive converts this pattern into binary ones and zeroes. Because the pits are so densely packed on the CD, a vast amount of data can be stored: A standard CD holds up to 5.2 billion bits, or 650 million bytes, of data. 

CD Formats 

The first CDs were designed for playing music and organized the music in a special for-mat called CD Digital Audio (CDDA), which we usually just call CD-audio. CD-audio divides the CD’s data into variable length tracks; on music CDs, each song gets one track. CD-audio is an excellent way to store music, but it lacks any error checking, file support, or directory structure, making it a terrible way to store data. For this reason, The Powers That Be created a special method for storing data on a CD, called are you ready CD-ROM. The CD-ROM format divides the CD into fixed sectors, each holding 2353 bytes. There are two other formats called CD-R and CD-RW. 

CD-ROM Speeds

The first CD-ROM drives processed data at roughly 150,000 bytes per second (150 KBps), copying the speed from the original CD-audio format. Although this speed is excellent for listening to music, the CDROM industry quickly recognized that installing programs or transferring files from a CD-ROM at 150 KBps was the electronic equivalent of watching paint dry. Since the day the first CD-ROM drives for PCs hit the market, there has been a desire to speed them up to increase their data throughput. Each increase in speed is measured in multiples of the original 150 KBps drives and given a “×” to show speed relative to the first (1×) drives. Here’s a list of the common CD-ROM speeds, including most of the early speeds that are no longer produced. 

CD/DVD Drive Speed

Maximum Data Transfer Rate
RPMs (revolutions per minute)

150 KB/sec
200 - 530

300 KB/sec
400 - 1060

600 KB/sec
800 - 2120
8X - 12X CD-ROM

1.2 MB/sec
1600 - 4240


Making CD-ROMs requires specialized, expensive equipment and substantial expertise, and it’s done by a relatively small number of CD-ROM production companies. Yet, since the day the first CD-ROMs came to market, demand has been terrific for a way that normal PC users could make their own CDs. The CD industry made a number of attempts to create a technology that would let users record, or burn, their own CDs. In the mid-1990s, the CD industry introduced the CD-record-able (CD-R) standard, which enables affordable CD-R drives, often referred to as CD burners, to add data to special CD-R discs. Any CD-ROM drive can then read the data stored on the CD-R, and all CD-R drives can read regular CD-ROMs. CD-R discs come in two varieties: a 74-minute disc that holds approximately 650 MB, and an 80-minute variety that holds approximately 700 MB. A CD-R burner must be specifically designed to sup-port the longer 80minute CD-R format. CD-R discs function similarly to regular CD-ROMs, although the chemicals used to make them produce a brightly colored recording side on almost all CD-R discs. CD-ROM discs, in contrast, have a silver recording side. CD-R technology records data using special organic dyes embedded into the disc. 


CD-R drives have disappeared from the market. Just as CD-R drives could both burn CD-R discs and read CD-ROMs, a newer type of drive called CD-re-writable (CD-RW) has taken over the burning market from CD-R drives. Although this drive has its own type of CD-RW discs, it also can burn to CD-R discs, which are much cheaper. CD-RW technology enables you not only to burn a disc, but to burn over existing data on a CD-RW disc. A CDRW drive works by using a laser to heat an amorphous (no crystalline) substance that, when cooled, slowly becomes crystalline. The crystalline areas are reflective, whereas the amorphous areas are not. Because both CD-R and CD-RW drives require a powerful laser, it was a simple process to make a drive that could burn CD-Rs and CD-RWs, making plain CD-R drives disappear almost overnight. CD-RW drive specs have three multiplier values. The first shows the CD-R write speed, the second shows the CD-RW rewrite speed, and the third shows the read speed. Write, rewrite, and read speeds vary tremendously among the various brands of CD-RW drives; here are just a few representative samples: 8×4×32×, 12×10×32×, and 48×24×48×. 


For years, the video industry tried to create an optical-media replacement for videotape. The 12 inch diameter laser-disc format originally introduced by Philips gained some ground in the 1980s and 1990s. But the high cost of both the discs and the players, plus various marketing factors, meant there was never a very large laser-disc market. The DVD was developed by a large consortium of electronics and entertainment firms during the early 1990s and released as digital video discs in 1995. The transformation of DVD to a data storage medium quickly required a name change, to digital versatile discs. You’ll still hear both terms used. The industry also uses the term DVD-video to distinguish the movie format from the data formats.  


The single best word to describe DVD is capacity. All previous optical media stored a maximum of 700 MB of data or 80 minutes of video. The lowest capacity DVD holds 4.37 GB of data, or two hours of standard definition video. The highest capacity version DVDs store roughly 16 GB of data, or more than eight hours of video! DVD achieves these amazing capacities using a number of technologies, but three are most important. First, DVD uses smaller pits than CD-media, and packs them much more densely. Second, DVD comes in both single-sided (SS) and dual-sided (DS) formats. As the name implies, a DS disc holds twice the data of an SS disc, but it also requires you to flip the disc to read the other side. Third, DVDs come in single-layer (SL) and dual-layer (DL) formats. DL formats use two pitted layers on each side, each with a slightly different reflective index. Here are list DVD’s along with their storage sides, Layers, Diameter & capacity.  



       List of various DVD along with their diameter capacity


DVD-ROM is the DVD equivalent of the standard CD-ROM data format except that it’s capable of storing up to almost 16 GB of data. Almost all DVD-ROM drives also fully support DVD-video, as well as most CDROM formats. Most DVD drives sold with PCs are DVD-ROM drives.  

Record-able DVD

The IT industry has no fewer than six distinct standards of record-able DVD-media: DVD-R for general use, DVD-R for authoring, DVD-RW, DVD+R, DVD+RW, and DVD-RAM. Both DVD-R standard discs and DVD+R discs work like CD-Rs. You can write to them but not erase or alter what’s written. DVD-RW, DVD+RW, and DVD-RAM discs can be written and rewritten, just like CD-RW discs. Most DVD drives can read all formats with the exception of DVD-RAM. DVD-RAM is the only DVD format that uses a cartridge, so it requires a special drive DVD-RAM is still around but fading away.  

Blue 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. 

External Optical Drives

Almost all new PCs have one or both external expansion buses, USB and Fire-wire, and the makers of optical drives have quickly taken this fact to heart. Many manufacturers have released external versions of CD and DVD drives, both readers and burners. 

External Storage drives

Nearly all personal computers come with an internal hard drive. This drive stores the computer's operating system, programs, and other files. For most users, the internal hard drive provides enough disk space to store all the programs and files. However, if the internal hard drive becomes full or if the user wants to back up the data on the internal hard drive, and external hard drive may be useful. External hard drives typically have one of two interfaces - USB or Fire-wire. USB hard drives commonly use the USB 2.0 interface because it supports data transfer rates of up to 480 Mbps. USB 1.1 only supports transfers of up to 12 Mbps, which would make the hard drive seem slow to even the most patient people. Fire-wire drives may use either Fire-wire 400 or Fire-wire 800, which support data transfer rates of up to 400 and 800Mbps respectively. The most likely users to need external hard drives are those who do audio and video editing. This is because high-quality media files can fill up even the largest hard drives. Fortunately, external hard drives can be daisy chained, which means they can be connected one after the other and be used at the same time. This allows for virtually unlimited amounts storage. Users who do not require extra storage may still find external hard drives useful for backing up their main hard drive.  External hard drives are a great backup solution because they can store an exact copy of another hard drive and can be stored in a safe location. Using the drive to restore data or perform another backup is as simple as connecting it to the computer and dragging the necessary files from one drive to another. While most external hard drives come in heavy, protective cases, some hard drives are designed primarily for portability. These drives usually don't hold as much data as their larger desktop counterparts, but they have a sleek form factor and can easily be transported with a laptop computer. Some portable drives also include security features such as fingerprint recognition that prevent other people from accessing data on the drive in case it is lost. 

There are various reason to use the external storage drives, such as

➣ Most users who use this device are those who do video or audio editing. These media files require high-quality settings, and therefore take up a large amount of disk space. One advantage to these external drives is that they can be connected or daisy chained, meaning they can be connected together and be used all at once to create unlimited storage capacity. 
➣ There are those who use these devices as back up for their computer files. They can accommodate the exact copy of the files from another drive. Because an external hard drive is portable, it can also be stored in a safe, secure location. 
➣ With portability, hard drives nowadays are designed to be lightweight and can be carried anywhere. Some external devices come with security features like fingerprint recognition, which prevents other people from gaining access to the stored data.


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