The Network

A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network.

Introduction

A network is a collection of computers and devices connected to each other. The network allows computers to communicate with each other and share resources and information. The Advance Research Projects Agency (ARPA) designed "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense. It was the first computer network in the world in late 1960's and early 1970's.

Network classification

The following list presents categories used for classifying networks.

Connection method

Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber, Ethernet, Wireless LAN, HomePNA, or Power line communication.

Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.

Scale

Based on their scale, networks can be classified as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN), Virtual Private Network (VPN), Campus Area Network (CAN), Storage Area Network (SAN), etc.

 Functional relationship (network architecture)

Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., Active Networking, Client-server and Peer-to-peer (workgroup) architecture.

Network topology

Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network, star-bus network, tree or hierarchical topology network. Network topology signifies the way in which devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a bus topology. In this regard the visual and operational characteristics of a networkare distinct; the logical network topology is not necessarily the same as the physical layout. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

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IP Addressing

Every IP address consists of network identifier and node identifier. The IP network is divided based on Class of network. The class of network is determined by the leading bits of the IP address as shown below. 

Address Classes

• Class A addresses begin with 0xxx, or 1 to 126 decimal.
• Class B addresses begin with 10xx, or 128 to 191 decimal.
• Class C addresses begin with 110x, or 192 to 223 decimal.
• Class D addresses begin with 1110, or 224 to 239 decimal.
• Class E addresses begin with 1111, or 240 to 254 decimal.

Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine. Class D addresses are reserved for multicasting. Class E addresses are reserved for future use. They should not be used for host addresses.

Now we can see how the Class determines, by default, which part of the IP address belongs to the network (N) and which part belongs to the Host/node (H).

• Class A: NNNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH
• Class B: NNNNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH
• Class C: NNNNNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

In the example, 192.189.210.078 is a Class C address so by default the Network part of the address (also known as the Network Address) is defined by the first three octets (192.189.210.XXX) and the node part is defined by the last one octets (XXX.XXX.XXX.078).

In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 192.189.210.0 specifies the network address for 192.189.210.078. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 192.189.210.255 specifies the broadcast address.

Private Subnets

For dial-up, you need a modem, active telephone line and an internet service provider

For high-speed, you need a highspeed router and modem, and an active internet service provider
 

Cable Modem - A cable modem is a unique type of modem that is designed to modulate a data signal over cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on a cable television network.

The bandwidth of residential cable modem service typically ranges from 3 Megabits per second (Mbit/s) up to 15 Mbit/s or more. The upstream bandwidth on residential cable modem service usually ranges from 384 Kilobits per second (kbit/s) to 2 Mbit/s or higher. VoIP and other new data services requiring broadband Internet access are driving demand for increased bandwidth delivery via cable modems.

Digital Subscriber Line (DSL) - DSL is a family of technologies that provides digital data transmission over the wires of a local telephone network.

Typically, the download speed of DSL ranges from 128 kilobits per second (kbit/s) to 24,000 kbit/s depending on DSL technology and the service level implemented. Upload speed is slower than download spped for Asymmetric Digital Subscriber Line (ADSL) and equal to the download speed for Symmetric Digital Subscriber Line (SDSL).

56K Modems - 56K modems are analog modems capable of speeds near 56 kbit/s when connecting to a service that has a digital connection to the phone network. It is important to note that this technique cannot be used between two 56K modems and that when two 56K modems connect they will revert to the slower standard analog methods.

Second half of 1950s- Second generation: transistors

In the second half of the 1950s bipolar junction transistors (BJTs) replaced vacuum tubes. Their use gave rise to the "second generation" computers. Initially, it was believed that very few computers would ever be produced or used. This was due in part to their size, cost, and the skill required to operate or interpret their results. Transistors greatly reduced computers' size, initial cost and operating cost. Compared to vacuum tubes, transistors have many advantages: they are less expensive to manufacture and are much faster, switching from the condition 1 to 0 in millionths or billionths of a second. Transistor volume is measured in cubic millimeters compared to vacuum tubes' cubic centimeters. Transistors' lower operating temperature increased their reliability, compared to vacuum tubes.

Normally, second-generation computers were composed of large numbers of printed circuit boards such as the IBM Standard Modular System each carrying one to four logic gates or flip-flops.

Transistorized electronics improved not only the CPU (Central Processing Unit), but also the peripheral devices. The IBM 350 RAMAC was introduced in 1956 and was the world's first disk drive. The second generation disk data storage units were able to store tens of millions of letters and digits. Multiple Peripherals can be connected to the CPU, increasing the total memory capacity to hundreds of millions of characters.

During the second generation remote terminal units saw greatly increased use. Telephone connections provided sufficient speed for early remote terminals and allowed hundreds of kilometers separation between remote-terminals and the computing center. Eventually these stand-alone computer networks would be generalized into an interconnected network of networks — the Internet.

Advances in the 1960’s

In the 1960’s, efforts to design and develop the fastest possible computer with the greatest capacity reached a turning point with the LARC machine, built for the Livermore Radiation Laboratories of the University of California by the Sperry - Rand Corporation, and the Stretch computer by IBM. The LARC had a base memory of 98,000 words and multiplied in 10 Greek MU seconds. Stretch was made with several degrees of memory having slower access for the ranks of greater capacity, the fastest access time being less then 1 Greek MU Second and the total capacity in the vicinity of 100,000,000 words. During this period, the major computer manufacturers began to offer a range of capabilities and prices, as well as accessories such as:

• Consoles
• Card Feeders
• Page Printers
• Cathode - ray - tube displays
• Graphing devices

These were widely used in businesses for such things as:

• Accounting
• Payroll
• Inventory control
• Ordering Supplies
• Billing

CPU’s for these uses did not have to be very fast arithmetically and were usually used to access large amounts of records on file, keeping these up to date. By far, the most number of computer systems were sold for the more simple uses, such as hospitals (keeping track of patient records, medications, and treatments given). They were also used in libraries, such as the National Medical Library retrieval system, and in the Chemical Abstracts System, where computer records on file now cover nearly all known chemical compounds.

More Recent Advances(Post 1960: third generation and beyond)

The trend during the 1970’s was, to some extent, moving away from very powerful, single - purpose computers and toward a larger range of applications for cheaper computer systems. Most continuous-process manufacturing, such as petroleum refining and electrical-power distribution systems, now used computers of smaller capability for controlling and regulating their jobs.

In the 1960’s, the problems in programming applications were an obstacle to the independence of medium sized on-site computers, but gains in applications programming language technologies removed these obstacles. Applications languages were now available for controlling a great range of manufacturing processes, for using machine tools with computers, and for many other things. Moreover, a new revolution in computer hardware was under way, involving shrinking of computer-logic circuitry and of components by what are called large-scale integration (LSI techniques.

In the 1950s it was realized that “scaling down” the size of electronic digital computer circuits and parts would increase speed and efficiency and by that, improve performance, if they could only find a way to do this. About 1960 photo printing of conductive circuit boards to eliminate wiring became more developed. Then it became possible to build resistors and capacitors into the circuitry by the same process. In the 1970’s, vacuum deposition of transistors became the norm, and entire assemblies, with adders, shifting registers, and counters, became available on tiny “chips.”

In the 1980’s, very large scale integration (VLSI), in which hundreds of thousands of transistors were placed on a single chip, became more and more common. Many companies, some new to the computer field, introduced in the 1970s programmable minicomputers supplied with software packages. The “shrinking” trend continued with the introduction of personal computers (PC’s), which are programmable machines small enough and inexpensive enough to be purchased and used by individuals. Many companies, such as Apple Computer and Radio Shack, introduced very successful PC’s in the 1970s, encouraged in part by a fad in computer (video) games. In the 1980s some friction occurred in the crowded PC field, with Apple and IBM keeping strong. In the manufacturing of semiconductor chips, the Intel and Motorola Corporations were very competitive into the 1980s, although Japanese firms were making strong economic advances, especially in the area of memory chips.

Do you like new gadgets? Do you like flat screen monitors? Are you amaze how computers being much portable nowadays?...

 On the fast navigation on system this era gives you,..are you aware on its root?..Do you know its evolution(from 1950s up to present)?

If you’re interested on computers on this generation, why not also gain interest on its history?

Here, I’m gonna present to you the History of Computer Hardware from 1950s and beyond..

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