Computer virus

A computer virus is a computer program that can copy itself[1]  and infect a computer. The term "virus" is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware  programs that do not have the reproductive ability. A true virus can spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive. Viruses can increase their chances of spreading to other computers by infecting files on a network file system or a file system that is accessed by another computer.
As stated above, the term "computer virus" is sometimes used as a catch-all phrase to include all types of malware, even those that do not have the reproductive ability. Malware includes computer viruses, computer worms, Trojan horses, most rootkits, spyware, dishonest adware and other malicious and unwanted software, including true viruses. Viruses are sometimes confused with worms and Trojan horses, which are technically different. A worm can exploit security vulnerabilities to spread itself automatically to other computers through networks, while a Trojan horse is a program that appears harmless but hides malicious functions. Worms and Trojan horses, like viruses, may harm a computer system's data or performance. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious or simply do nothing to call attention to themselves. Some viruses do nothing beyond reproducing themselves.

RAM (RANDOM ACCESS MEMORY)

Random-access memory (RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). "Random" refers to the idea that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1]

By contrast, storage devices such as magnetic discs and optical discs rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than data transfer, and the retrieval time varies based on the physical location of the next item.

The word RAM is often associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. Many other types of memory are RAM, too, including most types of ROM and a type of flash memory called NOR-Flash

Hard disk drive

A magnetic disk on which you can store  computer  data. The term hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks. A hard disk, for example, can store anywhere from 10 to more than 100 gigabytes, whereas most floppies have a maximum storage capacity of 1.4 megabytes.

A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte hard disk for a PC might have two platters (four sides) and 1,053 cylinders. 

History

Main article: History of hard disk drives

router vs switch

What is the difference between a router and hub or switch?

Answer: A router  is a more sophisticated network device than either a switch  or a hub. Like hubs and switches, network routers are typically small, box-like pieces of equipment that multiple computers can connect to. Each features a number of "ports" the front or back that provide the connection points for these computers, a connection for electric power, and a number of LED lights to display device status. While routers, hubs and switches all share similiar physical appearance, routers differ substantially in their inner workings.

Traditional routers are designed to join multiple area networks (LANs and WANs). On the Internet or on a large corporate network, for example, routers serve as intermediate destinations for network traffic. These routers receive TCP/IP packets, look inside each packet to identify the source and target IP addresses, then forward these packets as needed to ensure the data reaches its final destination.

Routers for home networks (often called broadband routers) also can join multiple networks. These routers are designed specifically to join the home (LAN) to the Internet (WAN) for the purpose of Internet connection sharing. In contrast, neither hubs nor switches are capable of joining multiple networks or sharing an Internet connection. A home network with only hubs and switches must designate one computer as the gateway to the Internet, and that device must possess two network adapters for sharing, one for the home LAN and one for the Internet WAN. With a router, all home computers connect to the router equally, and it performs the equivalent gateway functions.

Additionally, broadband routers contain several features beyond those of traditional routers. Broadband routers provide DHCP server and proxy support, for example. Most of these routers also offer integrated firewalls. Finally, wired Ethernet broadband routers typically incorporate a built-in Ethernet switch. These routers allow several hubs or switches to be connected to them, as a means to expand the local network to accomodate more Ethernet devices.

In home networking, hubs and switches technically exist only for wired networks. Wi-Fi wireless routers incorporate a built-in access point that is roughly equivalent to a wired switch. 

 

Central processing unit

The Central Processing Unit (CPU) or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s [1]. The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same.

Early CPUs were custom-designed as a part of a larger, sometimes one-of-a-kind, computer. However, this costly method of designing custom CPUs for a particular application has largely given way to the development of mass-produced processors that are made for one or many purposes. This standardization trend generally began in the era of discrete transistor mainframes and minicomputers and has rapidly accelerated with the popularization of the integrated circuit (IC). The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of these digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in everything from automobiles to cell phones and children's toys

 Pronounced as separate letters it is the abbreviation for central processing unit. The CPU is the brains of the computer. Sometimes referred to simply as the central processor
, but more commonly called processor, the CPU is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.


On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor. Since the 1970's the microprocessor class of CPUs has almost completely overtaken all other CPU implementations.


The CPU itself is an internal component of the computer. Modern CPUs are small and square and contain multiple metallic connectors or pins on the underside. The CPU is inserted directly into a CPU socket, pin side down, on the motherboard. Each motherboard will support only a specific type or range of CPU so you must check the motherboard manufacturer's
specifications before attempting to replace or upgrade a CPU. Modern CPUs also have an attached heat sink and small fan that go directly on top of the CPU to help dissipate heat.


Two typical components of a CPU are the following:


    * The arithmetic logic unit (ALU), which performs arithmetic and logical operations.
    * The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

 

 

MOTHERBOARD

What is a motherboard?

So what is a motherboard? A computer motherboard (also known as the mainboard) is one of the most crucial components of a computer.

As the name suggests, a motherboard is the mother to all the other parts. In other words, everything in a computer connects to the motherboard. A motherboard (mobo) is the primary circuit board in a computer.

Motherboard (the mother to all the other components)

A typical motherboard has attachment points for all the common components in a computer. These are the Power Supply, CPU (Central Processing Unit), hard drive, RAM (Random Access Memory), graphics card, CD drive and other peripheral devices such as sound cards, network cards etc.

Network Adapters

The first piece of hardware that I want to discuss is a network adapter. There are many different names for network adapters, including network cards, Network Interface Cards, NICs. These are all generic terms for the same piece of hardware. A network card’s job is to physically attach a computer to a network, so that the computer can participate in network communications.

The first thing that you need to know about network cards is that the network card has to match the network medium. The network medium refers to the type of cabling that is being used on the network. Wireless networks are a science all their own, and I will talk about them in a separate article.

At one time making sure that a network card matched the network medium was a really big deal, because there were a large number of competing standards in existence. For example, before you built a network and started buying network cards and cabling, you had to decide if you were going to use Ethernet, coaxal Ethernet, Token Ring, Arcnet, or one of the other networking standards of the time.  Each networking technology had its strengths and weaknesses, and it was important to figu
re out which one was the most appropriate for your organization.

In the first part of this article series, I talked about some basic networking hardware such as hubs and switches. In this article, I want to continue the discussion of networking hardware by talking about one of the most important networking components; routers.

Even if you are new to networking, you have probably heard of routers. Broadband Internet connections, such as those utilizing a cable modem or a DSL modem, almost always require a router. A router's job isn't to provide Internet connectivity though. A router's job is to move packets of data from one network to another. There are actually many different types of routers ranging from simple, inexpensive routers used for home Internet connectivity to the insanely expensive routers used by giant corporations. Regardless of a router’s cost or complexity, routers all work on the same basic principles.

That being the case, I'm going to focus my discussion around simple, low budget routers that are typically used to connect a PC to a broadband Internet connection. My reason for doing so is that this article series is intended for beginners. In my opinion, it will be a lot easier to teach you the basics if I am referencing something that is at least somewhat familiar to most people, and that is not as complicated as many of the routers used within huge corporations. Besides, the routers used in corporations work on the same basic principles as the routers that I will be discussing in this article. If you are wanting a greater level of knowledge though, don’t worry. I will talk about the science of routing in a whole lot more detail later in this article series.

As I explained earlier, a router's job is to move packets of data from one network to another. This definition might seem strange in the context of a PC that's connected to a broadband Internet connection. If you stop and think about it, the Internet is a network (actually it's a collection of networks, but that's beside the point).

So if a router's job is to move traffic between two networks, and the Internet is one of those networks, where is the other one? In this particular case, the PC that is connected to the router is actually configured as a very simple network.

To get a better idea of what I am talking about, take a look at the pictures shown in Figures A and B. Figure A shows the front of a 3COM broadband router, while Figure B shows the back view of the same router.

Figure A: This is the front view of a 3COM broadband router