Computer Networking Concepts PDF

A hard disk is coated with magnetic material that can be magnetised into a pattern of 0’s and 1’s. The disk has many lines which separate each source of data. A track is an individual line on the disk. A sector is a part of of the circular disk in the shape of a triangle or cone. A track sector is a...

A hard disk is coated with magnetic material that can be magnetised into a pattern of 0’s and 1’s. The disk has many lines which separate each source of data. A track is an individual line on the disk. A sector is a part of of the circular disk in the shape of a triangle or cone. A track sector is a track within the cone. And a cluster is usually near the outermost ring. It is more like an arc. Within a sector each track has the same amount of storage, usually around 512 bytes. Reading and writing on the disk is usually performed by a read/write head which is attached to/from the centre. The disk is continuously spinning so each sector is at some point under the head. The read/write head is really sharp so it is engineered in a way so that the disk and the head never touch but are very close. While the SSD is a really thin stick which doesn't need a disk to rotate so it is faster. Additionally because their size is very small they are used for smaller devices such as phones and laptops. Now onto computer networking, a network of computers are linked together by communication links. Either wired or wireless. Networks can be divided into Local Area Network and Wide Area Network. In Local Area network the computers are linked in a close range from each other. They are linked by dedicated cables which have a speed or up to 1000Mbps. Wide Area Networks are Local area networks divided by geographic distance. Communication over Networks consists of two major components, Software and Hardware. Software has protocols which are how computers in networks understand and react to messages. While hardware has network infrastructures which are channels of transmitting messages. Now let's talk about the differences between a switch and a router. A switch connects several devices to a LAN, governs data flow between devices in LAN and the internet, and also maintains communication within the devices, example(printer). When the switch does not have internet access the devices can still communicate with each other. Now we talk about Routers, in short, routers connect a network to the world via the internet and protect data from security threats. Many routers have built-in switches which allow connectivity between devices. Communication between different computers requires conventions ie.(protocol). Some common types of protocols are Hypertext transfer protocol (HTTP), internet protocols (IP), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP). The functions of each protocol are as follows. HTTP is for web page browsing. IP is for computers to communicate over the internet, FTP is to send and receive files, finally SMTP is for transferring emails across the world via network. Data is sent to access the network in simple chunks called packets. The packets take different paths but the data remains the same. This is very important, the OSI model. The model includes seven layers that describe each task to be performed to transfer information over a network. The seven layers are [ Application, Presentation, Session, Transport, Network, Data link and Physical]. Application layer initiates a request or accepts a request. The Presentation layer adds formatting,display and encryption, Session layer adds traffic flow to information to determine if packet is sent, Transport layer adds error-handling information, Network layer adds sequencing and address information to packets, Data link layer adds error-checking information and prepares data for going on to physical connection.Physical layer sends packets as bitstreams. Now lets move on to cryptography. We have encryption, decryption, plain text and cipher text. Obviously encryption encrypted the text and decryption decrypted the text. Plain text is the normal text and cipher text is the transformed text. Important part is the keys, we have two sets of cryptography. Symmetric key and Asymmetric key. The difference is symmetric keys are used when the same key is used for encryption and decryption. Asymmetric keys are when two different keys are used to encrypt and decrypt. Symmetric key cryptography is Data encryption standard (DES). and Asymmetric key cryptography is when plain text is encrypted by private public key and decrypted by private key.