pkb contents > hardware | just under 1945 words | updated 05/21/2017

1. Computer hardware: Information storage & processing

https://fossbytes.com/wp-content/uploads/2016/04/latest-computer-chart.jpg, https://fossbytes.com/wp-content/uploads/2016/04/the-complete-computer-hardware-chart.jpg, http://eent3.lsbu.ac.uk/units/compsys/1%20Network%20Computer%20HardwareSlides.htm

High-level languages must be translated into machine code. This translation is hardware-specific, not portable. Translation can be done once (when code is complied into an executable) or on-the-fly by an interpreter. http://stackoverflow.com/questions/30156349/is-bash-an-interpreted-language

Layers Block diagram of computer Case Ports

2. Networks: Information representation and transfer

Bits , binary digits, are the 'atoms' of computerized information. Bits can be represented and transmitted by any two-state medium plus a consistent bits-per-unit-time clock (since states may be consecutive). The bandwidth of a system, its capacity to transmit information, is also called its bitrate . Latency is also important: that's the time it take for a bit to travel from receiver to sender.

When bits flow between machines and the machines have protocols to interpret the bits, you have a network : devices that can communicate with each other. Most modern networks are packet-switched networks. Instead of sending a constant bitstream, devices on the network send packets of bits plus metadata. The router takes these packets and routes them efficiently but robustly to a destination device that reassembles the packets.

"Computer networks differ in the transmission medium used to carry their signals, the communications protocols to organize network traffic, the network's size, topology and organizational intent" [ 1 ]:

2.1. Home networks

Networks can be many different sizes and scopes : LAN, PAN, WAN, MAN, etc. A P2P network (most home networks) lacks a central computer or server; a LAN might include Ethernet cables, wi-fi/wireless radio signals, or powerline network adaptors connect each device to a switch or hub.

In data communication, a physical network node may either be a data communication equipment (DCE) such as a modem , hub , [bridge](https://en.wikipedia.org/wiki/Bridging_(networking) or switch ; or a data terminal equipment (DTE) such as a digital telephone handset, a printer or a host computer (router, a workstation or a server).

2.2. The Internet

The Internet is a network of networks with special protocols and entities. Internet means "interconnected networks". Internet is not WWW: the Internet is a technical infrastructure which allows billions of computers to be connected all together. Among those computers, some computers (called Web servers [or HTTP servers]) can send messages intelligible to web browsers. The Internet is an infrastructure, whereas the Web is a service built on top of the infrastructure. It is worth noting there are several other services built on top of the Internet, such as email and IRC. // The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web (WWW), electronic mail, voice over IP telephony, and peer-to-peer networks for file sharing. [ 3 ]. The Web is a graphical interface for some of the content that's available through the Internet.

An ISP is a company that manages some special routers that link all together and can also access other ISPs' routers. So the message from our network is carried through the network of ISP networks to the destination network. [ 5 ]

ISPs can connect to each other as peers via IXPs or to upstream providers: Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access. An upstream ISP usually has a larger network than the contracting ISP or is able to provide the contracting ISP with access to parts of the Internet the contracting ISP by itself has no access to (https://en.wikipedia.org/wiki/Internet_service_provider)

Under the Internet Protocol ( IPv4, IPv6 ), all devices on the Internet have a unique IP address, and bits travel in IP packets (rather than directly from one machine to another). Routers receive these packets and---following transmission control protocol (TCP), user datagram protocol (UDP), or some other packet directing protocol---send them along different routes from sender to receiver, depending on traffic and outages. A router also take inventory of packets when they arrive and tells the sending server to resend any that were incomplete or missing. each packet carries the intended IP address, a number to determine where the packet fits back into the data sent, how many packets to expect, as well as your IP address

The domain name system ( DNS ) associates IP addresses with more human-friendly URLs. The DNS system consists of many DNS servers, connected to each other in a distributed hierarchy. DNS servers are sometimes spoofed: malicious IPs are associated with a domain that people might navigate to. Type URL into browser; DNS converts to IP?; browser talks to server located at IP ...:

When you type an address such as www.codecademy.com in your browser, you are commanding it to open a TCP channel to the server that responds to that URL ... Once the TCP connection is established, the client sends an HTTP request to the server ...

URL OSI model layers

3. Sources

3.1. References

3.2. Read

3.3. Unread