brief introduction
1. World Wide Web (also known as Network, WWW, 3W, English Web or World Wide Web) is a data space. In this space: useful things are called "resources"; And is identified by a global uniform resource identifier (URL). These resources are transmitted to users through hypertext transfer protocol, and the latter obtains resources by clicking on links. From another point of view, the World Wide Web is a system that accesses tidal documents through the network. World Wide Web Consortium (W3C), also known as W3C Committee. 1994 10 was established in the computer science laboratory of Massachusetts Institute of Technology (MIT) with the title of "the best university in the world". The founder is Tim Berners Lee, the inventor of the World Wide Web. The World Wide Web is usually regarded as a synonym for the Internet, but in fact it is a service running on the Internet.
Cache [n] A special memory subsystem that copies frequently used data for quick access. The cache of the memory stores the contents of frequently accessed RAM locations and the storage addresses of these data items. When a processor references an address in memory, the cache checks whether the address exists. If the address exists, the data is returned to the processor; If the address is not saved, a conventional memory access is performed. Because cache memory is always faster than main RAM memory, cache memory is often used when the access speed of RAM is lower than that of microprocessor.
Memory is one of the important components in a computer, and it is a bridge to communicate with CPU. All programs in a computer run in memory, so the performance of memory has a great influence on the computer. Memory, also called internal memory, is used to temporarily store the operation data in CPU and the data exchanged with external memory such as hard disk. As long as the computer is running, the CPU will transfer the data to the memory for operation, and the CPU will transfer the results after the operation is completed. The operation of the memory also determines the stable operation of the computer. Memory consists of memory chips, circuit boards, gold fingers and other components.
External storage refers to storage other than computer memory and CPU cache. Generally speaking, this kind of memory can still save data after power failure. Common external storage includes hard disk, floppy disk, CD, U disk, etc.
There are many kinds of memories, which can be divided into main memory and auxiliary memory according to their uses. The main memory is also called internal memory, and the auxiliary memory is also called external memory. External memory is usually magnetic media or optical disk, such as hard disk, floppy disk, magnetic tape, optical disk, etc. Can save information for a long time and does not rely on electricity to save information, but is driven by mechanical parts, which is much slower than CPU. External storage floppy disk, hard disk, CD-ROM drive and U disk are all external storage. From the working principle of von Neumann's stored program and the composition of the computer, the computer can be divided into arithmetic unit, controller, memory and input/output devices, in which the memory refers to memory and the hard disk belongs to input/output devices. The program code and data needed for CPU operation come from memory, and the things in memory come from hard disk. So the hard disk doesn't directly deal with the CPU. Hard disk is external storage relative to memory. Memory is used to store data. Memory includes cache and memory. Computer memory and external storage are external storage similar to U disk. Internal storage is fast, expensive and small in capacity. After power failure, the data in the memory will be lost. External memory has low unit price, large capacity and slow speed, and data will not be lost after power failure.
3. The simplest definition of computer network is: a collection of interconnected and autonomous computers for the purpose of * * * enjoying resources [TANE96].
The simplest computer network has only two computers and a link connecting them, namely, two nodes and a link. Because there is no third computer, there is no replacement problem.
The largest computer network is the Internet. It consists of many computer networks interconnected by many routers. Therefore, the Internet is also called "the network of networks".
In addition, from the perspective of network media, computer network can be regarded as a new media that is connected by multiple computers through specific equipment and software.