• A thread is a flow of execution through the process code, with its own program counter that keeps way of which instruction to execute next, system registers which hold its existing working variables, and a stack which contains the execution history. A thread is also called as lightweight process.
• A thread shares with its peer threads few information like code segment, data segment and open files.
• To improve application performance through parallelism.
• Threads represent a software approach to improving performance of operating system by reducing the overhead thread is equivalent to a classical process.
• Each thread has exactly one process and no thread can exist outside a process. Each thread signifies a separate flow of control.
• Implementing network servers and web server.
• They are also offer a suitable foundation for parallel execution of applications on shared memory multiprocessors.
• The working process of a single-threaded and a multithreaded are shows in the following figure.

• The context switching time minimize in thread concepts.
• Use of threads offers concurrency within a process.
• Efficient communication.
• It is more economical to create and context switch threads.
• Threads allow utilization to a greater scale and efficiency of multiprocessor architectures.

• There are two types of thread,
  • User Level Threads.
  • Kernel Level Threads.

• In this case, the thread management kernel is not aware of the existence of threads.
• The thread library contains code for creating and destroying threads, for transient message and data between threads, for scheduling thread execution and for saving and reestablishing thread settings.
• From the single thread start the application.

• Kernel is done thread management.
• In the application area there is no thread management code.
• The operating system directly supported Kernel threads.
• Multithreaded can be programmed in an any application.
• An application is supported within a single process.

• Scheduling is an essential part of a Multiprogramming operating systems.
• Such operating systems allow more than one process to be loaded into the executable memory at a given time and the loaded process shares from the CPU using time multiplexing.
• The Operating System maintains the following important process scheduling queues −
  • Job queue − This queue preserves all the processes in the system.
  • Ready queue − This queue keeps a set of all processes residing in main memory, ready and waiting to execute. A new process is always placed in this queue.
  • Device queues − The processes which are blocked due to inaccessibility of an I/O device establish this queue.

• The OS can use different procedures to manage each queue (FIFO, Round Robin, Priority, etc.).
• The OS scheduler determines how to move from processes between the ready and run queues which can only have one entry per processor core on the system; in the above diagram, it has been combined with the CPU.

• Long-Term Scheduler
• Short-Term Scheduler
• Medium-Term Scheduler

• It is also called a job scheduler.
• It selects processes from the queue and loads into memory for execution.
• The long-term scheduler may not be accessible or minimal.
• No long-term scheduler in the time-sharing operating systems.
• Use of long-term scheduler when a process changes the state from new to ready.

• Short term scheduler is also known as CPU scheduler.
• It is used to improve system performance.
• It is change from ready state to running state of the process.
• Short term scheduler is faster than compared to long term scheduler.

• Medium-term scheduling is a part of swapping.
• Medium Term Scheduler has removed the processes from the memory.
• To remove the process from memory and make space to the other processes, the postponed process is moved to the secondary storage.
• This process is called swapping.

• Caching is an area of a computer’s memory devoted to temporarily storing recently used data.
• In caching the content are which includes HTML pages, images, files and Web objects, is stored on the local hard drive in order to make it faster for the user to access it, which helps to develop the efficiency of the computer and its overall performance.
• For example, when a user returns to a Web page they have recently accessed, the browser can pull those files from the cache instead of the original server because it has stored the user’s activity.
• The storing of that information saves the user can getting to it faster, and less time to the traffic on the network.

• When a cache client wants to access data, it first checks the cache. Cache hit is known as when the requested data is found.
• The current of attempts that result in cache hits is known as the cache hit rate or ratio.
• If the requested data isn’t found in the cache a situation known as a cache miss. It is getting from main memory and through into the cache. How this is done, and what data is ejected from the cache to make room for the new data, depends on the caching algorithm or policies the system uses.

• Web browsers, such as Internet Explorer, Firefox, Safari and Chrome, use a browser cache to develop performance of frequently accessed webpages.
• When we visit a webpage, the requested files are stored in computing storage in the browser’s cache.
• Clicking back and returning to a previous page enables from the browser to retrieve most of the files it needs from the cache instead of having them all resent from the web server.
• This approach is called read cache. The browser can read data from the browser cache much faster than from the webpage it can reread the files.

• Some examples of cache algorithms they are,
  • Least Frequently Used (LFU)
  • Least Recently Used (LRU)
  • Most Recently Used (MRU)

• Keeps track of how often an entry is accessed. The data that has to use lowest count gets then removed first.

• Puts recently accessed data to near the top of the cache. When the cache reaches its limit, the least recently accessed data are removed.

• Removes the most recently accessed data first. This approach is best when older items are more likely to be used.

• LAN stands for Local Area Network, LAN (Local Area Network) is a network which is established to small areas. It used in home, offices, airports and in small college computer labs.
• LAN (Local Area Network) was established to good interconnections within the individual computer units.

How LAN Works

• Early LAN (Local Area Network) networks were designed as coaxial cable, coax is an electric cable and to carry radio signals.
• LAN (Local Area Network) setup is developed by the connecting two or more computers with each other using a physical connection in order to share files and information actively.
• To connect the radio transmitters with their antennas by using this cable.
• However, it is also used for developing internet connections.
• Ethernet is the most common type of developing LAN (Local Area Network).
• Data and physical link layer are a major termed as Ethernet.
• Today ethernet can be given the maximum data rate of up to 100 Mbps.
• Ethernet cables are extended to the length of 100 meters, but this is not the ultimate limit. Ethernet cables is also extended according to the need.
• Microsoft windows will be provided as special internet sharing features which help LAN (Local Area Network).

• Ping is a basic Internet tool that allows a user to validate that a specific IP address exists and they also can be the accept requests.
• The act of using the ping utility or command. Ping is used diagnostically to ensure that a host computer we are trying to reach is actually operating. If, for example, the user will be unable to use the File Transfer Protocol (FTP) to send files to that host while they cannot ping a host.
• Using ping, we can also learn the number form of the IP address from the symbolic domain name.
• The process of transfer a message to all the members of a mailing list requesting an ACK (acknowledgment code).
• This is done before sending e-mail in order to confirm that all of the addresses are reachable.

• The original PING command stood for “Packet Internet Groper”, and was a package of analytic utilities used by DARPA personnel to test the act of the ARPANET.
• However, the current Internet Ping command refers to a program was written by Mike Muuss in December, 1983, which has since become one of the most multipurpose and extensively used diagnostic tools on the Internet.

• The Internet Ping program works much like a sonar echo-location, sending a small packet of data containing an ICMP ECHO_REQUEST to a quantified computer, which then sends an ECHO_REPLY packet in arrival.
• The IP address 127.0.0.1 is set by convention to always indicate on the computer. Therefore, a ping to that address will always ping yourself and the delay should be very short. The most basic test of local communications to be provided.

• An addressing scheme is obviously a requirement for communications in a computer network.
• An addressing scheme, packets are forwarded from one place to another.
• Each of the three layers, 2, 3, and 4, of the TCP/IP protocol stack model produces a header, as indicated in below diagram.
• In this figure, host 1 communicates with host 2 on a network of seven nodes, R1 through R7, and a payload of information encapsulated in a frame by the link layer header, the network layer header, and the transport layer header is carried over a link.
• Within any of these three headers, each source or destination is allocated an address as identification for the corresponding protocol layer.
• The three types of addresses are summarized as follows.
  • Link layer (layer 2) address
  • Network layer (layer 3) address
  • Transport layer (layer 4) address

• A 6-byte (48-bit) field called Media Access Control (MAC) address that is signified by a 6-field hexadecimal number, such as 89-A1-33-2B-C3-84, in which each field as taken as two bytes long.
• Every interface has a unique MAC address. Every input or output of a networking device has an interface to its connected link.
• Normally, the same MAC address doesn’t share two interfaces then only safe. Both MAC addresses of a source interface and a destination interface contains by link layer header.

• A 4-byte (32-bit) field called Internet Protocol (IP) address that is signified by a 4-field dot-separated number, such as 192.2.32.83, in which each field is taken as one byte long.
• An IP address can be known worldwide at the network level.
• A network layer header contains both IP addresses of a source node and a destination node.

• A 2-byte (16-bit) field called port number that is characterized by a 16-bit number, such as 4,892. The port numbers identify the two end hosts’ ports in a communication.
• Any host can be running several network applications at a time and thus each application needs to be identified by another host communicating to a targeted application.
• For example, source host 1 requires a port number for communication to uniquely identify an application process running on the destination host 2.
• A transport layer header contains the port numbers of a source host and a destination host, as seen in the figure. Note that a transport-layer “port” is a logical port and not an actual or a physical one, and it serves as the end-point application identification in a host.

• Pattern programs in C print various patterns of numbers and stars. These codes explain how to create various patterns using C programming. The C programs involve usage of nested for loops (a for loop inside a for loop).
• A pattern of numbers, star or characters is a way of arranging these in some logical manner or they may form a sequence. Some of these patterns are triangles which have special importance in mathematics.