Operating system

An operating system is system software that manages computer hardware, software resources, provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is executed directly by the hardware and makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers; the dominant desktop operating system is Microsoft Windows with a market share of around 82.74%. MacOS by Apple Inc. is in second place, the varieties of Linux are collectively in third place. In the mobile sector, Google Android's share is up to 70% in the year 2017.

According to third quarter 2016 data, Android's share on smartphones is dominant with 87.5 percent with a growth rate of 10.3 percent per year, followed by Apple's iOS with 12.1 percent with per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent. Linux distributions are dominant in supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency; this is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs.

Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking. 32-bit versions of both Windows NT and Win9x used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources to multiple users. A distributed operating system manages a group of distinct computers and makes them appear to be a single computer.

The development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine; when computers in a group work in cooperation, they form a distributed system. In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system saving it as a tool for multiple running virtual machines; the technique is used both in virtualization and cloud computing management, is common in large server warehouses. Embedded operating systems are designed to be used in embedded computer systems, they are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources, they are compact and efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time.

A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts. A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their more complex forms until the early 1960s.

Hardware features were added, that enabled use of runtime libraries and parallel processing. When personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems. Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards; these were special-purpose systems that, for example, generated ballistics tables for the military

Envelope (radar)

Radar envelope is a critical Measure of Performance identified in the Test and Evaluation Master Plan. This is the volume of space where a radar system is required to reliably detect an object with a specific size and speed; this is one of the requirements. Radar systems have natural deficiencies because the laws of physics create performance constraints that cannot be altered; the ambiguity function associated with pulse compression and scalloping associated with moving target indication are two examples. Complete coverage requires multiple different kinds of radar. Radar system specifications require a specific level of performance within a specific radar envelope; this performance includes the following characteristics. Cross section Blind range Radial velocity Instrumented range Scan time Altitude Elevation angle Bearing coverage Sidelobe performanceData is extracted and recorded from the radar system while aircraft, ships, missiles or other objects are moved within the radar envelope; the recorded data is compared to distance and speed of the objects to evaluate the pass-fail criteria.

These are the typical shapes of the physical radar envelope. Flattened donut Cylinder with spherical void near the center Disk with spherical void near the center Pie with a missing slice and spherical void near the center The cross-section is the minimum apparent surface area observed in the direction of the radar that must be detectable. Cross section for anything except a perfect sphere depends upon the aspect angle, which how far the reflector is rotated with respect to the radar pulse; the blind range for a radar system is the distance occupied by the transmit pulse and the setup time for the receiver. Blind range = 0.5 × C ×. Non-Doppler radar are blind for the duration of the transmit pulse. Setup time is associated with two devices. Branch-duplexer receiver protection Antenna beamformingThe branch-duplexer includes a gas-filled tube that has high attenuation for high power microwaves but no attenuation for low power microwaves; this produces microwave noise during the setup-time at the end of the transmit pulse.

Phased-array antennas use phase shifters that require adjustment after the end of the transmit pulse, these phase shifters create modulation and high sidelobes that corrupts receive signals until after the setup time. Active phased-array radar may not have this limitation. Nap-of-the-earth flying techniques can be used to avoid detection when the blind range exceeds the radar horizon. H e i g h t < C 2 × 2 8 × E a r t h R a d i u s Radial velocity is the speed along the line of sight of toward the radar and away from the radar. This kind of motion degrades cross section performance due to the following phenomenon. Scalloping Doppler ambiguity function Moving target indication blind velocities The instrumented range is the maximum distance where full performance is required; this means that an object no larger than the cross section area must be detectable at all altitudes and velocities. The scan time is the time between re-scan of the same volume. For example, if a radar rotates at a fixed speed of 4 RPM the scan time is 15 seconds.

Scan time performance interacts with high-speed objects. Excessive scan time allows high-speed objects to travel a large distance toward the radar without being detected. Altitude is the distance from the earth surface; this measure of performance interacts with elevation angle. The Kármán line is accepted as the boundary between air and space; this is 100 km. There are two difficulties associated with altitude; the first difficulty is that the Outer Space Treaty requires international disclosure for space operations. This can include RF emissions from radar systems; the second difficulty is. Reflections from distances beyond the instrumented range can degrade performance; the elevation angle performance of a radar is determined by the type of antenna. The antenna panels used with phased array radar may be designed with an overlap that fills in any gap above a operational radar; the radiation pattern of a rotating truncated parabolic antenna for radar fixed pedestal has a fan shaped beam with a vertical gap in coverage.

Objects located directly above the radar may not be detected. Low elevation is a unique performance region. Pulse-Doppler radar and Continuous-wave radar are required for high performance in this area because these exclude low-velocity reflections; this is a critical measure of performance for land-based radar. P


Sunnal is a village in Belgaum district of Karnataka, India. Sunnal is a small village near Ramdurg, five kilometers from Ramdurg on Belgavi road, this village is famous for Maruthi Temple which has idol of lord Hanuman from ancient times, it is believed by thousands of devotees that by praying to lord Hanuman at Sunnal will be blessed twice by the lord Hanuman as his idol is seeing the devotees by both the eyes i.e. idol of lord Hanuman is in front facing towards the devotees. The Lord Hanuman temple of this village is popularly known as "Sunnal Hanumappa"; the stretch of forest along Sunnal and Halloli Villages is a place comprising Bears. These are popularly known as "Sunnal Karadi" or "Sunnal Kaddi" in Kannada