Operating System

Dual-Mode Operation


An automatic transmission for an automotive vehicle includes a continually variable drive mechanism having one sheave assembly fixed to an intermediate shaft and the input sheave assembly supported on an input shaft, gearset driveably connected to the input shaft and an output shaft, a fixed ratio drive mechanism in the form of a chain drive providing a torque delivery path between the intermediate shaft and the carrier of the gearset, a transfer clutch for connecting and releasing the first sheave of the variable drive mechanism and input shaft, a low brake, and a reverse brake.

• Mode bit added to computer hardware to indicate the currentmode: monitor (0) or user (1).• When an interrupt or fault occurs hardware switches to monitormodeuser monitorinterrupt/faultset user mode• Privileged instructions can be issued only in monitor mode.
Sharing system resources requires operating system to ensurethat an incorrect program cannot cause other programs toexecute incorrectly.• Provide hardware support to differentiate between at least twomodes of operations.1. User mode – execution done on behalf of a user.2. Monitor mode (also supervisor mode or system mode) –execution done on behalf of operating system.



I/O Protection
• All I/O instructions are privileged instructions.• Must ensure that a user program could never gain control ofthe computer in monitor mode (i.e., a user program that, aspart of its execution, stores a new address in the interruptvector).

Memory Protection

• Must provide memory protection at least for the interrupt vectorand the interrupt service routines.• In order to have memory protection, add two registers thatdetermine the range of legal addresses a program may access:– base register – holds the smallest legal physical memoryaddress.– limit register – contains the size of the range.• Memory outside the defined range is protected.



CPU Protection

The CPU protection feature enhances the efficiency of an HP device’s CPU and Content Addressable Memory (CAM). Some denial of service attacks make use of spoofed IP addresses. If the device must create CAM entries for a large number of spoofed IP addresses over a short period of time, it requires excessive CAM utilization. Similarly, if an improperly configured host on the network sends out a large number of packets that are normally processed by the CPU (for example, DNS requests), it requires excessive CPU utilization. The CPU protection feature allows you to configure the HP device to automatically take actions when thresholds related to high CPU or CAM usage are exceeded.

How the CPU Protection Feature Works The CPU protection feature uses the concepts of normal mode and exhausted mode. The device transitions from normal mode to exhausted mode when specified thresholds for conditions related to high CPU usage and CAM usage are exceeded. When the device enters exhausted mode, actions can be taken to reduce the strain on system resources. You can define the conditions that cause the device to enter exhausted mode, the actions to take while the device is in exhausted mode, and the conditions that enable the device to go back to normal mode. For example, you can specify that a CPU usage percentage of 90% is a condition that will cause the device to go from normal mode to exhausted mode. When the device enters exhausted mode, you can specify that the action to take is to forward unknown unicast traffic in hardware instead of sending it to the CPU. You can further specify that a CPU usage percentage of 80% will cause the device to go back to normal mode.

Caching
A cache is a block of memory for temporary storage of data likely to be used again. The CPU and hard drive frequently use a cache, as do web browsers and web servers.
A cache is made up of a pool of entries. Each entry has a datum (a nugget of data) which is a copy of the datum in some backing store. Each entry also has a tag, which specifies the identity of the datum in the backing store of which the entry is a copy.

A cache has proven to be extremely effective in many areas of computing because access patterns in typical computer applications have locality of reference. There are several kinds of locality, but this article primarily deals with data that are accessed close together in time (temporal locality). The data might or might not be located physically close to each other (spatial locality).

greatly increases the speed at which your computer pulls bits and bytes from memory.


Coheren

Client-server systems are not limited to traditional computers. An example is an automated teller machine (ATM) network. Customers typically use ATMs as clients to interface to a server that manages all of the accounts for a bank. This server may in turn work with servers of other banks (such as when withdrawing money at a bank at which the user does not have an account). The ATMs provide a user interface and the servers provide services, such as checking on account balances and transferring money between accounts.
To provide access to servers not running on the same machine as the client, middleware is usually used. Middleware serves as the networking between the components of a client-server system; it must be run on both the client and the server. It provides everything required to get a request from a client to a server and to get the server's response back to the client. Middleware often facilitates communication between different types of computer systems. This communication provides cross-platform client-server computing and allows many types of clients to access the same data.


Peer-to-peer (P2P) networking is a method of delivering computer network services in which the participants share a portion of their own resources, such as processing power, disk storage, network bandwidth, printing facilities. Such resources are provided directly to other participants without intermediary network hosts or servers.[1] Peer-to-peer network participants are providers and consumers of network services simultaneously, which contrasts with other service models, such as traditional client-server computing

symmetric multiprocessing or SMP involves a multiprocessor computer-architecture where two or more identical processors can connect to a single shared main memory. Most common multiprocessor systems today use an SMP architecture. In the case of multi-core processors, the SMP architecture applies to the cores, treating them as separate processors.
SMP systems allow any processor to work on any task no matter where the data for that task are located in memory; with proper operating system support, SMP systems can easily move tasks between processors to balance the workload efficiently.


Asymmetric multiprocessing or ASMP is a type of multiprocessing supported in DEC's VMS V.3 as well as a number of older systems including TOPS-10 and OS-360. It varies greatly from the standard processing model that we see in personal computers today. Due to the complexity and unique nature of this architecture, it was not adopted by many vendors or programmers during its brief stint between 1970 - 1980.

In terms of disproportionality, Parallel systems usually give results which fall somewhere between pure plurality/majority and pure PR systems. One advantage is that, when there are enough PR seats, small minority parties which have been unsuccessful in the plurality/majority elections can still be rewarded for their votes by winning seats in the proportional allocation. In addition, a Parallel system should, in theory, fragment the party system less than a pure PR electoral system.

batch system is Jobs with similar needs are batched together and run through the computer as a group, by an operator or automatic job sequencer. Performance is increased by attempting to keep CPU and I/O devices busy at all times through buffering, off-line operation, spooling, and multiprogramming. one in which jobs are bundled together with the instructions necessary to allow them to be processed without intervention.

multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task.

Time-sharing is sharing a computing resource among many users by multitasking.

An operating system is the framework that allows you to communicate with computer hardware in an interactive way. Without this, you would not be able to tell the computer to do anything and it would have any instructions to follow. This is why it is important for a computer to have an operating system .In early days without OS so much problems where faced like acessing or getting output it takes two days. To make it much more efficient OS is used.



§Interleave the execution of the number of processes to maximize processor utilization while providing reasonable response time
§The main idea of scheduling:
The system decides:
¨ Who will run
¨ When will it run
¨ For how long
In order to achieve its goals


Quality criteria for scheduling (algorithm)
§ Fairness: each process gets a “fair share” of the cpu
§ Efficiency: “keep the cpu busy”
§ Response time: minimize, for interactive users
§ Turnaround: for batch users (total time of batch)
§ Throughput: maximal number of processed jobs per unit time
§ Waiting time: minimize the average over processes

Scheduling – quality measures

§Throughput – number of processes completed per unit time
§ Turnaround time – interval of (real) time from process submission to completion
§ Waiting time – sum of time intervals the process spends in the ready queue
§ Response time – the time between submitting a command and the generation of the first output
§ CPU utilization – the part of the total (elapsed) time, the cpu is computing some process – between 0 and 100%

Conflicting Goals

§Response Time vs Turnaround time:
A conflict between:
Interactive and batch users.
§ Fairness vs Throughput:
Consider a very long job.
should it be run?