STORAGE HIERARCHY

1. caching

Caching is a well known concept in computer science: when programs continually access the same set of instructions, a massive performance benefit can be realized by storing those instructions in RAM. This prevents the program from having to access the disk thousands or even millions of times during execution by quickly retrieving them from RAM. Caching on the web is similar in that it avoids a roundtrip to the origin web server each time a resource is requested and instead retrieves the file from a local computer's browser cache or a proxy cache closer to the user.

2. coherency and consistency-

STORAGE STRUCTURE

1. main memory

Refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.

2. magnetic disk

A memory device, such as a floppy disk, a hard disk, or a removable cartridge, that is covered with a magnetic coating on which digital information is stored in the form of microscopically small, magnetized needles

• moving head disk mechanism
  

3. magnetic tapes

Magnetic tape is a medium for magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of plastic. Nearly all recording tape is of this type, whether used for recording audio or video or for computer data storage. It was originally developed in Germany, based on the concept of magnetic wire recording. Devices that record and playback audio and video using magnetic tape are generally called tape recorders and video tape recorders respectively. A device that stores computer data on magnetic tape can be called a tape drive, a tape unit, or a streamer.


HARDWARE PROTECTION

1. Dual-Mode operation

• Sharing system resources requires operating system to ensuthat an incorrect program cannot cause other programs toexecute incorrectly

• Provide hardware support to differentiate between at least twmodes of operations.

a. User mode – execution done on behalf of a user.

b. Monitor mode (also supervisor mode or system mode) –execution done on behalf of operating system.

......Dual-Mode Operation (Cont.)......

• Mode bit added to computer hardware to indicate the currentmode: monitor (0) or user (1)
  
  

• When an interrupt or fault occurs hardware switches to monitomode

2. input/output 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).

3. 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

4. CPU protection-

1. Bootstrap program

answer:
In computing, booting (booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. A boot sequence is the initial set of operations that the computer performs when power is switched on. The bootloader typically loads the main operating system for the computer.

2. Difference of interrupt and their use

answer:
An interrupt is an event in hardware that triggers the processor to jump from its current program counter to a specific point in the code. Interrupts are designed to be special events whose occurrence cannot be predicted precisely (or at all). The MSP has many different kinds of events that can trigger interrupts, and for each one the processor will send the execution to a unique, specific point in memory. Each interrupt is assigned a word long segment at the upper end of memory. This is enough memory for a jump to the location in memory where the interrupt will actually be handled. Interrupts in general can be divided into two kinds- maskable and non-maskable.

*A maskable interrupt is an interrupt whose trigger event is not always important, so the programmer can decide that the event should not cause the program to jump.

*A non-maskable interrupt (like the reset button) is so important that it should never be ignored. The processor will always jump to this interrupt when it happens. Often, maskable interrupts are turned off by default to simplify the default behavior of the device. Special control registers allow non-maskable and specific non-maskable interrupts to be turned on. Interrupts generally have a "priority;" when two interrupts happen at the same time, the higher priority interrupt will take precedence over the lower priority one. Thus if a peripheral timer goes off at the same time as the reset button is pushed, the processor will ignore the peripheral timer because the reset is more important (higher priority).


3. Monitor mode

answer:
Monitor mode, or RFMON (Radio Frequency Monitor) mode, allows a computer with a wireless network interface card (NIC) to monitor all traffic received from the wireless network. Unlike promiscuous mode, which is also used for packet sniffing, monitor mode allows packets to be captured without having to associate with an access point or ad-hoc network first. Monitor mode only applies to wireless networks, while promiscuous mode can be used on both wired and wireless networks. Monitor mode is one of the six modes that 802.11 wireless cards can operate in: Master (acting as an access point), Managed (client, also known as station), Ad-hoc, Mesh, Repeater, and Monitor mode.

4. user mode

answer:
In Kernel mode, the executing code has complete and unrestricted access to the underlying hardware. It can execute any CPU instruction and reference any memory address. Kernel mode is generally reserved for the lowest-level, most trusted functions of the operating system. Crashes in kernel mode are catastrophic; they will halt the entire PC4. User mode

5. Device status table

answer:

6. Direct memory access

answer:
Direct memory access (DMA) is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors, especially in multiprocessor system-on-chips, where its processing element is equipped with a local memory (often called scratchpad memory) and DMA is used for transferring data between the local memory and the main memory. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel. Similarly a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time and allowing computation and data transfer concurrency

7. Differrence of RAM and DRAM

answer:
RAM-RandomRandom accessaccessaccess memory or RAM most commonly refers to computer chips that temporarily store dynamic data to enhance computer performance. By storing frequently used or active files in randomrandomrandom accessaccessaccess memory, the computer can accessaccessaccess the data faster than if it to retrieve it from the far-larger hard drive. RandomRandomRandom accessaccessaccess memory is also used in printers and other devices.
RandomRandomRandom accessaccessaccess memory is volatile memory, meaning it loses its contents once power is cut. This is different from non-volatile memory such as hard disks and flash memory, which do not require a power source to retain data. When a computer shuts down properly, all data located in randomrandomrandom accessaccessaccess memory is committed to permanent storage on the hard drive or flash drive. At the next boot-up, RAM begins to fill with programs automatically loaded at startup, and with files opened by the user.

DRAM-Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory.

8. main memory

answer:
Refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.
The computer can manipulate only data that is in main memory. Therefore, every program you execute and every file you access must be copied from a storage device into main memory. The amount of main memory on a computer is crucial because it determines how many programs can be executed at one time and how much data can be readily available to a program.
Because computers often have too little main memory to hold all the data they need, computer engineers invented a technique called swapping, in which portions of data are copied into main memory as they are needed. Swapping occurs when there is no room in memory for needed data. When one portion of data is copied into memory, an equal-sized portion is copied (swapped) out to make room.
Now, most PCs come

9. magnetic disk

answer:
A memory device, such as a floppy disk, a hard disk, or a removable cartridge, that is covered with a magnetic coating on which digital information is stored in the form of microscopically small, magnetized needles

10. Storage hierarchy

answer:
To clarify the ``guarantees'' provided at different settings of the persistence spectrum without binding the application to a specific environment or set of storage devices, MBFS implements the continuum, in part, with a logical storage hierarchy. The hierarchy is defined by N levels:

1.

LM (Local Memory storage): very high-speed volatile storage located on the machine creating the file.

2.

LCM (Loosely Coupled Memory storage): high-speed volatile storage consisting of the idle memory space available across the system.

3.

-N DA (Distributed Archival storage): slower speed stable storage space located across the system.

Logically, decreasing levels of the hierarchy are characterized by stronger persistence, larger storage capacity, and slower access times. The LM level is simply locally addressable memory (whether on or off CPU). The LCM level combines the idle memory of machines throughout the system into a loosely coupled, and constantly changing, storage space. The DA level may actually consist of any number of sub-levels (denoted DA₁, DA₂, ..., DA_n) each of increasing persistence (or capacity) and decreasing performance. LM data will be lost if the current machine crashes or loses power. LCM data has the potential to be lost if one or more machines crash or lose power. DA data is guaranteed to survive power outages and machine crashes. Replication and error correction are provided at the LCM and DA levels to improve the persistence offered by those levels.

Each level of the logical MBFS hierarchy is ultimately implemented by a physical storage device. LM is implemented using standard RAM on the local machine and LCM using the idle memory of workstations throughout the network. The DA sub-levels must be mapped to some organization of the available archival storage devices in the system. The system administrator is expected to define the mapping via a system configuration file. For example, DA-1 might be mapped to the distributed disk system while DA-2 is mapped to the distributed tape system.

8.)Define the essential properties of the following types of OS:

ANSWER:
a. Batch-In a computer, a batch job is a program that is assigned to the computer to run without further user interaction. Examples of batch jobs in a PC are a printing request or an analysis of a Web site log. In larger commercial computers or servers, batch jobs are usually initiated by a system user. Some are defined to run automatically at a certain time.

In some computer systems, batch jobs are said to run in the background and interactive programs run in the foreground. In general, interactive programs are given priority over batch programs, which run during the time intervals when the interactive programs are waiting for user requests.

The term originated with mainframe computers when punched cards were the usual form of computer input and you put a batch of cards (one batch per program) in a box in the sequence that they were to be fed into the computer by the computer operator.

b.Time Sharing-Refers to the concurrent use of a computer by more than one user -- users share the computer's time. Time sharing is synonymous with multi-user. Almost all mainframes and minicomputers are time-sharing systems, but most personal computers and workstations are not.

c.Real Time-Occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across the screen at the same speed that they would actually move.

d.Network- In information technology, a network is a series of points or nodes interconnected by communication paths. Networks can interconnect with other networks and contain subnetworks.

The most common topology or general configurations of networks include the bus, star, Token Ring, and mesh topologies. Networks can also be characterized in terms of spatial distance as local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs).

A given network can also be characterized by the type of data transmission technology in use on it (for example, a TCP/IP or Systems Network Architecture network); by whether it carries voice, data, or both kinds of signals; by who can use the network (public or private); by the usual nature of its connections (dial-up or switched, dedicated or nonswitched, or virtual connections); and by the types of physical links (for example, optical fiber, coaxial cable, and Unshielded Twisted Pair). Large telephone networks and networks using their infrastructure (such as the Internet) have sharing and exchange arrangements with other companies so that larger networks are created.

network Last modified: Monday, November 13, 2006

(n.) A group of two or more computer systems linked together. There are many types of computer networks, including: local-area networks (LANs) : The computers are geographically close together (that is, in the same building). wide-area networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves. campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base. metropolitan-area networks MANs): A data network designed for a town or city. home-area networks (HANs): A network contained within a user's home that connects a person's digital devices. In addition to these types, the following characteristics are also used to categorize different types of networks: topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. See the Network topology diagrams in the Quick Reference section of Webopedia. protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network . architecture : Networks can be broadly classified as using either a peer-to-peer or client/server architecture.

1. What is the difference of OS in terms of user view and system view?

ANSWER:
Users view-the user view of the computer varies by the interface being used. Most computer users sit in front of a PC, consisting of a monitor, keyboard, mouse and system unit. Such a system is designed for one user to monopolize its resources, to maximize the work that the user is performing. In this case,the operating system is designed mostly for ease of use, with some attention paid to performance, and none paid to resource utilization.

Some users sit at a terminal connected to a mainframe or minicomputer. Other users are accessing the same computer through other terminals. These users share resources and may exchange information. The operating system is designed to maximize resource utilization.
Other users sit at workstations, connected to networks of other workstations and servers. These users have dedicated resources at their disposal, but they also share resources such as networking and servers.

Recently, many varieties of handheld computers have come into fashion. These devices are mostly standalone, used singly by individual users. Some are connected to networks, either directly by wire or through wireless modems. Due to power and interface limitations they perform relatively few remote operations. These operating systems are designed mostly for individual usability, but performance per amount of battery life is important as well.

System View-We can view an operating system as a resource allocator. A computer system has many resources - hardware and software - that may be required to solve a problem. The operating system acts as the manager of these resources.
An operating system can also be viewed as a control program that manages the execution of user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

2. Explain the goals of OS

What is the purpose of an operating system?

ANSWER:

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.

In the simplest terms, the purpose of an operating system is to allow a user to utilize various types of software to perform various tasks.

3. Whats the difference between batch system, multiprogrammed systems and time sharing systems?

4. Advantages of parellel system

ANSWER:
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.

5. Differentiate of symmetric multiprocessing and asymmetric multiprocessing.

answer:
Asymmetric multiprocessing - In asymmetric multiprocessing (ASMP), the operating system typically sets aside one or more processors for its exclusive use. The remainder of the processors run user applications. As a result, the single processor running the operating system can fall behind the processors running user applications. This forces the applications to wait while the operating system catches up, which reduces the overall throughput of the system. In the ASMP model, if the processor that fails is an operating system processor, the whole computer can go down.Symmetric mMultiprocessing - Symmetric multiprocessing (SMP) technology is used to get higher levels of performance. In symmetric multiprocessing, any processor can run any type of thread. The processors communicate with each other through shared memory.SMP systems provide better load-balancing and fault tolerance. Because the operating system threads can run on any processor, the chance of hitting a CPU bottleneck is greatly reduced. All processors are allowed to run a mixture of application and operating system code. A processor failure in the SMP model only reduces the computing capacity of the system.SMP systems are inherently more complex than ASMP systems. A tremendous amount of coordination must take place within the operating system to keep everything synchronized. For this reason, SMP systems are usually designed and written from the ground up.

6. Differetiate of client server systems to peer-to-peer system

ANSWER:
Client-server describes the relationship between two computer programs in which one program, the client program, makes a service request to another, the server program. Standard networked functions such as email exchange, web access and database access, are based on the client-server model. For example, a web browser is a client program at the user computer that may access information at any web server in the world. To check your bank account from your computer, a web browser client program in your computer forwards your request to a web server program at the bank. That program may in turn forward the request to its own database client program that sends a request to a database server at another bank computer to retrieve your account balance. The balance is returned to the bank database client, which in turn serves it back to the web browser client in your personal computer, which displays the information for you.The client-server model has become one of the central ideas of network computing. Many business applications being written today use the client-server model. So do the Internet's main application protocols, such as HTTP, SMTP, Telnet, DNS. In marketing, the term has been used to distinguish distributed computing by smaller dispersed computers from the "monolithic" centralized computing of mainframe computers. But this distinction has largely disappeared as mainframes and their applications have also turned to the client-server model and become part of network computing.Another type of network architecture is known as peer-to-peer, because each host or instance of the program can simultaneously act as both a client and a server, and because each has equivalent responsibilities and status. Peer-to-peer architectures are often abbreviated by P2P.Both client-server and P2P architectures are in wide usage today. Details may be found in Comparison of Centralized (Client-Server) and Decentralized (Peer-to-Peer) Networking

7. Differentiate the design issues of OS between a stand alone PC and a workstation connected to a network.

ANSWER:
Many operating systems now can run on standalone computers and also on networked computers. Standalone or generic operating systems are the ones which run on standalone computers like Windows operating system running on a PC. Network operating systems are the ones which run on a server and can be accessed through client machines connected on the network. e.g. Solaris or Linux running on a server can be used as network operating systems. Even there are Windows server operating systems which can be used by clients connected on the network. A computer that is connected to a network is a workstation, although a terminal is just a monitor and a keyboard that do not have there own computer.