HARDWARE PROTECTION

• When executing in kernel mode, the operating system has unrestricted access to both kernel and user’s memory.
• The load instructions for the base and limit registers are privileged instructions.

DUAL OPERATION

• Mode bit added to computer hardware to indicate the current mode: kernel (0) or user (1).
• When an interrupt or fault occurs hardware switches to kernel mode.

I/O PROTECTION

• All I/O instructions are privileged instructions.
• Given the I/O instructions are privileged, how does the user program perform I/O?
• System call – the method used by a process to request action by the operating system.
– Usually takes the form of a trap to a specific location in the interrupt vector.
– Control passes through the interrupt vector to a service routine in the OS, and the mode bit is set to kernel mode.
– The kernel verifies that the parameters are correct and legal, executes the request, and returns control to the instruction following the system call.

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 that determine the range of legal addresses a program may access:
– base register – holds the smallest legal physical memory address.
– Limit register – contains the size of the range
• Memory outside the defined range is protected.

CPU PROTECTION

• Timer – interrupts computer after specified period to ensure operating system maintains control.
– Timer is decremented every clock tick.
– When timer reaches the value 0, an interrupt occurs.
• Timer commonly used to implement time sharing.
• Time also used to compute the current time.
• Load-timer is a privileged instruction.

STORAGE HEIRARCHY

• Storage systems organized in hierarchy.
– Speed
–cost
– volatility
• Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage.

STORAGE STRUCTURE

• Main memory – only large storage media that the CPU can access directly.
• Secondary storage – extension of main memory that provides large nonvolatile storage capacity.
• Magnetic disks – rigid metal or glass platters covered with magnetic recording material
– Disk surface is logically divided into tracks, which are subdivided into sectors.
– The disk controller determines the logical interaction between the device and the computer.

8.) MAIN MEMORY

-Refers to physicalmemory that is internal to thecomputer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory isRAM.

7.) DIFFERENCE OF RAM AND DRAM

-These terms all refer to different types of computer memory, or RAM - Random Access Memory. The "random" part means that any area of the memory can be communicated with. When people talk about how much memory or RAM their computer has, they are usually referring to DRAM (or in newer systems, SDRAM). (S)DRAM is a computer's main memory that holds onto information for the mictorprocessor. The "D" stands for dynamic, meaning the RAM needs to have the information it's holding continuously renewed or "refreshed". SDRAM (Synchronous DRAM) is a newer faster type of DRAM. Designed to keep up with today's high-speed microprocessors, SDRAM can typically run at the same speed as the overall system.

6.) DIRECT MEMORY ACCESS

-Direct memory access (DMA) is a feature of moder 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 drivecontrollers, graphics cards, network cards andsound cards. DMA is also used for intra-chip data transfer in multi-core processors, especially inmultiprocessor 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. Without DMA, using programmed input/output (PIO) mode for communication with peripheral devices, or load/store instructions in the case of multicore chips, the CPU is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done. This is especially useful in real-time computingapplications where not stalling behind concurrent operations is critical. Another and related application area is various forms of stream processing where it is essential to have data processing and transfer in parallel, in order to achieve sufficient throughput.

4.) USER MODE

-In User mode, the executing code has no ability to directly access hardware or reference memory. Code running in user mode must delegate to system APIs to access hardware or memory. Due to the protection afforded by this sort of isolation, crashes in user mode are always recoverable. Most of the code running on your computer will execute in user mode.

2.) DIFFERENCE OF INTERRUPT AND TRAP AND THIER USE.

-An interrupt is generally initiated by an I/O device, and causes the CPU to stop what it's doing, save its context, jump to the appropriate interrupt service routine, complete it, restore the context, and continue execution. For example, a serial device may assert the interrupt line and then place an interrupt vector number on the data bus. The CPU uses this to get the serial device interrupt service routine, which it then executes as above.

-A trap is usually initiated by the CPU hardware. When ever the trap condition occurs (on arithmetic overflow, for example), the CPU stops what it's doing, saves the context, jumps to the appropriate trap routine, completes it, restores the context, and continues execution. For example, if overflow traps are enabled, adding two very large integers would cause the overflow bit to be set AND the overflow trap service routine to be initiated.

3.) MONITOR MODE

-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.

1.) BOOTSTRAP PROGRAM

-In computing, booting is a bootstrapping process that starts operating systems when the user turns on a computer system.
Most computer systems can only execute code found in the memory (ROM or RAM); modern operating systems are mostly stored on hard disk drives, LiveCDs and USB flash drive. Just after a computer has been turned on, it doesn't have an operating system in memory. The computer's hardware alone cannot perform complicated actions of the operating system, such as loading a program from disk on its own; so a seemingly irresolvable paradox is created: to load the operating system into memory, one appears to need to have an operating system already installed.

5. Differentiate symmetric multi processing and asymmetric multiprocessing.

Symmetric multiprocessing - in 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 - 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.

3. What’s difference between batch systems, multi-programmed systems and time sharing systems?

batch system- is 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.

2. Explain the goals of OS

-It is easier to define an operating system by what it does than what it is, but even this can be tricky. The primary goal of some operating system is convenience for the user. The primary goal of other operating system is efficient operation of the computer system. Operating systems and computer architecture have influenced each other a great deal. To facilitate the use of the hardware, researchers developed operating systems. Users of the operating systems then proposed changes in hardware design to simplify them. In this short historical review, notice how identification of operating-system problems led to the introduction of new hardware features.

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

A. batch

-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.

B. time sharing

-sharing a computing resource among many users by multitasking Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major historical shift in the history of computing. By allowing a large number of users to interact simultaneously on a single computer, time-sharing dramatically lowered the cost of providing computing, while at the same time making the computing experience much more interactive.

C. real timeReal

-Time Operating System (RTOS) is a multitasking operating system intended for real-time applications. Such applications include embedded systems (programmable thermostats, household appliance controllers), industrial robots, spacecraft, industrial control (see SCADA), and scientific research equipment.

D. network

-Network operating systems typically are used to run computers that act as servers. They provide the capabilities required for network operation. Network operating systems are also designed for client computers and provide functions so the distinction between network operating systems and stand alone operating systems is not always obvious.

E. distributed

-with the advent of computer networks, in which many computers are linked together and are able to communicate with one another, distributed computing became feasible. A distributed computation is one that is carried out on more than one machine in a cooperative manner. A group of linked computers working cooperatively on tasks.

F. handheld

-A handheld PC's operating system determines not only what you see onscreen, but also how you interact with the device and what kind of services you can get from it. The two dominant handheld OSes are Palm and Pocket PC but Symbian and Linux are both up and coming. To help you decide which OS you want on your next handheld, here's a breakdown of these four operating systems plus a few of our hardware picks to get you started.

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

-Stand-alone PC - a desktop or laptop computer that is used on its own without requiring a connection to a local area network (LAN) or wide area network (WAN). Although it may be connected to a network, it is still a stand-alone PC as long as the network connection is not mandatory for its general use.Workstation - is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems.

6.) Differentiate client-server system and peer to peer system?

-Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another system, the server, which fulfils the request. In a network, the client/server model provides a convenient way to efficiently interconnect programs that are distributed across different locations
Another structure for distributes system is the peer - to peer (P2P) system model. In this model, clients and servers are not distinguished from one another; instead, all nodes within the system may act as either client or a server, depending on whether it is requesting or providing a service.
In client server system, the server is a bottle neck; but in a peer-to peer system, services can be provided by several nodes throughout the network.

4.) Advantage of parallel system?

-In terms of disproportional, 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.