OPERATING SYSTEM. PREPARED BY : DHAVAL R. PATEL Page 1. Q.1 Explain Memory

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1 Q.1 Explain Memory Data Storage in storage device like CD, HDD, DVD, Pen drive etc, is called memory. The device which storage data is called storage device. E.g. hard disk, floppy etc. There are two types of memory. 1) Primary memory 2) Secondary memory Primary memory Primary memory is an internal memory. e.g. RAM & ROM This type of memory fitting inside the computer. Generally it stores a data temporary. RAM: (Random access memory) Ram stored the data temporary when power supply is on is stored the data temporary & when power supply is off is erase the data so it is also called erasable memory volatile. Ram stored a data randomly. Ram is a one type fetch memory which supported to main memory to increase a speed. Ram has a both process read & write. ROM: (Read Only Memory) Rom is a permanent memory. It stores the BIOS setup. Rom can done only real process. There are three types of rom. (i) (ii) (iii) PROM (Programmable ROM) EPROM (Erasable Programmable ROM) EEPROM (Electrical Erasable Programmable ROM) PREPARED BY : DHAVAL R. PATEL Page 1

2 Q.2 Explain Main Memory and Process: Main memory is a workstation of memory system. It is also known as physical memory. It is internally connect with chip & externally connect with disc. It is also called physical memory. Main memory is the middle later of the memory. In compare of catch memory it speed is slow. Catch memory supported to main memory to increase a speed. e.g. RAM This memory has a layers size. Our data are store in main memory. It stores a data sequentially. The address generated by the main memory is called physical address. The data storage in the memory block at particular place is called address. Address start from 0. Process Process in main memory. The main memory process is required a program & data. Program means instruction code. Process control block control the process using information. Program required a data getting from the data block stack is required in address space. Address generated by the process is called logical address. Q.3 Logical Address v/s Physical Address Logical Address: Definition: Logical address generated by the C.P.U is called logical address. Process address space used a sequential list of byte & each byte have a particular address is called Logical address. It use a logical address space for process. Process can read and write address of it over logical address space. Logical addresses are limited by address size of process. Physical address Definition: Physical address generated by the memory is called physical address. The entire physical memory locate at sequential byte & each sequential byte have a particular address. This address is called physical address. Physical address space used for execution process of main memory. Process can read & write only their only physical address which have own physical address space. The physical address have a limited address depend on installation of data. PREPARED BY : DHAVAL R. PATEL Page 2

3 Q.4 Memory Manager (Memory Management) Part of O.S. connect with the main memory is called memory management. It is also called Memory Management Unit (MMU). The main goal of memory management is increase the efficiency of main memory. The requirement for memory management Fetch: It find when data or a information move from disc to main memory. Placement: Placement find where fetch information can locate on main memory. Replacement: Some data are not detect that are removed from memory. Sharing: Sometime there are multiple process step at that time memory unit sharing the process. Address Translation: The convert the logical address to physical address is called address translation. Protection: An authorize person can not access the data that point must be required for the memory. Q.5 MEMORY ALLOCATION The main goal of memory allocation are. 1) High Utilization: Maximum memory used. No any single block of memory is wasted. 2) High concurrency: Maximum possible process should be done in main memory. Maximum time CPU is busy so no time wasted. There are two types of memory allocation. (i) Contiguous memory allocation. (ii) Non Contiguous memory allocation. (I) Contiguous memory allocation: It is simple and old type of memory allocation in modern O.S. this type of memory allocation is not used. Each process take a block in main memory & process together in block contiguous. In contiguous memory allocation if required space is not available the process wait until they getting the space. Logical address space is not divide in contiguous memory allocated. Physical address space is contiguous. E.g. 1) Single process monitor. PREPARED BY : DHAVAL R. PATEL Page 3

4 2) Multi programming with fix partition. 3) Multi programming with dynamic partition. Advantages: It is very easy to implement. It is very easy to understand. Disadvantages: Very poor memory utilization. (II) Non contiguous memory allocation: In non contiguous memory allocation the logical address space divided in to block (A,B,C) here physical address space is non contiguous. Process divided into block see in fig (A,B,C) take place into memory. Advantages: Very good memory utilization. Disadvantages: Very complex to implement. E.g. paging & segment Q.6 Single process monitor: It is the very simple type of memory allocation. Only single process is allowed to run. Memory showed between O.S. & user program. See in fig. there are two possibilities of process. 1) O.S. at bottom side and user program a the top. 2) O.S. at top side and user program at the bottom. Using this system 1st time command comport (ms dos) attach with O.S. Advantages: PREPARED BY : DHAVAL R. PATEL Page 4

5 Very simple. Disadvantages: Only one process done at a time. Q.7 Multiprogramming with Fix partition: Here memory is sharing between O.S. and process. In multiprocessing O.S. there are more than a one process can done by CPU. So CPU is always busy (means the system increase the CPU utilization.) In this type of memory allocation memory divided into fix size block. All block have a equal or unequal partition. The process can place in the block which is suitable for process size e.g. suppose process size is 90 kb it place in 100 kb block see in fig. PREPARED BY : DHAVAL R. PATEL Page 5

6 It use a Queue for decide the turn from multiple process. We use a Queue as a two way 1) Multiprogramming using separate I/p Queue for each partition. 2) Multiprogramming using common I/p Queue for all partition. (1) Multi Program using I/p Queue for each partition: In this type of process every block use a separate Queue. Process take place in a Queue depend on their size. Some disadvantages in this process is that the process waiting until first process not done, In compare other block is free at that time. E.g. the small process placed into small block Queue (this process also done in large size block) but because of process take place in small block Queue can not go at large size block (If large size block is free). (2) Common Queue for all partition: There are common Queue used for the all block. The process take place in partition from the Queue depends on their size. PREPARED BY : DHAVAL R. PATEL Page 6

7 Advantages: Disadvantages: Very easy to implement. We cannot change the size of block. There are problem of internal fragmentation. INTERNAL FRAGMENTATION: The process have a small size in compare of partition size at that time wastage a memory size is called internal fragmentation. PREPARED BY : DHAVAL R. PATEL Page 7

8 Q.9 Multiprogramming with Dynamic partition: (A) Initial State, (B) Process1 Enters, (C) Process2 Enters, (D) Process1 Enters, (E) Process1 Enters, (F) Process1 Enter In Multiprogramming with dynamic partition memory share between OS and process (Single partition). When process enters in memory it take required space of memory (means memory block divide in a block 1) for process 2) preface). See in fig. (B) Process1 take a 20 MB from 56 MB memory block. When another processes enter it take memory from remain preface. See in fig. (C) Such away all process take place in memory. When process is terminated it free the memory space see fig (E). We can again enter next process in free block as shown in fig (F). Sometime the memory block is larger than process at that time. Some memory are wasted is called external fragmentation. PREPARED BY : DHAVAL R. PATEL Page 8

9 Advantages: The memory block are not fix we can change the size of memory block. Better utilization of memory. Disadvantages: External fragmentation. DEF: It refers to the wastage of free memory between partitions, caused by scattered non-contiguous free space. Q.10 PAGING: DEF: Logical address space divided into fix size block is called pages. Physical memory divided into fix size block is called frame. The page and frame will be same size & it s size calculate using power of 2 (2ⁿ). e.g. suppose n = 8 bit the size equal to 2^8 = 256 bit. When process is executed the page are move from secondary storage device to free frame in physical memory. PREPARED BY : DHAVAL R. PATEL Page 9

10 OS used a maintained table is called page table. It stored the information by frame no. Logical address divided into two part page no. which gives the page no to process & offset (d) which give actually location (address). Q.11 IMPLEMENTATION OF PAGING: During the process execution CPU generates logical address & logical address divided into two part page no & offset. The logical address used a page table & find the free frame from the physical memory at that time the address generated by physical memory is called physical address & It is divided into two part frame no & offset. Address transaction PREPARED BY : DHAVAL R. PATEL Page 10

11 Page size - 2ⁿ byte. Page number (ø) = L/2ⁿ Page offset (d) = L%2ⁿ Physical address ( ) = (F 2ⁿ) + d e.g. -> Logical address generated by CPU is 7 & size of page is 3 byte then find the page no & offset. It use second frame of physical address space then find physical address. Page size = 2ⁿ = 3 byte Physical address P = L/2ⁿ d = 7%3 = 1 = 7/2 = 2 P = (2 3) +1 = 6+1 = 7 Advantages: Memory allocation & de-allocation is very fast. Swap in & swap out operation is very fast. There is no any external fragmentation. Disadvantages: Additional memory requires a page table to read information. Size of page table is very large. There are internal fragmentation. EXTERNAL FRAGMENTATION: The small block are not used for any process. So this memory is wasted means size of block is small than process is called external fragmentation. PREPARED BY : DHAVAL R. PATEL Page 11

12 Q.12 SEGMENT: Basic concept of Segmentation The logical address space divided into block of variable size is called Segment. Logical address space used for any process like code, data, function, stack etc. Code is used for main function or user define function. Data is used take data variable, global variable, local variable etc. Each segment contain the logical unit for process. Here logical address start from 0 to maximum limit. When process is executed the segment are moved from secondary storage to main memory. It used a segment table for each process. Segment table contain for process (base). PREPARED BY : DHAVAL R. PATEL Page 12

13 Q.13 Implementation of Segment: During the execution process CPU generated logical address to access a data. This logical address divided into two part segment no(s) & offset(d). Address Translation In Segmentation Segment no. connect with segment table & segment table contain the base & limit. Base means starting address of physical memory. Limit means process size. The limit must be less than the offset(d) otherwise there will be addressing error generated. Base & limit combine with located the physical address. Advantages: All segment are independent. The sharing process of data are very simple. It gives the various type of protection like read only. There is no internal fragmentation. Disadvantages: External fragmentation is possible.. There are difficulty to use a free memory. PREPARED BY : DHAVAL R. PATEL Page 13

14 Q.14 SWAPING: There are some technique used to executed a process. 1) Swapping 2) Virtual memory Definition: Swapping is technique in which process are move between main memory. Sometime there is not enough space in main memory to hold a current activity of process. In this case it move a data to disk & take again when required. Swapping used a some memory space of secondary storage device (disk) this space is called swapping area or swap area. Operation of moving a process from memory to swap area is called swap out. Operation of moving a process from swap area to memory is called swap in. External fragmentation is disadvantages of swapping. Q.16 VIRTUAL MEMORY: Virtual memory is technique that allows a process to execute & it partially located in main memory. When virtual memory remove a process the main memory should executed the process. So that is big advantages is that done large size of process than main memory. The logical address refer for virtual address & virtual address space is larger than physical memory. PREPARED BY : DHAVAL R. PATEL Page 14

15 Advantages: The process are not contain the physical memory size. We can done the large size of process than main memory. It is suitable for multiprogramming. Disadvantages: Program contain code to handle a unusual error condition. Array are allocated more memory than actually requirement. Implementation: 1) Demand paging 2) Demand Segmentation 3) Segmentation with paging. Q.17 Demand paging: PREPARED BY : DHAVAL R. PATEL Page 15

16 Demand Paging steps in handling page fault Process are keep in secondary storage device (disk). After executing process it swap into main memory. Page table is used for valid & invalid entry using bit. If bit is set to valid it include a page and load in memory. If it set a n invalid page table not load process in memory. Six Steps: 1) Whenever any logical address is generated page table is searched. If page validity bit is set to invalid, it means that required page is not available in memory. This is called page fault. 2) Operating system is required to bring this page into memory disk. 3) Operating system determines the location of that page on the disk. 4) That page is brought into free frame in memory. If free frame is not available, some replacement algorithm is used to replace occupied frame 5) Frame number is entered in the page table entry and valid bit is set to valid. 6) Instruction referenced by that logical address is restarted. Q.18 Memory hierarchy: Resister: Register is toppest layer of memory hierarchy. It store a instruction and temporary data. Data access time of resister is in sec. Memory capacity is < 1 KB. PREPARED BY : DHAVAL R. PATEL Page 16

17 Cache memory: Cache memory is fastest & small size memory. It supports to increases the speed of main memory. E.g. RAM Data access time of cache memory in n sec. Data capacity is 1 MB. Main memory: Main memory is most important part of computer system to done the process. Any data first access time of main memory is 10 n sec. Data capacity of main memory is MB. Magnetic Disk: It is used to store the permanent data. E.g. Hard Disk Data access time of magnetic disk is 10 m sec. Data capacity 5 50 GB. Magnetic Tape: Magnetic tape is used to store the backup data. Data access time is 100 sec. Data capacity is GB. Q.20 HARD DISK (MAGNETIC DISK, PLATERS) There are two type of structure of hard disk. 1) Physical structure 2) Logical structure PHYSICAL STRUCTURE: PREPARED BY : DHAVAL R. PATEL Page 17

18 Track: Sectors: In hard disk the platters are locate on the spindle. We can store the information at both side of surface. (Upper surface & lower surface). Cylinder: The circular part on magnetic disk which have a numbers of block is called track. There are number of blocks on track. In which we can store the data is called sectors. The tracks of every magnetic disk (platters) are connected with each other using cylinder. Read Write Head: Read write head, write a data on disk & read a data from disk. PREPARED BY : DHAVAL R. PATEL Page 18

19 Q.21 What is Operating System? List the different types of them. Operating system is as system software which interface the user and hardware it provide the plate from for application software 1. Simple Batch System 2. Multiprogramming Batch System 3. Multiprocessor System 4. Distributed Operating System 5. Real-time Operating System 6. Multithreading Operating System 7. Network Operating System. Q.22 Explain Batch Operating System In this type of system, there is no direct interaction between user and the computer. The user has to submit a job to a computer operator. Then computer operator places a batch of several jobs on an input device. Jobs are batched together by type of languages and requirement. Then a special program, the monitor, manages the execution of each program in the batch. The monitor is always in the main memory and available for execution. Following are some disadvantages of this type of system : 1. No interaction between user and computer. 2. No mechanism to prioritize processes. PREPARED BY : DHAVAL R. PATEL Page 19

20 Q.23 Explain Multiprogramming Batch System In this the operating system execute one job from memory. If there are one job in memory the next is ready and wait. Jobs in the memory are always less than the number of jobs on disk. If several jobs are ready to run at the same time, then system chooses which one to run. It used CPU Scheduling for select the job. In Multiprogramming system, CPU will never be idle and keeps on processing. Q.24 Explain Real Time Processing System. In this system Response Time is already fixed. That has been fixed by the Processor or CPU. Real Time System is used at those Places in which we Requires higher and Timely Response. These Types of Systems are used in Reservation. So when we specify the Request, the CPU will perform at that Time. There are two Types of Real Time System PREPARED BY : DHAVAL R. PATEL Page 20

21 1) Hard Real Time System: 2) Soft Real Time System: In the Hard Real Time System, Time is fixed and we can t Change any Moments of the Time of Processing. In the Soft Real Time System, we can change the time using command. Q.25 Explain multiprocessor system. A multiprocessor system consists of several processors in one physical memory. Multiprocessor system provides higher computing power and speed. In multiprocessor system all processors operate under single operating system. Following are some advantages of this type of system. 1. Good performance 2. Execution of several tasks by different processors concurrently. 3. increases the system's throughput 4. If possible, system divides task into many subtasks and then these subtasks can be executed in parallel in different processors. Q.26 Explain distributed operating systems. Distributed Means Data is Stored and Processed on Multiple Locations. When a Data is stored on to the Multiple Computers, those are placed in Different Locations. Distributed means In the Network, Network Collections of Computers are connected with Each other. If we want to Take Some Data From other Computer, Then we uses the Distributed Processing System. We can also Insert and Remove the Data from another Location. In this Data is shared between many users. And we can also Access all the Input and Output Devices by Multiple Users. PREPARED BY : DHAVAL R. PATEL Page 21

22 Q.27 Explain Network Operating System. A network operating system (NOS) is software that controls a network and their component access by multiple users. In this system we can share the hard disk, printer etc resources between computers. We can also make the group user system In this system there are server is used as main computer on them we install this syetm. It store central data Example : Window NT, Window 2003 server, Window 2008 server etc. Q.28 Explain Multithreading Operating System. Multithreading more than one user can done the process at a time, It manage multiple requests by the same user at a time. Each user request have separate identity is called thread. Threads are known as Lightweight processes. As each thread has its own independent resource for process execution. A multiple processes can required number of threads. Thread is an execution unit which consists of its own program counter, a stack, and a set of registers. Threads are implemented in following two ways User Level Threads User managed threads Kernel Level Threads Operating System managed threads Q.29 Explain LINUX Operating System. The Linux is open source operating system. Linux OS, is a freely distributable, cross-platform operating system based on Unix. That can be installed on PCs, laptops, netbooks, mobile and tablet devices, video game consoles, servers, supercomputers and more. The Linux OS is frequently packaged as a Linux distribution for both desktop and server use, and includes the Linux kernel It more support to network. Example : Ubuntu, Fedora, Red Hat PREPARED BY : DHAVAL R. PATEL Page 22

23 Q.30 Explain Different between windows and Linux. Q.31 Components of Linux System Linux Operating System has primarily three components Kernel o o o It is responsible for all major activities of this operating system. It consists of various modules and it interacts directly with the underlying hardware. Kernel provides system or application programs. System Library o System libraries are special functions or programs using which application programs or system utilities accesses Kernel's features. PREPARED BY : DHAVAL R. PATEL Page 23

24 System Utility o System Utility programs are responsible to do specialized, individual level tasks. Q.32 Basic Features of Linux/Unix. Following are some of the important features of Linux Operating System. Portable Portability means software can works on different types of hardware in same way. Open Source Run on any OS Multi-User multiple users can access system at same time. Multiprogramming Linux is a multiprogramming system means multiple applications can run at same time. Hierarchical File System Linux provides a standard file structure in which system files/ user files are arranged. Shell Linux provides a special interpreter program which can be used to execute commands of the operating system. Security Linux provides user security using authentication features like password protection/ controlled access to specific files/ encryption of data. PREPARED BY : DHAVAL R. PATEL Page 24

25 Q.33 Unix Architecture The following illustration shows the architecture of a Linux system The architecture of a Linux System consists of the following layers Hardware layer Hardware consists of all peripheral devices (RAM/ HDD/ CPU etc). Kernel It is the core component of Operating System, interacts directly with hardware, provides low level services to upper layer components. Shell An interface to kernel, hiding complexity of kernel's functions from users. The shell takes commands from the user and executes kernel's functions. Utilities Utility programs that provide the user most of the functionalities of an operating systems. Q.34 Unix Command. Q.35 Unix Shell Script. PREPARED BY : DHAVAL R. PATEL Page 25