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COP 4610 Essay Quest
Essay Question Review for final
| Question | Answer |
|---|---|
| UNIX System V Implements a mechanism called STREAMs. What is this mechanism? | STREAMS enables an application to assemble pipelines of driver code dynamically. A stream is a full-duplex connection between a device driver and a user-level process. |
| What is the purpose of a UNIX mount table? | The UNIX mount table associates prefixes of path names with specific device names. To resolve a path name, UNIX looks up the name in the mount table to fin the longest matching prefix |
| Why buffering is performed? | A buffer is a memory area that stores data while they are transferred between two devices or between a device and an application. |
| Three Reasons for buffering. | 1. is to handle data when speed mismatches between the producer and consumer of a data stream exist. 2. is to adapt between devices that have different data-transfer sizes. 3. is to support copy semantics for application I/O |
| Give an example of when a application may need a nonblocking I/O system call. | if the user is viewing a web browser, then the application should allow keyboard and mouse input while it is displaying information to the screen. if it is not used, then the user would have to wait for the application to finish displaying information |
| What is the purpose of a programmable interval timer? | the programmable interval timer is hardware used to measure elapsed time and to trigger operations. the scheduler uses this mechanism to generate an interrupt that will preempt a process at the end of slice |
| Why is DMA used for devices that execute large transfers? | Without DMA, programmed i/o must be used. this involves using the CPU to watch status bits and feed data into a controller register one byte at a time. DMA was developed to lessen the burden on the CPU |
| What is interrupt chaining? | Interrupt chaining is a technique in which each element in the interrupt vector points to the head of a list of interrupt handlers. interrupt is raised, the handlers on the corresponding list are called one by one, until found. |
| Explain the concept of polling between a host and a controller. | When a host tries to access the controller, it constantly reads the status of a "busy register" and waits for the register to clear. This repetitive checking is termed polling. |
| Explain the difference between a serial-port controller and a SCSI bus controller. | A serial-port controller is a simple device controller with a single chip that controls the signals on the wires of a serial port. Contrast, SCSI bus controller is not simple. SCSI protocol is complex,it is often |
| Explain the concept of a bus and daisy chain. Indicate how they are related. | A bus is merely a set of wires and a rigidly define protocol that specifics a set of message that can be sent on the wires. A daisy chain is a device configuration where one device has a cable that connects another devices which has a cable that connects |
| Describe how Zf5 uses checksums to maintain the integrity of data. | ZF5 maintains checksums of all data and metadata blocks. When the file system detects a back checksum for a block, it replaces the bad block with a mirrored block that has a valid checksum. |
| Describe why Solaris systems only allocate swap space when a page is force out of main memory, rather than when the virtual memory page is first created. | Solaris systems only allocate swap space when a page is force out of main memory, because modern computers typically have much more physical memory than older systems and-as a result-page less frequently. |
| Describe an approach for managing bad blocks. | 1. approach to managing bad blocks is sector sparing. When the disk controller detects a bad sector, it reports it to the operating system. os will then replace the back sector with a spare sector. whenever the bad sector is request, the os will translate |
| Describe the three most important aspects of tertiary-storage performance. | the three most important aspects of tertiary-storage performance are speed, reliability, and cost. The speed of tertiary storage has two aspects: bandwidth and latency. Optical disks, whereas fixed drives are generally more reliable than a magnetic disk. |
| Describe one technique that can enable multiple disks to be used to improve data transfer rate. | 1 is bit-level striping which consists of splitting the bits of each byte across multiple disks so that the data can be accessed from multiple disks in parallel. 2 is block-level striping where blocks of a file are striped across multiple disks. |
| What are the factors influencing the selection of a disk-scheduling algorithm? | Performance of a scheduling algorithm depends heavily on the number and types of requests. Requests for disk service can be greatly influenced by the file-allocation method. The location of directories and index blocks is also important. |
| What is the advantage of LOOK over SCAN disk head scheduling? | the LOOK algorithm is a type of SCAN algorithm. the difference is that instead of forcing the disk head to fully traverse the disk, as is done in the SCAN, the disk head moves only as far as the final request in each direction. |
| What is the disadvantage of the SSTF scheduling algorithm? | Although the SSTF algorithm is a substantial improvement over the FCFS algorithm, it is not optimal. SSTF may cause starvation of some requests. if a continual stream of requests arrives near one another, a request of a cylinder far away from the |
| What is a storage-area network? | A storage-area network is a private network (using storage protocols rather than networking protocols) connecting servers and storage units. The power of a SAN lies in it flexibility, Multiple hosts and multiple storage arrays can attach to the same SAN |
| What is constant angular velocity in relation to disk drives? | If the rotation speed of a disk is to remain constant, the density of the bits must be changed for different tracks to ensure the same rate of data moving under head. |
| Explain how a snapshot is taken in the WAFL file system. | To take a snapshot, WAFL creates a duplicate root inode. Any file or metadata updates after that go to new blocks rather than overwriting their existing blocks. The new root inode points to metadata and data changed as a result of these writes. |
| Describe the counting approach to free space management. | The counting approach takes advantage of the fact that, generally, several contiguous blocks may be allocated or freed simultaneously. rather than keeping a list of n free disk addresses, just need the address of the 1 block free followed by the n number |
| What are the problems associated with linked allocation of disk space routines? | the major problem is that a linked allocation can be used effectively only for sequential-access files. disadvantage is the space required for the pointers. Yet another problem of linked allocation is the decreased reliability due to lost or damaged ptr |
| How is a hash table superior to a simple linear list structure? What issue must be handled by a has table implementation? | A hash table implementation uses a linear list to store directory entries, however, a hash data structure allows the file name to be used to help compute the file's location within the linear list. |
| What is the main disadvantage to using a linear list to implement a directory structure? What steps can be taken to compensate for this problem? | Linear lists are slow to search. This slowness would be noticeable to users as directory information is used frequently in computer systems. Many operating systems implement a software cache to store the most recently used directory information. |
| What are the two most important functions of the virtual file system layer? | the VFS separates the file-system-generic operations from their implementation by defining a clean VFS interface. Several of these implementations may coexist on the same machine allowing transparent access to different types of locally mounted file |
| What do the terms raw and cooked mean when used to describe a partition? | a raw disk is used where no file system is appropriate. raw partitions can be sued for a UNIX swap space as it does not need a file system cooked disk is a disk that contains a file system. |
| to create a new file, an application program calls the logical file system. Describe the steps the logical file system takes to create the file. | logical file system allocates a new FCB. if the file-system implementation creates all FCBs at file-system creation time, an FCB is allocated from the set of free FCBX the system then reads the appropriate directory into memory, updates it with the new |
| Briefly describe the in-memory structures that may be used to implement a file system. | in-memory mount table contains information about each mounted volume. an in-memory directory-structure cache holds the directory info of recently accessed directories. system-wide open-file table contains a copy of the FCB of each open file. |
| What are the advantages and disadvantages of access control lists? | access control lists have the advantage of enabling complex access methodologies. the main problem with ACLs is their length. constructing the list may be a tedious task. |
| Describe how the UNIX network file system recovers from server failure in a remote file system? | in the situation where the server crashes but must recognize that it has remotely mounted exported file systems and open files, NFS takes a simple approach, implementing a stateless DFS. it assumes that a client request for a file read or write |
| Describe three common methods for remote file-sharing. | disk space is always allocated in fixed sized 1 implemented method involves manually transferring files between machines via programs like FTP. 2 major method uses a distributed file system DFS in which remote directories are visible from a local machine |
| Why do all file system suffer from fragmentation? | disk space is always allocated in fixed sized blocks. a file is written to disk, it usually does not fit exactly within an integer number of blocks so that a portion of a block is wasted when storing the file onto the device. |
| Briefly explain the two forks of a file in the Macintosh operating system. | a file in the Macintosh operating system consists of a resource fork and a data fork. resource fork contains information of interest to the user, such as labels buttons |
| What are the advantages of using file extensions? | file extensions allow the user of the computer system to quickly know the type of a file by looking at the file's extension. the operating system can use the extension to determine how to handle a particular file |
| What is the difference between an operating system that implements mandatory locking and one that implements advisory file locking? | mandatory locking requires that the operating system not allow access to any file that is locked, until it is released, even if the program does not explicitly ask for a lock on the file. advisory file locking scheme will not prevent access to a locked |
| Distinguish between an absolute path name and a relative path name. | An absolute path name begins at the root and follows a path of directories down to the specified file, giving the directory names on the path. a relative path name defines a path from the current directory. |
| What are common attributes that an operating system keeps track of and associates with a file? | attributes of the file are: name-the human-readable name of the file, identifier-the non-human-readable tag of the file, type of file, location of the file, size, file protection through access control info, time, date, user identification |
| if you were creating an operating system to handle files, what would be the six basic file operations that you should implement? | six basic file operations include: creating a file, writing a file, reading a file, repositioning within a file, deleting, truncating a file. these operations comprise the minimal setoff required file operations. |
| Explain the usefulness of a modify bit. | a modify bit is associated with each page frame. if a frame is modified the modify bit is then set. modify bit is useful when a page is selected for replacement. if the bit is not set the page does not need to be written to disk. |
| What is the benefit of using sparse addresses in virtual memory? | virtual address spaces that include hles between the heap and stack are known as sparse address spaces. using a sparse address space is beneficial because the holes can be filled as the stack or heap segments grow, or when we wish to dynamically link lib |
| discuss two strategies for increasing TLB reach. | tlb reach refers to the amt of memory accessible from the TLB and is the page size * by number of entries in the tlb. 2 approaches for increasing tlb reach increasing the number of entries in the tlb, increasing page size. |
| explain the distinction between global allocation versus local allocation | when a process incurs a page fault, it must be allocated a new frame for bringing the faulting page into memory. two gerneal strategies for allocating a new frame are global and local allocation policies. global allocation scheme, a frame is allocated |
Created by:
haddockmelissa