Operating System

91.How can the index blocks be implemented in the indexed allocation scheme? 

The index block can be implemented as follows 

a. Linked scheme 

b. Multilevel scheme 

c. Combined scheme 

92.Define rotational latency and disk bandwidth. 

Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head. The disk bandwidth is the total number of bytes transferred, divided by the time between the first request for service and the completion of the last transfer. 

93.How free-space is managed using bit vector implementation? 

The free-space list is implemented as a bit map or bit vector. Each block is represented by 1 bit. If the block is free, the bit is 1; if the block is allocated, the bit is 0. 

94.Define buffering. 

A buffer is a memory area that stores data while they are transferred between two devices or between a device and an application. Buffering is done for three reasons 

a. To cope with a speed mismatch between the producer and consumer of a data stream 

b. To adapt between devices that have different data transfer sizes 

c. To support copy semantics for application I/O 

95.Define caching. 

A cache is a region of fast memory that holds copies of data. Access to the cached copy is more efficient than access to the original. Caching and buffering are distinct functions, but sometimes a region of memory can be used for both purposes. 

96.Define spooling. 

A spool is a buffer that holds output for a device, such as printer, that cannot accept interleaved data streams. When an application finishes printing, the spooling system queues the corresponding spool file for output to the printer. The spooling system copies the queued spool files to the printer one at a 

time. 

97.What are the various disk-scheduling algorithms? 

The various disk-scheduling algorithms are 

a. First Come First Served Scheduling 

b. Shortest Seek Time First Scheduling 

c. SCAN Scheduling 

d. C-SCAN Scheduling 

f. LOOK scheduling 

98.What is low-level formatting? 

Before a disk can store data, it must be divided into sectors that the disk controller can read and write. This process is called low-level formatting or physical formatting. Low-level formatting fills the disk with a special data structure for each sector. The data structure for a sector consists of a header, a data area, and a trailer. 

99.What is the use of boot block? 

For a computer to start running when powered up or rebooted it needs to have an initial program to run. This bootstrap program tends to be simple. It finds the operating system on the disk loads that kernel into memory and jumps to an initial address to begin the operating system execution. The full bootstrap program is stored in a partition called the boot blocks, at fixed location on the disk. A disk that has boot partition is called boot disk or system disk. 

100.What is sector sparing? 

Low-level formatting also sets aside spare sectors not visible to the operating system. The controller can be told to replace each bad sector logically with one of the spare sectors. This scheme is known as sector sparing or forwarding.