Page 268 - DCAP103_Principle of operating system

Unit 7: Secondary Storage Structure

11. If multiple devices have the same priority, swap-space is allocated from the devices in a Notes
...................... fashion.

7.9 Summary

• Secondary storage devices which are usually accessed via some kind of controller. This
contains registers that can be directly accessed by the CPU like main memory (“memory
mapped”).
• Secondary storage, sometimes called auxiliary storage, is storage separate from the
computer itself, where you can store software and data on a semi-permanent basis. To
provide the bulk of secondary storage for modern computer systems Disc used and
Magnetic tape was used as an early secondary-storage medium, but the access time is
much slower than for disks.

• In multiprograming systems, many processes may be generating requests for reading and
writing disk records.
7.10 Keywords

Bit-level Stripping: Data striping consists of splitting the bits of each byte across multiple disks;
such striping is called bit-level striping.
Constant Linear Velocity (CLV): Constant linear velocity (CLV) is a qualifier for the rated speed
of an optical disc drive and may also be applied to the writing speed of recordable discs.
Data Stripping: The distribution of a unit of data over two or more hard disks, enabling the
data to be read more quickly, known as data striping.

Error Correcting Code (ECC): Error correction code is a coding system that incorporates extra
parity bits in order to detect errors.

Logical Blocks: The logical block is the smallest unit of transfer. The size of a logical block is
usually 512 bytes.
Logical Formatting: Logical formatting is the process of placing a file system upon a hard disk
drive partition of a hard disk so that an operating system can use available hard disk platter
space to store and retrieve files.
Low-level Formatted: The sector identification on a disk that the drive uses to locate sector for
reading and writing is called low level formatted.

7.11 Review Questions

1. Consider a file system on a disk that has both logical and physical block sizes of 512 bytes.
Assume that the information about each file is already in memory. For each of the three
allocation strategies (contiguous, linked, and indexed), answer these questions:

(a) How is the logical-to-physical address mapping accomplished in this system? (For the
indexed allocation, assume that a file is always less than 512 blocks long.)

(b) If we are currently at logical block 10 (the last block accessed was block 10) and want
to access logical block 4, how many physical blocks must be read from the disk?

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