File Management Chapter 8 PDF

File Management Chapter 8 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part....

File Management Chapter 8 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1  After completing this chapter, you should be able to describe: Learnin How files are managed How files are named and the role g of extensions Objectiv How variable-length record storage differs from fixed-length es (1 of records How several file storage 2) techniques compare 2 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Learning Objectives (2 of 2) 01 02 03 Comparisons Access The of sequential control importance of and direct file techniques data access and how they compression compare in file storage 3 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Introduction File Manager’s efficiency directly affected by: How the system’s files are organized How files are stored How each file’s records are structured How user access to all files is protected 4 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  The File Manager Known as File File access management system responsibilities Creating, deleting, modifying, Software controlling Access to files, manage resources used by files 5 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Four tasks File storage tracking-keep track where each file is stored. Policy implementation Determine where and how files are Responsibili stored ties of the Efficiently use available storage space File Provide efficient file access Manager (1 File allocation if user access cleared of 3) Record file use File deallocation Return file to storage Communicate file availability 6 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Responsibilities of the File Manager (2 of 3) Factor 1: Policy b) Access to flexibility of determines: material access to information a) File storage Two factors: Share files location Provide How a System distributed and user can access access the file Allow users to browse public directories 7 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Responsibilities of the File Manager Factor 2: (3 of 3) Prevent system malfunctions subsequent Security checks Account numbers and passwords protection Activate secondary storage device, load file into memory, File allocation and update records File Update file tables, rewrite file (if revised), and notify waiting processes of file availability deallocation File management in Same concepts the cloud 8 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Definitions (1 of 3) Field Group of related bytes Identified by user (name, type, size) Record Group of related fields Group of related records File Information used by specific application programs Flat file No connections to other files; no dimensionality 9 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Definitions (2 of 3) Director Databas Progra Data ies e m files files (folders) Listings of Group of Contain filenames and Contain data related files instructions their attributes Interconnecte d at various levels Give users flexibility of access to stored data 10 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Definitions (3 of 3) (figure 8.1) Files are made up of records, in this case records 19 through 22. Records consist of fields. © Cengage Learning 2018 11 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Interacting with the File Manager (1 of 3) Most common user commands o OPEN, DELETE, RENAME, COPY (figure 8.2) 1 A typical file menu showing the available options for this 2 particular file. Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Interacting with the File Manager (2 of 3) Device-independent if information about physical location, medium and network knowledge already available in device driver. Physical location: knowledge not needed Cylinder, surface, sector Device medium: knowledge not needed Tape, magnetic disk, optical disc, flash storage Network knowledge: not needed 13 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Interacting with the File Manager (3 of 3) Logical commands when accessing a file is: Broken into lower-level signals Example: READ Move read/write heads to record cylinder Wait for rotational delay (sector containing record passes under read/write head) Activate appropriate read/write head and read record Transfer record to main memory Send flag indicating free device for another request System monitors for error conditions 14 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Typical Volume Configuration (1 of 4) Volume Each volume in the system is Volume: Each Secondary storage unit given a name File manager writes this name and other (removable, nonremovable) descriptive information on Easily accessible Multi-file volume place : Contains many files Innermost part of CD, beginning of tape, first sector of outermost track Multi-volume files Extremely large files spread across several volumes 15 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Typical Volume Configuration (2 of 4) (figure 8.3) The volume descriptor, which is stored at the beginning of each volume, includes this vital information about the storage unit. © Cengage Learning 2018 16 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Typical Volume Configuration (3 of 4) Master file directory (MFD) Stored immediately after volume descriptor Lists Names and characteristics of every file in volume File names (program files, data files, system files) Subdirectories listed in MDF If supported by file manager Remainder of volume Used for file storage 17 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Typical Volume Configuration (4 of 4) Single directory per volume Supported by early operating systems Disadvantages Long search time for individual file Directory space filled before disk storage space filled Users cannot create subdirectories Users cannot safeguard their files Each program needs unique name Even those serving many users 18 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Filename compone Relative filename and extension nts File- Naming Complete filename Conventi (absolute Includes all path information ons (1 of filename) 4) Name without path information Appears in directory listings, folders Relative Provides filename differentiation within directory filename Varies in length One to many characters Operating system specific Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 19 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  File-Naming Conventions (2 of Operatin Case Special Characters Not Extensio Maximu 4) g System Sensitiv Allowed n m e Require Characte d r Length (table 8.1) Android Yes *?$&[]/\ No 126/255* Linux Yes *?$&[]/\ No 256 Typical file name (Ubuntu) parameters for several Mac OS X Yes Colon No 255 operating systems, listed MS-DOS No Only hyphens and Yes 8.3 here in alphabetical underlines allowed order. Note: Specific versions of these UNIX Yes *?$&[]/\ No 256 operating systems may Windows No Most special characters Yes 255/256 have different are not allowed parameters. See your system for specifics. © Cengage Learning 2018 20 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  File-Naming Conventions (3 of 4) Extensions Appended to relative filename Two to four characters Separated from relative filename by period Identifies file type or contents Example BASIA_TUNE.MPG Unknown extension Requires user intervention 21 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  File-Naming Conventions (4 of 4) Operating system specifics Windows C:\IMFST\FLYNN\INVENTORY_COST.DOC Drive label and directory name, relative name, and extension UNIX/Linux /usr/imfst/flynn/inventory_cost.doc Forward slash (master directory/root), first subdirectory, sub- subdirectory, file’s relative name 22 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Arrangement of records within files File All files composed of Organizati records on Modify command Request to access record within a file Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 23 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Record Format (1 of 2) Fixed-length records Direct access: easy If it’s too small to hold the entire record, then the data that is leftover is truncated, thereby, corrupting the data. if the record size is too large—larger than the size of the data to be stored—then storage space is wasted. Variable-length records Direct access: difficult No empty storage space and no character truncation File descriptor stores record format Used with files accessed sequentially Text files, program files Index used to access records 24 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Record Format (2 of 2) (figure 8.6) Data stored in fixed length fields (top) that extends beyond the field limit is truncated. Data stored in variable length fields (bottom) is not truncated. © Cengage Learning 2018 25 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  The physical organization of a file decided by:  Record arrangement  medium characteristics Magnetic disks file organization Physical Sequential, direct, indexed sequential File File organization scheme selection considerations Organizati Data volatility -the frequency with which on (1 of 6) additions and deletions are made File activity- the percentage of records accessed File size o Response time -the amount of time the user is willing to wait before the requested operation is completed 26 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Sequential record organization Records stored and retrieved Physical serially File One after the other Easiest to implement Organizati File search: beginning until record on (2 of 6) found 27 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Direct record organization uses Direct access files Requires direct access storage device implementation Random organization Physical Random access files File Relative address record identification Organizati Known as logical addresses on (3 of 6) Computed when records stored and retrieved Hashing algorithms Transform each key into a number 28 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Direct record organization Advantages Fast record access Sequential access if starting at first relative address and incrementing to Physical next record Updated more quickly than sequential File files Organizati No preservation of records order Adding, deleting records is quick on (4 of 6) Disadvantages Hashing algorithm collision: records with unique keys may generate the same logical address 29 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Physical File Organization (5 of 6) (figure 8.7) The hashing algorithm causes a collision. Using a combination of a street address and a postal code, the hashing algorithm generates the same logical address (152132737) for three different records. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 30 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Physical File Organization (6 of 6) Indexed sequential record organization Best of sequential and direct access Indexed Sequential Access Method (I S A M) software Advantage: no collisions (no hashing algorithm) Generates index file for record retrieval Divides ordered sequential file into equal sized blocks Each entry in index file contains the highest record key and physical data block location Search index file Overflow areas 31 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Physical Storage Allocation (1 of 2) File manager Records works with Within file subdivided into File storage files fields As whole Records must Application Refers to units have same programs record As logical format manage storage units or Record record records lengths may structure vary 32 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Physical Storage Allocation (2 of 2) (figure 8.8) Every record in a file must have the same format but can be of different sizes, as shown in these five examples of the most common record formats. The supplementary information in (b), (c), (d), and (e) is provided by the File Manager, when the record is stored. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 33 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Contiguous Storage Records stored one after another o Advantages Any record found once starting address, size known Easy direct access o Disadvantages Difficult file expansion; fragmentation Free File A File A File A File A File A File B File B File B File B Free File C Space Record Record 2 Record 3 Record 4 Record 5 Record Record 2 Record Record 4 Space Record 1 (figure 8.9)1 1 3 With contiguous file storage, File A cannot be expanded without being rewritten in its entirety to a larger storage area. File B can be expanded by only one record, if the free space preceding File 3 4 C is used. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Noncontiguous Storage (1 of 5) Files use any available disk storage space File records stored in contiguous manner If enough empty space Remaining file records and additions Stored in other disk sections (extents) Extents Linked together with pointers Physical size determined by operating system Usually 256 bytes 35 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Noncontiguous Storage (2 of 5) File extents linked in two ways Storage level Each extent points to next one in sequence Directory entry: filename, storage location of first extent, location of last extent, and total number of extents (not counting first) Directory level Each extent listed with physical address, size, pointer to next extent Null pointer indicates last one 36 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Noncontiguous Storage (3 of 5) Advantage Eliminates external storage fragmentation Eliminates need for compaction Disadvantage No direct access support Cannot determine specific record’s exact location 37 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Noncontiguous Storage (4 of 5) (figure 8.10) Noncontiguous file storage with linking taking place at the storage level. The directory lists the file’s starting address, ending address, and the number of extents it uses. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 38 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Noncontiguous Storage (5 of 5) (figure 8.11) Noncontiguous storage allocation with linking taking place at the directory level for the files shown in Figure 8.10. © Cengage Learning 2018 39 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Indexed Storage (1 of 2) Allows direct record access Index block Brings pointers together linking every extent file Every file has own index block Disk sector addresses for file Lists entry in order sectors linked Supports sequential and direct access Does not necessarily improve storage space use Larger files experience several index levels 40 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Indexed Storage (2 of 2) (figure 8.12) Indexed storage allocation with a one- level index, allowing direct access from the index block to each record for the files shown in Figures 8.10 and 8.11. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 41 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Dictated by a file organization Most flexibility: indexed sequential files Least flexible: sequential files Sequential file organization Supports only sequential access Access Records: fixed or variable length Methods Access next sequential record Use address of last byte read Current byte address (C B A) Updated every time record accessed 42 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Update C B A Fixed-length records Sequenti Increment CB C B A = C B A + RL al Variable-length records Access Add length of record (RL) plus numbers of bytes used to hold (1 of 2) record to C B A C B A = C B A + N + RL 43 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Sequential Access (2 of 2) (figure 8.13) Fixed- versus variable length records. Fixed length records (a) each have the same number of bytes, so the record length (RL) variable is constant (x). With variable-length records (b), RL isn’t a constant, so record length is recorded on the sequential media with each record. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 44 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Direct Access Fixed-length records Variable-length (RN: desired record Indexed sequential file records number) C B A = (RN − 1) * Virtually impossible Accessed RL Address of desired sequentially or record cannot be directly easily computed Index file searched Requires sequential for pointer to data search through block records Keep table of record numbers and C B A s 45 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Levels in a File Management System (1 of 3) (figure 8.14) Typical modules of a file management system showing how communication is sent from the File Manager to the Device Manager. © Cengage Learning 2018 46 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Level implementation Structured and modular Levels in a programming techniques Hierarchical File Highest module passes Managem information to lower module ent Modules further subdivided System (2 More specific tasks of 3) Uses information of basic file system Logical file system transforms record number to byte address Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 47 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Levels in a File Management System (3 of 3) Verification at every level Directory level File system checks if requested file exists Access control verification module Determines whether access allowed Logical file system Checks if requested byte address within file limits Device interface module Checks if storage device exists 48 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Access Control Verification Module File sharing Data files, user-owned program files, system files Advantages Save space, synchronized updates, resource efficiency Disadvantage Need to protect file integrity File actions READ only, WRITE only, EXECUTE only, DELETE only, or a combination 49 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Advantages o Easy to implement o Works well in system with few files, users Access Control Matrix (1 of 2) 5 0 (table 8.3) An access control matrix showing access rights for each user for each file. Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Access Control Matrix (2 of 2) Disadvantages o As files and/or users increase, matrix increases Possibly beyond main memory capacity o Wasted space: due to null entries (table 8.4) 5 The five access codes for User 2 from Table 8.3. The resulting code 1 for each file is created by assigning a one for each checkmark, and a zero for each blank space. Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Access Control Lists (1 of 2) Modification of access control matrix technique (table 8.5) An access control list showing which users are allowed to access each of the five files. This method uses storage space more efficiently than an access control matrix. © Cengage Learning 2018 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 52 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Contains user names granted file access User denied access grouped under “WORLD” Shorten list by categorizing Access users SYSTEM (ADMIN) Control Personnel with unlimited access to all files Lists (2 OWNER (USER) Absolute control over all files of 2) created in own account GROUP All users belonging to appropriate group have access WORLD All other users in system Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 53 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Capability Lists Lists every user and respective file access Can control access to devices as well as to files Most common (table 8.6) A capability list shows files for each user and requires less storage space than an access control matrix. © Cengage Learning 2018 5 4 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Saves space in files Two algorithm types Data Lossless: retains all data Compressi in the file on Text or arithmetic files applications Lossy: removes some data without compromising file quality Image and sound file applications Mchoes/Flynn, Understanding Operating Systems, 8 Edition. © 2018 Cengage. All Rights Reserved. th May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 55  Records with repeated characters Repeated characters are replaced with a code Repeated terms Text Compressed using symbols to represent most commonly used Compressi words on University student database common words Student, course, grade, Front-end department compression each are represented with takes Entry singlegiven character number of characters fr om previous entry that they have in common Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 56 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  Lossy compression Irreversible: original file cannot be reconstructed Image and Compression algorithm highly dependent on file Sound type JPEG: still images Compressi MPEG: video images on International Organization for Standardization (I S O) World’s leading developer of international standards Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. 57 May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  File manager Controls every file and processes user commands Manages access control procedures Maintain file integrity and security File organizations Sequential, direct, indexed sequential Conclusi Physical storage allocation schemes on Contiguous, noncontiguous, indexed Record types Fixed-length versus variable-length records Access control methods Data compression techniques 58 Mchoes/Flynn, Understanding Operating Systems, 8th Edition. © 2018 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.