A computer system consists of hardware, system programs, and application programs figs 6

INTRODUCTION TO MULTIMEDIA 7.2 MULTIMEDIA FILES 7.3 VIDEO COMPRESSION 7.4 MULTIMEDIA PROCESS SCHEDULING 7.5 MULTIMEDIA FILE SYSTEM PARADIGMS 7.6 FILE PLACEMENT 7.7 CACHING 7.8 DISK SCHEDULING FOR MULTIMEDIA 7.9 RESEARCH ON MULTIMEDIA 7.10 SUMMARY

(a) (b) (c)

1 Record

Ant Fox Pig

Hen Ibis Lamb

1 Byte

Fig 6-2 Three kinds of files (a) Byte sequence (b) Record

sequence (c) Tree.

Object module

Object module

Module name

Date Owner Protection Size

/*File copy program Error checking and reporting is minimal.*/

#include <sys/types.h> /*include necessary header files*/

#include <fcntl.h>

#include <stdlib.h>

#include <unistd.h>

int main(int argc, char*argv[]); /*ANSI prototype*/

#define BUF 3 SIZE 4096 /*use a buffer size of 4096 bytes*/

#define OUTPUT 3 MODE 0700 /*protection bits for output file*/ int main(int argc, char*argv[])

{

int in 3 fd, out 3 fd, rd 3 count, wt 3 count;

char buffer[BUF 3 SIZE];

if (argc != 3) exit(1); /*syntax error if argc is not 3*/ /*Open the input file and create the output file*/

in 3 fd = open(argv[1], O 3 RDONLY); /*open the source file*/

if (in 3 fd < 0) exit(2); /*if it cannot be opened, exit*/ out 3 fd = creat(argv[2], OUTPUT 3 MODE); /*create the destination file*/

if (out 3 fd < 0) exit(3); /*if it cannot be created, exit*/ /*Copy loop*/

while (TRUE) {

rd 3 count = read(in 3 fd, buffer, BUF 3 SIZE); /*read a block of data */

if (rd 3 count <= 0) break; /*if end of file or error, exit loop*/

wt 3 count = write(out 3 fd, buffer, rd 3 count); /*write data*/

if (wt 3 count <= 0) exit(4); /*wt 3 count <= 0 is an error*/ }

/*Close the files*/

Data (a)

Program text

Program

xyz Data

(b)

Fig 6-6 (a) A segmented process before mapping files into its

address space (b) The process after mapping an existing file abc into one segment and creating a new segment for file xyz.

Root directory

Fig 6-7 A single-level directory system containing four files,

owned by three different people, A, B, and C.

User directory

directory

User subdirectories

C C C

B B

C C C B

Root directory

User file

Fig 6-9 A hierarchical directory system.

Root directory

bin etc lib usr

astjim

tmp

jim

binetclibusrtmp/

ast

/usr/jimlib

lib

dict

Fig 6-10 A UNIX directory tree.

Entire disk

Disk partition Partition table

Files and directories Root dir

I-nodes Super block Free space mgmt

Boot block

MBR

Fig 6-11 A possible file system layout.

File A

(4 blocks)

File C (6 blocks)

File B

(3 blocks)

File D (5 blocks)

File F (6 blocks)

File E (12 blocks)

File G (3 blocks)

(a)

… (File A) (File C)

(b)

Fig 6-12 (a) Contiguous allocation of disk space for seven files.

(b) The state of the disk after files D and F have been removed.

File block 1

File block 2

File block 3

File block 4

File B

0

File block 0

File block 1

File block 2

File block 3

Fig 6-13 Storing a file as a linked list of disk blocks.

block

File A starts here

File B starts here

Unused block

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

10 11 7

3 2

12 14 -1

-1

Fig 6-14 Linked list allocation using a file allocation table in main memory.

File Attributes Address of disk block 0 Address of disk block 1 Address of disk block 2 Address of disk block 3 Address of disk block 4 Address of disk block 5 Address of disk block 6 Address of disk block 7 Address of block of pointers

Disk block containing additional disk addresses

Fig 6-15 An example i-node.

games mail news work

Fig 6-16 (a) A simple directory containing fixed-size entries with the disk addresses and attributes in the directory entry (b) A direc- tory in which each entry just refers to an i-node.

File 1 entry length File 1 attributes

Pointer to file 1's name File 1 attributes Pointer to file 2's name File 2 attributes Pointer to file 3's name File 2 entry length

o t d

j - g

p e b e

r c u t

o t d

j - g p

r n

s e

Entry for one file

C's directory B's directory C's directory B's directory

Owner = C Count = 1

Owner = C Count = 2

Owner = C

Count = 1

(a) (b) (c)

Fig 6-19 (a) Situation prior to linking (b) After the link is

created (c) After the original owner removes the file.

Block size (bytes)

Fig 6-20 The solid curve (left-hand scale) gives the data rate of a disk The dashed curve (right-hand scale) gives the disk space efficiency All files are 2 KB.

(a) (b)

Free disk blocks: 16, 17, 18

A bitmap

A 1-KB disk block can hold 256

32-bit disk block numbers

86 234 897 422 140 223 223 160 126

142 141

1001101101101100 0110110111110111 1010110110110110 0110110110111011 1110111011101111 1101101010001111 0000111011010111 1011101101101111 1100100011101111

0111011101110111 1101111101110111

230 162 612 342 214 160 664 216 320

180 482

Disk Main

memory

Fig 6-22 (a) An almost-full block of pointers to free disk blocks

in memory and three blocks of pointers on disk (b) Result of ing a three-block file (c) An alternative strategy for handling the three free blocks The shaded entries represent pointers to free disk blocks.

free-Open file table Quota table

Soft block limitHard block limitCurrent # of blocks

# Block warnings leftSoft file limitHard file limitCurrent # of files

# File warnings left

Fig 6-23 Quotas are kept track of on a per-user basis in a quota table.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 (d)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 (c)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 (b)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 (a)

Fig 6-25 Bit maps used by the logical dumping algorithm.

Rear (MRU) Hash table Front (LRU)

Fig 6-27 The buffer cache data structures.

I-nodes are located near the start

of the disk

Disk is divided into cylinder groups, each with its own i-nodes

Cylinder group

Fig 6-28 (a) I-nodes placed at the start of the disk (b) Disk

divided into cylinder groups, each with its own blocks and i-nodes.

1 1 8 8 7 1 2 4

Location of file

Extended attribute record length

Directory entry length

File Size Date and time CD # L File name Sys

Padding

Flags Interleave Base name • Ext ; VerBytes

Fig 6-29 The ISO 9660 directory enty.

BIOS CP/M Shell

User program

Zero page

Address 0xFFFF

0x100 0

Fig 6-30 Memory layout of CP/M

8 3 1 1 1 4 2 2 Base name

Last write date/time

Last access

Attributes

of starting block

Lower 16 bits

of starting block

Fig 6-34 The extended MOS-DOS directory entry used in

Windows 98.

68 d o g A

A A A

0 CKC K C K C K

0 0 0

0 0 0 0 N

z x

Bytes 2 14

File name

I-node number

Fig 6-37 A UNIX V7 directory entry.

Attributes

Single indirect block

Double indirect block

Triple indirect block

Addresses of data blocks

Fig 6-38 A UNIX i-node.

I-node 26

is for /usr/ast

Block 406

is /usr/ast directory

Looking up

usr yields

i-node 6

I-node 6 says that /usr is in block 132

/usr/ast

is i-node 26

/usr/ast/mbox

is i-node 60

I-node 26 says that /usr/ast is in block 406

dick erik jim ast bal

26 6 64 92 60 81 17

grants books mbox minix src

Mode size times 132

Mode size times 406

Fig 6-39 The steps in looking up /usr/ast/mbox.