1. William StallingsComputer Organizationand Architecture 6 thEdition Chapter 6 Memria Externa

2. Introduo 3. Tipos de Memria Externa

Magnetic Disk

• RAID (outra apresentao)

4. Removable

Optical (outra apresentao)

• CD-ROM

5. CD-Recordable (CD-R)

6. CD-R/W 7. DVD

Magnetic Tape

8. Disco Magntico

Disk substrate coated with magnetizable material (iron oxiderust)

9. Substrate used to be aluminium 10. Now glass

• Improved surface uniformity

• • Increases reliability

• Reduction in surface defects

• • Reduced read/write errors

• Lower flight heights (See later)

11. Better stiffness

12. Better shock/damage resistance 13. Disco Magntico 14. Disco Magntico 15. Vdeo sobre funcionamento do disco rgido 16. Vdeo sobre disco rgido de vidro 17. Histria

O primeiro disco rgido foi construdo pela IBM em 1956, e foi lanado em 16 de Setembro de 1957.[1] Era formado por 50 discos magnticos contendo 50 000 setores, sendo que cada um suportava 100 caracteres alfanumricos, totalizando uma capacidade de 5 megabytes, incrvel para a poca

18. Em 1973 a IBM lanou o modelo 3340 Winchester, com dois pratos de 30 megabytes e tempo de acesso de 30 milissegundos. Assim criou-se o termo 30/30 Winchester (uma referncia espingarda Winchester 30/30), termo muito usado antigamente para designar HDs de qualquer espcie. 19. Ainda no incio da dcada de 1980, os discos rgidos eram muito caros e modelos de 10 megabytes custavam quase 2 mildlares americanos, 20. Usos

Os discos rigidos foram criados originalmente para serem usados em computadores em geral. Mas no sculo 21 as aplicaes para esse tipo de disco foram expandidas e agora so usados em cmeras filmadoras, ou camcorders nos Estados Unidos; tocadores de msica como Ipod, mp3 player; PDAs; videogames, e at em celulares. Para exemplos em videogames temos o Xbox360 e o Playstation 3, lanados em 2005 e 2006.

21. J para celular os primeiros a terem esse tecnologia foram os da Nokia e da Samsung.[2] E tambm devemos lembrar que atualmente o disco rigido no s interno, existem tambm os externos. 22. Leitura e gravao

Os discos magnticos de um disco rgido so recobertos por uma camada magntica extremamente fina. Na verdade, quanto mais fina for a camada de gravao, maior ser sua sensibilidade, e conseqentemente maior ser a densidade de gravao permitida por ela.

23. Read and Write Mechanisms

Recording and retrieval via conductive coil called a head

24. May be single read/write head or separate ones 25. During read/write, head is stationary, platter rotates 26. Write

• Current through coil produces magnetic field

27. Pulses sent to head

28. Magnetic pattern recorded on surface below

Read (traditional)

• Magnetic field moving relative to coil produces current

29. Coil is the same for read and write

Read (contemporary)

• Separate read head, close to write head

30. Partially shielded magneto resistive (MR) sensor

31. Electrical resistance depends on direction of magnetic field 32. High frequency operation

• • Higher storage density and speed

33. Cabea magntica tradicional

Funcionamento

Sua construo consiste de um solenide (bobina) enrolado sobre um anel, ou forma semelhante. O anel feito de um material de alta permeabilidade magntica (condutor magntico), exceto por um pequeno vo (gap), na extremidade oposta ao solenide, propositadamente construdo com material de baixa permeabilidade magntica.

Gravao

O sinal eltrico desejado aplicado ao solenide, que gera um campo eletromagntico sobre o anel ferromagntico. No gap, as linhas de fora do campo magntico espalham-se pelo espao circundante, de modo que, quando prxima ou em contato com o gap, a fita magntica fica "imersa" no campo magntico gerado. Se este campo for convenientemente forte, ser capaz de reorientar permanentemente os elementos magnticos depositados sobre a mdia.

Leitura

Para ler a informao gravada numa mdia, acontece o processo exatamente oposto: os elementos magnticos da fita, que foram previamente orientados, ao passarem pelo gap, induzem um pequeno sinal eltrico no solenide, que pode ento ser tratado adequadamente pelo circuito eletrnico.

34. Cabea magntica tradicional 35. Inductive Write MR Read (moderno) 36. Organizao de dados e formatao

Anis concntricos ou trilhas

37. Espaos entre as trilhas

• Reduce gap to increase capacity

38. Same number of bits per track (variable packing density)

39. Constant angular velocity

Tracks divided into sectors

40. Minimum block size is one sector 41. May have more than one sector per block 42. Organizao dos dados no disco 43. Controle 44. Formatao 45. Formatao 46. Caractersticas fsicas 47. Cabeotes fixo e mvel 48. Discos simples ou mltiplos 49. Whinchester

Alm do corpo lacrado do disco, o winchester ainda permitia maior densidade de gravao de dados (trilhas menores) devido ao cabeote que era mantido a uma pequena distncia do disco pelo prprio deslocamento de ar gerado pelo ltimo.

50. Disk Velocity

Bit near centre of rotating disk passes fixed point slower than bit on outside of disk

51. Increase spacing between bits in different tracks 52. Rotate disk at constant angular velocity (CAV)

• Gives pie shaped sectors and concentric tracks

53. Individual tracks and sectors addressable

54. Move head to given track and wait for given sector 55. Waste of space on outer tracks

• • Lower data density

Can use zones to increase capacity

• Each zone has fixed bits per track

56. More complex circuitry

57. Disk Layout Methods Diagram 58. Finding Sectors

Must be able to identify start of track and sector

59. Format disk

• Additional information not available to user

60. Marks tracks and sectors

61. ST506 format (old!)

Foreground reading

• Find others

Gap1 Id Gap2 Data Gap3 Gap1 Id Gap2 Data Gap3 Track Sync Byte Head Sector CRC Sync Byte Data CRC 62. Characteristics

Fixed (rare) or movable head

63. Removable or fixed 64. Single or double (usually) sided 65. Single or multiple platter 66. Head mechanism

• Contact (Floppy)

67. Fixed gap

68. Flying (Winchester) 69. Fixed/Movable Head Disk

Fixed head

• One read write head per track

70. Heads mounted on fixed ridged arm

Movable head

• One read write head per side

71. Mounted on a movable arm

72. Removable or Not

Removable disk

• Can be removed from drive and replaced with another disk

73. Provides unlimited storage capacity

74. Easy data transfer between systems

Nonremovable disk

• Permanently mounted in the drive

75. Multiple Platter

One head per side

76. Heads are joined and aligned 77. Aligned tracks on each platter form cylinders 78. Data is striped by cylinder

• reduces head movement

79. Increases speed (transfer rate)

80. Multiple Platters 81. Cylinders 82. Floppy Disk

8, 5.25, 3.5

83. Small capacity

• Up to 1.44Mbyte (2.88M never popular)

Slow

84. Universal 85. Cheap 86. Obsolete? 87. Winchester Hard Disk (1)

Developed by IBM in Winchester (USA)

88. Sealed unit 89. One or more platters (disks) 90. Heads fly on boundary layer of air as disk spins 91. Very small head to disk gap 92. Getting more robust 93. Winchester Hard Disk (2)

Universal

94. Cheap 95. Fastest external storage 96. Getting larger all the time

• Multiple Gigabyte now usual

97. Removable Hard Disk

ZIP

• Cheap

98. Very common

99. Only 100M

JAZ

• Not cheap

100. 1G

L-120 (a: drive)

• Also reads 3.5 floppy

101. Becoming more popular?

All obsoleted by CD-R and CD-R/W?

102. Speed

Seek time

• Moving head to correct track

(Rotational) latency

• Waiting for data to rotate under head

Access time = Seek + Latency

103. Transfer rate 104. Timing of Disk I/O Transfer 105. Optical Storage CD-ROM

Originally for audio

106. 650Mbytes giving over 70 minutes audio 107. Polycarbonate coated with highly reflective coat, usually aluminium 108. Data stored as pits 109. Read by reflecting laser 110. Constant packing density 111. Constant linear velocity 112. CD Operation 113. CD-ROM Drive Speeds

Audio is single speed

• Constant linier velocity

114. 1.2 ms -1

115. Track (spiral) is 5.27km long 116. Gives 4391 seconds = 73.2 minutes

Other speeds are quoted as multiples

117. e.g. 24x 118. Quoted figure is maximum drive can achieve 119. CD-ROM Format

Mode 0=blank data field

120. Mode 1=2048 byte data+error correction 121. Mode 2=2336 byte data 122. Random Access onCD-ROM

Difficult

123. Move head to rough position 124. Set correct speed 125. Read address 126. Adjust to required location 127. (Yawn!) 128. CD-ROM for & against

Large capacity (?)

129. Easy to mass produce 130. Removable 131. Robust

Expensive for small runs

132. Slow 133. Read only 134. Other Optical Storage

CD-Recordable (CD-R)

• WORM

135. Now affordable

136. Compatible with CD-ROM drives

CD-RW

• Erasable

137. Getting cheaper

138. Mostly CD-ROM drive compatible 139. Phase change

• • Material has two different reflectivities in different phase states

140. DVD - whats in a name?

Digital Video Disk

• Used to indicate a player for movies

• • Only plays video disks

Digital Versatile Disk

• Used to indicate a computer drive

• • Will read computer disks and play video disks

Dogs Veritable Dinner

141. Officially - nothing!!! 142. DVD - technology

Multi-layer

143. Very high capacity (4.7G per layer) 144. Full length movie on single disk

• Using MPEG compression

Finally standardized (honest!)

145. Movies carry regional coding 146. Players only play correct region films 147. Can be fixed 148. DVD Writable

Loads of trouble with standards

149. First generation DVD drives may not read first generation DVD-W disks 150. First generation DVD drives may not read CD-RW disks 151. Wait for it to settle down before buying! 152. CD and DVD 153. Magnetic Tape

Serial access

154. Slow 155. Very cheap 156. Backup and archive 157. Digital Audio Tape (DAT)

Uses rotating head (like video)

158. High capacity on small tape

• 4Gbyte uncompressed

159. 8Gbyte compressed

Backup of PC/network servers