Magnetic Tape

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Magnetic Tape

• Sequential Access Device
• Types
• Tape Cartridge (4mm, 8mm, VHS, etc)
• ex) DDS
• reel Tape

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Data on 9-Tack Tapes

• 1 bytes 1 parity bit
• odd parity

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Estimating Tape Length Requirements

• Tape Density (bpi)
• Tape Speed (inches per second, ips)
• IBG (inch)
• 1,000,000 100-byte records
• 6250-bpi tape, IBG 0.3 inch
• s n ( b g)
• n of blocks
• b the length of a block
• g the length of IBG

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• 1 record per block (bf 1)
• b 100 / 6250 ( block_size / density) 0.016
  inch
• n 1,000,000
• s 1,000,000 (0.016 0.3) 316,000 inches
• bf 50
• b 5000/6250 0.8 inch
• n 20,000
• s 20,000 ( 0.8 0.3) 22,000 inches
• Effective recording density
• of bytes per block / the length required to
  store a block
• bf 1 100/0.316 316.4 bpi
• bf 50 5000/1.1 4545.5 bpi (cf. 6250-bpi
  tape)

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Data Transmission Time

• Nominal data transmission time
• tape_density tape_speed
• 6250 bpi 200 ips 1,250 Kbytes/sec
• Effective data transmission time
• effective_recording_density tape_speed
• 316.4 200 63.3 Kbytes/sec (bf 1)
• 4545.5 200 909.1 Kbytes/sec (bf 50)

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DISK vs TAPE
Main memory (buffer)

• In the past
• Disk random, short-term storage
• Tape sequential, long-term storage
• Use of disk for most sequential processing
• enough I/O buffer space
• decreasing costs of disks
• Tertiary Storage

Disk
Tape, CD-ROM
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CD-ROM

• Compact Disc, Read-Only Memory
• cheap reproduction 1 per copy
• large capacity more than 600Mb per disc
• read-only, write-once (publishing media)
• CD-RW CD, ReWritable

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History

• 1960s 1970s videodisc for movies
• LaserVision store analog video signal
• Philips Sony
• CD audio (1984) store digital data to optical
  disc
• CD-ROM (1985)
• CD-ROM 12X (12 times CD audio speed)
• DVD (Digital Video Disc)

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Adv. Disadv. of CD-ROM

• Adv.
• high storage capacity
• inexpensive price
• durability
• Disadv.
• too slow seek performance

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Physical Organization of CD-ROM

• Huge market size of CD audio
• inexpensive CD-ROM and its drivers
• But, audio CDs are designed to play music
• high capacity, moderate transfer rate, bad seek
  performance
• Master Disc

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pit
land

• Pits land
• CLV (Constant linear velocity)
• high capacity, poor seek time
• Addressing
• minutesecondsector

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• CD audio
• 16 bits for each sample
• sampling frequency 44.1 KHz (20KHz)
• stereo
• 44.1K 2 bytes 2 176400 bytes/sec
• 176.4 K 3600 635 M
• 75 sectors/sec
• 176400 / 75 2352 bytes/sector

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A Journey of a Byte
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(No Transcript)
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Buffer Management

• How many buffers are used
• at least 2, one for input, the other for output
• Double buffering (for output)