eet 450 - advanced digital chapter 8 mass storage
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EET 450 - Advanced Digital
Chapter 8
Mass Storage
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Technologies
One of the primary ‘blocks’ of the computer system is Mass Storage.
Store large amounts of Data and Program information, available quickly– Not as fast as Main Memory– Speeds can be improved with Cache
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Technologies
Magnetic– can detect the change of a magnetic field
• motion• varying field
– A wire must break the lines of magnetic flux
Materials– iron, nickel, cobalt
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Technologies
– materials dictate issues of speed (coercivity), life of stored information (retentivity)
Magneto-Optical– use laser to direct magnetic field in
recording data image– laser alone is used to read– Very high storage density
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Technologies
Optical – CD technology used to optically record and
read digital information.• CD• DVD• CDR• CDRW
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Types of Mass Storage
Hard Disks Floppy Disks PC Cards Magneto-optical Drives CD-Rom/CDR/CDRW
– DVD ROM / DVD Ram Tape Drives
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Magnetic Optical Solid State
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Access
Random Access– Any bit w/in access time for device
Sequential– Tape drive
New Technologies– DVD - optimized for sequential access, but
does random
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Magnetic Media
Based on some form of magnetic compound– Wire– Tape - mylar with magnetic compound
adhered to it.– Disks/Drums/Platters
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Magnetic Media
magnetism and electricity are related– moving a wire in a magnetic field
generates electrical current– running a current through an electrical wire
produces a magnetic field The magnetic materials - iron, nickel,
cobalt are the common ones - consist of small particles with magnetic properties
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Magnetic Media
At the small level, these particles can be viewed as a group of little magnets.
These little magnets are originally in Random order.
By imposing a magnetic field, the little magnets line up.
When these lined up magnets are MOVED near a wire – electricity.
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Magnetic Media
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Magnetic Media
The affect of magnetic field or induced current is magnified at a gap
Only a change in magnetic field can be detected
These CHANGES are used to encode digital information
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Recording Methods
to record magnetic information, a timed sequence of flux transitions occurs.
Recording – Frequency Modulation - FM– Modified Frequency Modulation - MFM
• Saves space by eliminating clock pulses
– Run Length Limited - RLL
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Drives
Older technology drives were delivered unformatted– Using a low level program, the drive was formatted
- writing sector information and tracks– The disk would then be partitioned– The OS must then format the partition
Current versions - IDE, Ultra, SCSI, etc. do not require low level formatting.
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Drives
Various methods of data compression have been used to increase storage space
compression, typically software based, took up speed by loading the main processor with compression/decompression responsibilities.
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Hard Drives
Increased storage has been gained, by advanced formulations of magnetic compounds.
more precise movement in mechanisms more precise manufacturing - leading to
smoother, more even emulsion layers. Fast rotation speeds and powerful head
movement mechanisms
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Advanced Storage Systems
Drive Arrays– RAID
Parallel Access Arrays Magneto-Optical systems
– Optically assisted magnetic write with, optical read
– magnetically erased– SLOW
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Drive Interfaces
The physical drive has limitations for size and speed.
The electronic connection to the ‘system’ imposes it’s own limitations.
See Table 9.1– note that transfer rate is the only figure of
merit in this table (besides # of devices)
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Table 9.1
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Drive interfaces
Note P1394 - fire wire FC-AL: Fiber Channel-Arbitrated Loop
– SSA System Storage Arch. Aaron -a blend of fiber connections Current USB is being used
– see Apple G3
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Performance of AT drives
see Table 9.2 – speeds to 16 Mbps
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Table 9.2Transfer Mode Cycle Time
nsSpeedMbps
Standard
PIO Mode 0 600 1.67 ATA
PIO Mode 1 383 2.61 ATA
PIO Mode 2 240 4.17 ATA
PIO Mode 3 180 11.1 ATA-2
PIO Mode 4 120 16.7 ATA-3
PIO Mode 5 90 22
DMA, sw, M 0 960 1.04 ATA
DMA, sw, M1 480 2.08 ATA
DMA, sw, M2 240 4.17 ATA
DMA, mw, M0 480 4.17 ATA
DMA, mw, M1 150 13.3 ATA-2
DMA, mw, M2 120 16.7 ATA-3
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Addressing Limit
Legacy limit of drive size -– DOS imposed
504Mb limit Solution - bypass INT13h access of
drives
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ATAPI
AT Attachment interface with Packet control commands
for CDRom and Tape drives
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Implementations
ATA EIDE ATA-2 (Fast-ATA)
– Up to 137.4 GB ATA-3
– Added S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology)
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ATA/ATAPI
ATA/ATAPI-4 – Packet Int. Ext– Defined 80 cond. 40 pin cable– UDMA/33– Enhanced BIOS for over 9.4 trillion
gigabytes (ATA is still <= 137.4GB) ATA/ATAPI-5 – w/ Packet Int.
– Requires 80 conductor cable for UDMA/66
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Physical Wiring
Drive Cables– Terminated cable end– 40 pin cable - ribbon– 44 pin connector - pins 41-44 provide power
• 50 pin variant - provides drive selection
– 68 pin connector - PC Card
Pin assignments - see table 9.7 Power
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Master/Slave selection
ATA - supports two drives per channel Choices
– Master– Slave– Only Drive
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SCSI
Small Computer System Interface SCSI-1,2,3 Advanced SCSI
– Wide SCSI - 32 bit wide– Ultra SCSI 10 MHz timing - 40 Mb/sec transfer
Table 9.11 - transfer rate versus Cable length Addressing 15 devices
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Table 9.11
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SCSI
Termination – See figure 9.12 - page 459
Connectors– 25 pin D type connectors– 50 pin amphenol– 68 pin - Wide SCSI-2/3 devices
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Floppy Drive connections
34 pin ribbon termination twist
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Power Connections
+ 12 V for motor controls on some drives
+ 5 V for logic Some older drives with ROM on board
may require -12v, etc. but this is not typical in today’s systems.
Two connector types - D shaped, ‘3.5 inch drive’ type
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Other connections
legacy connections - MFM/RLL type – separate data cables