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Types of Disk Subsystems/Protocols - Quick Reference

IDE / ATA

  • Electronic controller card built into the hard drive itself
  • Two channels with a maximum of two disk drives per channel (one designated as Master and the other as Slave)
  • Uses 40-pin cable
  • LImited to 18 inches in cable length, using parallel data transfer

40-pin IDE flat data cable

EIDE / ATA2

  • Same general layout of IDE, but can achieve faster data transfer rates due to increases in technology

Ultra ATA / Ultra DMA

  • Improves performance by using Direct Memory Access (DMA) to allow the drive to access main memory without involving the processor
  • Connector heads for Ultra ATA cables are typically in blue to distinguish it from a IDE/EIDE cable

40-pin Ultra ATAdata cable

SCSI (Small Computer Systems Interface)

  • Pronounced "skuzzy"
  • More flexible and efficient
  • More devices can be connected; externally or internally
  • SCSI devices needing to transfer data between itself can be handled by SCSI controller, the CPU need not be involved
  • Uses a host adapter to improve performance and allow more devices to connect both internally and externally
  • Both ends of the SCSI chain must be terminated
  • Three main standards
    • SCSI-1 (aka Narrow SCSI)
      • Adopted in 1984
      • 8-bit wide bus
      • 5Mbps transfer rate
      • 7 devices can be attached to the same cable
      • 6 meter maximum cable length
    • SCSI-2
      • Adopted in 1994
      • 8- (Fast SCSI -2) and 16-bit (Wide SCSI-2) bus
      • 20Mbps transfer rate
      • 15 devices can be attached to the same cable
      • 25 meter maximum cable length
    • SCSI-3 (aka Ultra SCSI)
      • Adopted in 1998
      • 16-bit wide bus
      • 300+Mbps transfer rate
      • 15 devices can be attached to the same cable
      • 25 meter maximum cable length
    • Ultra3 Wide SCSI
      • 16-bit wide bus
      • 80 MB/s
      • 15 devices can be attached to the same cable
      • 25 meter maximum cable length
    • Ultra3 SCSI (aka, Ultra-160, Fast-80 Wide)
      • 16-bit wide bus
      • 160 MB/s
      • 15 devices can be attached to the same cable

Serial Storage Architecture (SSA)

  • Invented in 1990 by IBM
  • Can support 192 hot swappable drives
  • Supports full-duplex communication at over 40Mbps per channel
  • Replaced by Fibre Channel

Fibre Channel

  • Introduced in 1988
  • Allows hundreds of devices to be connected through a loop
  • Original version had data transfer rate of 12.5 Mbps
  • 128GFC "Gen6" introduced in 2016 offers data transfer rate of 12.8 Gbps
  • Active development expected to continue through 2022

Serial ATA

  • Uses 4 wires to carry a serial (one bit at a time) signal through the cable. This allow for more flexibility and longer cables as well as faster data transfer
  • Data cable is 7-pin
  • Generations:
    • SATA/150 (aka SATA1) - first generation, 1.5 Gb/s
    • SATA/300 - 3.0 Gb/s

SATA cable

Storage Area Network (SAN) / Network Attached Storage (NAS)

  • Use the network and even the Internet to access data that is stored for the client in large "server farms"

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