Explain logical components of connectivity in storage system environment

The popular interface protocol used for the local bus to connect to a peripheral device is peripheral component interconnect (PCI). The interface protocols that connect to disk systems are Integrated Device Electronics/ Advanced technology Attachment (IDE/ATA) & small computer ststem Interface (SCSI)

PCI :-

PCI is a specification that standardized how PCI expansion cards, such as network cards or modems, exchange information with the CPU PCI provides the interconnection between the CPU & attached devices.

  • The plug & play functionality of PCI enables the host to easily recognize & configure new cards & devices.

  • The width of a PCI bus can be 32 bits or 64 bits. A 32 bit PCI bus can provide a throughout of 133 MB/S.

  • PCI express is an enhanced version of PCI bus with considerably higher throughout & clock speed.


IDE/ ATA is the most popular interface protocol used on modern disk. This protocol offers excellent performance at relatively low cost.

Details of IDE/ ATA

  • IDE supports the IDE protocol.

  • The IDE component in IDE/ ATA provides the specification for the controllers connected to the computers motherboard for communicating with the device attached.

  • The ATA component is the interface for connecting storage devices, such as CD-ROM's floppy disk drives & HDD's to the motherboard.

  • ATA has variety of standards & names such as ATA




Fast ATA


Ultra ATA &

Ultra DMA


  • SCSI has emerged as a preferred protocol in high-end computers.

  • This interface is far less commonly used than IDE/ ATA on personl computers due to its higher cost.

  • SCSI was initially used as a parallel interface, enabling the connection of devices to a host.

  • SCSI has been enhanced & now includes a wide variety of related technologies & standards.

  • The SCSI devices are identified by a specific member called a SCSI ID.

  • In narrow SCSI (bus width = 8), the devices are numbered 0 through 7.

  • In wide (bus width = 16 ) SCSI, the devices are numbered 0 through 15.

These ID numbers set the device priorities on the SCSI bus in narrow SCSI, the device ID's from 8 to 15 have the highest priority but the entire sequence of wide .

  • SCSI ID's has lower priority than narrow SCSI IDs .Therefore, the overall priority sequence for a wide SCSI is 7,6,5,4,3,2,1,15,14,13,12,11,10,9 & 8.

  • When a device initialized , SCSI allows for automatic assignment of device IDs on the bus, which prevents two or more devices from using the same SCSI ID.

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