Logical components of connectivity in storage system environment

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

• PCI :

PCI is a specification that standardizes how PCI expansion cards ,such as network cards as modem exchange information with the CPU.PCI provides the interconnection between yje CPU & attached devices.The plug and play functionality of the PCI enables the host to easily recognise & configure new cards & devices.The width of PCI bus can be 32bits or 64bits .A 32bit PCI bus can provide a throughput of 133MB/S.PCI express is an enhanced version of PCi bus with considerability higher thorughput & clock speed.

• IDE/ATA :

IDE/ATA is the msot populat 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

ATA/ATAPI

EIDE

ATA-2

Fast ATA

ATA-3

ultra ATA

ultra DMA

• SCSI :

SCSI has emerged as a preferred protocol in high end computers,This interface is far less commonly used than IDE/ATA on perosnal 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 & nw includes a wide variety of related technologies & standards.The SCSI devices are identified by a specific number called a SCSI IO.In the narrow SCSI(bus width = 8),the devices are numbered 0 through 7.In the nude (bus width = 16) SCSI ,the devices are numbered 0 through 15.There IO numbers set the device priorities on the SCSI bus in narrow SCSI ,7 has the highest priority & 0 has the lowest priority.In wide SCSI the devices IO's from 8 to 15 have the highest priority but the entire sequence of mide.SCSI ID's has lower priority than narrow SCSI ID's.Therefore ,the overall priority sequence for a wide SCSI is 7,6,5,4,3,2,1,0,15,14,13,12,11,10,9}.When a device initialised ,SCSI allows for automatic assignments two or more devices from using the same SCSI IO.