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 :

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

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 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.