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 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
Ultra ATA &
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.