The logical components of connectivity in storage system environment are as follows:

1. PCI
2. IDE/ATA
3. SCSI

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) and Small Computer System Interface (SCSI).

PCI

PCI is a local computer bus for attaching the hardware devices in a computer

• The PCI bus supports the functions found on a processor bus but in a standardized format that is independent of any particular processor's native bus.

• Devices connected to the PCI bus appear to a bus master to be connected directly to its own bus and are assigned addresses in the processor's address space.

• Attached devices can take either the form of an integrated circuit fitted onto the motherboard itself or an expansion card that fits into a slot. It provides the interconnection between the CPU and attached devices.

• The plug-and-play functionality of PCI enables the host to easily recognize and configure new cards and devices. The width of a PCI bus can be 32 bits or 64 bits.

• A 32-bit PCI bus can provide a throughput of 133 MB/s. PCI Express is an enhanced version of PCI bus with considerably higher throughput and clock speed.

• Typical PCI cards used in PCs include: network cards, sound cards, modems, extra ports such as USBor serial, TV tuner cards and disk controllers.

IDE/ATA

• The primary interface used to connect a hard disk drive to a PC is typically called IDE (Integrated Drive Electronics). IDE refers to the fact that the interface electronics or controller is built into the drive and is not a separate board. Although technically the correct name for the interface is ATA, many persist in using the IDE designation today. The primary purpose of the hard disk controller, or interface, is to transmit and receive data to and from the drive.

• IDE/ATA is an interface standard for the connection of storage devices such as hard disks, floppy drives, and optical disc drives in computers. ATA is a 16-bit parallel interface, meaning that 16 bits are transmitted simultaneously down the interface.

• Its controllers are on each drive, meaning the drive can connect directly to the motherboard or controller. IDE and its updated successor, Enhanced IDE (EIDE), are the most common drive interfaces found in IBM compatible computers today. Below, is a picture of the IDE connector on the back of a hard drive, a picture of what an IDE cable looks like, and the IDE channels it connects to on the motherboard.

• Four main types of IDE interfaces have been based on three bus standards.

1. Serial AT Attachment (SATA)
2. Parallel AT Attachment (ATA) IDE based on 16 bit ISA
3. XT IDE (based on 8-bit ISA)
4. MCA IDE (based on 16-bit Micro Channel) Of these, only the ATA versions are used today.

SCSI

• Small Computer System Interface (SCSI) was for a long time the technology for I/Obuses in Unix and PC servers, is still very important today and will presumably remainso for a good many years to come.

• SCSI defines a parallel bus for the transmission of data with additional lines for the control of communication. The bus can be released in the form of printedconductors on the circuit board or as a cable.

• SCSI is a set of standards for physically connecting and transferring data between computers and peripheral devices. It has emerged as a preferred protocol in high-end computers.

• The SCSI standards define commands, protocols and electrical and optical interfaces. It is most commonly used for hard disks and tape drives, but it can connect a wide range of other devices, including scanners and CD drives, although not all controllers can handle all devices.

• It is an intelligent, peripheral, buffered, peer to peer interface. It hides the complexity of physical format.

• This interface is far less commonly used than IDE/ATA on personal 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 and now includes a wide variety of related technologies and standards.