Input–Output Design and Organization - Fundamentals of Computer Organization and Architecture - page 182

TABLE 8.4 Continued

Bus / Interface Description

Universal serial bus
(USB)

USB is an external bus developed by Intel, Compaq, DEC, IBM,
Microsoft, NEC and Northern Telcom. It was released in 1996 with
the Intel 430HX Triton II Mother Board. USB has the capability of
transferring 12 Mbps, supporting up to 127 devices. Many devices
can be connected to USB ports, which support plug and play.

FireWire (IEEE
1394)

FireWire is a type of external bus, which supports very fast transfer
rates: 400 Mbps. Because of this, FireWire is suitable for
connecting video devices, such as VCRs, to the computer.

Small computer
system interface
(SCSI)

SCSI is a type of parallel interface that is commonly used for mass
storage devices. SCSI can transfer data at rates of 4 MB / s; in
addition, there are several varieties of SCSI that support higher
speeds: Fast SCSI (10 MB / s), Ultra SCSI and Fast Wide SCSI
(20 MB / s), as well as Ultra Wide SCSI (40 MB / s).

Integrated drive
electronics (IDE)

IDE is a commonly used interface for hard disk drives and
CD-ROM drives. It is less expensive than SCSI, but offers
slightly less in terms of performance.

Enhanced integrated
drive electronics
(EIDE)

EIDE is an improved version of IDE, which offers better
performance than standard SCSI. It offers transfer rates between
4 and 16.6 MB / s.

PCI-X PCI-X is a high performance bus that is designed to meet the

increased I / O demands of technologies such as Fibre Channel,
Gigabit Ethernet, and Ultra3 SCSI.

Communication and
network riser
(CNR)

CNR was introduced by Intel in 2000. It is a specification that
supports audio, modem USB and local area networking interfaces
of core logic chipsets.

8.7. SUMMARY

One of the major features in a computer system is its ability to exchange data with
other devices and to allow the user to interact with the system. This chapter focused
on the I

O devices exchange data in a
computer system. The chapter described three ways of organizing I

O system and the way the processor and the I

/ /

O: programmed

/

I O, the CPU handles the trans-

fers, which take place between registers and the devices. In interrupt-driven I

/ O, interrupt-driven I / O, and DMA. In programmed I /

/ O, CPU

handles data transfers and an I O module is running concurrently. In DMA, data are

transferred between memory and I

/

O devices without intervention of the CPU. We
also studied two methods for synchronization: polling and interrupts. In polling, the
processor polls the device while waiting for I

/

O to complete. Clearly processor
cycles are wasted in this method. Using interrupts, processors are free to switch to
other tasks during I / O. Devices assert interrupts when I / O is complete. Interrupts

/