SCSI
scsi, stands for Small Computer System Interface, i.e., small computer system interface. Is a method for a computer and its peripheral devices (disk, between the tape , the CD-a ROM , rewritable optical disk drives , printers , scanners and communications equipment, etc.) of the system-level interfaces independent processors standard .
SCSI standard defines a command, and the electrical characteristics of the communication protocol entities (replaced OSI say, is occupied by the physical layer, link layer, a socket layer, application layer), the largest part of the application is on a storage device (e.g. hard disks, tape drives ).
SCSI interface
SCSI interface is a common interface to , the SCSI bus on may be connected host adapter and eight SCSI peripheral controller.
Such an interface is a system to facilitate integration, reduce costs and improve efficiency of interface standards, more and more equipment using the SCSI interface standard, therefore, SCSI hard drives and SCSI interface with optical disc drive lot.
SCSI interfaces entirely controls data read and write operations through a separate high-speed SCSI cards, CPU does not have to waste time waiting, apparently can improve overall system performance.
SCSI interface and IDE, SATA interfaces
scsi disks on the system is still essentially a server ready, and it places great emphasis on all of the control system can be done by scsi own, no cpu control , so scsi very provincial resources.
IDE works require full participation of the CPU, CPU to read and write data when no longer carry out other operations, in this case
Windows 95
/ NT is
a multi-tasking operating system
, the natural reaction will cause the system to slow down considerably. And SCSI
interfaces
, is completely controlled by a separate data read and write operations of the high-speed SCSI cards, CPU does not have to waste time waiting, apparently can improve overall system performance. However, IDE interface to improve this problem also done a great improvement, ready to use DMA mode instead of PIO mode to read and write, is responsible for the exchange of data by the DMA channel, the occupation of the CPU can be greatly reduced. Nevertheless, in comparison SCSI and IDE CPU usage, you can still find SCSI still has a considerable advantage.
advantage
1.SCSI can support multiple devices, and also supports a very wide SCSI devices, such as CD-ROM, DVD, CDR, hard disks,
tape drives
,
scanners
and so on.
3.SCSI occupied
CPU
is very low, indeed occupies a distinct advantage in a multitasking system. Because SCSI card itself with the CPU, can handle all the affairs SCSI devices, as long as the host CPU to issue commands to the SCSI card at work, SCSI card will have their own work, the results to the CPU to return to work after work, throughout the process , CPU can be carried out their work.
4.SCSI device also has intelligence, SCSI cards themselves can
be queued for CPU instructions
, thus improving efficiency. In the hard disk will be the current head position, the adjacent task to complete in multitasking, and then processed one by one.
The fastest SCSI bus has a bandwidth 160MB / s, which requires the use of a 64-bit PCI slots 66MHz, so the PCI-X
bus standard
in the maximum achievable speed of 80MB / s, if the fitting 10, 000
RPM
or speed 15,000rpm using dedicated hard drive will bring significant performance gains.