SCSI connector

SCSI connector:

1、 What is a SCSI connector?

SCSI connector is an independent processor standard used for system level interface between computer and its peripheral devices (hard disk, floppy disk drive, optical disk drive, printer, scanner, etc.). SCSI standards define commands, communication protocols, and the electrical characteristics of entities (in OSI terms, they occupy the physical layer, link layer, socket layer, and application layer). The largest part of applications are on storage devices

2、 Main features of SCSI connector:

1. The SCSI connector interface is a universal interface. Host adapters and eight SCSI peripheral controllers can be connected on the SCSI bus. Peripherals can include disks, tapes, CD ROMs, rewritable optical disk drives, printers, scanners, communication devices, etc.

2. SCSI connector is a multi task interface with bus arbitration function. Multiple peripherals attached to a SCSI bus can work at the same time. Devices on SCSI share the bus equally.

3. SCSI connector can transmit data synchronously or asynchronously, with synchronous transmission rate of 10MB/s and asynchronous transmission rate of 1.5MB/s.

4. When the SCSI connector is connected to an external device, its connecting cable can be as long as 6m.

3、 Advantages of SCSI:

1. Fast

The speed of the hard disk used by the server is fast, which can reach 7200 or 10000 revolutions per minute, or even higher; It also has a large write back cache (generally 2MB or 4MB); The average access time is relatively short; The external transmission rate and internal transmission rate are higher. The SCSI hard disks of Ultra Wide SCSI, Ultra2 Wide SCSI, Ultra160 SCSI, Ultra320 SCSI and other standards are used, and the data transmission rate per second can reach 40MB, 80MB, 160MB and 320MB respectively.

2. High reliability

Because the server hard disk is running almost 24 hours a day, it is bearing a huge workload. It can be said that if the hard disk fails, the consequences will be unimaginable. Therefore, today's hard disks all use S.M.A.R.T technology (self-monitoring, analysis and reporting technology), and hard disk manufacturers all use their own unique advanced technology to ensure data security. In order to avoid accidental losses, the server hard disk can generally withstand the impact of 300G to 1000G. The SCSI device is also intelligent. The SCSI card can queue CPU instructions by itself, which improves the work efficiency.

3. Multiple use of SCSI interfaces

It can support multiple devices and SCSI hard disks with very low CPU occupancy. SCSI hard disks can only be used through SCSI interfaces. Some server motherboards integrate SCSI interfaces, and some have special SCSI interface cards. One SCSI interface card can connect 7 SCSI devices, which is incomparable to IDE interfaces. More than WideSCSI-2, 16 SCSI devices can be connected.

4. Support hot plug

Hot Swap is a hard disk installation method supported by some servers. You can unplug or insert a hard disk when the server is not down, and the operating system automatically recognizes changes to the hard disk. This technology is very important for servers running 24 hours a day. Because SCSI cards have CPUs, they can handle SCSI devices.

4、 The scsi connection line facing the industrial control industry makes the peripheral connection more convenient

1. The SCSI signal specification specifies the signal delay, small pulse width and hold time of the SCSI bus. However, users do not have to worry about this, because the SCSI protocol chip will manage most of the timing restrictions. SCSI protocol chips include AIC-6250 of Adaptec and 5380 and 539 of NCR, which use an interlocking symbol exchange mode to send data to the entire bus. This communication protocol is based on Q&A symbol exchange. The bus status of SCSI is called phases. There are eight possible bus phases, and all but one are asynchronous transmission.

2. In the data phase, information can be exchanged in either synchronous or asynchronous ways. Synchronous transmission is used only when both the host computer and the target device allow it. The data is transmitted to the whole bus in a parallel way of one byte at a time, using eight data lines. The typical asynchronous transmission rate is about 2 megabytes per second, and the synchronous transmission rate can be as high as 5 megabytes per second.

3. The universality of SCSI has made it a standard in the system level and external storage equipment products of most companies. The SCSI standard connection cable can easily connect multiple peripherals, and its standard command set simplifies the selection of SCSI peripherals from the system host, while ensuring compatibility.

5、 SCSI

The future of SCSI SCSI is an advancing technology. The latest specifications include Fibre Channel SCSI, IEEE 1394 (Firewire) and SCSI 3 (160MB/s). The upcoming specifications are SCSI 4 (320MB/s) and SCSI 5 (640MB/s). Starting from SCSI 3, SCSI can rapidly improve performance as required, and has nearly perfect backward compatibility, which protects users' investment.

With the increasing speed, SCSI has also begun to focus on ease of use. CAM (Common Access Model) is used to add a control layer between many SCSI command sets and program adjustments, making SCSI programming more convenient.

I believe that with the development of the industry, SCSI will have another technical peak, and SCSI will develop better in the future. Now there are VHDCI68 and VHDCI100