SCSISmall Computer System Interface is the abbreviation of Small Computer System Interface, which is a data transmission interface technology specially used for servers and high-end workstations.SCSI card is the abbreviation of SCSI control card.LikeDisplay cardWorking ina main boardandmonitorThe SCSI card works on the computer motherboard and SCSI devices (such asSCSI HardDisk 、SCSICD drive、SCSI interfaceOfScanner）On.
useIDEInterface will be subject to system IRQ（interrupt number）And IDE channel restrictions, which is a standarda main boardAt most 4 IDE devices can be connected, while using SCSI interface, more than 15 devices can be connected, and all these devices only occupy oneIRQSCSI also supports a wide range of devices.
Low CPU utilization
When using the traditional IDE interface,CPUIt is necessary to control data transmission online all the time, so during IDE data transmission, the CPU cannot do anything and must wait until the end of transmission before executing subsequent instructions.Under the SCSI interface, the CPU can process subsequent commands immediately after sending them to the SCSI. The processing chip on the SCSI card is responsible for the transmission;And the transmission processDMA(Direct Memory Access) mode, which allows SCSI to access memory directly.
High bandwidth
Theoretically, the fastest SCSIBus320MB/s bandwidth, i.e. Ultra 320/s SCSI;This meansHard diskThe transmission rate will be up to 320MB/s.At present, the fastest IDE interface hard disk has a speed of only 133MB/s (ATA133), and there are quite few hard disks using this interface.
structure
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SCSI card is a 32-bit or 64 bitPCIThe device needs to be plugged ina main boardOn a 32-bit or 64 bit PCI slot.Ifa main boardIf the SCSI controller has been integrated on the, it is unnecessary to install a SCSI card, just like if the integrated motherboard has integrated a display card, it is unnecessary to install another display card.The function of the SCSI card is to connect and control SCSI devices in seriesComputer motherboardIt can quickly transfer data to and from connected SCSI devices.The number of connected SCSI devices varies with the type of SCSI card. Earlier SCSI cards can connect 6 SCSI devices, while newer SCSI cards can connect 16 SCSI devices.
A SCSI card consists of six parts: SCSI control chip, SCSI BIOS, built-in SCSI interface, external SCSI interface, PCI pin and SCSI terminator.
1. SCSI control chip
SCSI card
SCSI devices are operated by SCSI controllers and are the most important part of SCSI cards.SCSI control chip is equivalent to a smallCPU, has its own command set andcache。The SCSI card has an independent chip responsible for SCSI data processing. When the CPU transmits instructions to SCSI, it will process subsequent instructions. Other related work will be handed over to the SCSI control chip for processing. When the SCSI "processor" finishes processing, it will send control information to the CPU, and then the CPU will carry out subsequent work. Therefore, the SCSI system has a low CPU utilization rate.In addition, SCSI controllers andHard diskOne user is allowed to transmit data while another user canData Lookup, which is the SCS controller andHard diskparallel processing The embodiment of ability.These two characteristics are very necessary for high-end applications, because in such areas asNetwork serverAnd other applications, ifHard diskNot very strongparallel processing Ability. When many users access at the same time, the system will become extremely slow and easy to causeSystem crash。
2. Built in SCSI interface
SCSI card
SCSI interfaces are called "high-density interfaces". There are many kinds of SCSI interfaces, and the number of interface pins varies.There are 50 pin and 68 pin built-in SCSI interfaces for connecting built-in SCSI devices, such as SCSIHard disk、SCSICD driveEtc.Currently connected to SCSIHard disk68 pin built-in SCSI interface is the mainstream.
3. External SCSI interface
As we know, the IDE interface has no external interface, so only the built-in interface can be installedHard diskandCD drive。The SCSI interface is different. It can not only connect the built-in SCSIHard diskAnd SCSICD driveIn addition, there are external interfaces, which can install scanners with SCSI interfaces and other external SCSI devices.The external SCSI interface looks like a print interface.
4、SCSI BIOS
SCSI card
BIOSIt is the abbreviation of "Basic Input/Output System".SCSI BIOS anda main board、Graphics cardLike BIOS, it provides basic SCSI settings.When you turn on the computer, an English prompt for entering BIOS settings will appear. At this time, press the prompted key combination to enter the SCSI BIOS setup program.Users can download a new version on the Internet to update SCSI BIOS.
5. PCI pin
As for the PCI pin, the SCSI card is connected with thea main boardPCI slots on the.
6. SCSI Terminator
The IDE interface is very easy to use. It can be used as long as the master device and slave device are set, while the use of SCSI is troublesome. You need to set the "termination" to use it.The so-called "termination" is to set one on the last SCSI deviceJumperOr install a terminator to notify the SCSI controller SCSIBusThis is the end.The SCSI card itself is a SCSI device, so it uses an ID number. If there is no connection on the cardHard diskOr other equipmentJumperSet to "On", otherwise set to "Off".
Core processing chip
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Apple SCSI，There are 25 stitches in total, divided into two rows, 8 positions
SCSI devices are operated by SCSI controllers and are the most important part of SCSI cards.This SCSI control chip is the core processing chip of the SCSI card.It is equivalent to a small CPU with its ownCommand SetAnd cache.The SCSI card has an independent chip responsible for SCSI data processing. When the CPU transmits instructions to SCSI, it will process subsequent instructions. Other related work will be handed over to the SCSI control chip for processing. When the SCSI "processor" finishes processing, it will send control information to the CPU, and then the CPU will carry out subsequent work. Therefore, the SCSI system has a low CPU utilization rate.In addition, SCSI controllers andHard diskAllow one user to transmit data while another user can search data, which is called SCS controller and hard diskparallel processing The embodiment of ability.These two characteristics are very necessary for high-end applications, because in applications such as network servers, if the hard disk does not have strong parallel processing capability, when many users access at the same time, the system will become extremely slow and easily lead to system crash.
Interface type
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Sun Microsystem DD-50SA, 50 pins in total
There are two types of SCSI connectors: built-in and external. The appearance of the built-in data cable is the same as that of the IDE data cable, but the number of pins and specifications are slightly different. It is mainly used for connectionCD driveandHard disk。40 pin IDE cable has 40 wires, 40 pin ATA66 has 80 wires, and SCSI built-in is divided into 50 pin, 68 pin, and 80 pin.As for the SCSI external data cable, there are the following specifications with different densities.
Bus speed
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SCSI-2 ，There are 50 stitches in total, divided into two rows, 8 positions.
Centronics，There are 50 stitches in total, divided into two rows, 8 positions
SCSI has experienced several generations of development, and its transmission speed is getting faster and faster.(1) SCSI-1: It is the earliest SCSI interface, which was developed by Shugart in 1979（SeagateSASI (Shugart Associates System Interface) developed by the predecessor of the company and recognized by the American standard agreement in 1986.It is characterized by supportingsynchronizationAnd asynchronous SCSIPeripherals, support 7 8-bit peripherals, maximumData transmission rateIt is 5MB/s and supports Worm peripherals.(2) SCSI-2: It is the successor interface of SCSI-1. It was proposed in 1992 and is also called Fast SCSI.If the original 8-bit parallel data transmission is used, it is called "Fast SCSI"Data transmission rate10MB/s, and the maximum number of connected devices is 7.Later, the 16 bit parallel data transmission mode "Fast W" appearedideSCSI”，itsData transmission rateIt is increased to 20MB/s, and the maximum number of connected devices is 15.
(3) SCSI-3: It is the "Ultra SCSI" controller type introduced after SCSI-2. In this category, data can also beBit widthTwo sub categories have been introduced successively.If the original 8-bit parallel data transmission is used, it is called "Ultra SCSI"Data transmission rateIt is 20MB/s, and the maximum number of connected devices is 8.In theBus bandwidth"Ultra W" appears after increasing to 16 bitsideSCSI”，Its transmission rate has doubled to 40MB/s, and the maximum number of connected devices is 15.
SCA，80 stitches in total, divided into two rows
(4) Ultra2 SCSI: It is a SCSI interface type introduced on the basis of Ultra SCSI.It was proposed in 1997 that LVD (Low Voltage Differential) transmission mode was adopted, allowing the maximum length of interface cable to be 12 meters, which greatly increased the flexibility of equipment;Like the above SCSI interfaces, it is also divided into 8-bit Narrow mode and 16 bit W modeidepattern.The 8-bit Narrow mode is "Ultra2 SCSI". Its transmission rate is 40MB/s, and the maximum number of connected devices is 7;16 bit WideThe mode is called "Ultra2 Wide SCSI", which increases the transmission rate to 80MB/s, and supports a maximum of 15 connected devices.
(5) Ultra3 SCSI: It is an updated interface of Ultra2 SCSI. It was proposed in September 1998. In addition to supporting the existing SCSI specifications and using the same interface cables and terminators as Ultra2 SCSI, it also includes some new functions.First, Ultra3 SCSI uses double transition clocking, while Ultra2 SCSI uses single transition clocking, so the transmission rate of Ultra3 SCSI is twice that of the former, namely 160MB/s;In addition, Ultra3 SCSI also provides Domain Validation, CRC (Cyclic Redundant Check)PacketPacketized Protocol and Quick Arbitrate&Select;In order to speed up the introduction of new Ultra3 SCSI technology, many manufacturers first introduced Ultra160/m SCSI. The Ultra160/m SCSI technology is the same as Ultra3 SCSI, but it does not have the two functions of quick arbitration selection and encapsulation. It can be said that Ultra160/m SCSI is a subset of Ultra3 SCSI.
SCSI
(6) Ultra320 SCSI: its full name is "Ultra320 SCSI SPI-4" technical specification.Ultra320 SCSI single channelData transmission rateUp to 320M/S, if usedDual channelSCSI controller can reach 640M/s.From the perspective of infrastructure development, the upgrade from 160M/S to 320M/S is not technically complicated and costs littleSystem integratorFor servers, the technology transition from SCSI Ultra160 to Ultra320 SCSI is very easy.
RAID function
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Different SCSI cards support different RAID functions.It supports RAID0, RAID1, RAID3, RAID4, RAID5 and RAID10.RAIDIt is the abbreviation of Redundant Array of Independent Disks in English, which means“Redundant array of independent disks”, sometimes referred to asdisk array （Disk Array）。
RAID
To put it simply, RAID is a way to separate multiple blocksHard disk(Physical hard disk) is combined in different ways to form a hard disk group (logical hard disk), thus providing a higherstoragePerformance and deliveryData backupTechnology.formdisk array The different methods of are called RAID Levels.Data backupOnce the user data is damaged, the backup information can be used to restore the damaged data, thus ensuring the security of user data.From the user's perspective, the disk group is like aHard disk, users can partition and format it.In short, yesdisk array Operation and singleHard diskas like as two peas.The difference is that,disk array OfstorageSpeed is faster than singleHard diskMuch higher, and can provide automaticData backup。RAID technology has two major characteristics: speed and security. Because of these two advantages, RAID technology was early applied to the SCSI interface in advanced serversHard diskIn the systemcomputer technologyWith the development of, the CPU speed of PC has entered the GHz era.IDE interfaceHard diskNot to be left behind, ATA66 and ATA100 hard disks have been launched.This makes it possible for RAID technology to be applied to low-end and even personal PCs.RAID is usually created byHard diskRAID controller in the array tower or RAID card in the computer.
Through continuous development, RAID technology now has seven basic RAID levels from RAID 0 to 6.In addition, there are some combinations of basic RAID levels, such as RAID 10 (combination of RAID 0 and RAID 1), RAID 50 (combination of RAID 0 and RAID 5), etc.Different RAID levels represent different storage performance, data security, and storage costs.However, the following RAID forms are most commonly used.
