SCSI Small Computer System Interface Interface
(English: Small Computer System Interface; short: SCSI), one for computers and intelligent devices (hard disk, floppy, CD drives, printers, scanners, etc.) independent of system-level interface processor standards. SCSI is an intelligent universal interface standard. It is a variety of computer and standard interface between external devices.
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About Type 1.SCSI-12.SCSI-23.SCSI-3SCSI and related technologies IDE introduces a distinction, SCSI advantage of the second, SCSI shortcomings five terminator VI The seven SCSI ID, SCSI equipment selection profile
● SCSI interface is a common interface, the SCSI bus can be connected on the SCSI host adapter and eight peripheral controllers, peripheral devices can include disk, tape, , CD-ROM, rewritable optical drives, printers, scanners and communications equipment. ● SCSI is a multi-tasking interface with bus arbitration function. Hanging in a number of peripherals on the SCSI bus can work. Equal share SCSI devices on the bus. ● SCSI interface can be synchronous or asynchronous transmission of data, synchronous transfer rate up to 10MB / s, asynchronous transfer rate of up to 1.5MB / s. ● SCSI interface, receives an external device. It's connecting cable can be up to 6m. The original SCSI standard maximum synchronous transfer rate of 5MB / s (SCSI-1, also known as Narrow SCSI, 1986, the maximum support 7 devices, the clock frequency of 5MHz), then the SCSI II provides for the choice of 2 kinds of speed . A data transmission to improve the frequency, that is, Fast SCSI (1994 years, the maximum support 7 devices), the frequency doubled, up to 10MB / s (10MHz); the other option is to increase the speed of transmission frequency doubling while also increasing the width of the data path from 8 bits to 16 bits, that is, Wide SCSI, the maximum synchronous transfer rate of 20MB / s (clock frequency of 10MHz, 1996, the maximum support to 15 devices). Appeared around 1995, the third generation of SCSI, but there is no uniform standard: 1. Maximum synchronous transfer speed 20MB / s for Ultra SCSI (also called Fast-20 SCSI, the clock frequency of 20MHz); 2. Maximum synchronous transfer speed 40MB / s for Ultra Wide SCSI (with 1); 3. Maximum synchronous transfer speed 40MB / s of Ultra2 SCSI (also called Fast-40 SCSI, the clock frequency of 40MHz, 1997 years). Later, there was some newer SCSI standards: 1. Maximum synchronous transfer speed 80MB / s of Ultra2 Wide SCSI (a clock frequency of 40MHz); 2. Maximum synchronous transfer speed 160MB / s for Ultra 3 SCSI (also known as Ultra-160 or Fast-80 Wide SCSI, the clock frequency of 40MHz data rate doubled in 1999); 3. Maximum synchronous transfer speed 320MB / s for Ultra 320 SCSI (also known as Ultra 4 SCSI, 80MHz clock frequency of double data rate increases, 2002); 4. Maximum synchronous transfer speed 640MB / s for Ultra 640 SCSI (plus a clock frequency of 160MHz double data rate, in 2003, is the latest SCSI standard) this interface is an easy system integration, reduce costs and improve efficiency interface standards, more and more devices will use the SCSI interface standard, therefore, with the SCSI interface, SCSI CD-ROM drive, hard disk and there are many, but because of costs, mainly for high-end servers and workstations. Type 1.SCSI-1 SCSI-1 is the original version, the frequency of ATM 3MB / S, synchronous transmission frequency 5MB / s. While it is almost eliminated, but will also use the scanner and in a number of internal ZIP drive, uses a 25-pin interface. In other words, if the SCSI-1 devices connected to your SCSI card, there must be an internal 25-pin interface cable for 50; if an external device, you can not use any of the internal interface (ie, at this time internal interfaces are not available.) 2.SCSI-2 early in the SCSI-2, known as FastSCSI, by increasing the frequency of the synchronous transfer rate of data transmission from the original 5MB / s increased to 10MB / s, support for 8-bit parallel data transfer, can be even outside the 7 set. Subsequently the WideSCSI, supports 16-bit parallel data transfer, data transfer rate up to a 20MB / s, 16 peripherals can be connected. This version uses a 50-pin SCSI interface,
red sole shoes, mainly used for scanners, CD-ROM drive and the old hard drive. 3.SCSI-3 1995, the birth of a more high-speed SCSI-3, known as UltraSCSI, data transfer rates, the 20MB / s. Synchronous transfer clock frequency will increase to 20MB / s, higher data transfer rate technology. If you use 16-bit Wide mode of transmission, the data transfer rate can also be increased to 40MB / s. This version uses a 68-pin SCSI interface, mainly used in hard disk. Typical features of SCSI-3 bus frequency is greatly increased, and reduce signal interference, in order to enhance its stability. In addition to the difference between SCSI and IDE SCSI, IDE is also a very common interface. From the perspective of ease of use, IDE is more suitable for ordinary users, along with PC users only need to configure the peripheral small, and the speed requirements are not high, IDE interface, so choose something more appropriate. In addition, IDE also has a high cost performance, wide range of applications and so on. The SCSI interface, although has many unique features, but no matter from which point of view, the interface and its use of the interface peripherals price too high, the average user simply can not afford, which also determines the scope of its limited practical use ######. 1.IDE the work involved in the entire process needs CPU, CPU time can not read and write data to other operations, the situation in Windows95/NT multi-tasking operating system, will naturally result in much slower system response. The SCSI interface is completely independent of the speed through the SCSI card to control data read and write operations, CPU will not have to waste time to wait, obviously you can improve overall system performance. Nevertheless, the IDE interface is also made to improve this great improvement, ready to use PIO mode instead of DMA mode to read and write, the exchange of data by the DMA channel responsible for the occupation of the CPU can be greatly reduced. However, SCSI and IDE compare the occupancy rate in the CPU, or can be found SCSI still has a considerable advantage. 2.SCSI large scalability than IDE, the general system for each IDE has two IDE channels,
cheap christian louboutin, with a total of 4 IDE devices, and SCSI interface, a device can be connected to 7-15, a lot more than IDE, and the connection cable far longer than the IDE. 3. Although the SCSI equipment prices higher, compared with the IDE, SCSI and more stable performance, durability, reliability and better. Introduced a related technology, SCSI advantage 1.SCSI can support multiple devices, SCSI-2 (FastSCSI) can connect up to seven SCSI devices, WideSCSI-2 can be accessed by more than 16 SCSI devices. In other words, all the equipment only takes one IRQ, while SCSI devices also support an extremely broad, such as CD-ROM, DVD, CDR, hard drives, tape drives, scanners and so on. 2.SCSI also allows a device to transfer data at the same time, another device to find its data. This can be a multitasking operating system such as Linux, WindowsNT to get higher performance. 3.SCSI CPU-low, indeed multi-task system occupies a distinct advantage. SCSI card itself with the CPU, SCSI devices can handle all the affairs of the host CPU at work as long as work orders issued to the SCSI card, SCSI card will have their own work, work to return to work after the end of the results to the CPU, in the process , CPU can be carried out their work. 4.SCSI device also has the intelligence, SCSI card, your CPU instructions can be queued, thus improving work efficiency. When the hard disk in a multi-task in the current head position, close to first complete the task, then one by one for processing. 5. The fastest SCSI bus with 160MB / s bandwidth, which requires the use of a 64-bit 66MHz PCI slots, so PCI-X bus standard that can achieve a maximum speed of 80MB / s, if the tie 10, 15,000 rpm speed 000rpm or use a dedicated hard drive will bring significant performance gains. Second, SCSI SCSI advantage of the shortcomings of nature is very attractive, but also want the user decided to use, do not overlook its shortcomings. 1. Through access to information to the conclusion that: in the same condition, SCSI internal hard disk transfer rate slower than the IDE. Because the SCSI hard drive IDE hard drive than the complexity of control instructions, SCSI hard disk sectors in the identification of linear time by the concept that drives only the first sector 1, sector 2, unlike the IDE hard disk, a cylinder, head, sectors such three-dimensional format. Within the current operating system, also using a linear number of sectors, but the BIOS only accept requests for three-dimensional format of the disk, so the operating system, the request must be converted into three-dimensional format the disk, so that IDE hard drives can be used directly, but is also compatible with SCSI BIOS in order and three-dimensional format of the disk was converted to a linear number request, so the hard drive data transfer rate is greatly reduced. This we published data from the factory you can see, for example Seagate7200 / min of the . SCSI hard disk so only in UNIX, WindowsNT, and other tasks can play under the edge in the WIN95 environment, pretty good, but in DOS, to absolutely no advantage at all (although DOS is now rarely used.) Now Apple's G4, iMac and other models have begun to support the IDE interface. (Note: this section discusses the equipment mentioned in the last century in the late 90's is completely out of date, the software in addition to the various branches of UNIX operating systems continue to exist in the form outside the other are roughly the same period of time out, it was comment on the discusses the type of information is now insufficient data. In addition, in the year 2000-2004 has been produced on the server SCSI hard disk drives and IDE hard disk drives use LBA addressing non-discriminatory basis to support the emergence of new technologies and more under high-capacity SCSI hard disk devices.) 2. the last point to be emphasized, SCSI performance and low cost is not high. Things, SCSI ridiculously expensive little piece of the most popular type of AdaptecAHA-2940SCSI card is enough to exchange for a BX motherboard, the same speed and brand of CD-ROM, SCSI more than twice as expensive than the IDE, a 4.5GB7200 r / min Hope in the choice of SCSI, before considering their own economic strength, and then consider its price value for money. (Note: The above text is in 10-15 years under certain market conditions make the arbitrary assertion, the arguer will be for low-end of the BX motherboard and SCSI for high-end applications, confused, completely ignoring the target user needs arising from the performance differences. So the obvious interests of the bias argument, so Buzuweiping. In fact, in the high-end applications such as large RDBMS, B2C, infrastructure and so on SCSI and its branch FC-SCSI, iSCSI, SAS, are still widely adopted, because good performance, scalability, and reliability of the reliability of the whole system will be effectively guaranteed. Correspondingly, IDE PATA】 【modified with SATA performance bottleneck because there are some, but only as a cheap disk storage solutions - This is the original semantics of the term RAID implementation.) V. terminator SCSI chain SCSI devices use the final terminator, middleware is not the end device. Once the intermediate device using the terminator, then the SCSI card will not be able to find after the SCSI device. The last device is useless if the terminator, SCSI is not work. Terminator is a resistor, and at the end of the SCSI bus, used to reduce the mutual influence of the signal, to maintain constant voltage on the SCSI chain. Most of the SCSI device is a built-in terminator, and with a jumper to control the ON / OFF. The SCSI devices are highly intelligent and can automatically control the terminator ON / OFF, such as a hard drive and a CD-ROM attached to the end regardless of the hard disk device ON or OFF,
christian louboutin shoes, CD-ROM can be used normally. When two hard drives connected,
christian louboutin pumps, the situation becomes complicated, two Seagate hard drive connected before the end of a hard disk device must be OFF, and when a Seagate hard drive and a Quantum drive connected before the end of a hard disk device, whether ON or OFF, can be used normally. VI, SCSI to SCSI ID system, each device must have its own unique ID (identification number), the numbers from 1 to 15. SCSIAdapter system default ID is 7. This ID can be located on the front of the jumper to set. It is located in the hard disk drive for the front or rear. VII, SCSI devices SCSI card selection 1.SCSI card SCSI device chain, the whole key, select the following factors to be considered when: (1) SCSI card brand choice brand of course very important, Adaptec SCSI card is fine, CPU industry as Intel, already the standard SCSI world,
louboutin sale, of course, compatibility is no problem, but high prices may be the only problem. In other words, if we allow economic conditions, or recommend choosing Adaptec SCSI card. (2) The SCSI bus interface PCI card is selected, ISA's SCSI cards are now basically no one bought, should be noted that some of the scanner's SCSI card with the ISA is not a generic SCSI card, although it has the standard SCSI connectors , but can only access the scanner used. Secondly, we must try to avoid the integration of optional SCSI board and the board, mainly on account of the compatibility problems, particularly noteworthy. (:2000-2003 produced by the servers are all built-in SCSI chip series, such as Compaq DL380R1 integrated Compaq Smart Array Controller, supports RAID-0, 0 +1,5 three array level, the interface can be connected to an external tape library Thus, it is the thesis of the professional review is problematic.) (3) SCSI type commonly used 8-bit data path of a SCSI-2 data transfer rate of 10Mbps, SCSI is the most common type. From a general consideration, or use personal data channel 8-bit SCSI-2 is appropriate (Note: outdated thesis, and now Ultra SCSI-3 has been in the mainstream, a typical SCSI cards, such as Adaptec ASC-29160 already can do all compatible) . On the one hand, only the hard drive supports 16-bit data channel WideSCSI, and 16-bit data path WideSCSI equipment prices to be higher than many 8-bit SCSI-2; the other hand, 16-bit data path WideSCSI cards generally built-in 8-bit, 16 bit interface to each one, but only one external 16-bit SCSI interface to D-68 hole, and the general external SCSI devices such as: CD-ROM, CDR / W (by: CD-ROM and CD-R / W within the general realized in the form set of equipment, due to built-in can save unnecessary power supply circuit and the interface circuit the extra cost. and the current practice is to use all of these devices is relatively easy to implement IDE interfaces, SCSI interfaces are still rare ), scanners, SCSI devices are 8-bit (only 50 holes D-type interface, if you want to receive a 16-bit SCSI interface, 68 holes requires a 68-50 D-hole converter, the converter is not only difficult to purchase, and the compatibility also need further examination. (Note: these scanners have already eliminated in 2000, is now commercially available scanner under the standard USB 2.0 interface, the performance has made great breakthroughs in) (4) SCSI with special reference to the final price of the course is the price, at different speeds to determine the different prices. so based on actual need to select the appropriate card, 10MB card DC310/390 general is 100 yuan (Note: outdated quotation); 20MB of DC390U/DC395U/DC315 in 200 -500 yuan; 40MB of DC390F/DC395UW to meet high-speed applications, the price will be around the thousand dollars or more; undoubtedly DC390U2 for the application of the top series, both models 390U2W and 390U2B is 80MB, the price of 2900 / 2200 yuan or so, the difference is more than a LSI53C141 U2W chip,
christian louboutin uk, and the interface more than the U2B, the card U2W there are two 68-pin, a 50-pin interface, for a variety of equipment or need to continue to expand in future occasions, and U2B is only a 68-pin, prices cheaper, higher cost performance, no need to extend for an independent applications. so you can pick out affordable SCSI card. (Note: the above quotes are out of date with the SCSI card , Buzuweiping.) entries Atlas Atlas more extended reading: 1
http://en.wikipedia.org/wiki/SCSI
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http://www.fix. com.cn/Superiority/newsdetail/2007917107919.htm