A little Linux-Hard Disk knowledge every day

nowadays, disk interfaces are mainly divided into two types: IDE (integrated drive electronics) and SCSI (small computer system interface ). They each have some differentiation or evolution, so the technical terms on disk interfaces are more and more complicated. Of course, the disk interface also has other technologies, such as optical fiber technology and familiar USB.

The following describes the IDE technology. IDE is developed as a simple and cheap interface for PC. It places the hardware controller and the hard disk chip in the same box, in addition, a relatively high-level protocol is used between the computer and the hard disk for communication, which is the origin of the IDE name. IDE hard drive is characterized by medium speed, large capacity, and low cost, mainly used for personal computers. PATA (parallel Advanced Technology Attachment), the first implementation of the IDE technology, came into being in the late 1980s S. ATA-2, with better Pio (programmed I/O), supporting DMA mode, LBA addressing. ATA-3, increased reliability, with better power management features. The transmission speed reaches 133 Mb/s until the ATA-7. The maximum cable length allowed by the ATA hard drive is 18 inch, which is very short, so the ATA hard drive is almost always used internally. In addition, an IDE bus can only accommodate two devices, therefore, most manufacturers provide more than one ide bus on their motherboard, usually two, called primary and secondary. If two devices are connected to one IDE, you must specify one of them as the master device and the other as the slave device. This is done through jumper settings, and the operation as the master device does not have any performance improvement, the master disk and slave disk are two hard disks. Apart from connecting to the same ide bus, they have nothing to do with each other. The master-slave relationship is only from the perspective of the IDE bus layer. generally, if the ATA hard disk does not work, check whether the cable length exceeds the maximum allowed length and whether the hard disk is used as the slave hard disk (some hard disks do not like the slave hard disk ). in addition, winding cables are more conducive to the cleanliness and ventilation of the chassis than band cables. SATA (Serial Advanced Technology Attachment), the subsequent Technology of IDE, it has a faster speed, higher reliability, longer cable length and clear connections, supports hot swapping, command queue; it does not need to specify the Master/Slave Device, because a channel can only connect to one hard disk; The SATA-2 transmission rate is as high as 600 Mb/s, but you need to know that this is only the speed allowed by the bus. the following describes the SCSI technology. SCSI standard goes through SCSI-1, SCSI-2, SCSI-3, it can mount multiple hard disks on one bus, support multiple rates and communication types; particularly, it supports long cable lengths, therefore, it can be used as an external hard disk and is generally used in the server field. generally speaking of SCSI-2, people use "fast" and "wide" to describe: "fast" refers to the bus speed, it transmits 32-bit or 16-bit at the same time, rather than the usual 8-bit; "Wide" indicates that multiple devices are supported at the same time. "wide" indicates 16 devices, and "narrow" indicates 8 devices. comparison between IDE and SCSI. the SCSI hard disk occupies an advantage in the server field, but the SATA hard disk is getting better and can almost replace the SCSI hard disk. however, SCSI is irreplaceable in terms of high performance, large-scale concurrency, and multi-device connection. rpm, round per minute, disk speed, an indicator of performance, the faster it means faster read/write speed, but also greater heat, the mainstream market standard is 7200. finally, ATA, SATA, SCSI is just a bus interface technology, they are not only used for hard disks, but also for other devices, such as CD-ROM.