1. HDD) is also the basic external storage device of microcomputer system. Different from floppy disk drive, its disk is cemented carbide and is fixedly installed inside the drive, so it can also be collectively called hard disk. Compared with floppy disk, its storage capacity is much larger and its speed is much faster. And its volume is very small. The capacity of 3 "floppy disk is 1.44MB, while the capacity of PC hard disk is 40GB to 160GB now. At present, the mainstream hard disk brands in the market are Quantum, Seagate, Maituo, Western Digital, IBM and so on. The hard disk subsystem includes hard disks (including hard disks). Driver and hard disk interface. The controller of the hard disk is built in the hard disk, and the interface is integrated on the motherboard. The driver of the hard disk is included in the system BIOS program. The composition and working principle of hard disk are similar to those of floppy disk. It uses its own dedicated microprocessor as the controller, and the internal ROM solidifies the control software to realize self-diagnosis and running state detection when it is powered on. Spindle motor speed adjustment and head position control. The internal hardware of hard disk drive is mainly composed of circuit board and head disk assembly (HDA). (as shown in Figure 6.4-1) The internal structure diagram of 6.4-1hard disk can be divided into 5.25, 3.5, 2.5, 1.8 inches according to its disk diameter. According to their interface types, there are many IDE interfaces and SCSI interfaces. At present, the most widely used is the 3.5-inch hard disk with IDE interface. IDE interface comes from IBM at machine, and its signal definition is similar to AT machine bus, so it is also called AT bus. The hard disk cable with IDE interface is a 40-wire flat cable, and the red line is 1. As shown in Figure 7-6, two hard disks are connected to an IDE interface, and the jumper on one hard disk should be set to "master" and the jumper on the other hard disk should be set to "slave". The power cord of the hard disk is 4 wires, namely+12V (yellow), ground (black) and +5V (red), 65438. 5V power supply circuit components. 2. Hard disk interface technology, hard disk interface has always been a technology that people care about. With the great improvement of the performance of other microcomputer accessories (such as CPU, memory, display and other subsystems), the interface transmission rate of hard disk increasingly reflects its bottleneck role in the whole microcomputer system. People pay more and more attention to hard disk interface. (1) IDE Interface IDE (Intelligent Device Electronics) is the most basic hard disk interface widely used in PC at present. Except for the necessary control of ISA bus signal on the motherboard, the 40 pins of IDE interface are basically sent to the hard disk intact. Therefore, IDE interface is usually called ATA interface. The PC motherboard usually provides two ide interfaces, each ID can connect two IDE devices, and 40-wire flat cable is used to transmit control and data signals. At present, IDE interfaces used are ATA (or Ultra DMA) 33 and 66. 100 and other new high-speed interfaces. (2) SCSI Interface Type SCSI (Small Computer System Interface) is an external interface adapter card for high-speed peripherals, also known as the disk coprocessor board. It is also commonly called a "dirty" card. SCSI interface has always occupied a noble position in computer peripheral interface, especially in external storage device interface, not only because of its advanced technical performance, but also because of its high price. SCSI means small computer system interface, which is made on a special system expansion card. SCSI was developed in the late 1970s with SCSI- 1. SCSI-2 and SCSI-3, etc. SCSI- 1 is the first version, with the asynchronous data transmission rate of 3MB/ s and the synchronous data transmission rate of 5mb/ s, using a special 25-pin SCSI interface. SCSI-2, formerly known as FAST SCSI, has 8-bit parallel data transmission, and the data transmission rate is increased to 10 MB/s, which can connect 7 peripherals. The standard interface is 50 wires, and the signals are divided into differential mode and single end. SCSI-2 is used for hard disks, optical disk drives and scanners. SCSI-3, also called Ultra SCSI, has a data transmission rate of 20 MB/s. If 16 bit transmission mode is used, the data transmission rate can reach 40MB/S, and SCSI-3 can be increased to 68-pin interface. Used to add 8-bit data to 32-bit data. Ultra 2 SCSI was released in 1997, using low-voltage differential technology, using 16 bit transmission mode, and the data transmission rate reached 80mb/s. Ultra 160/m SCSI was released in 1998, using low-voltage differential technology, each clock can send two bits of data. Hard disks produced after 160mb/s and 1998 began to adopt this interface. 3.FAT 16, FAT32 and NTFS Windows mainly use partition formats such as FAT 16, FAT32 and NTFS. Almost all operating systems support FAT 16. FAT (file allocation table) means "file allocation table". As the name implies, it is a table used to record the location of files, which is very important for the use of hard disks. If the file allocation table is lost, the data on the hard disk will be unusable because it cannot be located. Different operating systems use different file systems, which are usually used in personal computers. OS/2 uses HPFS；; Windows NT/XP/2000/2003 uses NTFS, but MS-DOS 7. 10 and above all support FAT32. FAT 16 uses 16 bits to represent the configuration file of each sector, so it is called FAT 16. FAT 16 is limited by 16 bits, so every time it exceeds a certain capacity, the size of the cluster it uses must be expanded to adapt to the larger disk space. The so-called cluster is the allocation unit of disk space, just like the bookshelf in the library. Each file to be saved to disk must be configured with a sufficient number of clusters. It can only be stored on disk. FAT32 uses 32-bit space to represent the situation of each sector configuration file. The maximum size of a single partition that can be used with FAT32 can reach 2TB(2048GB), and the size of clusters that can be used by partitions of various sizes is also suitable. The above two advantages make the use of hard disk more efficient. The sizes of partitions and clusters are summarized as shown in Table 6.4-2. Table 6.4-2 FAT 16 and FAT32 Partition and Cluster Size Summary Table Partition Size FAT 16 Cluster Size FAT32 Cluster Size 16MB 2KB does not support 32MB- 127 MB 2kB 565438. Byte128mb-255mb4kb512 Byte 256 MB-259 MB 8KB 5 12 Byte 260mb-51mb8kb4kb512mb-1023mb. Some shortcomings of file system, among which the biggest improvement is fault tolerance and security performance. NTFS can automatically repair disk errors without displaying error messages. When Windows 2000 writes a file to an NTFS partition, it keeps a copy of the file in memory, and then checks whether the file written to disk is consistent with the file in memory. If they don't agree, Windows will mark the corresponding sector as bad, stop using it (cluster remapping), and then write the file to disk again, and keep a copy of the file in memory. If there is an error reading the file, NTFS will return a reading error message and inform the corresponding application that the data has been lost. NTFS partition has very strict restrictions on user permissions, and each user can only operate according to the permissions given by the system. Any attempt to exceed the authority will be banned by the system. At the same time, it also provides a fault-tolerant structure log, which can record all the operations of users, thus protecting the security of the system. In addition, NTFS also has file-level repair and hot repair functions, and the partition format is stable, so it is not easy to generate file fragments. These are beyond the scope of other partition formats. These advantages further enhance the security of the system. 4. Commonly used terms and technologies of hard disk (1) Spindle speed is one of the decisive factors of the internal transmission rate of hard disk, and it is also an important symbol to distinguish the grades of hard disk. The speed of hard disk is mostly 5400 rpm. Hard disks with 7200 rpm and 10000 rpm have become the mainstream, but hard disks with 5400 rpm still have the advantage of high cost performance. When buying a hard disk, you will find that the price of the hard disk often rises by about 20% every time the speed of the hard disk is upgraded. Its performance will also be improved. (2) Cache is the place where the hard disk exchanges data with the external bus. The reading process of hard disk is to convert magnetic signals into electrical signals, and then send them out step by step according to the cycle of PCI bus through repeated filling and emptying of cache, so the role of cache can not be underestimated. The capacity and speed of cache are directly related to the transmission speed of hard disk. Cache is a kind of static memory, which is different from memory (dynamic memory). There is no need to refresh regularly, and the capacity is 128KB, 256KB, 5 12KB, or even 2MB. Cache is some high-speed DRAM, the type is EDO DRAM or SDRAM, and there are two types: direct write and write back. When reading the hard disk, the system first checks the request instruction to see if the required data is in the cache. If it is, it is called a hit, so the cache is called. Write-through data is read only. At present, most hard disks use write-back cache which can read and write data, which can improve performance more than direct-write cache. Cache is also a main basis for buying hard disks. At present, the cache of mainstream hard disks is generally larger than 5 12KB, or even 2MB. For example, both Maxtor and IBM's new hard disks have products that use 2MB cache. The performance is obviously improved than before. (3) average seek time average seek time refers to the time required for the head to move to the track where the data is located, which is an important indicator to measure the mechanical capacity of the hard disk. Generally, it is between 5 ms and 13 ms, and the average delay time refers to the time when the sector where the corresponding data is located turns to the bottom of the head, generally between 1 ms and 6 ms, and the average access time is the sum of average seek time and the average delay time. It can best represent the time it takes for the hard disk to find some data. (4) Data transmission rate Data transmission rate can be divided into external transmission rate and internal transmission rate. External transmission rate is also called burst data transmission rate or interface transmission rate. Refers to the speed of data output from the hard disk cache. At present, the external transmission rate using UDMA/66 technology has reached 66.6 MB/s; The internal transfer rate, also known as the maximum or minimum continuous transfer rate, refers to the speed at which the hard disk reads and writes data on the disk. At present, most mainstream hard disks are between 20MB/s and 30 MB/s. Because the internal transmission rate of hard disks is less than the external transmission rate, the internal transmission rate is the decisive factor to evaluate the overall performance of a hard disk, so only the internal transmission rate can be used as the real standard to measure the performance of hard disks. Generally speaking, under the condition of the same hard disk speed, each disk has higher storage capacity. When the storage capacity of each disk is the same, the internal transmission rate of the high-speed hard disk is also high; When the rotational speed is close to the storage capacity of each disk, the internal transmission rate of the new hard disk will be higher because of the advanced processing technology.