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1、第四章存储设备Fourth chapter storage device1. briefly describe the advantages of USB flash memory.Answer: USB flash advantages:(1) no drive, no external power supply.(2) large capacity, the highest has reached 64GB.(3) small in size, light in weight and only about 20 grams in weight.(4) USB interface, easy
2、 to use, good compatibility, plug and play, plug and play.(5) access speed is about 15、30 times of the speed of floppy disk.(6) good reliability and can be repeatedly erased 1 million times, data can be stored for at least 10 years.(7) shock resistant, damp proof, high and low temperature resistant,
3、 easy to carry.(8) write protection to prevent accidental erasure or infection of the files.(9) there is no need to install drivers (Windows, Me or more, including Windows 2000/XP/Vista).2. briefly describe the main performance indicators of the optical disk drive.Answer: (1) data transmission rate,
4、 it is the most basic performance index of CD driver, it is to point to what CD drive can read inside the biggest data quantity.(2) average seek time means that the laser head of the optical drive moves from the original position to the specified data sector and reads the first data on the sector in
5、to the average time spent by the cache. The shorter the average seek time, the better the performance of the drive.(3) CPU takes up time, that is, when the CD driver keeps a certain speed and data transmission rate, it takes up CPU of the time. This is an important indicator of the performance of CD
6、-ROM drive, CPU less time to drive, the overall performance of the system will be better.(4) internal cache, mainly for storing read data. The principle of internal cache is similar to that of Cache on the motherboard. It can effectively reduce the number of read disk and improve the data transmissi
7、on rate.(5) no performance parameters are listed in any optical drive performance index, but this is a real CD-ROM evaluation standard.3. briefly describe the working principle of the CD-ROM drive.Answer: the laser head is the central component of the optical drive, and the optical drive is to read
8、the data through it. CD-ROM information is read, the laser head to a disc laser beam, when the laser beam to an optical disc or non concave concave, the intensity of the reflected beam will change, CD-ROM according to the reflected beam intensity, the reduction of the information on the disc into di
9、gital information, which is 0 or 1，then the corresponding control system to transmit data to the computer.In the CD free state, after the optical drive is powered on, the laser head component starts, and the drive panel indicator light is on. The laser head assembly moves to the vicinity of the spin
10、dle motor and moves from inside to outside along the guide rail, and finally back to the spindle motor. The focusing lens of the laser head will move up 4 times to search the optical disk, and the spindle motor will start 4 times clockwise. Then the laser head assembly is reset, the spindle motor st
11、ops running, and the panel indicator goes out.After the optical disk is inserted into the optical disk, the laser head focus lens repeats the search action, and after the disc is found, the spindle motor will accelerate the operation. At this point, if you read the disc, the panel indicator will fli
12、cker continuously. The stepper motor drives the laser head component to move to the optical disk data, and the focusing lens reflects the data to the receiving photoelectric tube, and then transmits the data to the system. If you stop reading the disc, the laser head assembly and the motor will stil
13、l be loaded, and the panel indicator will go out. However, current high-speed optical drives are designed to allow the spindle motor and the laser head to stop working in 40 seconds or minutes until the data is read again. This can save energy effectively and prolong the use time.4. briefly describe
14、s the working principle of CD burner.Answer: there is a film on the surface of the optical storage disk. When burning, the burner will irradiate the high-power laser according to the information required to burn the film, and the film will form the corresponding plane (Land) and Pit. The optical dis
15、k reader converts the planar and pit information into 0 and 1, converting the physical information of the compact disk into digital information.For CD-R and DVD-R/DVD+R discs, the physical changes of the film are one-time and cannot be modified after writing.As a result, the CD-R and DVD-R/DVD+R dis
16、ks can only be written once and cannot be repeated.The material on the CD-RW and DVD-RW/DVD+RW discs is mostly silver, selenium, or tellurium crystals. This kind of film can present two states: crystalline and noncrystalline. In the laser beam, the material can be converted between two states, so the CD-RW and DVD-RW/DVD+RW disks can be written repeatedly.5. sketch the external structure and internal structure of the hard disk.Answe
