Data recovery base – 4. HDD mystery boot processes and performance index


1.1.4 Hard boot process
Hard drive is like a mini-computer, from power to be ready, but also requires a process. Now, let's look at the hard disk boot process.
After (1) hard power, DSP ROM first run the program, part of the hard disk will check the integrity of the components.
(2) is then transferred from the disc motor, when the speed reaches a predetermined speed, heads began to move, navigate to the firmware of the disc area, read the hard drive firmware and bad sectors form part of the hard drive will first series of the ROM memory Compared with the number carried on the disc, and if not, the hard disk will terminate initialization. If the key sectors or file firmware damage, hard knocking may occur, can not be identified or BIOS recognition errors and other failures.
(3) When all of the normal firmware must be read, the disk that is in the ready state, waiting to receive the work instruction data read and write operations.


1.1.5 hard drive performance
1. Hard drive speed (Spindle Speed)
Hard disk rotational speed refers to the speed of the hard drive spindle motor, generally expressed in the number of revolutions per minute (rpm). Hard disk drive spindle motor rotates at high speed, the head floats in buoyancy above the disk. To access the data of the sector to be moved to the bottom of the head, the faster the speed, the waiting time is shorter. With the increasing capacity of the hard disk, hard drive speed has also been improved. However, increasing the speed also brought increased wear, temperature, noise increases and a series of negative effects.
2. Hard disk data transfer rate (Data Transfer Rate)
Data transfer rates include external data transfer rate (External Transfer Rate, also known as the burst transfer rate) and internal data transfer rate (Internal Transfer Rate) two kinds. We often say ATA100 of 100 represents the theoretical value of the hard drive is an external data transfer rate of 100Mb / s, which is the highest rate of computer data is read from the hard disk via the internal data bus buffer. The internal data transfer rate may not be known to everyone, but it is an important indicator of good or bad performance of a hard drive, it refers to the data transfer rate between the head to the disk cache.
3. Hard disk cache
Hard disk cache is a place to exchange data with external bus. Hard disk read process data is the data to be read into the cache, the cache fills up, such as data or to read all the data read from the cache after an external hard drive transfer rate of data transfer to the external bus. You can say that it has played a balancing role of internal and external data transfer.
Seen, the cache function is very important. Currently there are mainstream hard drive 8MB cache and 2MB two kinds, generally SDRAM based. Depending on the writing mode, there are two kinds of writing formula and write-back. Most hard drives are now using write-back.

4. Average seek time (Average Seek Time)

Average seek time refers to the corresponding command from the beginning to the hard disk heads move to designated tracks the average time used so far, in milliseconds (ms). This is a very important indicator of the hard disk, the average access time to talk about this indicator and rear closely linked.
5 cylinder switch time (Cylinder Switch Time)
Also referred to the cylindrical channel switching time Shido switching time (Track to Track Time), the switching means is used for the time between two adjacent cylinders, in particular adjacent to the track is the head movement from the current track to the top The top of the track elapsed time, in milliseconds (ms).
6 The average incubation period (Average Latency Time)
The average incubation period means that the head is moved to the specified track, you also need to specify how much time (that is to be read or written) will go to the next sector to read or write to the heads of related operations. Obviously, this time about the speed of the disc, with an average incubation period generally refers to the disc rotation used half the time, in milliseconds (ms). So that we can easily translated the correspondence between the hard disk speed and average latency. Conversion formula is:
(60 × 1000) / (hard drive speed × 2) = average incubation period
7 average access time (Average Access Time)
The indicator in the official technical documentation generally does not appear, it refers to the instruction issued from the corresponding read or write instruction is beginning to have the specified sector to head waiting to be read or written (some are called from read / write command is issued to the first data read / write time used during this time) until.  
Data recovery base – 4. HDD mystery boot processes and performance index
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