Data Recovery Fundamentals: Introduction to hard disks, partitions, and file systems

Data Recovery Fundamentals: Introduction to hard disks, partitions, and file systems

Hard disk internal structure

On the hard disk structure of the article has been very much, but really want to say clearly, even if the book is also out of a book, so here is no longer elaborate from the beginning.
The most basic part of the hard disk is made of hard metal material coated with magnetic media discs, different capacity hard disk disc number. Each disc has two sides, can record information. The disc is divided into a number of sectors, each area is called a sector, each sector can store 128 × 2 N power (N = 0.1.2.3) byte information. In DOS, each sector is 128 × 2 of the second power = 512 bytes, the disc surface to the center of the disc as the center, different radius of the concentric circle called the track. Hard disk, different discs of the same radius of the composition of the cylinder is called the cylinder. Tracks and cylinders are circles with different radii. In many cases, tracks and cylinders can be used interchangeably. We know that each disk has two faces, each with a head, which is used to distinguish it from the head The Sector, track (or cylinder) and the number of heads constitute the basic parameters of the hard disk structure. In the old hard drive, are used in this relatively old CHS (Cylinder / Head / Sector) structure system. Because a long time ago, the capacity of the hard disk is still very small, people use a similar structure with the floppy disk to produce hard drives. That is, each track of the hard disk has the same number of sectors, resulting in the so-called 3D parameters (Disk Geometry), that is, the number of heads (Heads), the number of cylinders (Cylinders), the number of sectors (Sectors ) And the corresponding 3D addressing mode. For now the new hard drive, all have not used this structure, but the use of a more scientific structure, the current hard disk is a linear addressing that is directly used to access the hard disk sector, 137G the following hard disk 32-bit integer as the sector number, and 137G or more hard disk using 48-bit integer as the sector number.

CHS structural system

Which: the number of heads that the hard disk has a total of several heads, that is, there are several face discs, up to 255 (with 8 binary bit storage); cylinder number that the hard disk each side of the disc has several tracks, With 10 binary bits); the number of sectors indicates that there are several sectors on each track, with a maximum of 63 (stored with 6 binary bits); each sector is typically 512 bytes, and in theory you can Take any one you like the value, but it seems that has not yet found the value of the other. So the maximum capacity of the disk is:
255×1023×63×512/1048576=8024MB(1M=1048576Bytes)
Or hard drive manufacturers commonly used units:
Because the number of sectors per track is equal to the number of sectors per track in the CHS structure of the old hard drive, the recording density of the track is much lower than that of the internal track, so it will waste a lot of disk space (the same is the floppy disk). In order to further improve the hard disk capacity, and now hard drive manufacturers have to use equal density structure to produce hard drives. That is to say, the length of the tracks per sector is equal and the sectors of the outer ring tracks are larger than the inner track. With this structure, the hard disk no longer has the actual 3D parameters, addressing mode is also changed to linear addressing, that is, the sector as a unit for addressing. In order to be compatible with older software using 3D addressing (such as software that uses the BIOSInt13H interface), vendors typically install an address translator inside the hard disk controller, which is responsible for translating old 3D parameters into new linear parameters. This is why the 3D parameters of the hard disk can now have a variety of reasons for the selection (different working modes can correspond to different 3D parameters such as LBA, LARGE, NORMAL). With the increase in the density of the disk, the organization’s further complex, functional and speed improvement, and now the hard disk will be inside the disk to separate a larger capacity, known as the “system reserved area” area for storage hard disk All kinds of information, parameters and control procedures, and some even the hard disk Fireware also made the system to retain the area inside (the original information is stored in the hard disk control circuit board chip). Although this can further simplify the production process, speed up production and reduce production costs, but on the other hand, but greatly increased the chance of fatal damage to the hard disk and shorten the life of the hard disk.