Sectors, tracks, sector of the hard disk

Fan:cylinder/Track:track/sectorsSector:Sector/headChs:cylinder, Head, Sector/track, as follows: Cylinder the number of cylinders indicates that there are several tracks on each face of the hard disk, numbering starts from 0 and the maximum is 1023, indicating that there are 1024 tracks. Head head number indicates that the disk has a few heads, that is, a few faces, numbering starting from 0, the maximum is 255, indicating that there are 256 heads. The number of Sector/track sectors indicates that there are several sectors on each track, numbering starting at 1, maximum 63, representing 63 sectors, 512 bytes per sector, and he is the minimum storage unit for the disk. 1024 cylinders x 63 sectors X 256 heads x 512byte = 8455716864byte (or 8.4G) logical block BLOCK: Logical block is the smallest storage unit specified when partition is in filesystem format. The size of the block is the sector multiplier of 2. The head can read a block at a time. Block units are planned to take into account the performance of data read and the utilization of hard disk space.
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Although the internal and external track length is different, but the number of sectors on each track is the same, that is, the inner ring density is large, the outer ring density is small.

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How do I calculate capacity?

Generally we buy the hard disk first is to pay attention to its capacity, and then see its number of turns (the higher the better), the head read and write speed,cache size and flow data. So how do we know the capacity? The simplest is to look at the model and factory information, but not through the technical approach, the following to teach you how to calculate the capacity of the hard disk, but first of all, to understand the structure of the disk drive.

If the hard drive is turned on (but do not do so on your own hard drive!) because the hard drive is sealed and almost useless once it is opened, you will find a bunch of metal discs with a center axis, which have been magnetized. All the material is recorded on the surface of these smooth metal discs. Each metal magnetic sheet usually has two sides, each with its own read-write Head (head) . ﹕

Then the disk rotates, the head does not move on the surface relative to the draw of a circle, it can be said to be a magnetic track. At a certain distance from the center of the circle, the magnetic track of the same circumference on all surfaces is stacked up from top to bottom, and the abstract view is a magnetic column (Cylinder) .

Then, it is also from the center of the circle, on the same surface to draw an infinite number of radii, and then each of the two radii divided by the magnetic track, we call the Magnetic region (Sector). 512byte (0.5KB) of data is usually available for each magnetic area. Please see the legend:

Well, if the above information (Cylinder/heads/sector) is known, it is easy to ask for the capacity of the hard disk. The formula is:

Number of heads (actually readable and writable surfaces) x number of magnetic columns (in fact, each surface of the magnetic track) x number of magnetic regions per magnetic track x capacity per magnetic region = HDD capacity

Example: If you see a hard disk that says:

Cylinder	Heads	Sector
1647	16	63

So,1647x16x63x0.5kb=830088kb/1024 is a 811MB hdd. If you want the system to be able to read this hard disk, the data must be written into the BIOS, but now the BIOS is mostly automatic detection function, as long as the BIOS in the selection of auto can be, it is more convenient, especially for new hard disk.

Today's manufacturing technology continues to improve, the hard disk is becoming thinner and smaller, so the magnetic disk can be more loaded (relative to the more readable surface more and more), and the density of the surface is increasing and read and write accuracy is more and more high (relative to track and sector also more and more), So the capacity of the hard disk is increasing.

However, in addition to this factor, the method of increasing the disk capacity is called the multi-zone record (multiple zone recording) technology. Before the introduction of this technology, each track above the number of sector is the same, so that the periphery of the sector across the sector is clearly more than the inside (the center) of the wider, but also a lot of waste. So after quoting the MZR, we can divide the outer track into more sector, so that the capacity will be relatively increased.

* Physical composition of the hard disk

We should all look at the perfect dish! The HDD is divided into 3.5-and 2.5-inch sizes based on desktop and notebook computers. We use the hard drive to describe the 3.5-inch desktop computer. In the case of the hard drive is actually a lot of round disk disk, mechanical arm, disk reading head and spindle motor composition, the entire interior as shown:

Physical structure of hard disk
Figure 2.4.1, hard disk physical structure (image taken from Wikipedia)

The actual material is written on the disk with magnetic material, and the reading and writing is achieved mainly through the reading Head (head) on the robotic arm. In practice, the spindle motor rotates the disk, and the arm stretches to allow the reading head to read and write on the disk. In addition, because of the limited capacity of a single disk disk, there will be more than two disk drives inside the drive Oh!

* Data on disk disk

Since the data are written to the disk, then how to write the data on the disk disk? In fact, the data above the disk is a bit like the following illustration:

Data format on disk disk
Figure 2.4.2, data format on disk disk

The whole disk is like a circular graph drawn by concentric circles, and the smallest storage unit of the disk is split radially by the center, that is, the magnetic region (Sector), in the physical component surface, each magnetic region size of 512Bytes, this value will not change. and the magnetic area to form a circle becomes the magnetic track, if it is on a multi-disc hard disk, on all disk disk on the same magnetic track can be composed of a magnetic column (Cylinder), magnetic column is generally the smallest unit we split the hard disk!

When calculating the storage capacity of the entire hard disk, the simple formula is: ' Number of headers * Number of magnetic poles per header * * Number of magnetic regions per magnetic column * Magnetic region capacity ', unit conversion to ' header * Cylinder/header * secter/ Cylinder * 512bytes/secter ', the simple wording is as follows: Head x cylinder x Sector x Bytes. However, it is important to note that the general HDD manufacturers in the display of the capacity of the hard disk, most of the number is numbered in decimal, so the market for 500GB hard drives, theoretically only 460GBytes of capacity Oh!

Sectors, tracks, sector of the hard disk