Hard drive is the primary external storage device of the computer. The type of computer storage devices in a very large, there are common floppy disk, hard disk, U disk, etc., and even network storage SAN, NAS, etc., but we use the most or hard disk.
If the medium for storing data distinguishing up, then the hard drive can be divided into mechanical hard disk (Hard Disk Drive, HDD) and SSD (Solid State Disk, SSD), mechanical hard drive to store data using a magnetic disc, and a flash SSDs particles to store data.
Mechanical hard drive (HDD)
the physical structure of the mechanical hard disk
Let's take a look at the most common mechanical hard disk. Mechanical hard look we might have seen, then open the mechanical hard drive is what look like? As shown in Figure 1.
A mechanical hard drive configuration diagram
Mainly by mechanical hard disk platters, heads, spindles and drive shafts and other components, our data is stored in the disk platters them. We've seen old-fashioned phonograph it? Record on the phonograph and the use of our disk platters are very similar, except that only a gramophone head, while the hard disk is a double head down, the disc rotates at high speed in the middle of two heads, similar to Figure 2.
Figure 2 disk platter
That is, the mechanical hard disk is vertically read data simultaneously. And the rotational speed of the hard disk is much higher than the mechanical LP (now common mechanical hard disk rotational speed is 7200 r / min), the mechanical hard disk to read or write data, and very afraid shaking bump. Further, since the ultra-high speed mechanical hard disk, if the internal dust, will cause damage to the head or disk, internal hard drive is the mechanical closed, if not in a clean environment, it is not disassemble mechanical hard drive.
Mechanical hard drive logical structure
we already know that the data is written to disk platter, the data structure is in accordance with what is written in it? The logical structure of the mechanical hard disk is divided into tracks and sectors Zhu surface. We look at Figure 3.
3 tracks and sectors
What track is it? Each platter has a lot of concentric logically, 0 is the outermost concentric track. Each track will be referred to as concentric circles (note, only the logical structure of the track, in the disk does not really concentric circles). HDD track density is very high, usually on one side there are thousands of tracks. But not the immediately adjacent tracks, because the magnetization unit spaced too close to each other will have an impact.
That sector but also what it ten? In fact, it is the image of the sector, we have now seen the folded paper fans, paper fan after opening semicircular or fan-shaped, but this sector is formed by each combination of fan bone. On each disk track is concentrically, radially outwardly generating the division lines (Shan Gu), each track divided into a plurality of arc from the center, each arc segment is one sector. The size of each sector is fixed, is 512Byte. Sector is the smallest unit of disk storage.
What cylinder is it? If the hard disk is composed of a plurality of disks, each disk surface is divided into an equal number of tracks, then the disk are all carried out from the outside track number, 0 is the outermost track. With the same number of tracks will form a cylinder, the cylinder will be referred to as cylinders of the disk, as shown in FIG.
FIG cylinder 4
Hard disk size is calculated using such a formula "size x the number of heads x number of cylinders x number of sectors for each sector." Wherein the number of heads (Heads) indicates a total number of hard disk head, can be understood as a few hard disk, and then multiplied by 2; the number of cylinders (Cylinders) represents the hard disk has several tracks on each side; the number of sectors ( sectors) expressed several sectors on each track; the size of each sector is generally 512Byte.
Hard disk interface
mechanical hard disk connected to the computer via an interface board. Read and write speeds and hard disk interface has a great relationship. We've all seen it auditorium, auditorium can accommodate a lot of people, but if there is only a very small door, it is difficult to get into or out of the people, this will cause congestion, or even an accident. Mechanical hard disk read and write is the same, if the poor performance of the interface, it will also affect the performance of mechanical hard disk.
At present, the common mechanical hard disk interface has several such.
IDE hard disk interface (Integrated Drive Eectronics, parallel, i.e., an integrated drive electronics) is also referred to as "ATA hard" or "the PATA hard" is the primary interface early mechanical hard disk, ATA133 hard theoretical speed can reach 133MB / s (this speed Theory average), IDE hard disk interface as shown in FIG.
FIG 5 IDE hard disk interface
SATA interface (Serial ATA, serial interface) hard disk standard is a higher speed, with a higher transmission speed, and with a stronger error correction capability. SATA is now three generations, theoretical transmission speed of 600MB / s (this theoretical average speed), as shown in FIG.
FIG 6 SATA hard disk interface
Interface SCSI (Small Computer System Interface, Small Computer System Interface) is widely used on a server, having a wide range of applications, multitasking, wide bandwidth, CPU occupancy rate is low and the hot swap, etc., theoretical transmission speed of 320MB / s, such as Figure 7.
FIG 7 SCSI disk interface
solid state drive (SSD)
SSD and traditional mechanical hard disk biggest difference is no longer used for data storage disk, memory chip employed for data storage. SSD memory chip is divided into two: one is to use a flash memory as a storage medium; the other is the use of DRAM as a storage medium. Currently using more flash memory is mainly used as a solid-state storage medium, as shown in FIG.
8 SSDs
Comparative mechanical hard drives and solid state mainly in the following features, as shown in Table 1.
Table 1 SSDs and mechanical hard drive comparison
contrast project SSDs mechanical hard drive
capacity is smaller large
read / write speed fast - like
the number of writes 5000~100000 times there is no limit
work have extremely low noise
operating temperature is very low high
shockproof good fear vibration
weight low high
price level
we can find, because SSD discarded mechanical hard disk physical structure, it has a low energy consumption compared to mechanical hard drive, noise-free, anti-vibration, low heat dissipation, small size and fast speed advantages; however higher price compared to mechanical hard drives, and limited service life.
