Hard disk: the principle of operation and basic characteristics
Hard drives, or, as they are called,Winchesters, are one of the most important components of a computer system. Everyone knows this. But far from every modern user even in principle guesses about how the hard disk functions. The principle of work, in general, for a basic understanding is quite simple, but there are some nuances about which we will go further.
Questions about the purpose and classification of hard disks?
The question of purpose is, of course, rhetorical. Any user, even the most basic level, immediately responds that the hard drive (which is also a hard drive, aka Hard Drive or HDD) immediately responds that it serves to store information.
In general, it is true. Do not forget that on the hard disk, in addition to the operating system and user files, there are boot sectors created by the OS, thanks to which it starts, as well as some labels on which you can quickly find the information on the disk.
Modern models are quite diverse: ordinary HDD, external hard drives, high-speed SSD solid-state drives, although they are not strictly classified as hard disks. Next, it is proposed to consider the device and the principle of the hard disk, if not in its entirety, then at least in such a way as to be sufficient to understand the basic terms and processes.
Please note that there is also a special classification of modern HDD according to some basic criteria, among which are the following:
- method of information storage;
- type of carrier;
- way of organizing access to information.
Why is a hard drive called a hard drive?
Today, many users are thinking about why hard drives are called small-capacity hard drives. It would seem that there can be a common between these two devices?
The term itself appeared back in 1973,when the world's first HDD appeared on the market, the design of which consisted of two separate compartments in one sealed container. The capacity of each compartment was 30 MB, which is why engineers have given the code name for the disc "30-30", which was fully in tune with the brand popular at the time the gun "Winchester, 30-30". However, in the early 90's in America and Europe, this name almost out of use, but still remains popular in the post-Soviet space.
The device and the principle of the hard disk
But we digress. The principle of operation of a hard disk can be briefly described as a process of reading or writing information. But how does this happen? In order to understand the principle of the magnetic hard disk, first of all it is necessary to study how it is arranged.
The hard drive itself is a set ofplates, the number of which can vary from four to nine, connected by a shaft (axis), called a spindle. The plates are placed one above the other. Most often, the material for their production is aluminum, brass, ceramics, glass, etc. The plates themselves have a special magnetic coating in the form of a material called a platter, based on gamma-ferrite oxide, chromium oxide, barium ferrite, etc. Each such plate has a thickness of about 2 mm.
For the recording and reading of information, the radialheads (one for each plate), and in the plates both surfaces are used. For the rotation of the spindle, whose speed can be from 3600 to 7200 rpm, and the movement of the heads corresponds to two electric motors.
In this case, the basic principle of the hard diskcomputer is that information is written not just anywhere, but in strictly defined locations, called sectors, which are located on concentric tracks or tracks. In order to avoid confusion, unified rules are applied. It means that the principles of hard drives on the basis of their logical structure are universal. So, for example, the size of one sector, accepted for a single standard all over the world, is 512 bytes. In turn, sectors are divided into clusters, which are sequences of a number of sectors. And features of the principle of hard disk in this respect are that the exchange of information is just made by whole clusters (an integer number of sectors chains).
But how do you read the information? The principles of operation of the hard disk drive are as follows: using a special bracket, the reading head in the radial (helical) direction moves to the desired track and when positioned, it is positioned above the given sector, all the heads can move simultaneously, reading the same information not only from different tracks , but also from different disks (plates). All tracks with the same ordinal numbers are called cylinders.
One more principle of hard disk operation can be distinguished: the closer the reading head to the magnetic surface (but does not touch it), the higher the recording density.
How is the information recorded and read?
Hard disks, or hard drives, therefore were called magnetic, that they use the laws of physics of magnetism, formulated yet Faraday and Maxwell.
As already mentioned, the plates ofnon-magnetically sensitive material, a magnetic coating is applied, the thickness of which is only a few micrometers. In the process of work, a magnetic field arises that has a so-called domain structure.
The magnetic domain is strictlybounded by the boundaries of the magnetized region of the ferroalloy. Further, the operation principle of a hard disk can be briefly described as follows: when an external magnetic field occurs, the proper field of the disk begins to orient strictly along the magnetic lines, and upon termination of the action on the disks, remanent magnetization zones appear in which information that was previously contained in the ground field .
For creating an external field when writing,reading head, while reading the zone of residual magnetization, being opposite the head, creates an electromotive force or EMF. Further everything is simple: the change in EMF corresponds to one in the binary code, and its absence or termination is zero. The time for changing the EMF is usually called a bit element.
In addition, the magnetic surface is pure fromConsiderations of informatics can be associated, as a certain bit sequence of bits of information. But, since the location of such points can not be accurately calculated, it is necessary to install some pre-defined marks on the disk, which helped to determine the desired location. Creating such labels is called formatting (roughly speaking, splitting the disk into tracks and sectors clustered into clusters).
Logical structure and operating principle of the hard disk in terms of formatting
As for the logical organization of HDD, here onthe first place is formatting, in which two basic types are distinguished: low-level (physical) and high-level (logical). Without these steps, there is no need to talk about bringing a hard drive into the working state. About how to initialize a new hard drive, will be discussed separately.
Low-level formatting assumesphysical impact on the surface of the HDD, at which sectors are created along the tracks. Curiously, the principle of the hard disk is that each created sector has its own unique address, which includes the sector number, the track number on which it is located, and the side number of the plate. Thus, in the organization of direct access, the same RAM is accessed directly from the given address, and does not search for the necessary information on the entire surface, due to which the speed is achieved (although this is not the most important thing). Note that when performing low-level formatting, absolutely all information is erased, and in most cases it is not subject to recovery.
Another thing - logical formatting (inWindows systems are quick format or Quick format). In addition, these processes are also applicable to the creation of logical partitions, representing a certain area of the main hard disk, operating on the same principles.
Logical formatting, first of all,affects the system area, which consists of the boot sector and partition tables (boot record Boot record), file allocation tables (FAT, NTFS, etc.) and the Root Directory (Root Directory).
The recording of information in sectors is done throughcluster in several parts, and in the same cluster can not contain two identical objects (file). Actually, the creation of a logical partition, as it were, separates it from the main system partition, so that the information stored on it, when errors and failures occur, is not subject to change or removal.
Main characteristics of HDD
I think, in general terms, the principle of hard workdisk is a little understandable. Now let's pass to the basic characteristics, which give a complete picture of all the possibilities (or disadvantages) of modern hard drives.
The principle of hard disk and basiccharacteristics can be completely different. In order to understand what is at issue, let us single out the most basic parameters that characterize all the known information storage devices:
- capacity (volume);
- speed (data access speed, reading and writing information);
- interface (connection method, controller type).
Capacity is the total quantityinformation that can be written and saved on the hard drive. The industry for HDD production is developing so quickly that today the hard disk drives with volumes of about 2 TB and higher have already come into use. And, it is believed, this is not the limit.
The interface is the most significant characteristic. It determines how the device connects to the motherboard, which controller it uses, how it reads and writes, etc. The main and most common interfaces are IDE, SATA and SCSI.
Disks with an IDE interface are not very highcost, but among the main disadvantages can be allocated a limited number of simultaneously connected devices (maximum four) and a low data transfer rate (even with direct access to Ultra DMA memory or Ultra ATA protocols (Mode 2 and Mode 4). , their use makes it possible to increase the read / write speed to 16 Mb / s, but in reality the speed is much lower.In addition, to use UDMA mode, you need to install a special driver, which, in theory, should be bundled with the m terinskoy board.
Speaking of what the principle ishard drive performance and performance, you can not ignore the SATA interface, which is the heir of the IDE version of the ATA. The advantage of this technology is that the read / write speed can be increased to 100 Mb / s due to the use of the high-speed Fireware IEEE-1394 bus.
Finally, the SCSI interface compared to the twothe previous ones are the most flexible and fastest (the writing / reading speed reaches 160 Mb / s and higher). But even these hard drives are almost twice as expensive. But the number of simultaneously connected storage devices is from seven to fifteen, the connection can be made without de-energizing the computer, and the cable length can be about 15-30 meters. Actually, this type of HDD is mostly used not in user PCs, but on servers.
Speed, characterizing the transmission rateand I / O bandwidth, is usually expressed by the transmission time and the amount of transmitted sequentially transmitted data and is expressed in Mb / s.
Some additional parameters
Speaking of what the principle iswork hard disk and what parameters affect its operation, you can not ignore and some additional characteristics, which can depend on the speed or even the life of the device.
Here in the first place is the speedrotation, which directly affects the time of search and initialization (recognition) of the desired sector. This is the so-called latent search time - the interval during which the required sector rotates to the reading head. Today, several standards are adopted for the spindle rotation speed, expressed in revolutions per minute with a delay time in milliseconds:
- 3600 - 8.33;
- 4500 - 6.67;
- 7200 - 4.17.
It is easy to see that the higher the speed, the less time is spent searching for sectors, and in physical terms - on the turn of the disk before installing the head for the desired positioning point of the plate.
Another parameter is the internal transfer rate. On external tracks it is minimal, but increases with a gradual transition to internal tracks. Thus, the same defragmentation process, which is the movement of frequently used data to the fastest areas of the disk, is nothing more than transferring them to the inner track with a faster reading speed. The external speed has fixed values and directly depends on the interface used.
Finally, one of the importantThe presence of a hard disk of its own cache memory or buffer. In fact, the principle of the hard disk in terms of using the buffer in something similar to the operating or virtual memory. The larger the cache (128-256 KB), the faster the hard disk will work.
Main requirements for HDD
The basic requirements, which in most cases are presented to hard drives, is not so much. The main thing is a long service life and reliability.
The main standard for most HDDs is thethe service life of the order of 5-7 years with the operating time not less than five hundred thousand hours, but for high-end hard drives this figure is not less than one million hours.
As for reliability, the functionself-test S.M.A.R.T., which monitors the status of individual elements of the hard disk, performing continuous monitoring. On the basis of the collected data, even a forecast of the appearance of possible malfunctions in the future can be formed.
It goes without saying that the user does notmust remain aloof. For example, when working with HDD it is extremely important to observe the optimal temperature regime (0 - 50 ± 10 degrees Celsius), avoid shaking, punching and falling of the hard drive, dust or other small particles getting into it, etc. Incidentally, many will It is interesting to know that the same particles of tobacco smoke are approximately twice as long as the distance between the reading head and the magnetic surface of the hard drive, and the human hair is 5-10 times.
Initialization issues in the system when replacing the hard drive
Now a few words about what you need to do if for some reason the user changed the hard drive or installed a secondary one.
We will not completely describe this process, butwe will dwell only on the main stages. First, the hard drive must be connected and viewed in the BIOS settings, if new hardware is detected, initialize it in the disk administration section and create a boot record, create a simple volume, assign it an identifier (letter), and format with the choice of the file system. Only after this, the new "screw" will be fully ready for work.
That, in fact, and everything that briefly concernsfundamentals of functioning and characteristics of modern hard drives. The principle of operation of an external hard disk was not considered here in principle, since it practically does not differ from what is used for stationary HDDs. The only difference is only in the method of connecting an additional drive to a computer or laptop. The most common connection is via a USB interface, which is directly connected to the motherboard. In this case, if you want to ensure maximum performance, it is better to use the USB 3.0 standard (the port inside is painted in blue), of course, provided that the external HDD itself supports it.
In the rest, it seems, to many at least a littleit became clear how the hard disk of any type functions. Perhaps, too much technical information has been given above, especially from the school course of physics, nevertheless, without it, one can not understand all the basic principles and methods laid down in the technologies of production and use of HDDs without understanding it.