What is a Computer Hard Drive
Surely everyone heard the words hard drive, hard drive, or screw, but it may not be clear to a novice user what relation they have to the computer . Fill this gap in knowledge and deal with the purpose, device and basic characteristics of the computer's hard drive.
A hard disk is used for long-term storage of information in a computer, that is, all your music, films, photos, documents, as well as installed programs and files of the operating system itself are stored on it. The computer's hard drive can be compared to a notebook where a student writes lectures and other information that he will need in the future. As long as there are blank pages in the notebook, they can be used to record new data or, if necessary, change already recorded data using the "putty".
The key word here is for long-term storage of information, since only information that is required in the future and at any time is recorded in it. If the data is needed for a short time, then the person will simply remember it or write it on a sticker to throw it away immediately as soon as they become unnecessary.
The same principle is used to store information in a computer. The hard drive has a non-volatile memory, and turning off the power does not affect their safety. This is a fundamental difference from the random access memory of a computer. Details of the interaction of various components of a computer system can be found here .
Hard drive device
The correct name of this device sounds like - a hard disk drive or hard (magnetic) disk drive in English. The following options are also widespread: Winchester, screw, hard, HDD, HDD, HMDD. Why it is called a Winchester there are many versions, but the most common version is that the first hard drive in the modern sense of the word developed by IBM had the internal abbreviation "30-30", which coincided with the popular Winchester Model 1894 hunting rifle using the .30-30cartridge Winchester . The name "screw" is its abbreviation in computer slang.
We will not describe in detail the principles of magnetic recording and the HDD device, as ordinary users do not need it, but consider the main points of the hard drive and its characteristics. Technically, it is a device for recording and storing information based on the principle of magnetic recording. Information is recorded on round hard drives (plates or pancakes) coated with a layer of ferromagnetic material and located on the same axis of the drive. Reading and writing data is carried out using movable read heads. The principle resembles a turntable on vinyl records, but in a hard drive the reading heads do not touch the surface of the plates, unlike the needle of the turntable. In the working position, they soar above the surface of the plates at a height of several nanometers due to the flow of incoming air from the rapid rotation of the plates.
The presence of moving mechanical parts somewhat reduces the reliability of the device, however, the lack of direct mechanical contact between the moving parts compensates for this drawback and ensures the reliability and long service life of the hard drives. However, sometimes damaged areas may still appear on the disk for various reasons. In addition to the plates, the drive and the read heads, the control electronics is located in the same housing as them.
It is worth noting that solid-state drive (SSD) technology is actively developing. It is also used for long-term storage of information in a computer, but they use memory chips and no moving parts. In addition, there are hybrid hard drives that combine a single hard drive and a small cache SSD in one device.
The moving head consists of two parts: a read head and a write head. Depending on the operation necessary at the given moment of time, the necessary head is used. The number of plates in the hard disk case can be different and depends on its capacity and the recording technologies used. A smaller number of plates reduces power consumption, reduces the number of moving parts, improves the temperature regime of the drive, which positively affects its reliability and durability. True, this is all in theory, but in practice, each particular instance is individual and it is wrong to say that a drive with four plates is worse than with two.
So that information can be recorded on the plates, their surface is divided into tracks - concentric annular regions. All tracks on all HDD plates located at the same distance from the center are called a cylinder. In turn, the tracks are divided into equal segments called sectors. A cluster is formed from the union of neighboring sectors into a group. The figure below shows a simplified diagram of the structure of a plate of a computer hard drive.
The Figures indicate:
1 - geometric sector
2 - sector of track
3 - track
4 - cluster
A cluster is a minimal logical cell for storing information on a computer's hard drive. Currently, a cluster of 4,096 bytes , consisting of eight sectors of 512 bytes each, is standard . You can learn more about the effect of its size on the HDD parameters in the article on the file system in the Windows operating system.
Methods of magnetic data recording to disk
In a nutshell, the principle of recording information is as follows. The hard drive plates rotate at high speed (usually 5,400 or 7,200 rpm for personal computers), and the heads hover above them. When an alternating electric current is applied to the head, an alternating magnetic field arises which changes the direction of the magnetization vector of the domains under the head at the given moment depending on the signal size. In other words, the plates are filled with logical zeros and onesor recording process. Reading data from the surface of the plates occurs in the reverse order, the movement of the magnetized domains under the read head leads to the appearance of an alternating electrical signal in the coil of the head under the influence of electromagnetic induction. Since the physical dimensions of the plates are limited and standardized, increasing the capacity of hard drives is possible in two directions: increasing the number of plates in one device or increasing the amount of recorded information on one plate (recording density).
Longitudinal recording method
The traditional recording method used in magnetic disk drives. The domain magnetization vector is parallel to the plate surface. The increase in the capacity of hard drives led to the fact that it no longer allowed to provide the necessary capacity of the drives. Currently practically not used.
Perpendicular recording method
This method has replaced the traditional method. Due to the vertical orientation of the domains, the recording density has increased significantly and therefore more information can be recorded on one plate.
Technologies do not stand still and research is underway to further increase the recording density on the plate, for example, the method of thermal magnetic recording or the method of self-assembly of polymers.
Key Features of Hard Drives
Form factor - determines the width of the hard drive in inches. The drives have standardized sizes of 0.85, 1, 1.3, 1.8, 2.5, 3.5 inches. Standard for desktops is 3.5 inches and 2.5 for laptops.
Interface - provides the interaction of the hard disk with the computer motherboard. Disks intended for installation inside personal computers use the SATA interface of different versions. The main differences in data transfer rates are: Revision 1.0 up to 1.5 Gb / s, Revision 2.0 up to 3 Gb / s (SATA / 300), Revision 3.0 up to 6 Gb / s (SATA / 600). Winchesters with PATA interface (IDE) are almost out of use and are used only with old equipment.
Capacity - the maximum amount of information that a hard disk can store is measured in gigabytes. Since manufacturers equate one kilobyte with one thousand bytes (actually 1 KB = 1,024 bytes) , then a 500 GB labeled hard drive has a real capacity of 465.7 GB.
Spindle Speed - The number of spindle revolutions per minute. It has standard speeds, usually 5,400 or 7,200 rpm on desktop computers , and 4,500 or 5,400 rpm on laptops . Server hard drives typically have a rotation speed of 10,000 or 15,000 rpm . The higher the rotation speed, the shorter the access time to information.
Buffer volume - a special high-performance memory built into the hard drive that serves to speed up the drive and smooth out the difference in read / write and transfer speeds.
Random access time - determines the average amount of time required for the head to position on an arbitrary section of the plate. Variable value depending on the initial and final position of the head and the positioning position. The lower this indicator, the faster the disk is able to give the requested information.
MTBF is the average uptime calculated by the manufacturer. It is an analogue of the reliability parameter and, accordingly, the larger it is, the better.
Impact resistance - the ability of a hard drive to easily tolerate impacts and a sharp change in pressure. It is measured in units of permissible overload, separately for on and off state. The greater the impact resistance, the better. More relevant for laptops and portable hard drives.
Noise level - noise produced by the hard drive during operation is measured in decibels. Includes noise of rotating plates, aerodynamic and noise of moving heads.
Several computers can be installed on one computer. The total number is limited by the availability of space in the computer case and the number of connectors for connecting to the motherboard. There is also the possibility of combining several drives into a single disk array to increase the speed and reliability of information storage.
We examined the main points of the device and the operation of the hard disk in the computer. Now, even if you are a teapot, you know what to look for when buying a new hard drive.
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