Hard disk or HDD This is a device that allows you to store information for a long time and which is non-volatile. In simple words, an iron box where all your documents, movies, operating system and everything else are located. If we draw a life analogy, then this is something like a big album. Taking a pencil in hand, you can draw or write essays. If you don't like something, you can always take the "eraser". The bottom line is that while the album is on the shelf, all the data remains intact.
There are two important aspects in this case. The first is long-term storage. The second is energy independence. If in the first case everything should be clear from the album example, then for the second case I will give some explanations. The bottom line is that the hard drive does not require power to store information, unlike RAM. So you can turn off your computer from the network and know that the data will be safe.
Note: There is a common version of where the slang names of this box came from. Today, a hard drive is often referred to as a hard drive or, for short, a screw. It came from the fact that the first such device had a code similar to Winchester rifle cartridges. It is hard to say how true this is, but the version is considered the most real.
Let's take a closer look at this box.
If you notice, then I have already mentioned the abbreviation HDD several times and for a reason. The fact is that the technical name of this box is a hard disk drive or hard (magnetic) disk drive.
But, back to the hard drive device. This box is based on the technology of magnetic recording of information. And here's how it works. There are round hard drives (they are also often called pancakes) covered with a ferromagnetic material (it can change its magnetic properties). There is a special moving head (consists of two parts), which, in fact, reads and writes data (part of the head for reading, part for writing).
The process itself is as follows. The disk is constantly spinning at a fairly high speed, and the head walks along the disk and either reads data or writes at the right time. It is important to note that the head does not touch the disk, otherwise the disk coating could be damaged. When the disk is turned off, the head is in a special zone (parking), again to protect the ferromagnetic coating from damage.
It is worth knowing that the internal mechanism is designed in such a way that, purely physically, it would be very difficult to damage the surface of the data disk. However, over time, parts of the ferromagnetic surface may become unusable. Here, as in the well-known expression - "Nothing lasts forever."
It is also worth knowing that there may be several such plates inside the hard drive box. As you may have guessed, the number of pancakes affects the amount of information stored. But, it is not limited to this. For example, a long time ago, disks were 1.5 times larger than today's, and 20-40MB were placed on them.
Figure 1 Simplified Diagram of a Round Hard Drive
Note: In the figure, the numbers indicate: 1 - geometric sector, 2 - track sector, 3 - track, 4 - cluster.
Consider, in a little more detail, the very surface of the pancakes. So that the storage and recording of information can be structured, the entire surface is divided into special tracks. Then the entire disk is divided into geometric sectors (equal to each other). The part of the track that is inside this geometric object is called the track sector or simply sectors. The combination of several sectors is called a cluster.
Since the disks spin at a fairly high speed (for example, 7200 rpm), it is the cluster that is used as the minimum storage unit. Typically, a cluster is represented by a size of 4 KB and consists of 8 sectors of 512 bytes. By the way, this is why the actual size of a text file consisting of only one character will be 4 KB, since, in principle, the size is divided precisely into clusters.
Note: It is worth knowing that there are methods that allow you to store data of several files in one cluster, but usually the division goes exactly by clusters.
Note: I also advise you to read the article Solid state hard drive or SSD drive, as this is the next round of data storage devices.
Hard drive specifications
If with a hard drive device, I hope it became clear to you, then for the sake of completeness, it remains to consider the issue of the main characteristics of the HDD.
1. Form Factor. The words are terrible, but in fact they mean only the physical size of the disk. For desktop computers, it is usually 3.5 inches, for laptops it is less, only 2.5 inches.
2. Capacity. This is essentially the size of how much data a hard drive can store. Today, disks are measured in gigabytes and terabytes.
3. Spindle speed. This is exactly the same speed with which pancakes are spinning. Usually it is 5400 for laptops and 7200 for regular computers. There are other speeds, but they are simply not needed for home use.
4. Noise level. Here, probably, you can guess what is at stake. There are very loud hard drives, usually the simplest ones, and there are also quieter ones.
5. Shock resistance or in the common people survivability. In fact, it indicates what kind of overloads the hard drive can endure without damaging data. However, I strongly advise you not to check this characteristic.
6. Access interface. The interface defines the connectors that are used to connect drives to the computer. Previously, almost all HDDs for home computers were IDE, but today we are mainly talking about SATA. In the case of external drives, usually USB. It is worth knowing that in reality the connector of the disk itself is not USB, just an adapter with a controller is used inside the box.
HDD is a data storage device - a hard disk drive. "HDD" is an abbreviation for the English phrase Hard Disk Drive. Other names for HDD: hard drive, hard drive, hard drive, screw, hard, tin, tin.
What is HDD for?
HDD is used to store information. Information stored on a hard drive is called data. The data on the disk is organized by means of a file system and is represented by files.
HDD is computer memory. Do not confuse with RAM. The hard drive is non-volatile memory, RAM is volatile.
Winchester is now the main storage device, and if you have a computer, then there is a screw.
Working principle of HDD
Hard drives, that is, HDDs, work in a similar way to a device that everyone has long forgotten about - a "player", with a rotating disk and a needle for playing music. The converting elements (read/write heads) used in hard drives are similar to the read/write heads used in VCRs and stereo cassette recorders to access information on magnetic media.
In hard drives, information is stored on a rotating metal or glass plate covered with a magnetic material. As a rule, a disk consists of several plates connected by a common rod - a spindle. Each plate is something like a vinyl record with a record played by a turntable. Information is usually stored on both sides of the plate.
As the disk spins, an element called the head reads or writes binary data to the magnetic media. Information is written to the disk using some encoding method, of which there are a great many. The encoding method and recording density is determined by the disk controller.
Without delving further into the description of the principle of operation of the HDD, we can say that the hard drive is, in fact, a super-player with a bunch (or maybe just one) of records inside. Although, of course, due to the complexity of the device, the player did not lie next to it.
The past and future of HDD
The very first HDD was developed by IBM in the early 70s.
In 1983, with the release of the first IBM PC / XT computer, a hard drive from Seagate Technology appeared in the lives of thousands of newly minted, yet wild users. The early hard drive interface, designed by Alan Shugart (founder of Seagate Technology), was the de facto standard for HDDs for many years. In the future, Seagate's developments formed the basis of the ESDI and IDE interfaces. Shugart also developed the SCSI interface, which is now used in many modern computers.
By the way, now Seagate hard drives are the best-selling in Europe. And in Russia, who does not know the famous Barracudas?
The most important direction in the development of hard disk technology has always been an increase in their (drives) capacity. Progress in this area is especially driven by the ever-increasing demands of software. Increasing the capacity of drives is possible either by increasing the size of the drives themselves or by increasing the density of data storage. The HDD size limit has been reached, but the storage density limit has not yet been reached. But it didn't last long.
Need to know
1. HDD is a complex thing for storing information
2. The hard drive is short-lived and with constant use is unlikely to live more than three years
3. It is extremely undesirable to carry a hard drive (somewhere), turn it in your hands and generally remove it from the computer case. Winchester is very sensitive to vibration!
4. The internal structure of HDD is very complex. If you once went to a circle of young radio amateurs, this does not mean at all that you can now repair hard drives. Repairing hard drives requires more than just a soldering iron!
5. Fans of poking around in hardware need to remember that by opening the HDA of a disk, you thereby put an end to both the information and the hard drive itself
6. In terms of storage security, storage media can be arranged in the following order (with increasing risk of data loss): head, paper, hard drive. Do not store important information on the HDD! And if you have to - always make backups!
7. If the information on the hard drive is not available for any reason, do not try to restore it! Most likely, you will only finally destroy it - it is better to contact professionals. Restoring information is not for you!
8. The word "HDD" is abusive and is not used in polite society, it characterizes something (to put it mildly) unreliable, short-lived and disgusting
During computer startup, a set of firmware stored in the BIOS chip checks the hardware. If everything is in order, it transfers control to the operating system loader. Then the OS loads and you start using the computer. At the same time, where was the operating system stored before turning on the computer? How did your essay that you wrote all night stay intact after turning off the power of the PC? Again, where is it kept?
Okay, maybe I've gone too far and you all know very well that computer data is stored on a hard drive. Nevertheless, not everyone knows what it is and how it works, and since you are here, we conclude that we would like to know. Well, let's find out!
By tradition, let's look at the definition of a hard drive on Wikipedia:
HDD (screw, hard drive, hard disk drive, HDD, HDD, HMDD) is a random access storage device based on the principle of magnetic recording.
They are used in the vast majority of computers, as well as separately connected devices for storing backup copies of data, as file storage, etc.
Let's figure it out a little. I like the term hard disk drive ". These five words convey the whole point. HDD is a device whose purpose is to store data recorded on it for a long time. HDDs are based on hard (aluminum) disks with a special coating, on which information is recorded using special heads.
I will not consider in detail the recording process itself - in fact, this is the physics of the last grades of the school, and I am sure you have no desire to delve into this, and the article is not about that at all.
Also note the phrase: random access ” which, roughly speaking, means that we (computer) can read information from any section of the railway at any time.
It is important that the HDD memory is not volatile, that is, it does not matter whether the power is connected or not, the information recorded on the device will not disappear anywhere. This is an important difference between a computer's permanent memory and temporary ().
Looking at a computer hard drive in real life, you will not see any disks or heads, since all this is hidden in a sealed enclosure (hermetic zone). Externally, the hard drive looks like this:
Why does a computer need a hard drive?
Consider what an HDD is in a computer, that is, what role it plays in a PC. It is clear that it stores data, but how and what. Here we highlight the following functions of HDD:
- Storage of OS, user software and their settings;
- Storage of user files: music, video, images, documents, etc.;
- Using part of the hard disk space to store data that does not fit in RAM (paging file) or storing the contents of RAM while using sleep mode;
As you can see, a computer hard drive is not just a dump of photos, music and videos. It stores the entire operating system, and in addition, the hard drive helps to cope with the workload of RAM, taking on some of its functions.
What is a hard drive made of?
We partially mentioned the components of the hard drive, now we will deal with this in more detail. So, the main components of the HDD:
- Frame Protects hard drive mechanisms from dust and moisture. As a rule, it is airtight so that the same moisture and dust do not get inside;
- Disks (pancakes) - plates made of a certain metal alloy, coated on both sides, on which data is recorded. The number of plates can be different - from one (in budget options) to several;
- Engine - on the spindle of which pancakes are fixed;
- Head block - a design of interconnected levers (rocker arms), and heads. The part of a hard drive that reads and writes information to it. For one pancake, a pair of heads is used, since both the upper and lower parts of it are working;
- Positioning device (actuator ) - a mechanism that drives the block of heads. Consists of a pair of permanent neodymium magnets and a coil located at the end of the head unit;
- Controller - an electronic microcircuit that controls the operation of the HDD;
- parking zone - a place inside the hard drive next to the disks or on their inside, where the heads are lowered (parked) during downtime, so as not to damage the working surface of the pancakes.
Such a simple hard drive device. It was formed many years ago, and no fundamental changes have been made to it for a long time. And we move on.
How a hard drive works
After power is supplied to the HDD, the engine, on the spindle of which the pancakes are fixed, begins to spin up. Having gained a speed at which a constant stream of air is formed near the surface of the discs, the heads begin to move.
This sequence (first the disks spin up, and then the heads start working) is necessary so that the heads hover over the plates due to the resulting air flow. Yes, they never touch the surface of the disks, otherwise the latter would be instantly damaged. However, the distance from the surface of the magnetic platters to the heads is so small (~10 nm) that you cannot see it with the naked eye.
After starting, first of all, service information about the state of the hard disk and other necessary information about it, located on the so-called zero track, is read. Only then does the work with the data begin.
Information on the computer's hard drive is recorded on tracks, which, in turn, are divided into sectors (such a pizza cut into pieces). To write files, several sectors are combined into a cluster, which is the smallest place where a file can be written.
In addition to such a "horizontal" partitioning of the disk, there is also a conditional "vertical" one. Since all heads are combined, they are always positioned over the same track number, each over its own disc. Thus, during the operation of the HDD, the heads, as it were, draw a cylinder:
While the HDD is working, in fact, it performs two commands: reading and writing. When it is necessary to execute a write command, the area on the disk where it will be performed is calculated, then the heads are positioned and, in fact, the command is executed. The result is then checked. In addition to writing data directly to disk, information also ends up in its cache.
If the controller receives a read command, first of all, it checks for the presence of the required information in the cache. If it is not there, the coordinates for positioning the heads are calculated again, then the heads are positioned and read the data.
After the work is completed, when the power supply to the hard drive disappears, the heads are automatically parked in the parking zone.
This is how a computer hard drive works in general terms. In reality, everything is much more complicated, but the average user, most likely, does not need such details, so we will finish this section and move on.
Types of hard drives and their manufacturers
Today, there are actually three main manufacturers of hard drives on the market: Western Digital (WD), Toshiba, Seagate. They fully cover the demand for devices of all types and requirements. The rest of the companies either went bankrupt, or were taken over by someone from the main three, or re-profiled.
If we talk about the types of HDD, they can be divided in this way:
- For laptops, the main parameter is the device size of 2.5 inches. This allows them to be compactly placed in the laptop case;
- For PC - in this case, it is also possible to use 2.5 ″ hard drives, but as a rule, 3.5 inches are used;
- External hard drives are devices that are separately connected to a PC / laptop, most often acting as file storage.
There is also a special type of hard drives - for servers. They are identical to conventional PCs, but may differ in interfaces for connection, and greater performance.
All other divisions of HDD into types come from their characteristics, so we will consider them.
Hard drive specifications
So, the main characteristics of a computer hard drive:
- Volume - an indicator of the maximum possible amount of data that can be accommodated on the disk. The first thing they usually look at when choosing an HDD. This figure can reach 10 TB, although 500 GB - 1 TB is more often chosen for a home PC;
- Form Factor - the size of the hard drive. The most common are 3.5 and 2.5 inches. As mentioned above, 2.5″ in most cases are installed in laptops. They are also used in external HDDs. 3.5″ is installed on the PC and on the server. The form factor also affects the volume, as more data can fit on a larger disk;
- Spindle speed - How fast do pancakes rotate? The most common are 4200, 5400, 7200 and 10000 rpm. This characteristic directly affects the performance, as well as the price of the device. The higher the speed, the greater both values;
- Interface - method (connector type) of connecting the HDD to the computer. The most popular interface for internal hard drives today is SATA (older computers used IDE). External hard drives are usually connected via USB or FireWire. In addition to those listed, there are other interfaces such as SCSI, SAS;
- Buffer volume (cache memory) - a type of fast memory (by type of RAM) installed on the HDD controller, designed for temporary storage of data that is most often accessed. The buffer size can be 16, 32 or 64 MB;
- Random access time - the time during which the HDD is guaranteed to write or read from any part of the disk. It fluctuates from 3 to 15 ms;
In addition to the above characteristics, you can also find indicators such as.
A hard drive, hard drive or just a screw, hard disk, hdd (Hard Disk Drive) - this storage device has several names, it is the main storage device for storing information in all modern computers, laptops and servers. It is on this device that all your photos, videos, music, movies are recorded, and the operating system of the computer itself is recorded on it. Now SSD drives and hybrid SSHD drives are becoming more common, we will talk about them and their pros and cons in a separate article.
What are the disks?
In the store today you can find hard drives of different parameters, how do they differ? Let's try to understand the main differences with you and highlight several characteristics of drives.
Form factor (size)
The parameter shows the width of the hard drive in inches. The main widths of 3.5 inches and 2.5 inches are used in modern computers and laptops, as well as in external portable and stationary drives and network storages.
For a stationary home computer, the standard size is 3.5 inches, in modern cases there are 2.5-inch drive bays, they are mainly designed to install an SSD drive, put in a computer instead of a 3.5-inch drive, 2.5-inch drives don’t make much sense , only in very compact cases, such as micro-ATX.
In laptops, on the contrary, space saving is very relevant and 2.5-inch form-facts are used for them. There are smaller drives - 1.8 inches, 1.3 inches, 0.8 inches, but in modern devices you will not find them anymore.
Capacity (Why is the capacity of the drive smaller than advertised?)
A parameter that directly affects how much information we can record and store on our computer or laptop. Manufacturers indicate the capacity at the rate of 1 kilobyte = 1000 bytes, and computers calculate differently 1 KB = 1024 bytes, hence the confusion arises for users who encounter this for the first time and the larger the volume, the greater the difference in the final volume. Now the volume of disks is measured in terabytes, which is more than enough to store a collection of not only photos, but also music with films.
Interface
You will find drives with a SATA connector in all modern devices today. The only difference is the data transfer rate.
SATA hard drive connector ATA aka PATA (IDE)
Drives with this interface are no longer manufactured or installed in modern devices, but you can find them in older computers. Initially, the interface was called ATA, but after the appearance of a more modern and high-speed SATA in 2003, it was renamed PATA.
PATA (ATA) aka IDE The name IDE was coined by WD (Western Digital) in 1986 for marketing reasons when it developed the first version of this connectivity standard.
SCSI and SAS
SAS drives are used in server hardware. Replaced the SCSI interface. The average user should know only that they are designed for completely different tasks and are not used in home PCs.
SCSI Spindle speed
The number of revolutions of the spindle (the axis on which the plate or several plates rotate inside the disk). There are several standards, in home computers and laptops drives with a rotation speed of 5400, 7200 and 10000 rpm are used, on server equipment there are rotation speeds of 15000 rpm. The parameter affects the time of access to information.
There are a few more parameters such as noise level, MTBF, etc. in modern drives, these parameters correspond to standard criteria and do not differ significantly, we will pay attention to them when we compare and select hard drives.
External drives (portable or desktop)
These are disks already familiar to us, enclosed in an external plastic or metal box, in which a control board or even a whole mini-PC is installed on the board. At the output of such drives there are various outputs, the main connectors are mini-USB, micro-USB, micro-USB 3.0, fireware and others, portable models are powered by a USB connector. Stationary have a separate power cable. Modern models of external drives can work over a wireless wi-fi network. Now on sale you can find network storages with several disks in one case, which can be connected into RAID arrays. Separately, we will talk about all these devices in future articles.
Every computer has a hard drive or, as it is often called, a hard drive, which is the main place to store all the information used by the computer and its user. The hard disk stores the installed operating system, all programs used by the user, and data. The processor takes the information necessary for processing from the hard drive and then writes it back to the media. The amount of information that is stored on a hard drive depends on its size.
The very first hard drive models allowed storing up to 10 MB of data on their disks, which was a lot in those days. Now modern media allow you to store thousands and tens of thousands of megabytes. The amount of memory on modern models is calculated in gigabytes and terabytes. This makes it possible to store a huge amount of movies, music, video clips, games and other data. A significant increase in the amount of memory on the HDD is associated with the progressive development of computer technology, as a result of which movies, games and other data take up more and more free space.
Design features of hard drives
A modern hard drive consists of several metal disks on which information is recorded. Discs are covered with iron oxide or other special compound capable of storing the effects of a magnetic field. The number of disks depends on the volume of the media and usually it is in the range from 1 to 3. Metal disks are perfectly even, smooth and balanced, due to which they can rotate at high speed, according to the standard it can be 5400, 7200 or 10000 rpm.
Special heads move along the discs with the highest positioning accuracy. Each disk has 2 magnetic heads. Reading data from the surface of the disks is carried out using the installation of special magnetoresistive heads, they work depending on how the magnetic field changes on the surface of the disk. Data is transmitted to a computer as a result of receiving an analog signal that turns into a digital form.
On discs, information is stored in tracks arranged around a circle. To work with the data on the media, the magnetic heads move along the tracks. The movement of the heads is carried out thanks to the use of a special solenoid drive. Such heads can access any location on the disc due to their high rotational speed. The heads are located on both sides of the disks, so each of them performs work on one side and is completely responsible for it.
A sector on a hard drive allows you to store 512 bytes of information, and each track of a hard drive consists of many sectors. The maximum amount of information that can be stored on a hard drive depends on the number of sectors, heads and cylinders. The number of HDDs may be the same, but their memory capacities will be completely different. This is due to the fact that in order to increase the volume, it is more convenient to increase the density of sectors on each of the disks than to increase their number, which will lead to a significant increase in the size of the media. The development of computer technology leads to the fact that each PC component becomes smaller in external dimensions, and the possibilities, on the contrary, increase.
There are such concepts as physical disk placement and logical. The physical is how the storage medium is arranged inside, and the logical is how the computer sees it. In reality, the physical and the logical are completely different. If physically, for example, 3 disks can be installed inside the hard drive, then logically there can be any number and any size, one logical disk can be the size of two or more physical ones and vice versa.
In the production of hard drives, it is almost impossible to avoid damage to sectors or tracks, but they are not used and are not taken into account by the media due to the marks.
Hard drives are designed for use in home PCs, and are for use in servers. The latter are subject to much greater requirements, because they work with a significant load and must provide high performance and speed.
Hard drive characteristics
In order to choose the right hard drive suitable for certain purposes, it is necessary to understand a large number of characteristics. The first thing you should pay attention to is the form factor. 3.5-inch hard drives are installed on stationary PCs, and 2.5-inch hard drives on laptops. There are also other less common form factors. The second important parameter is the interface through which the device connects to the computer. The PC uses various variations of the SATA interface.
One of the important parameters is the capacity, which determines the amount of data stored on the device. The speed of rotation of the shaft on which the disks are located affects the speed of working with information.
When choosing a hard drive, you should pay attention to the buffer size, which directly affects the speed of the device with information.
Each hard drive makes noise during operation, like any other mechanical device. During operation, noise can cause significant inconvenience, so you need to pay attention to its level when choosing a model suitable for your PC.
If the device is planned to be frequently transferred from one computer to another, then such a parameter as shock resistance is important. The higher it is, the less likely it is to lose information upon impact or damage the hard drive.
While working with information, the disk gives the requested information at a certain speed. This indicator is called "Random Access Time" and the smaller it is, the faster the request will be transmitted.
Having an idea about all the parameters, characteristics and design of modern hard drives, you can quickly choose the right hard drive to perform the tasks on your PC.
