How does hdd work? How a portable hard drive works using the example of WD Elements Ultra

Page 1 of 6

A brief description of the principles of operation of hard drives.

How does a hard drive work?

As a rule, all users are interested in one question: is the disk “fast”? The answer to this is ambiguous and requires a story about the following characteristics:

• Disk rotation speed
• Positioning delay
• Data access time
• Hard drive cache
• Placing data on disk
• Exchange speed between processor and disk
• Interface (IDE or SCSI)

Let us first describe how a hard drive is physically designed. A hard drive stores data on the magnetic surface of the disk. Information is recorded and recorded using magnetic heads (everything is almost like in a tape recorder). Inside hard drive Several plates (disks) can be installed, colloquially referred to as “pancakes”. The motor that rotates the disk turns on when power is applied to the disk and remains turned on until the power is removed. NOTE: If the Power Management section of the Setup program from the BIOS is set to turn off the hard drive when not accessed, the engine may be turned off BIOS program. The motor rotates at a constant speed, measured in revolutions per minute (rpm). Data is organized on a disk in cylinders, tracks, and sectors. Cylinders are concentric tracks on disks, located one above the other. The track is then divided into sectors. The disk has a magnetic layer on each side. Each pair of heads is mounted, as it were, on a “fork” that clasps each disk. This “fork” moves above the surface of the disk using a separate servo motor (and not a stepper, as is often mistakenly thought - stepper motor does not allow you to move quickly above the surface). All hard disks has spare sectors that are used by its management circuit if bad sectors are detected on the disk.

Disk rotation speed

Typically, modern hard drives have rotation speeds from 5400 to 7200 rpm. The higher the rotation speed, the higher the data exchange speed. It should only be taken into account that as the rotation speed increases, the temperature of the hard drive case increases and disks with a speed of 7200 rpm require either the use of a case with a well-designed design for heat dissipation purposes, or additional cooling with an external fan of the disk itself. The power supply fan is not enough for this. Even higher-speed disks with a rotation speed of 10,000 rpm, which are now produced by all manufacturers without exception, require both good ventilation inside the case and a “correct” case that dissipates heat well. Hard drives at 15,000 rpm without forced airflow are simply not recommended for use.

Number of sectors per track

Modern hard drives have different numbers of sectors per track depending on whether it is an external track or an internal one. The outer track is longer and can accommodate more sectors than the shorter inner track. Data on the blank disk also begins to be written from the external track.

Search time/head switching time/cylinder switching time

The seek time is minimal only if it is necessary to operate on a track that is adjacent to the one above which this moment the head is located. The longest search time is correspondingly when moving from the first track to the last. As a rule, the hard drive data sheet indicates the average seek time. All of the disk's magnetic heads are located above the same cylinder at any given time, and the switching time is determined by how quickly the heads switch between reads or writes. Cylinder switching time is the time required to move the heads one cylinder forward or backward. All times are indicated in the hard drive documentation in milliseconds (ms).

Positioning delay

Once the head is over the desired track, it waits for the required sector to appear on that track. This time is called positioning latency and is also measured in milliseconds (ms). The average positioning delay time is calculated as the time the disk rotates 180 degrees and therefore depends only on the rotation speed of the disk spindle. Specific data on the delay value are summarized in the table.

Data access time

Data access time is essentially a combination of search time, head switching time and positioning delay, also measured in milliseconds (ms). Search time, as you already know, is only an indicator of how quickly the head gets over the desired cylinder. Until data is written or read, time should be added for switching heads and waiting for the required sector.

Hard drive cache

As a rule, all modern hard drives have their own RAM, called cache memory or simply cache. Hard drive manufacturers often refer to this memory as buffer memory. The size and structure of the cache differ significantly among manufacturers and for different models of hard drives. Typically, cache memory is used for both writing and reading data, but on SCSI drives it is sometimes necessary to force write caching to be enabled, so disk write caching is usually disabled by default for SCSI. There are programs that allow you to determine how cache memory parameters are set, for example ASPIID from Seagate. As strange as it may seem to many, the size of the cache is not decisive for assessing the effectiveness of its operation. Organizing data exchange with the cache is more important to improve the performance of the disk as a whole. Some hard drive manufacturers, such as Quantum, use part of the cache for their software (for the Quantum Fireball 1.3 Gb model, for example, 48 Kb out of 128 are occupied by firmware). It seems to us that the method used by Western Digital is more preferable. To store firmware, specially designated sectors on the disk are used, invisible to any operating systems. When the power is turned on, this program is loaded into ordinary cheap DRAM on the disk and at the same time there is no need for a flash memory chip for storing firmware. This method makes it easy to fix the hard drive's firmware, which Western Digital often does.

Placing data on disk

Everyone has known since the beginning of the PC era that the disk configuration is determined by the number of cylinders, heads and sectors on a track. Although a few years ago it was mandatory to specify all these disk parameters in the SETUP program, this is no longer the case. Strictly speaking, the disk parameters that you see in the SETUP Standard CMOS Setup section, as a rule, have nothing in common with the real disk parameters, and you may notice that these parameters change depending on the type of translation of the disk geometry - Normal, LBA And Large. Normal- the geometry is in accordance with the manufacturer's documentation for the disk and does not allow DOS to see more than 504 Mb (1 Mb - 1048576 bytes). LBA- Logical Block Address - this setting allows you to see DOS disks up to 4 Gb. Large used by an operating system such as Unix. The parameters set in SETUP are converted into real ones by the control logic hard drive. Many modern operating systems work with the disk through LBA, bypassing the BIOS.

Many users are interested hard device disk. And for good reason, because today the most common storage device on a computer is the HDD. Next, the principles of its operation and structure will be discussed.

A Winchester is essentially like a record player. It also contains the platters and read heads. However, the HDD device is more complex. If we disassemble the hard drive, we will see that the plates are mostly metal and covered with a magnetic layer. This is where data is written. Depending on the volume of the hard drive, there are from 4 to 9 plates. They are mounted on a shaft, which is called a “spindle” and has a high rotation speed from 3600 to 10000 rpm for consumer products.

Next to the wafer block there is a read head block. The number of heads is determined by the number of magnetic disks, namely one for each disk surface. Unlike a hard disk player, the head does not touch the surface of the platters, but hovers above it. This eliminates mechanical wear. Since the plates have a high rotation speed, and the heads must be at an extremely small constant distance above them, it is very important that nothing can get into the housing. After all, the slightest speck of dust can cause physical damage. That is why the mechanical part is hermetically sealed with a casing, and the electronic part is taken outside.

Some users are interested in how to disassemble a hard drive. You need to understand that disassembling a working drive involves breaking its seal. And this, in turn, will render it unusable. Therefore, you should not do this unless you are ready to lose all the data on the storage medium. If you don’t have a pressing need to open the drive, but are just curious about what a hard drive is made of, you can look at a photo of a disassembled HDD.

This is why hard drives are magnetic disks during repairs, they are disassembled and assembled in a special laminar flow hood. Using a highly purified air supply system and tightness, it maintains the environment necessary for such work. By disassembling your disk at home, you will definitely render it inoperable.

When inoperative, the read heads are located next to the wafer block. This is also called “parking position”. A special device brings the heads into the working area only when the disk has accelerated to the required speed. They all move together, not each one separately. This allows you to have quick access to all data.

The electronic board, or controller, is usually attached to the bottom of the hard drive. Nothing protects it, and this makes it quite vulnerable to mechanical and thermal damage. It is she who controls the mechanics. The laptop hard drive differs from the standard 3.5-inch only in size. Principle work hard the disk is exactly the same. They can differ only in the number of magnetic pancakes and storage capacity.

As you can see, the hard drive device is subject to shock, shock, scratches, significant temperature changes and power surges. And this makes it not a completely reliable information carrier. It is because of this that the hard drive on a laptop fails more often than on a desktop PC. After all portable devices They are constantly shaken, sometimes dropped, taken out into the cold or placed in the sun. And this, in turn, negatively affects the hard drive.

To extend the life of the HDD, do not expose it to drops or shocks, make sure that there is sufficient ventilation of the case, and perform any manipulations with the disk only when the power is turned off. These shortcomings have led to the emergence of a new type of SSD hard drive. They are gradually replacing HDDs, which once looked like great storage media.

Logical device

We found out what a hard drive looks like inside. Now we will analyze its logical structuring. Data is written to the computer's hard drive on tracks that are divided into specific sectors. The size of each sector is 512 bytes. Consecutive sectors are combined into a cluster.

When installing a new HDD, you need to format it, otherwise the computer simply will not see the free space on the drive. Formatting can be physical or logical. The first involves dividing the disk into sectors. Some of them may be defined as “bad”, that is, unsuitable for recording data. In most cases, the drive is already formatted in this way before being sold.

Logical formatting involves creating a logical hard section disk. This allows you to significantly simplify and optimize your work with information. A specific area of ​​the drive is allocated for a logical partition (or, as it is also called, a “logical disk”). You can work with it as with a separate hard drive. To understand how a hard drive works with its partitions, it is enough to visually divide the hard drive into 2-4 parts, depending on the number of logical volumes. Each volume can have its own formatting system: FAT32, NTFS or exFAT.

Technical data

HDDs differ from each other according to the following data:

• volume;
• spindle rotation speed;
• interface.

Today, the average hard drive capacity is 500-1000 GB. It determines the amount of information that you can write to the media. The spindle speed will determine how quickly you can access data, that is, read and write information. The most common interface is SATA, which replaced the already obsolete and slow IDE. They differ from each other in bandwidth and type of connector connected to the motherboard. Note that the disk of a modern laptop can only have SATA interface or SATA2.

This article examined how a hard drive works, its operating principles, technical data and logical structure.

Hard drive(Hard Disk Drive, HDD) of a computer is the storage location, which is the main information (various data, attached programs, operating system). The necessary information will be read by the processor from the hard drive at the right time, then processed, and then the final result of the processed information should be written to the hard drive.

In 1957, IBM developed the very first hard drive, and it was developed even before the creation of personal computer. You would have to pay a tidy sum for it, although its volume was only 5 MB. Then a 10 MB hard drive was developed specifically for the IBM PC XT personal computer. The Winchester had a total of 30 tracks and another 30 sectors in each track. “Winchesters” - this is how hard drives began to be called, if abbreviated as “screws”, this came from an analogy with the marking of the Winchester carbine - “30/30”, which was multi-charged.

So, what is the design of a hard drive? The basis of the hard drive is a block of metal disks that are coated with a special substance that can perfectly support the storage of exposure to a magnetic field (for example, iron oxide). Nowadays, hard drives should contain from one to three such disks. Hard drives must have excellent balancing and a really flat surface, because when rotating, the speed can be quite high (7200 or 10000 rpm is standard speeds), but the heads must have high positioning accuracy.

Magnetic heads are specially used for recording any information on a disk (most often located on both sides of the disk, and two for each disk), which are capable of forming a magnetic field under the influence of current pulses. Such a magnetic head tries to magnetize a section of the disk with a moment that is magnetic, of a certain direction (logical “one” or logical “zero”, but this depends on the direction of the moment, which is magnetic). The magnetization process must occur by applying a current pulse to right moment time, while the magnetic head must be positioned in a certain place.

Magnetoresistive heads are specifically used for reading information from a disk; they can respond to changes in the magnetic field by using a current that is excited in the head. Such an analog signal must be read, converted to digital form, and then sent to computer system.

With the help of tracks, information on disks can be placed as circles that are concentric. During operation, the magnetic heads must move from one track to another. In the hard drives that we use nowadays, to move the magnetic heads, they use drive, which is solenoid. The heads move around their axis; the figure below should show their movement diagram. The coil, which is attached to the back of the heads, must be attracted in one direction or the other using an electromagnet. Due to the fact that hard drive disks can rotate, the head, when moving in one direction or another, must have access to almost any point on the disk. The heads, which were already counted after the power was turned off, begin to move away from the disk surface, then begin to park. The heads must not fall onto the disk surface!

Read the link for how the recording works.

Cylinder

As circles, which are concentric, the information on the disk continues to be stored. All heads must move at the same time because the head block is one piece. Only one side of one disk can be serviced by each head. All heads must be over the same track at any given time, but over different disks. It all adds up cylinder in a vertical plane.

Sectors

The maximum possible storage capacity hard information The size of a disk is determined by the product of three components: the number of heads, the number of sectors and the number of cylinders.

From a technological point of view, it is easiest to start making hard drives with fewer disks, but at the same time you need a higher density of tracks on one disk.

Logical and physical placement

This nuance should also be noted. Namely logical placement and physical placement sectors, cylinders, heads.

We have already touched on placement, which is physical, earlier. However, logically (after all, this is how the computer “sees” them), the Setup program should enter these parameters a little differently (most often they should be indicated on the hard drive cover), and it is with the logical partition of the hard drive that the computer subsequently operates. Translation of disk parameters is a special procedure that allows you to coordinate the logical and physical placement of disk parameters. The translation unit must reside on the hard drive itself and then convert logical coordinates to physical ones. At the same time, it must provide access to the heads to the desired area of ​​the physical disk.

Problems during hard drive manufacturing

During the manufacture of hard drives, it may not be possible to avoid a sufficient percentage of sectors that are defective, as well as tracks (the main thing is that the hard drive has the required volume). At low level formatting, when disk space is divided into logical cylinders, heads, sectors, such defective areas are marked and are not taken into account in the further operation of this hard drive.

Instructions

The hard drive design consists of a block of metal disks with a special coating that can remember and store the effects of a magnetic field. Modern designs consist of 1-3 disks that are perfectly balanced and have a perfectly flat surface, because the rotation speed is quite high and reaches from 7200 to 10000 rpm, and the positioning accuracy of the heads must be high.

Special magnetic heads are used to write and read information on the disk. Most often, two per disk - on both sides. When exposed to current pulses, the heads form a magnetic field and magnetize a section of the disk with a magnetic moment of a given direction (logical “one” or logical “zero”). The recording process is carried out by applying a current pulse at the required time, the magnetic head is positioned in the right place. When reading information from a disk, the heads react to changes in the magnetic field by exciting the current in them. This type of analog signal is read and converted to digital. In this form it is transferred to the computer system.

Information on a magnetic disk is placed and stored on tracks in the form of concentrated circles. All magnetic heads of the hard drive form one common block. Moves from one disc track to another at the same time. One head serves one side of the disk. That is, the heads are on the same track above different disks at any given time. Thus, this set of tracks forms a cylinder. Recently, a solenoid drive has been used to move the magnetic heads. They move around their axis. A coil attached to the back of the head moves them above the surface of the disk using an electromagnet. The heads are not allowed to touch the disk; when disconnected from the power supply, they are moved away from the surface to the side.

Each disk track is divided into sectors - the smallest elements disk space with a storage capacity of 512 bytes. The total memory capacity of a hard drive can be determined by the product of the number of heads, cylinders and sectors. It is also worth considering that during the manufacture of disks, defective sectors and tracks are formed. This process cannot be avoided. These areas are not taken into account during operation. The main thing is that the disk itself has the required total volume.

The logical placement of heads, cylinders and sectors is usually different from the physical one and is indicated on the hard drive cover. The parameters are saved to the hard drive by the Setup program, and then the computer operates with a logical breakdown. To coordinate the physical and logical values ​​of the device, a special procedure is used - translation of disk parameters. This block is located on the hard drive itself and converts logical corridors into physical ones, thereby providing access to the desired part of the physical disk.

A hard magnetic disk drive (HDD) \ HDD (Hard Disk Drive) \ hard drive (media) is a material object capable of storing information.

Information storage devices can be classified according to the following criteria:

• method of storing information: magnetoelectric, optical, magneto-optical;
• type of storage medium: drives on floppy and hard magnetic disks, optical and magneto-optical disks, magnetic tape, solid-state memory elements;
• the method of organizing access to information - direct, sequential and block access drives;
• type of information storage device - embedded (internal), external, stand-alone, mobile (wearable), etc.

A significant part of the information storage devices currently in use is based on magnetic media.

Hard drive device

The hard drive contains a set of plates, most often representing metal disks coated magnetic material– platter (gamma ferrite oxide, barium ferrite, chromium oxide...) and interconnected by a spindle (shaft, axis).
The discs themselves (approximately 2 mm thick) are made of aluminum, brass, ceramics or glass. (see pic)

Both surfaces of the discs are used for recording. Used 4-9 plates. The shaft rotates at a high constant speed (3600-7200 rpm)
Rotation of disks and radical movement of heads is carried out using 2 electric motors.
Data is written or read using write/read heads one for each surface of the disk. The number of heads is equal to the number of working surfaces of all disks.

Information is written to the disk in strictly defined places - concentric tracks (tracks) . The tracks are divided into sectors. One sector contains 512 bytes of information.

Data exchange between RAM and NMD is carried out sequentially by an integer (cluster). Cluster- chains of consecutive sectors (1,2,3,4,...)

Special engine using a bracket, positions the read/write head above a given track (moves it in the radial direction).
When the disk is rotated, the head is located above the desired sector. Obviously, all heads move simultaneously and read information; data heads move simultaneously and read information from identical tracks on different drives.

Hard drive tracks with the same serial number on different hard drive drives are called cylinder .
The read-write heads move along the surface of the platter. The closer the head is to the surface of the disk without touching it, the higher the permissible recording density.

Hard drive device

Magnetic principle of reading and writing information

Magnetic information recording principle

The physical foundations of the processes of recording and reproducing information on magnetic media are laid in the works of physicists M. Faraday (1791 - 1867) and D. C. Maxwell (1831 - 1879).

In magnetic storage media digital recording produced on magnetically sensitive material. Such materials include some varieties of iron oxides, nickel, cobalt and its compounds, alloys, as well as magnetoplasts and magnetoelastas with viscous plastics and rubber, micropowder magnetic materials.

The magnetic coating is several micrometers thick. The coating is applied to a non-magnetic base, which is made from plastics for magnetic tapes and floppy disks, and aluminum alloys and aluminum alloys for hard disks. composite materials substrates. The magnetic coating of the disk has a domain structure, i.e. consists of many magnetized tiny particles.

Magnetic domain (from Latin dominium - possession) is a microscopic, uniformly magnetized region in ferromagnetic samples, separated from neighboring regions by thin transition layers (domain boundaries).

Under the influence of an external magnetic field, the domains' own magnetic fields are oriented in accordance with the direction of the magnetic field lines. After the influence of the external field ceases, zones of residual magnetization are formed on the surface of the domain. Thanks to this property, information is stored on a magnetic medium in the presence of a magnetic field.

When recording information, an external magnetic field is created using a magnetic head. In the process of reading information, the zones of residual magnetization, located opposite the magnetic head, induce an electromotive force (EMF) in it during reading.

The scheme for writing and reading from a magnetic disk is shown in Fig. 3.1 A change in the direction of the EMF over a certain period of time is identified with a binary unit, and the absence of this change is identified with zero. The specified period of time is called bit element.

Surface magnetic media is considered as a sequence of dot positions, each of which is associated with a bit of information. Since the location of these positions is not precisely determined, recording requires pre-applied marks to help locate the required recording positions. To apply such synchronization marks, the disk must be divided into tracks
and sectors - formatting

Organization quick access to information on disk is an important stage of data storage. Quick access to any part of the disk surface is ensured, firstly, by giving it rapid rotation and, secondly, by moving the magnetic read/write head along the radius of the disk.
A floppy disk rotates at a speed of 300-360 rpm, and a hard disk rotates at 3600-7200 rpm.

Hard drive logical device

The magnetic disk is not initially ready for use. To bring him to working condition he must be formatted, i.e. the disk structure must be created.

The structure (layout) of the disk is created during the formatting process.

Formatting magnetic disks includes 2 stages:

1. physical formatting (low level)
2. logical (high level).

When physically formatting, the working surface of the disk is divided into separate areas called sectors, which are located along concentric circles - paths.

In addition, sectors that are unsuitable for recording data are determined and marked as bad in order to avoid their use. Each sector is the smallest unit of data on a disk and has its own address to allow direct access to it. The sector address includes the disc side number, track number, and sector number on the track. The physical parameters of the disk are set.

As a rule, the user does not need to deal with physical formatting, since in most cases hard drives arrive formatted. Generally speaking, this should be handled by a specialized service center.

Low Level Formatting must be done in the following cases:

• if there is a failure in track zero, causing problems when booting from a hard disk, but the disk itself is accessible when booting from a floppy disk;
• if you return to working condition old disk, for example, rearranged from a broken computer.
• if the disk is formatted to work with another operating system;
• if the disk has stopped working normally and all recovery methods have not yielded positive results.

Please keep in mind that physical formatting is a very powerful operation— when it is executed, the data stored on the disk will be completely erased and it will be completely impossible to restore it! Therefore, do not proceed with low-level formatting unless you are confident that you have stored all important data off the hard drive!

After you perform low-level formatting, the next step is to create a partition of the hard drive into one or more logical drives — the best way cope with the confusion of directories and files scattered across the disk.

Without adding any hardware elements to your system, you get the opportunity to work with several parts of one hard drive, like multiple drives.
This does not increase the disk capacity, but its organization can be significantly improved. In addition, various logical drives can be used for various operating systems.

At logical formatting The media is finally prepared for data storage through the logical organization of disk space.
The disk is prepared to write files to sectors created by low-level formatting.
After creating the disk partition table, the next stage follows - the logical formatting of individual parts of the partition, hereinafter referred to as logical disks.

Logical drive - This is some area of ​​​​the hard drive that works in the same way as a separate drive.

Logical formatting is a much simpler process than low-level formatting.
To run it, boot from the floppy disk containing the FORMAT utility.
If you have several logical drives, format them all one by one.

During the logical formatting process, the disk is allocated system area, which consists of 3 parts:

• boot sector and partition table (Boot record)
• File Allocation Tables (FAT), in which the numbers of tracks and sectors storing files are recorded
• root directory (Root Directory).

Information is recorded in parts through the cluster. There cannot be 2 different files in the same cluster.
In addition, on at this stage the disk can be given a name.

A hard drive can be divided into several logical drives and, conversely, 2 hard drives can be combined into one logical drive.

It is recommended to create at least two partitions (two logical drives) on your hard drive: one of them is allocated for the operating system and software, the second drive is exclusively allocated for user data. Thus the data and system files are stored separately from each other and in the event of an operating system failure there is a much greater likelihood of saving user data.

Characteristics of hard drives

Hard drives (hard drives) differ from each other in the following characteristics:

1. capacity
2. performance – data access time, speed of reading and writing information.
3. interface (connection method) - the type of controller to which the hard drive should be connected (most often IDE/EIDE and various SCSI options).
4. other features

1. Capacity— the amount of information that fits on the disk (determined by the level of manufacturing technology).
Today the capacity is 500 -2000 or more GB. You can never have enough hard drive space.

2. Speed ​​of operation (performance) disk is characterized by two indicators: disk access time And disk read/write speed.

Access time – the time required to move (position) the read/write heads to the desired track and the desired sector.
The average typical access time between two randomly selected tracks is approximately 8-12ms (milliseconds), faster disks have a time of 5-7ms.
The transition time to the adjacent track (adjacent cylinder) is less than 0.5 - 1.5 ms. It also takes time to turn to the desired sector.
The total disk rotation time for today's hard drives is 8 - 16ms, the average sector waiting time is 3-8ms.
The shorter the access time, the faster the disk will operate.

Read/write speed (throughput input/output) or data transfer rate (transfer)– the transfer time of sequential data depends not only on the disk, but also on its controller, bus types, and processor speed. The speed of slow disks is 1.5-3 MB/s, for fast ones 4-5 MB/s, for the latest ones 20 MB/s.
Hard drives with SCSI interface support a rotation speed of 10,000 rpm. and average search time 5ms, data transfer speed 40-80 Mb/s.

3.Hard drive interface standard - i.e. the type of controller to which the hard drive should be connected. It is located on the motherboard.
There are three main connection interfaces

1. IDE and its various variants

IDE (Integrated Disk Electronic) or (ATA) Advance Technology Attachment
Advantages: simplicity and low cost

Transfer speed: 8.3, 16.7, 33.3, 66.6, 100 Mb/s. As data develops, the interface supports expanding the list of devices: hard drive, super floppy, magneto-optics,
NML, CD-ROM, CD-R, DVD-ROM, LS-120, ZIP.

Some elements of parallelization (gneuing and disconnect/reconnect) and monitoring the integrity of data during transmission are introduced. The main disadvantage of the IDE is the small number of connected devices (no more than 4), which is clearly not enough for a high-end PC.
Today, IDE interfaces have switched to new Ultra ATA exchange protocols. Significantly increasing your throughput
Mode 4 and DMA (Direct Memory Access) Mode 2 allows data transfer at a speed of 16.6 MB / s, but the actual data transfer speed would be much lower.
Standards Ultra DMA/33 and Ultra DMA/66, developed in February 1998. by Quantum have 3 operating modes 0,1,2 and 4, respectively, in the second mode the carrier supports
transfer speed 33Mb/s. (Ultra DMA/33 Mode 2) To ensure such a high speed can only be achieved when exchanging with the drive buffer. In order to take advantage
Ultra DMA standards require that 2 conditions be met:

1. hardware support on the motherboard (chipset) and on the drive itself.

2. to support Ultra DMA mode, like other DMA (direct memory Access).

Required special driver for different chipsets are different. As a rule, they are included in the kit motherboard, if necessary, you can “download” it
from the Internet from the manufacturer's page motherboard.

The Ultra DMA standard is backward compatible with previous controllers operating in a slower version.
Today's version: Ultra DMA/100 (late 2000) and Ultra DMA/133 (2001).

SATA
Replacement IDE (ATA) not other High Speed ​​Serial Bus Fireware (IEEE-1394). Application new technology will allow you to increase the transfer speed to 100Mb/s,
The reliability of the system increases, this will allow you to install devices without turning on the PC, which is strictly prohibited in the ATA interface.

SCSI (Small Computer System Interface)— devices are 2 times more expensive than conventional ones, they require special controller on the motherboard.
Used for servers, publishing systems, CAD. Provide higher performance (speed up to 160Mb/s), a wide range of connected storage devices.
The SCSI controller must be purchased together with the corresponding disk.

SCSI has an advantage over IDE - flexibility and performance.
Flexibility lies in the large number of connected devices (7-15), and for IDE (4 maximum), a longer cable length.
Performance - high speed transfers and the ability to simultaneously process multiple transactions.

1. Ultra Sсsi 2/3 (Fast-20) up to 40 Mb/s 16-bit version Ultra2 - SCSI standard up to 80 Mb/s

2. Another SCSI interface technology called Fiber Channel Arbitrated Loop (FC-AL) allows you to connect up to 100 Mbps, with a cable length of up to 30 meters. FC-AL technology allows for “hot” connections, i.e. on the go, has additional lines for monitoring and error correction (the technology is more expensive than regular SCSI).

4. Other features of modern hard drives

The huge variety of hard drive models makes it difficult to choose the right one.
In addition to the required capacity, performance is also very important, which is determined mainly by its physical characteristics.
Such characteristics are the average search time, rotation speed, internal and external transfer speed, and cache memory size.

4.1 Average search time.

The hard drive takes some time to move the magnetic head from its current position to the new one required to read the next piece of information.
In each specific situation, this time is different, depending on the distance the head must move. Typically, specifications provide only averaged values, and the averaging algorithms used by different companies generally differ, so direct comparison is difficult.

So, from Fujitsu, Western Digital are carried out along all possible pairs of tracks; Maxtor and Quantum companies use the random access method. The resulting result can be further adjusted.

The search time for writing is often slightly higher than for reading. Some manufacturers provide only the lower value (for reading) in their specifications. In any case, in addition to the average values, it is useful to take into account the maximum (across the entire disk),
and minimum (i.e., track-to-track) search time.

4.2 Rotation speed

From the point of view of the speed of access to the desired fragment of the recording, the rotation speed affects the amount of the so-called latent time, which is required for the disk to rotate to the magnetic head with the desired sector.

The average value of this time corresponds to half a disk revolution and is 8.33 ms at 3600 rpm, 6.67 ms at 4500 rpm, 5.56 ms at 5400 rpm, 4.17 ms at 7200 rpm.

The value of latent time is comparable to average seek time, so in some modes it can have the same, if not greater, impact on performance.

4.3 Internal baud rate

— the speed at which data is written to or read from the disk. Due to zone recording, it has a variable value - higher on the outer tracks and lower on the inner ones.
When working with long files, in many cases this parameter limits the transfer speed.

4.4 External baud rate

— speed (peak) with which data is transmitted through the interface.

It depends on the interface type and most often has fixed values: 8.3; 11.1; 16.7Mb/s for Enhanced IDE (PIO Mode2, 3, 4); 33.3 66.6 100 for Ultra DMA; 5, 10, 20, 40, 80, 160 Mb/s for synchronous SCSI, Fast SCSI-2, FastWide SCSI-2 Ultra SCSI (16 bits), respectively.

4.5 Whether the hard drive has its own Cache memory and its volume (disk buffer).

The size and organization of cache memory (internal buffer) can significantly affect the performance of the hard drive. Same as for regular cache memory,
Once a certain volume is reached, productivity growth slows down sharply.

Large-capacity segmented cache memory is relevant for high-performance SCSI drives used in multitasking environments. The larger the cache, the faster the hard drive works (128-256Kb).

The influence of each parameter on overall performance is quite difficult to isolate.

Hard drive requirements

The main requirement for disks is reliability of operation, guaranteed by a long component life of 5-7 years; good statistical indicators, namely:

• mean time between failures of at least 500 thousand hours ( upper class 1 million hours or more.)
• built-in active monitoring system for the state of disk nodes SMART/Self Monitoring Analysis and Report Technology.

Technology S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) is an open industrial standard, developed at one time by Compaq, IBM and a number of others manufacturers of hard disks.

The meaning of this technology is the internal self-diagnosis of the hard drive, which allows you to assess its current condition and inform you about possible future problems that could lead to data loss or failure of the drive.

The condition of all vital disk elements is constantly monitored:
heads, working surfaces, electric motor with spindle, electronics unit. For example, if a signal weakening is detected, the information is rewritten and further observation occurs.
If the signal weakens again, the data is transferred to another location, and the given cluster is placed as defective and unavailable, and another cluster from the disk reserve is made available instead.

When working with a hard drive, you must comply with the temperature conditions in which the drive operates. Manufacturers guarantee trouble-free operation of the hard drive at ambient temperatures ranging from 0C to 50C, although, in principle, without serious consequences you can change the boundaries by at least 10 degrees in both directions.
For large temperature deviations air gap the required thickness may not be formed, which will lead to damage to the magnetic layer.

In general, HDD manufacturers pay quite a lot of attention to the reliability of their products.

The main problem is foreign particles getting inside the disk.

For comparison: a particle of tobacco smoke is twice the distance between the surface and the head, the thickness of a human hair is 5-10 times greater.
For the head, a meeting with such objects will result in a strong blow and, as a result, partial damage or complete failure.
Outwardly it is noticeable as the appearance large quantity regularly located unsuitable clusters.

Short-term, large accelerations (overloads) that occur during impacts, falls, etc. are dangerous. For example, from an impact the head sharply hits the magnetic
layer and causes its destruction in the corresponding place. Or, conversely, it first moves in the opposite direction, and then, under the influence of elastic force, it hits the surface like a spring.
As a result, particles of magnetic coating appear in the housing, which again can damage the head.

You should not think that under the influence of centrifugal force they will fly away from the disk - the magnetic layer
will firmly attract them to you. In principle, the terrible consequences are not the impact itself (you can somehow come to terms with the loss of a certain number of clusters), but the fact that particles are formed that will certainly cause further damage to the disk.

To prevent such very unpleasant cases, various companies resort to all sorts of tricks. In addition to simply increasing the mechanical strength of the disk components, intelligent S.M.A.R.T. technology is also used, which monitors the reliability of recording and the safety of data on the media (see above).

In fact, the disk is always not formatted to its full capacity; there is some reserve. This is mainly due to the fact that it is almost impossible to produce a carrier
on which absolutely the entire surface would be of high quality, there will definitely be bad clusters (failures). When a disk is low-level formatted, its electronics are configured so that
so that it bypasses these faulty areas, and it is completely invisible to the user that the media has a defect. But if they are visible (for example, after formatting
the utility displays their number other than zero), then this is already very bad.

If the warranty has not expired (and, in my opinion, it is best to buy a HDD with a warranty), then immediately take the disk to the seller and demand a replacement of the media or a refund.
The seller, of course, will immediately begin to say that a couple of faulty areas are not a reason for concern, but do not believe him. As already mentioned, this couple will most likely cause many more, and subsequently the complete failure of the hard drive is possible.

A disk in working condition is especially sensitive to damage, so you should not place the computer in a place where it may be subject to various shocks, vibrations, and so on.

Preparing the hard drive for work

Let's start from the very beginning. Let's assume that you bought a hard disk drive and a cable for it separately from the computer.
(The fact is that when buying assembled computer, you will receive a disk ready for use).

A few words about handling it. A hard disk drive is a very complex product that contains, in addition to electronics, precision mechanics.
Therefore, it requires careful handling - shocks, falls and strong vibration can damage its mechanical part. As a rule, the drive board contains many small-sized elements and is not covered with durable covers. For this reason, care should be taken to ensure its safety.
The first thing you should do when you receive a hard drive is to read the documentation that came with it - it will probably contain a lot of useful information. interesting information. In this case, you should pay attention to the following points:

• the presence and options for installing jumpers that determine the settings (installation) of the disk, for example, determining such a parameter as the physical name of the disk (they may be present, but they may not be present),
• number of heads, cylinders, sectors on disks, precompensation level, and disk type. You must enter this information when prompted by the computer setup program.
  All this information will be needed when formatting the disk and preparing the machine to work with it.
• If the PC itself does not detect the parameters of your hard drive, the bigger problem will be installing a drive for which there is no documentation.
  On most hard drives you can find labels with the name of the manufacturer, the type (brand) of the device, as well as a table of tracks that are not allowed for use.
  In addition, the drive can contain information about the number of heads, cylinders and sectors and the level of precompensation.

To be fair, it must be said that often only its title is written on the disc. But even in this case, you can find the required information either in the reference book,
or by calling the company's representative office. It is important to get answers to three questions:

• How should the jumpers be set in order to use the drive as master\slave?
• How many cylinders and heads are there on the disk, how many sectors per track, what is the precompensation value?
• Which type of disk from those recorded in the ROM BIOS best matches this drive?

With this information in hand, you can proceed to installing the hard drive.

For installing hard disk into your computer, do the following:

1. Disable completely system unit from the power supply, remove the cover.
2. Connect the hard drive cable to the motherboard controller. If you are installing a second disk, you can use the cable from the first one if it has an additional connector, but you need to remember that the operating speed of different hard drives will be compared to the slower side.
3. If necessary, change the jumpers according to the way you use the hard drive.
4. Install the drive in a free space and connect the cable from the controller on the board to the hard drive connector with the red stripe to the power supply, power supply cable.
5. Securely secure the hard drive with four bolts on both sides, arrange the cables inside the computer in order so that when closing the cover you do not cut them,
6. Close the system unit.
7. If the PC itself does not detect the hard drive, then change the computer configuration using Setup so that the computer knows that a new device has been added to it.

Hard drive manufacturers

Hard drives of the same capacity (but from different manufacturers) usually have more or less similar characteristics, and the differences are expressed mainly in the case design, form factor (in other words, dimensions) and warranty period. Moreover, special mention should be made about the latter: the cost of information on a modern hard drive is often many times higher than its own price.

If your disk has problems, trying to repair it often only means exposing your data to additional risk.
A much more reasonable way is to replace the faulty device with a new one.
The lion's share of hard drives on the Russian (and not only) market is made up of products from IBM, Maxtor, Fujitsu, Western Digital (WD), Seagate, Quantum.

name of the manufacturer producing this type storage,

Corporation Quantum (www. quantum. com.), founded in 1980, is one of the veterans in the disk drive market. The company is known for its innovative technical solutions aimed at improving the reliability and performance of hard drives, data access time on the disk and read/write speed on the disk, and the ability to inform about possible future problems that could lead to data loss or disk failure.

— One of Quantum’s proprietary technologies is SPS (Shock Protection System), designed to protect the disk from shock.

- built-in DPS (Data Protection System) program, designed to preserve the most valuable thing - the data stored on them.

Corporation Western Digital (www.wdс.com.) Also one of the oldest disk drive manufacturing companies, it has seen its ups and downs in its history.
The company has recently been able to introduce the latest technologies into its disks. Among them, it is worth noting our own development - Data Lifeguard technology, which is a further development of the S.M.A.R.T. system. It attempts to logically complete the chain.

According to this technology, the disk surface is regularly scanned during periods when it is not used by the system. This reads the data and checks its integrity. If problems are noted while accessing a sector, the data is transferred to another sector.
Information about bad sectors is entered into an internal defect list, which avoids future entries into bad sectors in the future.

Firm Seagate (www.seagate.com) very famous in our market. By the way, I recommend hard drives from this particular company as they are very reliable and durable.

In 1998, she brought attention to herself again by releasing a series of Medallist Pro discs
with a rotation speed of 7200 rpm, using special bearings for this. Previously, this speed was used only in SCSI interface drives, which made it possible to increase performance. The same series uses SeaShield System technology, designed to improve the protection of the disk and the data stored on it from the influence of electrostatics and shock. At the same time, the impact of electromagnetic radiation is also reduced.

All manufactured discs support S.M.A.R.T technology.
In new Seagate drives envisages the use of an improved version of its SeaShield system with greater capabilities.
It is significant that Seagate announced the highest shock resistance of the updated series in the industry - 300G when not in use.

Firm IBM (www. storage. ibm. com) Although it was not a major supplier on the Russian hard drive market until recently, it managed to quickly gain a good reputation thanks to its fast and reliable disk drives.

Firm Fujitsu (www.fujitsu.com) is a large and experienced manufacturer of disk drives, not only magnetic, but also optical and magneto-optical.
True, the company is by no means a leader in the market of hard drives with an IDE interface: it controls (according to various studies) approximately 4% of this market, and its main interests lie in the field of SCSI devices.

Terminological dictionary

Since some drive elements that play an important role in its operation are often thought of as abstract concepts, the most important terms are explained below.

Access time— The period of time required for a hard disk drive to search for and transfer data to or from memory.
The performance of hard disk drives is often determined by access (fetch) time.

Cluster- the smallest unit of space that the OS works with in the file location table. Typically a cluster consists of 2-4-8 or more sectors.
The number of sectors depends on the type of disk. Searching for clusters instead of individual sectors reduces OS time costs. Large clusters provide faster performance
drive, since the number of clusters in this case is smaller, but the space (space) on the disk is used worse, since many files may be smaller than the cluster and the remaining bytes of the cluster are not used.

Controller (Сontroller)- circuitry, usually located on an expansion card, that controls the operation of the hard disk drive, including moving the head and reading and writing data.

Cylinder- tracks located opposite each other on all sides of all disks.

Drive head- a mechanism that moves along the surface of the hard drive and provides electromagnetic recording or reading of data.

File Allocation Table (FAT)- a record generated by the OS that tracks the placement of each file on the disk and which sectors are used and which are free for writing new data to them.

Head gap— the distance between the drive head and the disk surface.

Interleave— the relationship between the disk rotation speed and the organization of sectors on the disk. Typically, the rotation speed of the disk exceeds the computer's ability to receive data from the disk. By the time the controller reads the data, the next sequential sector has already passed the head. Therefore, data is written to the disk through one or two sectors. Using a special software When formatting a disk, you can change the striping order.

Logical drive- certain parts of the working surface of the hard drive, which are considered as separate drives.
Some logical drives can be used for other operating systems, such as UNIX.

Parking- moving the drive heads to a specific point and fixing them stationary above unused parts of the disk, in order to minimize damage when the drive is shaken when the heads hit the surface of the disk.

Partitioning– operation of dividing a hard disk into logical drives. All disks are partitioned, although small disks may only have one partition.

Disk (Platter)- the metal disk itself, coated with magnetic material, on which data is recorded. A hard drive usually has more than one disk.

RLL (Run-length-limited)- an encoding scheme used by some controllers to increase the number of sectors per track to accommodate more data.

Sector- A disk track division that represents the basic unit of size used by the drive. OS sectors typically contain 512 bytes.

Positioning time (Seek time)- the time required for the head to move from the track on which it is installed to some other desired track.

Track- concentric division of the disk. The tracks are similar to the tracks on a record. Unlike the tracks on a record, which are a continuous spiral, the tracks on a disc are circular. The tracks are in turn divided into clusters and sectors.

Track-to-track seek time— the time required for the drive head to move to the adjacent track.

Transfer rate- the amount of information transferred between the disk and the computer per unit of time. It also includes the time it takes to search for a track.