Impact of buffer on hard drive performance

Vladimir Leonov

Modern series of hard drives from all manufacturers can be divided into two categories, differing in the size of the internal buffer (2 or 8 MB). A review of the price lists showed that the difference in the price of disks of the same size with different buffer sizes in Moscow now ranges from $ 3 to $ 19 and depends on the manufacturer and the seller. In this article, we will try to show the effect of internal buffer size on hard drive performance.

We will compare the performance using the example of HDS722516VLAT20 and HDS722516VLAT80 hard drives from the Deskstar 7K250 family of Hitachi. To be more precise, since last year, Hitachi has been manufacturing hard drives in a new division, HGST (Hitachi Global Storage Technologies), formed as a result of the merger of its own disk production and capacities acquired from IBM. Both disks have a volume of 160 GB and are completely identical in mechanical design. The tested drives had the same firmware version - V340A60A and differed only in the size of the internal buffer (2 and 8 MB, respectively).

We compared performance under the operating system Windows XP Professional.SP1 on a computer with the following configuration:

Motherboard - MSI 875P Neo (MS-6758);

Processor - Intel Pentium 4 3.06 GHz (533 FSB);

Memory - 1 GB (2Ѕ512 MB Kingston PC2700 DDR SDRAM);

Hard drive - Hitachi Deskstar IC35L090AVV207-0.

The tested disks were connected in turn as Secondary Master.

To compare performance, we took tests that simulate the operation of the disk subsystem in real conditions and differ in the way of assessing performance:

Ziff Davis WinBench 99 v. 2.0;

Futuremark PCMark2004;

FileCopy Test v. 0.5.3 (developed by F-Center).

In the Ziff Davis WinBench 99 v. 2.0 measures the performance of the disk subsystem when running real applications. This is a good test, but, unfortunately, it is no longer supported by the developer and the versions of the applications used in the test are very outdated. In addition to performance, the test determines the average access time to the disk and a graph of the dependence of the read speed on the location of the data on the disk (Fig. 1 and 2).

As expected, the disks have the same access time (Table 1) and the graphs of the read speed versus the data location on the disk for both disks are the same. In terms of performance in all subtests ahead HDD HDS722516VLAT80, and we can say that this advantage is completely determined by the buffer operation. As you can see from the table. 1, when using file system FAT-32 buffer effects are usually more noticeable.

Futuremark's PCMark04 benchmark suite is based on real-world applications and is designed to provide detailed insights into computer performance. The package consists of several sections, one of which is designed to determine the performance of the disk subsystem. To test the disk subsystem, the so-called traces are used - sequences of disk activity recorded in advance on a certain reference computer when performing various tasks. The performance indicator is the processing speed of the trace, measured in megabytes per second. Four traces are used to reproduce the performance of the hard disk in various tasks. The purpose of the tracks is clear from their name. These are loading the operating system, opening and closing several popular applications, copying files and simulating user work. The results are shown in table. 2. As in the previous test, the HDS722516VLAT80 hard drive is ahead. The effect of the increased buffer is most pronounced on the copy operations and least of all on the load of the operating system.

FileCopy Test utility v. 0.5.3 was developed by F-Center specialists and is designed to determine the performance of a hard disk when creating (writing) files on a disk, reading files from a disk and copying files from one part of a disk to another. The results shown are the operation time and speed, measured in megabytes per second (MB / s). When creating files, pre-prepared patterns are used - lists containing information about the length and number of files to be created. The pattern can be created either manually or automatically from any folder using the Scan option, which makes it easy to create a pattern with a real distribution of files by size. We used the patterns included in the distribution kit of the program. By the name of the patterns, it is easy to guess about their content. The test results are shown in table. 3. It can be seen from the table that the degree of influence of the buffer size on the hard disk performance depends on the operation being performed and the average size of the file being processed. For example, when writing and reading large files (ISO pattern) is performed separately, the buffer size has almost no effect on performance, and when copying such files, the effect of the buffer size is most pronounced.

From the above results, you can see that increasing the buffer size gives a significant performance gain for most operations. Only when writing and reading large files, that is, in a mode when the disk actually operates in sequential read / write mode, the buffer size did not affect performance.

Perhaps, on hard drives from other manufacturers and even on tested hard drives with a different firmware version, the effect of the buffer size will be slightly different, but the difference is unlikely to be significant. In our opinion, the installation in computer hard a disk with a larger buffer is more profitable in terms of investment efficiency.

The buffer size deserves special attention. HDDs are often equipped with 8, 16, 32 and 64 MB cache. When copying large files between 8 and 16 MB, there will be a significant difference in terms of performance, but between 16 and 32 it is less noticeable. If you choose between 32 and 64, then it will hardly be there at all. It should be understood that the buffer is often subjected to heavy loads, and in this case, the larger it is, the better.

Modern hard drives use 32 or 64 MB, less today can hardly be found anywhere. For a regular user, both the first and second values ​​will suffice. Moreover, in addition to this, performance is also affected by the size of its own built-in cache. It is he who increases the performance of the hard disk, especially with a sufficient amount of RAM.

That is, in theory, the larger the volume, the better the performance and the more information can be in the buffer and not load the hard drive, but in practice everything is a little different, and the average user, except in rare cases, will not notice much difference. Of course, it is recommended to choose and buy the largest size devices, which will greatly improve the performance of your PC. However, this should be done only if financial opportunities allow.

Purpose

It is intended for reading and writing data, however, on SCSI disks, in rare cases, you need to enable write caching, since by default it is set that write caching is disabled. As we said before, volume is not a critical factor in improving performance. To increase the performance of the hard drive, it is more important to organize the exchange of information with the buffer. In addition, it is also fully influenced by the functioning of the control electronics, the prevention of errors, and so on.

The most frequently used data is stored in the buffer memory, while the volume determines the capacity of this very stored information. Due to the large size, the performance of the hard drive increases significantly, since the data is loaded directly from the cache and does not require physical reading.

Physical reading - direct system access to the hard disk and its sectors. This process is measured in milliseconds and takes quite a long amount of time. At the same time, the HDD transfers data more than 100 times faster than when requested by physical access to the hard drive. That is, it allows the device to work even if the host bus is busy.

Main advantages

Buffer memory has a number of advantages, the main one of which is fast data processing that takes a minimum amount of time, while physical access to drive sectors requires a certain amount of time until the disk head finds the required piece of data and starts reading it. Moreover, the hard drives with the largest storage can significantly unload the computer's processor. Accordingly, the processor is used minimally.

It can also be called a full-fledged accelerator, since the buffering function makes the hard drive work much more efficiently and faster. But today, in the context of the rapid development of technology, it is losing its former importance. This is due to the fact that most modern models have 32 and 64 MB, which is enough for the normal functioning of the drive. As mentioned above, you can overpay the difference only when the difference in cost corresponds to the difference in efficiency.

Finally, I would like to say that the buffer memory, whatever it is, improves the performance of this or that program or device only if there is multiple access to the same data, the size of which is no larger than the cache size. If your work at the computer is associated with programs that actively interact with small files, then you need the HDD with the largest storage.

Register memory

Not to be confused with ECC memory, although registers always use ECC.

Registered memory (RDIMM, sometimes buffered memory) is a type of computer random access memory, the modules of which contain a register between the memory chips and the system memory controller. The presence of registers reduces the electrical load on the controller and allows you to install more memory modules in one channel. Register memory is more expensive due to less production and additional chips. It is usually used in systems that require scalability and fault tolerance at the expense of low cost (for example, in servers). Although most server memory modules are registered and use ECC, there are also modules with ECC but no registers (UDIMM ECC), they are also in most cases workable in desktop systems. There are no register modules without ECC.

Due to the use of registers, there is an additional delay when working with memory. Each read and write is buffered in the register for one clock cycle before being sent from the memory bus to the DRAM chip, so register memory is considered one clock cycle slower than unregistered memory (UDIMM, unregistered DRAM). For SDRAM, this latency is significant only for the first cycle in a burst.

Only control and addressing signals are buffered in register memory.

Buffered memory is an older term for register memory.

Some newer systems use fully buffered FB-DIMMs, which buffers not only control lines but also data lines using a dedicated AMB controller located on each memory module.

The registered memory technique can be applied to different generations of memory, for example: DDR DIMM, DDR2 DIMM, DDR3 DIMM, DDR4 DIMM

How a hard drive works

The HDD is essentially a drive that stores all user files, as well as the operating system itself. Theoretically, this detail can be dispensed with, but then the OS will have to be loaded from removable media or over a network connection, and working documents stored on a remote server.

The base of the hard drive is a round aluminum or glass plate. It has a sufficient degree of rigidity, which is why the part is called a hard drive. The plate is covered with a layer of ferromagnet (usually chromium dioxide), the clusters of which memorize one or zero due to magnetization and demagnetization. There can be several such plates on one axis. A small high-speed electric motor is used for rotation.

Unlike a gramophone, in which the needle touches the plate, the read heads do not adjoin the disks close to them, leaving a distance of several nanometers. Due to the absence of mechanical contact, the service life of such a device is increased.

However, no part lasts forever: over time, the ferromagnet loses its properties, which means it leads to a loss of hard disk space, usually along with user files.

That is why, for data that is important or dear to the heart (for example, a family photo archive or the fruits of the computer owner's work), it is recommended to do backup, but rather several at once.

What is cache

Buffer memory or cache is a special type of random access memory, a kind of "layer" between the magnetic disk and the PC components that process the data stored on the hard drive. It is intended for smoother reading of information and storage of data, which at the moment is most often accessed by the user or the operating system.

What affects the size of the cache: the larger the amount of data in it, the less often the computer has to access the hard disk. Accordingly, the performance of such a workstation increases (as you already know, in terms of performance, the magnetic disk of the hard drive is significantly inferior to the RAM chip), as well as, indirectly, the life of the hard disk.

Indirectly, because different users use the hard drive in different ways: for example, a movie lover who watches them in an online cinema through a browser will theoretically have a hard drive longer than a movie fan who downloads movies with a torrent and watches them using a video player.

Guess why? That's right, because of the limited number of data rewriting cycles on the HDD.

Optimal sizes for different tasks

A natural question arises: which buffer memory is better for home computer and what does it give in practical terms? Naturally, more is desirable. However, the hard drive manufacturers themselves impose a restriction on the user: for example, a hard drive with 128 MB of buffer memory will cost significantly higher than average.

It is precisely on this amount of cache that I recommend focusing on if you want to collect gaming computer, which will not become obsolete in a couple of years. For simpler tasks, you can do with simpler characteristics: 64 MB is enough for a home media center. And for a computer that is used purely for surfing the Internet and running office applications and simple flash games, 32 MB of buffer memory is quite enough.

As a "golden mean" I can recommend the Toshiba P300 1TB 7200rpm 64MB HDWD110UZSVA 3.5 SATA III hard drive - here the cache size is average, but the capacity of the hard disk itself is quite enough for a home PC. Also, for the sake of completeness, I recommend that you familiarize yourself with the publications about the best manufacturers of hard drives and HDD ratings, as well as what connectors are on hard drives.

What does the cache do on your hard drive?

Now let's take a look at the principle work hard HDD, which, although being supplanted in compact devices by solid-state drives, will probably remain the main means of storing information for a long time to come.

So, inside it are several rotating magnetic plates. The reading heads move to the desired sector and write or read information. (Visually, this all resembles a turntable).

As you can see, the mechanisms in this device it is enough, and, despite the ultra-high speeds of their movement, accessing the HDD for the next portion of data takes a lot (by the standards of CPU speed) time. Aggravates this situation the fact that information is recorded on the surface of the discs in fragments that can be located in different places and on separate plates.

So, in order for the system not to do the rough work of putting together separate blocks of information, it was decided to get this work on the hard disk itself, which will itself link them together in its own cache. Conventionally, we can outline the following analogy of this process: the boss needed all the information on the transaction and the subordinate, so as not to carry it to the office according to a separate document, pre-collects and groups them in his department.

I will add right away that in SSDs, the problem of inertia in reading information is not so critical. Here, the speed of this process is several orders of magnitude higher. But due to the fragmentation of recording large amounts of data, optimization of work with them is also necessary. Therefore, in some SSDs, cache is also present.

Cache memory is one of the parameters of the HDD

Let's go directly to the hardware in order to find out what constitutes a hard disk cache.

In addition to mechanical parts, the HDD has a control board with connectors. A special microcircuit is located on it, which is a memory with high-speed access. This is the cache. Its volume is relatively small and in ordinary hard drives it can be 32 and 64 megabytes (in some older models there are also values ​​of 8 or 16 MB). This is enough to make the operation of the personal computer system smooth and fast.

How much is better, you ask? It seems to me that the answer is obvious, but some bloggers point out that it is almost impossible to catch a significant difference between 32 and 64 MB in the process of using the HDD. I believe that with the increase in the complexity of software tasks, it will still be noticeable.

And if you expect to get the most out of your PC, then it's worth installing the best you can afford on it. This position is also supported by the fact that server hard drives already use 128 or even 256 MB of cache. I think this fact will help you answer the question: what does the buffer size affect?

It turns out that the size of the hard drive cache matters, and this parameter should be taken into account when choosing and buying an HDD. How can I find out this figure for new and purchased devices? The easiest and most reliable way is to clarify the marking of the model and find official information on the manufacturer's website. Also, the volume of the hard drive buffer can be suggested by programs such as AIDA64.

Algorithm of the hard disk cache

Let's see how the buffer memory of the hard drive works. The main consumer of the information located on it is the processor. Then the following scheme works:

• the CPU sends a request to the controller, which identifies the data by certain labels and immediately checks for their presence in the hard disk cache. If there are any, the HDD is not accessed;
  in the absence of the necessary information, they are read from the hard drive, and nearby data are additionally captured, which with a high probability may also be needed for subsequent requests;
• for this block of information in the cache memory, a corresponding space of a certain size is released. This procedure is not an easy task, since the computer must donate some data from the buffer. The choice is carried out using several algorithms that determine the degree of "unnecessary". For this, an assessment is made by the age of the last use of information, by the frequency of access to it.
• the actual data is loaded into the free space. Then the process of interaction between the processor and the hard disk continues according to this algorithm.

And one more thing: the cache of the hard drive is volatile memory. Therefore, before turning off the PC, the system copies information from the cache directly to the HDD itself, and after turning it on, transfer it back. This does not happen in the event of an emergency shutdown of the computer.

Here we smoothly come to the frequently asked question: is it necessary to clear the hard disk cache memory? If you are talking about those 64 megabytes that are stored on the chip, then my answer is: no, this is pointless. If you feel like it so badly, just unplug the computer and plug it back in. Did it make it easier for you? Another thing is the cache files that are left on the HDD by various programs. Over time, they take up an impressive volume and to eliminate them, you can simply use an application like CCleaner.

Data caching by the hard disk's own chip is designed to provide the system with solid blocks of data, which significantly increases its performance. But in addition to a separate board, information buffering can also be done in other ways that are well known to us.

• RAM is essentially a cache in relation to the HDD. It is several orders of magnitude larger, but the speed of its work is still inferior to its own module of the hard drive.
• A sector is allocated on the hard disk for temporary files that will be written without fragmentation. This is called a paging file (virtual memory) and can be larger than the RAM.

But these are completely different devices that require a separate article. And as for the hard disk cache itself, I have nothing to add and I will say goodbye to you.

Send me your questions, suggest interesting topics, and I will try to please you again on the pages of my blog.

See you soon!

Choosing a hard drive for a PC is a very demanding task. After all, it is the main repository of both service and your personal information. In this article, we will talk about the key characteristics of the HDD, which you should pay attention to when buying a magnetic drive.

Introduction

When buying a computer, many users often focus on the characteristics of such components as a monitor, processor, video card. And such an integral component of any PC as a hard drive (in computer slang - hard drive), buyers often acquire, guided only by its volume, practically neglecting other important parameters. Nevertheless, it should be remembered that a competent approach to choosing a hard disk is one of the guarantees of comfort during further work at the computer, as well as saving financial resources, in which we are so often constrained.

A hard disk or hard disk drive (HDD, HDD) is the main storage device in most modern computers, which stores not only information necessary for the user, including movies, games, photos, music, but also the operating system, as well as everything installed programs... That is why, as a matter of fact, the choice of a hard disk for a computer should be treated with due attention. Remember that if any element of the PC fails, it can be replaced. The only negative point in this situation is additional financial costs for repairs or the purchase of a new part. But a hard disk breakdown, in addition to unforeseen costs, can lead to the loss of all your information, as well as the need to reinstall the operating system and all required programs. The main purpose of this article is to help novice PC users in choosing a hard disk model that would best meet the requirements of specific "users" for a computer.

First of all, you should be clear about which computer device the hard drive will be installed and for what purposes it is planned to use this device. Based on the most common tasks, we can conditionally divide them into several groups:

• Mobile computer for general tasks (working with documents, "surfing" the world wide web, data processing and work with programs).
• A powerful mobile computer for gaming and resource-intensive tasks.
• Desktop computer for office tasks;
• Productive desktop computer(work with multimedia, games, audio, video and image processing);
• Multimedia player and data storage.
• For assembling an external (portable) drive.

In accordance with one of the listed options for using your computer, you can begin to select a suitable model of hard disk according to its characteristics.

Form Factor

Form factor is physical hard size disk. Today, most drives for home computers are 2.5 or 3.5 inches wide. The first, which are smaller, are intended for installation in laptops, the second - in stationary system units. Of course, a 2.5-inch drive can also be installed in a desktop PC if desired.

There are also smaller magnetic drives with sizes of 1.8 ", 1" and even 0.85 ". But these hard drives are much less common and are focused on specific devices, such as ultra-compact computers (UMPC), digital cameras, PDA and other equipment, where small dimensions and weight of components are very important. We will not talk about them in this article.

The smaller the disk, the lighter it is and the less power it requires to operate. Therefore, 2.5 "hard drives have almost completely replaced 3.5" models in external drives. After all, for the work of large external drives requires additional power from an electrical outlet, while the younger brother is content with only power from USB ports. So if you decide to assemble a portable drive yourself, it is better to use a 2.5-inch HDD for this purpose. It will be a lighter and more compact solution, and you will not have to carry the power supply with you.

As for installing 2.5-inch drives in a stationary system unit, then such a decision looks ambiguous. Why? Read on.

Capacity

One of the main characteristics of any drive (in this regard, a hard drive is no exception) is its capacity (or volume), which today for some models reaches four terabytes (in one terabyte 1024 GB). Even some 5 years ago, such a volume could seem fantastic, but the current OS assemblies, modern software, videos and photos high resolution, as well as three-dimensional computer video games, having a fairly solid "weight", need a large hard drive capacity. So, some modern games need 12 or even more gigabytes of free hard disk space for normal functioning, and an hour and a half HD-quality movie may require more than 20 GB for storage.

Today the capacities of 2.5-inch magnetic media range from 160 GB to 1.5 TB (the most common sizes are 250 GB, 320 GB, 500 GB, 750 GB and 1 TB). 3.5 ”desktop drives are larger and can store 160GB to 4TB of data (most common sizes are 320GB, 500GB, 1TB, 2TB, and 3TB).

When choosing HDD capacity, consider one important detail- the larger the hard disk, the lower the price of 1 GB of information storage. For example, a desktop hard drive for 320 GB costs 1600 rubles, for 500 GB - 1650 rubles, and for 1 TB - 1950 rubles. We consider: in the first case, the cost of a gigabyte of data storage is 5 rubles (1600/320 = 5), in the second - 3.3 rubles, and in the third - 1.95 rubles. Of course, such statistics does not mean that it is necessary to buy a disk of very large capacity, but in this example it is very clear that buying a 320 GB disk is inappropriate.

If you plan to use your computer mainly for solving office tasks, then a hard drive with a capacity of 250 - 320 GB is more than enough for you, or even less, unless, of course, there is no need to store huge archives of documentation on the computer. At the same time, as we noted above, buying a hard drive with a volume below 500 GB is unprofitable. By saving from 50 to 200 rubles, you end up with a very high cost per gigabyte of data storage. At the same time, this fact applies to drives of both form factors.

Do you want to build a gaming or multimedia PC for working with graphics and video, are you planning to download new films and music albums in large quantities to your hard drive? Then it is better to choose a hard drive with a volume of at least 1 TB for a desktop PC and at least 750 GB for a mobile one. But, of course, the final calculation of the capacity of the hard drive must correspond to the specific needs of the user, and in this case we only give recommendations.

We should also mention storage systems (NAS) and multimedia players that have become popular. As a rule, such equipment installs large 3.5 ”disks, preferably with a volume of at least 2 TB. After all, these devices are focused on storing large amounts of data, which means that the hard drives installed in them must be capacious with the lowest price for storing 1 GB of information.

Disc geometry, platters and recording density

When choosing a hard disk, one should not blindly rely only on its total capacity, according to the principle “the more, the better.” There are other important characteristics, including: the recording density and the number of platters used. Indeed, not only the volume of the hard drive, but also the speed of writing / reading data directly depends on these factors.

Let's make a small digression and say a few words about design features modern hard drives. Data are recorded in them on aluminum or glass disks, called plates, which are covered with a ferromagnetic film. For writing and reading data from one of the thousands of concentric tracks located on the surface of the plates, readheads are responsible, located on special rotary positioning arms, sometimes called "rocker arms". This procedure takes place without direct (mechanical) contact between the disc and the head (they are at a distance of about 7-10 nm from each other), which provides protection against possible damage and a long service life of the device. Each plate has two working surfaces and is served by two heads (one for each side).

To create an address space, the surface of magnetic disks is divided into many circular regions called tracks. In turn, the tracks are divided into equal segments - sectors. Due to such a ring structure, the geometry of the plates, or rather their diameter, affects the speed of reading and writing information.

Closer to the outer edge of the disc, the tracks have a larger radius (longer length) and accommodate large quantity sectors, which means more information that can be read by the device in one revolution. Therefore, on the outer tracks of the disc, the data transfer rate is higher, since the read head in this area travels a greater distance in a certain time interval than on the inner tracks, which are closer to the center. Thus, discs with a diameter of 3.5 inches have a higher performance than discs with a diameter of 2.5 inches.

Several platters can be located inside the hard disk at once, each of which can store a certain maximum amount of data. Strictly speaking, this determines the recording density, measured in gigabits per square inch (Gbit / in 2) or in gigabytes per platter (GB). The larger this value, the more information is placed on one track of the plate, and the faster the recording is carried out, as well as the subsequent reading of information arrays (regardless of the speed of rotation of the disks).

The total volume of the hard drive consists of the containers of each of the plates placed in it. For example, introduced in 2007, the first commercial 1000 GB (1TB) drive had as many as 5 platters with a density of 200 GB each. But technological progress does not stand still, and in 2011, thanks to the improvement of perpendicular recording technology, Hitachi introduced the first 1TB platter, which are ubiquitous in modern large-capacity hard drives.

Reducing the number of platters in hard drives has a number of important advantages:

• Decrease in data reading time;
• Reducing power consumption and heat dissipation;
• Increased reliability and resiliency;
• Reduced weight and thickness;
• Reduced cost.

Today in the computer market there are simultaneously models of hard disks that use plates with different recording densities. This means that hard drives of the same volume can have a completely different number of platters. If you are looking for the most efficient solution, it is better to choose HDD with the least number of platters and high recording density. But the problem is that, in almost no computer store, you will not find the value of the above parameters in the descriptions of the characteristics of disks. Moreover, this information is often absent even on the official websites of manufacturers. As a result, for ordinary ordinary users, these characteristics are far from always decisive when choosing a hard disk, because of their inaccessibility. Nevertheless, before buying, we recommend that you definitely look for the values ​​of these parameters, which will allow you to choose a hard drive with the most advanced and modern characteristics.

Spindle speed

The speed of a hard disk directly depends not only on the recording density, but also on the rotation speed of the magnetic disks located in it. All the plates inside the hard drive are rigidly attached to its internal axis, called the spindle, and rotate with it, as a whole. The faster the plate rotates, the sooner there is a sector that should be read.

In stationary home computers, models of hard drives are used that have an operating speed of 5400, 5900, 7200, or 10,000 rpm. Devices with a spindle speed of 5400 rpm are usually quieter than their high-speed "competitors" and have less heat. Winchesters with higher rpms, in turn, are distinguished by better performance, but at the same time they are more energy intensive.

For an ordinary office PC, a drive with a spindle speed of 5400 rpm will suffice. Also, such disks are well suited for installation in multimedia players or data storages, where the important role is played not so much by the speed of information transfer, but by the reduced power consumption and heat dissipation.

In other cases, in the overwhelming majority, discs with a rotational speed of 7200 rpm plates are used. This applies to both mid-range and top-end computers. The use of HDDs with a rotation speed of 10,000 rpm is relatively rare, since such models of hard drives are very noisy and have a rather high cost of storing one gigabyte of information. Moreover, recently, users increasingly prefer to use solid-state drives instead of productive magnetic disks.

In the mobile sector, dominated by 2.5-inch drives, the most common spindle speed is 5400 rpm. This is not surprising, since for portable devices low power consumption is important and low level heating parts. But they did not forget about the owners of productive laptops - there is big choice models with a rotation speed of 7200 rpm and even several representatives of the VelociRaptor family with a rotation speed of 10,000 rpm. Although the feasibility of using the latter even in the most powerful mobile PCs is in great doubt. In our opinion, if you need to install a very fast disk subsystem, here it is better to pay attention to solid-state drives.

Connection interface

Almost all modern models, both small and large hard drives, are connected to motherboards personal computers using the SATA (Serial ATA) serial interface. If you have very old computer, then it is possible to connect using the parallel interface PATA (IDE). But keep in mind that the range of such hard drives in stores today is very scarce, since their production has almost completely ceased.

As for the SATA interface, there are 2 variants of disks on the market: connection via the SATA II or SATA III bus. In the first variant, the maximum data transfer rate between the disk and RAM can be 300 MB / s (bus bandwidth up to 3 Gb / s), and in the second - 600 MB / s (bus bandwidth up to 6 Gb / s). Also, the SATA III interface has slightly improved power management.

In practice, the bandwidth of the SATA II interface is enough for any classic hard drives. After all, even the most productive HDD models have the speed of reading data from platters just above 200 MB / s. Another thing is solid-state drives, where data is stored not on magnetic platters, but in flash memory, the read speed from which is many times faster and can reach values ​​of over 500 MB / s.

It should be noted that all versions of the SATA interface retained compatibility with each other at the level of exchange protocols, connectors and cables. That is, a hard drive with a SATA III interface can be safely connected to the motherboard via the SATA I connector, although the maximum disk bandwidth will be limited by the capabilities of the older revision and will be 150 MB / s.

Buffer memory (Cache)

Buffer memory is fast intermediate memory (usually a standard type of random access memory) used to level (smooth out) the difference between read, write and transfer speeds over the data interface while the disk is running. The hard drive cache can be used to store the last read data, but not yet transmitted for processing, or those data that can be re-requested.

In the previous section, we already noted the difference between hard drive performance and throughput interface. It is this fact that determines the need for transit storage in modern hard drives. Thus, while data is being written or read from magnetic platters, the system can use the information stored in the cache for its own needs without being idle.

The size of the clipboard for modern hard drives made in the 2.5 ”form factor can be 8, 16, 32 or 64 MB. Older 3.5-inch brothers maximum value the buffer memory already reaches 128 MB. In the mobile sector, the most common disks with a cache of 8 and 16 MB. Among desktop hard drives, the most common buffer sizes are 32 and 64 MB.

Theoretically, the cache bigger size should provide better performance to disks. But in practice, this is far from always the case. There are various operations with the disk, in which the clipboard practically does not affect the performance of the hard drive. For example, this can occur when sequentially reading data from the surface of the platters or when working with large files. In addition, the efficiency of the cache is influenced by algorithms that can prevent errors when working with the buffer. And here a disk with a smaller cache, but advanced algorithms for its work, may be more productive than a competitor with a larger clipboard.

Thus, it is not worth chasing the maximum amount of buffer memory. Especially if you need to pay a lot for a large cache capacity. In addition, manufacturers try to equip their products with the most efficient cache size, based on the class and characteristics of certain disk models.

Other characteristics

In conclusion, let's take a quick look at some of the remaining characteristics that you may come across in the descriptions of hard drives.

Reliability or mean time between failures ( MTBF) - the average duration of the hard drive until its first breakdown or the need for repair. It is usually measured in hours. This parameter is very important for disks used in server stations or file storages, as well as in RAID arrays. Typically, specialized magnetic drives have an average runtime of 800,000 to 1,000,000 hours (for example, WD's RED series or Seagate's Constellation series).

Noise level - noise generated by the elements of the hard disk during its operation. Measured in decibels (dB). It mainly consists of the noise arising from the positioning of the heads (crackling) and the noise from the spindle rotation (rustling). As a rule, the lower the spindle speed, the quieter the hard drive works. A hard drive can be called quiet if its noise level is below 26 dB.

Power consumption - an important parameter for disks installed in mobile devices, where a lot of time is valued autonomous work... The heat dissipation of the hard drive also directly depends on energy consumption, which is also important for portable PCs. As a rule, the level of energy consumption is indicated by the manufacturer on the disc cover, but you should not blindly trust these figures. Very often they are far from reality, so if you really want to find out the power consumption of a particular disk model, then it is better to search the Internet for independent test results.

Random access time - the average time during which the positioning of the disk read head over an arbitrary section of the magnetic plate is performed, measured in milliseconds. A very important parameter that affects the performance of the hard drive as a whole. The shorter the positioning time, the faster data will be written to or read from the disk. Can range from 2.5ms (on some server disk models) to 14ms. On average, for modern disks for personal computers, this parameter ranges from 7 to 11 ms. Although there are also very fast models, for example, the WD Velociraptor with an average random access time of 3.6 ms.

Conclusion

In conclusion, I would like to say a few words about the increasingly popular hybrid magnetic drives (SSHD). Devices of this type combine a conventional hard disk drive (HDD) and solid state drive(SSD) is a small size that acts as additional cache memory. Thus, the developers are trying to combine the main advantages of the two technologies - the large capacity of magnetic plates and the speed of flash memory. At the same time, the cost of hybrid drives is much lower than that of newfangled SSDs, and slightly higher than that of conventional HDDs.

Despite the promise of this technology, so far SSHDs are very poorly represented on the hard disk market only small amount models in a 2.5-inch form factor. Seagate is the most active in this segment, although competitors Western Digital (WD) and Toshiba have already presented their hybrid solutions... All this leaves hope that the market for SSHD hard drives will develop, and we will soon see new models of such devices on sale not only for mobile computers, but also for desktops.

This concludes our review, where we examined all the main characteristics of computer hard drives. We hope that based on this material, you will be able to choose a hard drive for any purpose with the optimal parameters corresponding to them.

Which hard drive to choose. Choose the right hard drive to keep it fast, quiet and reliable. Unfortunately, before you have time to look back, the disk is already filled to capacity. There are users who, even after several years, have enough disk space to work for another 10 years.

But this, as a rule, is rather an exception. Many people have a sorely lack of hard disk space, and sometimes just somewhere. Nowadays, a computer is not just a typewriter. Many users are engaged in serious projects on it and earn good money on it. And a hard drive, as you know, stores a lot of useful information, so you don't have to buy it anyhow.

Which hard drive to choose

It all depends on what you will be doing on your computer. It is best if your computer has not one hard drive, but two or even three. Read how to install such a disk. On the main disk, you will have an operating system, and on the rest it is better to store your data.

Usually hard disk space is sorely lacking. Do not think that you are the only one. Now I even wonder how 10 GB was enough for me. The most annoying thing is that all the files are needed and expensive, and you don't want to delete anything at all.

Any device has its own parameters and resources, and the computer hard drive is no exception. If you just come to the store and ask for a disc, then you may not be advised what is necessary, but most likely what is more expensive. Why overpay if you can take the same or with the remaining money.

WHERE YOU CAN STORE YOUR DATA EXCEPT HARD DISK

Previously, you could burn your data to a "blank" (CD or DVD) and sleep peacefully. Now everyone has so much information on their computers that it is no longer possible to rewrite everything on a CD. At best, you can rewrite something that is most important.

And still it is not very convenient. You will not carry with you an entire briefcase of CDs or DVDs and insert one by one into the drive to find the information you need.

You can buy small in size, but large in volume external drive and carry it with you. But, again, there is no guarantee that it will never "glitch". And then "goodbye" valuable information. I recently did it. But, now is not about that.

External hard drive 2.5 '

Capacity (volume) of the hard drive

An operating system does not need a large disk space. Since the minimum disk size is now on sale is 500 GB, then this is enough for your eyes. But another disc, if you constantly download something from the Internet, you need to take as much volume as possible.

Spindle speed

The operating system needs a disk with a good spindle speed. At low speeds, your operating system will slow down, no matter what memory is, and no matter how fast the microprocessor is.

Everything should be integrated. Otherwise, you will throw money down the drain. You cannot save on hard drive!

Modern hard disks(HDD) 2.5 and 3.5 ”have a spindle speed of 5400 or 7200 rpm. The higher the spindle speed, the higher the speed of the disk.

For a home computer, the speed of the hard disk on which the operating system, graphics programs and your games will be installed must be at least 7200 rpm.

If you buy a disk for an office, then 5400 rpm will be enough. The same speed is also suitable for data storage, i.e. second hard drive, especially since it's cheaper.

There are SAS or SCSI drives, with speeds of 10,000 and 15,000 rpm, but they are used for servers and are not cheap.

SCSI hard drive

But if you have an old computer and an IDE hard drive, then the choice is not great, and you can forget about the good spindle speed of the drive. And finding such a disk is already problematic.

How to identify an old hard drive or not

If your disk has a wide ribbon cable, then this is an IDE interface. They are no longer used in new computers, and the speed of these drives is low.

Cable for connecting an IDE disk

New computers use SATA, SATA 2 and SATA 3 hard drives.

SATA drive cable

The transfer rate of SATA drive is 50% faster than IDE drive.

SATA, SATA 2 and SATA 3 drives are interchangeable. But the data transfer rate of SATA 3 is much better than that of SATA.

Please note that SATA and SATA2 drive cables do not fit SATA3 drive. Their frequency characteristics are different, although the connectors are the same and they will still work. The ribbon cable (cable) for SATA3 is thicker and usually black.

It is also important to know what type of SATA hard drive your motherboard otherwise the disk will not work on full power... But this is not critical. But if the motherboard is very old, then it may not support a SATA drive at all, i.e. it will not have a connector for it.

Buffer size or cache size

The next item to select a disk is cache size(buffer memory). There are 8, 16, 32, 64 and 128 MB cache sizes. The higher the number, the better the processing speed.

For data storage, 16 MB is suitable, and for the system it is better to buy from 32 MB. If you are engaged in graphics, then for programs such as Photoshop and AutoCAD it is better to take a hard drive with cache memory - 64 or 128 MB, especially since the difference in price between them is not significant.

Average linear read speed

Linear read speed means the speed of continuous reading of data from the surface of the platter (HDD) and is the main characteristic that reflects the real speed of the disk. It is measured in megabytes per second (Mbps).

Modern HDDs with SATA interface have an average linear read speed from 100 to 140 Mb / s.

The linear read speed of HDD disks depends on the density of data recording on the magnetic surface of the platters and the quality of the disk mechanics.

Access time

This is the speed at which the disk finds the required file after being accessed by the operating system or some program. Measured in milliseconds (ms). This parameter has a big impact on disk performance when working with small files and not a big one when working with large files.

Hard drives have access times from 12 to 18 ms. A good indicator is access time of 13-14 ms (depending on the quality (accuracy) of the disc mechanics).

Now there are new hard drives on the market - SSDs consisting of only microchips, but they are very expensive and therefore not intended for data storage. They are only good for running programs. SSD drives do not have a spindle, therefore they are completely silent, do not heat up, and are very fast.

And the most important! Avoid placing hard drives side by side. It is better if there is more space around them, because during operation, they get very hot and can fail from overheating.

Better yet, especially in summer, cool them by opening the computer lid and aiming the fan at them. Overheating for a hard drive is just as destructive as for a video card and microprocessor.

Any disc manufacturer company has discs that are more expensive and cheaper. But this does not mean that firms are hackneyed. Just one product for state employees, and the other for the wealthier. Both those and other discs are made conscientiously, but the details are from different materials, which have different wear periods.

Hard drive manufacturers

The main manufacturers of hard disk drives (HDD) are:

Fujitsu- a Japanese company, previously famous for the high quality of its products, is currently represented by a small number of models and is not very popular.

Hitachi- the Japanese company, both earlier and now, is distinguished by the stable quality of hard drives. Buying a Hitachi hard drive you will not go wrong, having received good quality for a reasonable price.

Samsung- this Korean company. Today Samsung produces the fastest and highest quality HDD disks. They may be priced slightly higher than the competition, but worth it.

Seagate Is an American technology pioneer company. Unfortunately, the quality of hard drives from this company leaves much to be desired.

Toshiba Is a Japanese company. Now it is represented by a small number of models on our market. In this regard, there may be problems in the service of such manufacturers.

Western Digital (WD) Is an American company specializing in the production of hard drives. Lately, the discs of this company do not stand out with outstanding performance, and are very noisy.

It is better to choose between Samsung or Hitachi as the highest quality, fastest and most stable.

So, the main characteristics of hard drives:

• Spindle speed
• HDD capacity
• Cache size
• Average linear read speed
• Noise level
• Manufacturer

Now you know which hard drive to choose. Unfortunately, shops don't always have a choice, so I prefer to order online. In big cities, there is more choice. Therefore, do not be lazy and study their main characteristics.

If you want to know what hard disk cache is and how it works, this article is for you. You will learn what it is, what functions it performs and how it affects the operation of the device, as well as the advantages and disadvantages of the cache.

Hard disk cache concept

The hard drive itself is a fairly leisurely device. Compared to RAM, a hard drive is orders of magnitude slower. This also causes a drop in computer performance when there is a shortage of RAM, since the shortage is compensated for by the hard disk.

So, the cache memory of the hard disk is a kind of RAM... It is built into the hard drive and serves as a buffer for read information and its subsequent transfer to the system, and also contains the most frequently used data.

Let's take a look at what a hard disk cache is for.

As noted above, reading information from a hard disk is very leisurely, since the movement of the head and finding the required sector takes a long time.

It is necessary to clarify that the word "slow" means milliseconds. And for modern technologies, a millisecond is a lot.

Therefore, like the hard disk cache, it stores data physically read from the disk surface, and also reads and stores sectors that are likely to be requested later.

This reduces the number of physical calls to the drive, while increasing performance. Winchester can work even if the host bus is not free. The transmission speed can increase hundreds of times with the same type of requests.

How hard drive cache works

Let's dwell on this in more detail. You already have a rough idea of ​​what the hard disk cache is for. Now let's find out how it works.

Let's imagine that the hard disk receives a request to read 512 KB of information from one block. The necessary information is taken from the disk and transferred to the cache, but along with the requested data, several neighboring blocks are read at the same time. This is called prefetching. When a new request for a disk arrives, the microcontroller of the drive first checks for the presence of this information in the cache, and if it finds them, it instantly transfers it to the system without accessing the physical surface.

Since the cache memory is limited, the oldest blocks of information are replaced with new ones. This is a circular cache or circular buffer.

Methods to increase the speed of the hard disk by means of buffer memory

• Adaptive segmentation. The cache memory consists of segments with the same amount of memory. Since the size of the requested information cannot always be the same size, then many of the cache segments will be misused. Therefore, manufacturers began to make cache memory with the ability to change the size of segments and their number.
• Prefetch. The hard drive's processor analyzes the previously requested and currently requested data. Based on the analysis, it transfers information from the physical surface that is more likely to be requested at the next moment in time.
• User control. More advanced models of hard drives give the user control over the operations performed in the cache. For example: disabling the cache, setting the segment size, toggling the adaptive segmentation feature, or disabling prefetching.

Which gives the device more cache memory

Now we will find out what volumes are equipped and what gives the cache memory in the hard disk.

Most often you can find hard drives with a cache size of 32 and 64 MB. But there are still 8 and 16 MB remaining. Recently, only 32 and 64 MB have been released. A significant breakthrough in performance came when 16 MB was used instead of 8 MB. And between caches with a volume of 16 and 32 MB, you no longer feel much difference, as well as between 32 and 64.

The average computer user will not notice the difference in the performance of hard drives with a cache of 32 and 64 MB. But it is worth noting that the cache memory periodically experiences significant loads, so it is better to purchase a hard drive with a higher cache size, if there is a financial opportunity.

The main advantages of cache memory

Cache has many benefits. We will consider only the main ones:

Disadvantages of cache memory

1. The speed of the hard drive does not increase if data is written on disks in a random way. This makes it impossible to prefetch information. This problem can be partially avoided by periodically defragmenting.
2. The buffer is useless when reading files larger than the cache memory can fit. So, when accessing a file of 100 MB, the 64 MB cache will be useless.

Additional Information

You now know the hard drive and what it affects. What else do you need to know? Currently, there is a new type of storage - SSD (solid state). Instead of disk platters, they use synchronous memory, like in flash drives. Such drives are tens of times faster than conventional hard drives, so the presence of a cache is useless. But even such drives have their drawbacks. First, the price of such devices increases in proportion to the volume. Secondly, they have a limited reserve of the cycle of rewriting memory cells.

There are also hybrid drives: a solid state drive with a conventional hard drive. The advantage is the ratio of high speed of work and a large amount of stored information with a relatively low cost.