home Internet The algorithm of the hard drive cache. What is hard disk cache memory and why is it needed Buffer memory hdd

The algorithm of the hard drive cache. What is hard disk cache memory and why is it needed Buffer memory hdd

It is known that hard drives are equipped with their own buffer memory of a relatively small amount. The buffer is used as a built-in cache for read and write operations, optimizing performance and minimizing time-consuming platter accesses. For example, when the buffer contains free place, the controller can temporarily place data that needs to be written there and wait for a convenient moment when there are no requests from the system (host). When making read requests, the controller stores the last read data in case the host requests it again - then there is no need to access the disk again. The controller often reads ahead in an attempt to predict the host's next requests, and buffers the data it reads as well. It turns out that the buffer is used hard drive constantly, and his role is very important.

Hard drive manufacturers have always sought to increase the amount of buffer memory. Today, this is easier to do, since conventional microcircuits are synchronous dynamic memory(SDRAM), and they are used in hard drives, they are quite inexpensive. In the late 90s, desktop hard drives were equipped with a 512 KB buffer, then most models received 2 MB of memory, and today hard drives with an 8 MB buffer are most common. However, there is no limit to perfection: WD has updated its mass-produced line of Caviar SE hard drives, supplementing it with Caviar SE16 models. Their main difference, as you may have guessed, is the doubled amount of buffer memory.

Why do we need 16 MB?

It would seem that the larger the amount of buffer memory, the higher the performance of the hard disk. The controller will be able to buffer more data, which means it will access magnetic platters less often. However, not everything is as simple as it seems at first glance.

Caching algorithms typically use an associative lookup technique to determine if the required data is in the buffer. To increase the amount of data stored in the cache, either increase the size of one block (cache line) or increase the number of lines. And this is fraught with the appearance of additional problems with associative search and data exchange with the cache.

However, for a hard drive, the caching speed is not so important, since in any case it is negligible compared to the delays when accessing a magnetic media. Another thing is whether the controller really needs additional memory. It is possible that the hard drive is not busy enough to fully utilize the available buffer capacity. For example, when simply copying and downloading programs, nothing needs to be cached, since the data is read only once. But when working in a server environment, when requests are received chaotically and continuously, a large buffer is a significant plus for a hard drive. Actually, that's why server hard drives were always equipped with a buffer of at least 8 MB. But on a desktop, read and access speed is more important than buffering efficiency.

(True, let's not forget about NCQ technology. With its help, the hard drive can manage the queue of requests, changing the order of their service. Since the nature of access to the media also changes in this case, additional buffering can help improve performance. But alas, most users still still does not know how NCQ can be used, since support from the hard drive alone is not enough here).

It turns out that a large buffer size is unlikely to have a significant impact on the overall speed. Putting a chip with a higher capacity is not enough to improve performance. Developers should not only redesign the microcode, but also improve the read / write speed of the media and the bandwidth of the interface.

Caviar SE16. Design features

We were able to match the WD2500KS from the Caviar SE16 line with the WD2000JS from the "standard" Caviar SE line. As it turned out, they have a minimum of differences: the markings of the HDA, connectors, and electronics boards are the same. Even the microcode version is the same. Consequently, the developers at WD used the old technology, simply replacing one memory chip with another.

For those who are not aware of the features of WD hard drives, we will report the following. This manufacturer uses only proven technologies and takes special care to protect discs from damage. The design of the HDA is standard: a massive body and a flat top cover hermetically connected, on the top of the lid there is air vent. But the electronics board is traditionally turned upside down by microcircuits and pressed against the case, there is a thermally conductive gasket. This technique allows you to protect the chips from overheating and external influences. There are two power connectors - a standard 4-pin and a new flat one, in accordance with the requirements of Serial ATA. To protect the Serial ATA interface connector from accidental disconnection, WD suggests using a special SecureConnect cable with latches.

The Caviar SE16 series is only available with Serial ATA support. Moreover, the hard disk controller supports the "second speed" 3 GB/s (300 MB/s). Other technologies, in particular, NCQ, have not yet been implemented - here WD lags behind other manufacturers.

Declared parameters of WD Caviar SE/SE16 hard drives
Marking
Spindle speed, rpm
Recording density, GB per platter
Cache buffer size, MB
Bearings
Interface
NCQ Support
Capacity range	120, 160, 200, 250
Int. data exchange speed, Mbit/s
Average access speed: average, ms
- by maximum radius, ms
- transition between tracks, ms
-write access speed, ms
Impact resistance (offline), G
Impact resistance (online), G
Noise level at idle, dB
Noise level during positioning, dB

The capacity range of Caviar SE16 hard drives is still small. On the WD website, we managed to find data on the 250 GB model, plus a 400 GB model has recently appeared. The manufacturer does not report the exact recording density and capacity of one platter, but, according to available data, 100 GB platters are used in the current series of hard drives. Today this is a modest result, however, WD practices the modernization of the line without changing the names and specifications, so it may well turn out that discs with more capacious platters are already on sale.

Testing

Hard drives from three manufacturers took part in testing - WD, Seagate and Samsung. At the time of writing, it was their products that were presented in a wide range. An instance of the Caviar SE16 series hard drive considered in the review had the following parameters:

marking WD2500KS-00MJB0;
volume 250 GB;
microcode version 02.01C03;
quiet positioning mode (AAM) disabled (0FEh).

We will compare the following hard drives with it:

Caviar SE, from the line with 8 MB buffer, 200 GB capacity:

marking: WD2000JS-00MHB0;
buffer size - 8 MB;
interface - Serial ATA 3 Gbit/s, NCQ is not supported;
microcode version - 02.01C03 (same);
quiet positioning mode (AAM) disabled (0FEh).

Samsung SpinPoint P120, 200 GB:

marking SP2004C;
buffer size - 8 MB;
interface – Serial ATA 3 Gbit/s, NCQ supported;
microcode version - VM100-33;
silent positioning mode enabled (code 00h).

Seagate Barracuda 7200.8, 200 GB:

marking ST3200826AS;
buffer size - 8 MB;
interface – Serial ATA 1.5 Gbit/s, NCQ supported;
microcode version - 3.03;
silent positioning mode disabled (control not available).

Hard drives Seagate and Samsung have higher recording densities than WD Caviar. In addition, Seagate has a higher positioning speed (8ms versus 8.9ms for Samsung and WD), and Samsung is quieter. That is, WD formally has no advantages over drives from other manufacturers. But in practice it can be the other way around.

The hard drives were connected to the second port of the Serial ATA controller built into the ICH5 south hub of the Intel 865G chipset. Unfortunately, the 865 series chipsets do not support 3 Gb/s and NCQ technology, so the capabilities of modern hard drives cannot be fully revealed. Other test configuration options:

host hard drive from which the OS was loaded and tests were launched - Seagate Barracuda 7200.7 PATA 80 GB;
processor Intel Pentium 4 2.80 (bus 800 MHz);
maternal Intel board D865GBF (Intel 865G);
2 x 256 DDR400 memory, dual-channel enabled;
video card GeForce FX 5600;
the hard drives were installed in a 2.5-inch basket of the Inwin J551 case, no special cooling was used.

Low Level Tests

The use of programs that work directly with the disk allows you to measure the theoretical parameters of the hard drive - random access speed, average (sustained) read and write speed, delayed write efficiency. At the same time, the influence of caching algorithms is minimal, since access is carried out continuously and according to a simple scheme.

Low-level parameters were calculated using programs:

IOMeter 2004.07.30;
HDTach 2.68;
HDTach 3.0.1.0;
Winbench 2.0 (the disk was formatted as one large NTFS partition).

Access speed turned out to be higher in Caviar, since WD hard drives do not use positioning delay algorithms (AAM). Seagate, despite the excellent declared numbers, was the last one. Oddly enough, the Caviar SE16 slightly (0.3 ms) lost to its counterpart, which can be explained either by the natural difference in technological parameters (nevertheless, the mechanics have some deviations in one direction or another), or by the influence of the third plate (the greater the number of heads, the more switching delay). Of course, the differences are actually very small, and we will not talk about a serious lag in the Caviar SE16. In terms of write access speed, WD hard drives are equal, providing a twofold acceleration compared to the read access speed. This is explained by the influence of the delayed write algorithm.

By sequential read/write speeds The Caviar SE16, on the other hand, is slightly ahead of the Caviar SE. But they were overtaken by the Seagate hard drive (+10%), which is natural due to the use of a higher recording density, while Samsung, on the contrary, is just as far behind.

A more accurate analysis of the read / write speed allows you to conduct IOMeter. If other programs work with 64 KB blocks, IOMeter may vary the block size.

Seagate is the leader in reading: it copes much better (+20%) with small and large blocks. Samsung, as it turned out, does not work very well with small blocks. And WD performed well in write tests, beating Seagate when working with blocks less than 64 KB.

The Winbench'99 program, despite its venerable age, builds a sequential reading graph quite accurately.

Both WD drives have the same shape of the graph, with no peaks or dips, which indicates a high read stability. The Caviar SE16 graph is more elongated, which is due to its larger capacity. Zooming in on the graph allows us to see short-term but strong speed dips in Seagate and Samsung (work of ECC error correction algorithms, delays in switching heads and changing tracks) and the absence of such in WD. And although the recording density of WD is worse, the proven production technology has its advantages - higher stability.

Application Simulation

The Workstation template of the IOMeter test allows you to generate a load on the disk subsystem that is close to real (statistics were collected using the Winstone 2002 Content Creation test). So, this test is more sensitive to access speed than to read / write speed, plus it takes into account the work of caching algorithms, since requests arrive with an increase in the queue depth.

According to the data, both WD drives slightly outperformed Samsung and literally crushed Seagate. Caviar SE is again slightly better than Caviar SE16, as they have a slight difference in access speed.

We pinned great hopes on the PCMark05 test, since it should show the advantage of a large cache buffer. This test uses patterns written with the Intel IPEAK SPT test suite when performing specific tasks. Therefore, PCMark05 can more or less believably simulate the operation of a hard drive in real conditions.

So, if in terms of speed Windows boot XP, file copying and scanning for viruses, WD hard drives are almost the same, then in terms of application loading speed and access to data while applications are running, Caviar SE16 is 10-15% faster than Caviar SE, not to mention Samsung and Seagate.

The advantage of a hard drive with a large buffer is also noticeable in the Winstone test, especially if the FAT32 file system is used.

conclusions

The test results prove that there is a positive effect of increasing the buffer. It is small, within 10-15%, and appears only when the hard drive is operating in conditions close to real. In low-level tests, there is practically no difference, which is consistent with the theory. The same theory suggests that as the interface bandwidth and recording density increase, as well as with the introduction of disk access optimization technologies, the buffer size will have to be increased. Therefore, the developers from WD hurried a little; however, it is better to start developing the technology now than to catch up with competitors later.

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A hard drive (hard drive, HDD) is one of the most important parts of a computer. After all, if the processor, video card, etc. breaks down, You feel regret only about losing money for a new purchase, if the hard drive breaks down, you risk losing irretrievably important data. The speed of the computer as a whole also depends on the hard drive. Let's figure it out how to choose the right hard drive.

Hard disk tasks

A task hard drive inside the computer - to store and issue information very quickly. The hard drive is an amazing invention of the computer industry. Using the laws of physics, this small device stores an almost unlimited amount of information.

Hard disk type

IDE - outdated hard drives are meant to be connected to old motherboards.

SATA - replaced hard drives IDEs have a higher transfer rate.

SATA interfaces come in different models, they differ from each other in the same speed of data exchange and support for different technologies:

SATA has a transfer rate of up to 150Mb/s.
SATA II - has a transfer rate up to 300Mb / s
SATA III - has a transfer rate up to 600Mb / s

SATA-3 began to be produced quite recently, since the beginning of 2010. When buying such a hard drive, you need to pay attention to the year of manufacture of your computer (without an upgrade), if it is lower than this date, then this hard drive will not work for you! HDD - SATA, SATA 2 have the same connection connectors and are compatible with each other.

Hard disk capacity

The most common hard drives used by most users at home have a capacity of 250, 320, 500 gigabytes. There are even fewer, but there are less and less 120, 80 gigabytes, and they are no longer on sale at all. To be able to store very big information there are hard drives 1, 2, 4 terabytes.

Hard drive speed and cache

When choosing a hard drive, it is important to pay attention to its speed (spindle speed). The speed of the entire computer will depend on this. The usual drive speeds are 5400 and 7200 rpm.

The amount of buffer memory (cache memory) - physical memory hard disk. There are several sizes of such memory 8, 16, 32, 64 megabytes. The higher the speed random access memory hard drive, the faster the data transfer rate will be.

In custody

Before buying, check which one is suitable for your motherboard: IDE, SATA or SATA 3. We look at the characteristics of the disk rotation speed and the amount of buffer memory, these are the main indicators that you need to pay attention to. We also look at the manufacturer and the volume that suits you.

We wish you successful shopping!

Share your choice in the comments, it will help other users to make the right choice!

Published by the hard drive.

Also, they did not bypass the HDD interface, where the main features and differences were considered SATA interface and legacy IDE. And of course, they did not forget, perhaps, the most important characteristic - this hard disk capacity.

In this material, we will talk about the remaining characteristics of hard drives, which are no less important than the above.

Hard Drive Form Factor

On the this moment, two form factors of hard drives are widely used - these are 2.5 and 3.5 inches. The form factor, to a greater extent, determines the dimensions of hard drives. By the way, a 3.5" hard drive can hold up to 5 platters, and a 2.5" hard drive can hold up to 3 platters. But in modern realities, this is not an advantage, since the developers have determined for themselves that it is not advisable to install more than 2 platters in ordinary high-performance hard drives. Although, the 3.5” form factor is not going to give up at all and, in terms of demand, confidently outweighs 2.5” in the desktop segment.

That is, for a desktop system, while it makes sense to purchase only 3.5 ”, since among the advantages of this form factor, one can note a lower cost per gigabyte of space, with a larger volume. This is achieved by a larger platter that, at the same recording density, can hold more data than 2.5”. Traditionally, 2.5" has always been positioned as a laptop form factor, largely due to its size.

There are other form factors as well. For example, in many portable devices 1.8 ”hard drives are used, but we will not dwell on them in detail.

Hard drive cache size

Cache- This is a specialized RAM that acts as an intermediate link (buffer) for storing data that has already been read from the hard disk, but has not yet been transferred directly to processing. The very presence of the buffer was caused by a significant difference in speed between the rest of the system components and the hard drive.

As such, a characteristic of HDD cache is volume. At the moment, the most popular hard drives with a buffer of 32 and 64 MB. In fact, buying a hard drive with a large amount of cache memory will not give a twofold increase in performance, as it might seem based on classical arithmetic. Moreover, tests have shown that the advantage of hard drives with 64 MB cache appears quite rarely and only when performing specific tasks. Therefore, if possible, it is worth buying a hard drive with a larger cache, but if this will go to a significant detriment to the price tag, then this is not the parameter that you should focus on in the first place.

Random access time

The hard disk random access time indicator characterizes the time during which the hard drive is guaranteed to carry out a read operation anywhere on the hard disk. That is, for what period of time, the read head will be able to get to the most distant sector of the hard disk. This, to a greater extent, depends on the previously considered characteristic of the speed of rotation of the hard disk spindle. After all, the higher the rotation speed, the faster the head can get to the desired track. In modern hard drives, this figure is from 2 to 16 ms.

Other HDD Specifications

Now briefly and briefly list the remaining characteristics of hard drives:

Energy consumption - hard drives consume very little. Moreover, the maximum power consumption is often indicated, which takes place only at intermediate stages of operation during peak load. On average, this is 1.5-4.5 W;
Reliability (MTBF) - the so-called time between failures;
Data transfer rate - from the outer zone of the disk: from 60 to 114 Mb / s, and from the internal - from 44.2 to 75 Mb / s;
The number of input / output operations per second (IOPS) - for modern hard drives, this figure is about 50/100 ops / s, with random and sequential access.

So we looked at all the characteristics of hard drives with the help of a small series of articles. Naturally, many parameters intersect and, to some extent, influence each other. But, on the other hand, based on information regarding all these parameters, you can simulate a future device for yourself, and when choosing, clearly understand which of the models should be given priority in your particular case.

But such toys can be obtained from old hard drives, or rather from the components of a hard drive. For example, the wheels are made from a hard drive spindle motor that drives an axle with a read head.

The question of upgrading a computer sooner or later arises before each user. Maybe you're building a new PC, or you want to store more information on your machine and use it effectively. To do this, you can not do without buying a new high-quality HDD (hard disc drive). In each case, you need to have a clear understanding of how to choose a good hard drive that will meet all your needs and be reliable in operation.

In each case, you need to have a clear understanding of how to choose a good hard drive that will meet all your needs and be reliable in operation.

At the first stage, you need to decide for what purpose you plan to use the data drive. Depending on the application, there are different price categories for hdd. Manufacturers produce a series of products designed primarily for: Archival function (data storage); Daily work (regular writing and reading information);

Active work with a large amount of data, where increased reliability is needed - such solutions serve the corporate sector.

physical dimensions hdd

Two form factors have been developed that determine the physical dimensions of hard drives. Smaller drives are used in portable PC models, while larger ones are designed for desktop computer. Distinguish the following options: 2.5 '' (inches) - for laptops of any configuration, in order to connect such a drive to a stationary machine, special mounts for the case will be required;

3.5'' (inches) - for personal workstations, is considered the "gold standard" for desktop computers.

Hard disk interface

Before buying, you must definitely find out which interface will be used to connect to motherboard new drive. A mismatch between the interfaces on the board and the hdd leads to the complete impossibility of using it or can significantly reduce the speed of work.

Older models used an IDE (or Parallel ATA) interface, which involves connecting the device in parallel to a computer. AT last years it has been replaced by a more modern and faster interface SATA (Serial ATA), which is used to serially connect hard drives to the motherboard and offers better read and write data compared to its predecessor.

There are three generations of SATA interfaces: SATA I, which transfers data at a speed of 1.5 Gb per second, is also becoming a thing of the past; SATA II, which transfers data at speeds up to 3 Gbps;

SATA III, the fastest interface with a transfer rate of about 6 Gbps;

Note that desktop and mobile machines using the IDE connector are not compatible with each other, therefore, if it becomes necessary to connect a hard drive from a laptop to a PC or vice versa, then a special adapter will be required.

The SATA II and SATA III connectors are designed to completely solve this problem. They are fully compatible, but be aware that if you connect a SATA III hard drive to a SATA II equipped motherboard, it will run slower and have the same performance as the second generation interfaces.

If you are thinking about how to choose a hard drive for your computer, then it is desirable that the model you choose has an interface of the second or third generation (SATA II, SATA III).

Capacity or volume hdd

When choosing the size of the drive, proceed from your needs and the tasks that the computer where you plan to connect the device will perform.

If you are choosing a new hard drive for a desktop computer, then you should be guided by the following numbers: Volume 320 GB, if the machine is needed in order to use text editors and browse the web; Volume from 500 GB to 1 TB, if, in addition to the most common programs, multimedia files (music, photos, movies) are stored on the disk and modern games are planned to be installed;

A volume of 2 to 4 TB will be needed for a PC on which professional processing of graphic files and video clips will be carried out, as well as storage and processing of large amounts of information.

Installing an hdd with a capacity of more than 2 GB is not possible on machines that do not support the UEFI standard, which is gradually replacing motherboards with BIOS. Therefore, if you have chosen a hard drive with a very large capacity, make sure that your computer belongs to the required PC class. The BIOS will not be able to identify and work correctly in the future with such a device.

When buying a new hard drive for a laptop, be guided by the following data: From 320 to 500 GB if you have a netbook, which is used as an additional car when traveling outside the home;

From 750 GB to 1 TB, if you use a laptop as a base workstation and, in addition to the installed operating system, you need to store a large amount of information and work with complex software.

If you need to pick up an hdd, keep in mind that you need to have additional space on it for backup copies of files. This will increase the reliability of the drive and reduce the chance of sudden loss of valuable data. In some cases, the best solution would be if you choose several drives for a special information duplication system.

Optimum hard drive speed

The main principle of the hard drive is the rotation of the disk platters around its axis, during which the magnetic head reads and writes data. The number of revolutions depends on the spindle speed. In proportion to the increase in this parameter, the intensity of information exchange with the system and the speed of the disk increase.

There are several types of disks based on the values of this indicator: Models operating at a speed of 5400 rpm are used mainly in laptops (for a desktop PC, you can choose for archival purposes), they have low power consumption, do not make noise, but work quite slowly; Drives with a speed of 7200 rpm - the most popular hard drives have such characteristics, as they are optimal for solving most of the tasks that users face;

Devices with a speed of 10,000 to 15,000 rpm - very fast and productive, used in the corporate sector, designed for powerful servers(for home use they are rarely chosen in case of non-standard needs);

Buffer memory (cache) size for hdd

Everyone who collects information on how to choose a hard drive for a PC should pay attention to the cache size of this device. It stores data that has been extracted from the media, but not yet loaded into RAM, and those that came from other system components and have not yet been written to the hdd. Too much small size buffer memory can slow down the disk.

On the modern market there are devices whose cache size ranges from 16 to 64 MB. A good hard drive should have a 32 MB or 64 MB buffer to keep it running efficiently. It is usually recommended to choose a hard drive with a large amount of cache.

Options for reading and writing information

The main parameters that determine how productively the device will exchange data with the rest of the computer are the speed of linear reading and writing data, as well as random access time.

The speed of the device is directly determined by the speed of linear reading, which should be remembered by every potential buyer who is thinking about which hard drive to choose for the system. The value of this characteristic, which lies in the range from 120 to 140 Mb / s, is considered optimal. You should not purchase a model that has a linear read speed below 100 MB per second.

The second important indicator of device performance is the random access time. It especially affects the time with which the head reads small files from the disk. For a high-quality hard drive, this figure is no more than 14 ms. Operational problems arise with devices whose random access time reaches 16-19 ms.

Be vigilant, because these indicators are not indicated by the manufacturer on the packaging of the device and they cannot be found on the websites of online stores. They are defined with a special software(for example, HD Tune 2.5) only on a working drive. Therefore, one of the instructions on how to choose a good hard drive is to search and study in detail the reviews and tests of the hdd model you like. It is from them that you can find out the real numbers and independently correctly evaluate before purchasing how this or that hard drive behaves in practice.

Top Hard Drive Manufacturers

There are several leaders in the hdd manufacturer market, which guarantee the high quality of their products, their reliability and durability. Before buying a hard drive, be sure to check the reputation of its manufacturer, as purchasing a model from an unknown company may cause data loss on your PC in the future.

Important information for those who want to know how to choose the right hard drive for your computer is that quality models are offered primarily by Seagate corporations and western digital(WD). Also in specialized stores you can find devices from Hitachi and Samsung, but their percentage of the total number of devices offered is not too large.

Manufacturers are launching various series of models on the market, which are aimed at private and corporate clients what caused the differences in price, volume and technical specifications products.

For example, Western Digital uses a simple color coding of its products, which can be used to correctly understand the specifics of using a particular device.

Hard drives with a blue mark on the case (Cover Blue) are budget solutions that have good performance parameters, but they should not be used to store especially important information.

Drives that have a green mark (Cover Green) are models that require little electricity to operate, they have average performance and produce little noise.

Devices with a red case marking (Cover Red) - drives with high speed work and high productivity, equipped with the most modern controllers.

HDDs with a black marking on the case (Cover Black) contain the best features of the models with a red marking and guarantee very high reliability of data storage.

Thanks to this detailed instructions Purchasing a good hard drive for your PC will not cause you any difficulties, because we talk about computers in Russian and make the information available to every user. Following this algorithm will allow you to choose exactly the hdd that will become a reliable component of your machine and help in solving all current problems.

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Form factor, buffer size and other HDD characteristics

In previous articles that dealt with the characteristics of the HDD, such parameters as the speed of rotation of the spindle and the noise level emitted by the hard drive were touched upon in some detail.

Also, they did not bypass the HDD interface, where the main features and differences between the SATA interface and the outdated IDE were considered. And of course, they did not forget, perhaps, the most important characteristic - this is the volume of the hard disk.

In this material, we will talk about the remaining characteristics of hard drives, which are no less important than the above.

Hard Drive Form Factor

At the moment, two form factors of hard drives are widely used - these are 2.5 and 3.5 inches. The form factor, to a greater extent, determines the dimensions of hard drives. By the way, a 3.5" hard drive can hold up to 5 platters, and a 2.5" hard drive can hold up to 3 platters. But in modern realities, this is not an advantage, since the developers have determined for themselves that it is not advisable to install more than 2 platters in ordinary high-performance hard drives. Although, the 3.5” form factor is not going to give up at all and, in terms of demand, confidently outweighs 2.5” in the desktop segment.

There are other form factors as well. For example, many portable devices use 1.8” hard drives, but we will not dwell on them in detail.

Hard drive cache size

Cache memory is a specialized RAM that acts as an intermediate link (buffer) for storing data that has already been read from the hard disk, but has not yet been transferred directly to processing. The very presence of the buffer was caused by a significant difference in speed between the rest of the system components and the hard drive.

Random access time

Other HDD Specifications

Now briefly and briefly list the remaining characteristics of hard drives:

Energy consumption - hard drives consume very little. Moreover, the maximum power consumption is often indicated, which takes place only at intermediate stages of operation during peak load. On average, this is 1.5-4.5 W;
Reliability (MTBF) - the so-called time between failures;
Data transfer rate - from the outer zone of the disk: from 60 to 114 Mb / s, and from the internal - from 44.2 to 75 Mb / s;
The number of input / output operations per second (IOPS) - for modern hard drives, this figure is about 50/100 ops / s, with random and sequential access.

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How to choose a hard drive

The hard disk drive (HDD) is an important element of the system unit. It stores user data and files. To choose the right hard drive, you need to know just a few parameters.

Main characteristics of the hard disk

Hard disk capacity

When choosing a hard drive, the first parameter that you should pay attention to is the volume. Volume - the amount of hard disk space, that is, this parameter displays how much information (movies, documents, folders, etc.) you can write to the hard disk. The volume of modern media is measured in gigabytes or terabytes. The larger the hard drive, the better. It is better to buy a hard drive for one or more terabytes.

Interface

The hard drive is connected to the motherboard via an interface cable. Internal hard drives, connect to a computer via an interface (IDE or SATA). IDE is an outdated interface. Modern hard drives are connected to the computer via the SATA interface. There are several options for the SATA interface: SATA I (up to 1.5 Gb / s), SATA II (up to 3 Gb / s), SATA III (up to 6 Gb / s). The higher the data transfer rate through the interface, the better. The best hard drive interface option is SATA III.

Spindle speed

The speed of data exchange depends on the spindle speed. It is measured in revolutions per minute (RPM). The higher the spindle speed, the better. The best option is 7200 rpm.

Buffer memory (Cache - memory)

Buffer memory is hard disk memory that stores data that has already been read from the hard disk but has not yet been transferred through the interface. The larger the amount of buffer memory, the more likely it is that the necessary data is in it and does not need to be searched on disk. Investigator, increase your speed work hard disk. At the moment, the maximum amount of memory is 64 MB.

Form Factor

The form factor of a hard drive is its physical dimensions (width, height, thickness). There are two main form factors: 2.5" (2.5") and 3.5" (3.5"). Hard drives with a 2.5” form factor are designed for use in laptops, although they can be inserted into a regular system unit using additional mounts and adapters. Due to the specifics of a laptop, budget 2.5” hard drives in most cases have a spindle speed of 5400 rpm.

3.5” hard drives are designed for installation in a regular system unit. When assembling home computer it is better to buy a 3.5” hard drive.

With these tips, you can choose a good hard drive for your computer.

The volume of the buffer deserves special attention. Often, HDDs are equipped with 8, 16, 32 and 64 MB caches. When copying large files between 8 and 16 MB, a significant difference in terms of performance will be noticeable, but between 16 and 32 it is already less noticeable. If you choose between 32 and 64, then there will be almost none at all. It must be understood that the buffer often experiences 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 normal user, both the first and second values will suffice. Moreover, in addition to this, performance is also affected by the size of its own cache built into the system. It is he who increases the performance of the hard drive, 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 regular user except in rare cases, you won't notice much of a difference. Of course, it is recommended to choose and buy devices with the largest size, which will greatly improve the performance of the PC. However, this should be done only if financial possibilities allow.

purpose

It is designed to read and write data, however, on SCSI drives, permission to write caching is rarely needed, since the default setting is that write caching is disabled. As we have already said, volume is not a decisive factor for improving work efficiency. 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 affected 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 most 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 a fairly large amount of time. At the same time, the HDD transmits data more than 100 times faster than when requested by physically accessing the hard drive. That is, it allows the device to work even if the host bus is busy.

Main advantages

Buffer memory has whole line advantages, the main of which is fast data processing, which takes a minimum amount of time, while physical access to the sectors of the drive requires a certain time until the disk head finds the required data section and starts reading them. Moreover, hard drives with the largest storage can significantly offload 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 much more efficient and faster. But today, with 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.

In conclusion, I would like to say that buffer memory, whatever it is, improves the performance of a particular program or device only if the same data is repeatedly accessed, the size of which is no larger than the cache size. If your work at the computer involves programs that actively interact with small files, then you need an HDD with the most storage.

Register memory

Do not confuse with ECC memory, although register modules always use ECC.

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

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

Only control and address signals are buffered in register memory.

Buffered memory is an older term for registered memory.

Some new systems use fully buffered FB-DIMM memory, which buffers not only the control lines, but also the data lines using a special AMB controller located on each memory module.

Registered memory technique can be applied to different memory generations, 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. Theoretically, you can do without this part, but then the OS will have to be loaded from removable media or via network connection, and store working documents 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 disk. The plate is covered with a layer of ferromagnet (usually chromium dioxide), the clusters of which remember one or zero due to magnetization and demagnetization. There can be several such plates on one axis. For rotation, a small high-speed electric motor is used.

Unlike the gramophone, in which the needle touches the record, the reading heads do not adjoin the disks closely, 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 the loss of hard disk space, usually along with user files.

That is why, for important or dear to the heart data (for example, a family photo archive or the fruits of creativity of the computer owner), it is recommended to do backup, and it is better to have several at once.

What is a cache

Buffer memory or cache is a special kind of RAM, a kind of “layer” between a magnetic disk and PC components that process data stored on a hard drive. It is intended for smoother reading of information and storage of data that is currently most often accessed by the user or the operating system.

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

Indirectly, because different users operate 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.

Guessed why? That's right, because limited quantity cycles of overwriting information on the HDD.

Optimum sizes for various tasks

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

It is this amount of cache that I recommend focusing on if you want to build a gaming computer that will not become obsolete in a couple of years. For simpler tasks, you can get by 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 buffer memory is enough.

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

What does the cache do in your hard drive?

Now let's take a look at how hardwiring works. HDD, which, although it is being replaced 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. Reading heads move to the desired sector and write or read information. (Visually, all this resembles a vinyl player).

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

So, in order for the system not to deal with the rough work of folding together individual blocks of information, this work it was decided to get the hard drive itself, which will itself link them together in its own cache. Conditionally, one can draw such an analogy this process: the boss needed all the information on the deal and the subordinate, in order not to carry a separate document to the office, first collects and groups them in his department.

I’ll add right away that in SSD the problem of inertness in reading information is not so critical. Here, the rate of this process is several orders of magnitude higher. But due to the fragmentation of recording large amounts of data, optimization of working with them is also necessary. Therefore, cache is also present in some solid state drives.

Cache memory is one of the HDD parameters

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

In HDD, in addition to mechanical parts, there is a control board with connectors. On it is a special microcircuit, which is a memory with high-speed access. This is the cache. Its volume is relatively small and in conventional hard drives it can be 32 and 64 megabytes (in some older models there are also values of 8 or 16 MB). This is quite 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 note 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 increasing complexity program objectives it will still be visible.

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

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

Hard drive cache algorithm

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

a request is sent from the CPU to the controller, which identifies the data by certain marks and immediately checks for their presence in the hard disk cache. If there are any, the HDD is not accessed;
in case of absence necessary information they are read from the hard drive, and nearby data is additionally captured, which, with a high probability, may also be needed in subsequent requests;
for this block of information in the cache memory, the corresponding space of a certain size is freed. This procedure is not an easy task, since the computer must sacrifice some data from the buffer. The choice is made using several algorithms that determine the degree of "uselessness". To do this, an assessment is made by the prescription of the last use of information, by the frequency of access to it.
Up-to-date data is loaded into free space. Further, the process of interaction between the processor and the hard disk continues again according to this algorithm.

And one more thing: hard drive cache 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 during an emergency shutdown of the computer.

Here we smoothly approached the frequently asked question: is it necessary to clear the cache memory of the hard drive? If you are talking about those 64 megabytes that are stored on the chip, then my answer is: no, it makes no sense. If you feel like it so badly, just unplug your 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 different programs. Here they take up an impressive volume over time, and to eliminate them, you can simply use an application like CCleaner.

Data caching by the hard drive'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 the same as a cache, in relation to the HDD. It is several orders of magnitude larger, but the speed of its work still loses to its own hard drive module.
A sector is allocated on the hard disk for temporary files that will be written without fragmentation. This is called the paging file (virtual memory) and its size can exceed the amount of RAM.

But these are completely different devices that require a separate article. And as for the cache memory of the hard disk 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!

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The algorithm of the hard drive cache. What is hard disk cache memory and why is it needed Buffer memory hdd

Hard disk tasks

Hard disk type

Hard disk capacity

Hard drive speed and cache

In custody

Hard Drive Form Factor

Hard drive cache size

Random access time

Other HDD Specifications

physical dimensions hdd

Hard disk interface

Capacity or volume hdd

Optimum hard drive speed

Form factor, buffer size and other HDD characteristics

Hard Drive Form Factor

Hard drive cache size

Random access time

Other HDD Specifications

How to choose a hard drive

Main characteristics of the hard disk

Hard disk capacity

Interface

Spindle speed

Buffer memory (Cache - memory)

Form Factor

purpose

Main advantages

Register memory

How a hard drive works

What is a cache

Optimum sizes for various tasks

What does the cache do in your hard drive?

Cache memory is one of the HDD parameters

Hard drive cache algorithm