Where does the memory go from drive C? Where does memory disappear on iPhone and where to look for it?

Good afternoon.

It often happens that no new files seem to have been downloaded to hard drive, but the space on it still disappears. This can happen for various reasons, but most often space is lost on the system drive C where Windows is installed.

Typically, such loss is not associated with malware or viruses. Often the fault is with the Windows OS itself, which uses free space for various tasks: space for backup save settings (for Windows recovery in case of failure), space for the swap halyard, remaining junk files etc.

We’ll talk about these reasons and ways to eliminate them in this article.

1) Where does space on your hard drive go: searching for “large” files and folders

This is the first question that is usually faced with a similar problem. You can, of course, manually search for folders and files that take up most of the disk space, but this is time-consuming and not rational.

Another completely different option - use special utilities for analysis occupied space on your hard drive.

There are quite a lot of such utilities, and I recently wrote an article on this issue on my blog. In my opinion it is quite simple and quick utility- this is Scanner (see Fig. 1).

2) Configure Windows recovery options

In general, having system backups is good, especially when you have to use a checkpoint. Only in cases where such copies begin to take up more and more more space on the hard drive - it becomes not very comfortable to work (Windows begins to warn that there is not enough space on the system disk, and this problem can also affect the performance of the system as a whole).

To disable (or limit HDD space) the creation of checkpoints, in Windows 7, 8, go to the control panel, then select “system and security”.

Then go to the "system" tab.

In the sidebar on the left, click on the “system protection” button. A window should appear “ System Properties"(see Fig. 3).

Here you can configure (select the drive and click the “Configure” button) the amount of space allocated for creating recovery checkpoints. Using the setup and delete buttons, you can quickly regain your hard drive space and limit the number of megabytes allocated.

By default, Windows 7, 8 includes control points recovery on the system disk and sets the value to the occupied space on the HDD around 20%. That is, if your disk volume on which the system is installed is, say, 100 GB, then about 20 GB will be allocated for checkpoints.

3) Setting up the swap file

The page file is a special place on the hard drive that is used by the computer when it does not have enough RAM. For example, when working with video in high resolution, highly demanding games, graphic editors etc.

Of course, reducing this page file can reduce the performance of your PC, but sometimes it is advisable to move the page file to another hard drive, or set its size manually. By the way, it is usually recommended to set the page file to approximately twice the size of your actual RAM.

To edit the swap file, go to the advanced tab (this tab is next to the Windows recovery settings - see paragraph 2 of this article above). Further opposite speed Click on the “Options” button (see Fig. 5).

Rice. 5. System properties - go to system performance parameters.

Rice. 6. Performance parameters

After this, you need to uncheck the box next to “ Automatically select paging file size» and set it manually. By the way, here you can specify the hard drive to place the paging file - it is recommended to place it not on the system drive on which Windows is installed (thanks to this, you can speed up the PC somewhat). Then you should save the settings and restart the computer (see Fig. 7).

4) Removing junk and temporary files

Such files usually mean:

Browser cache;

When you view Internet pages, they are copied to your hard drive. This is done so that you can quickly load frequently visited pages. After all, you will agree that it is not at all necessary to download the same elements again; it is enough to check them with the original, and if they remain the same, load them from disk.

Temporary files;

Folders with temporary files take up the most space:

C:\Windows\Temp

C:\Users\ Administrator\AppData\Local\Temp(where "Administrator" is the name account user).

These folders can be cleaned; they accumulate files that are needed at a certain point in the program’s operation: for example, when installing an application.

Various log files, etc.

Cleaning all this “good” manually is a thankless task, and not a quick one. Eat special programs, which will quickly and easily clean your PC from all kinds of “garbage”. I recommend using similar utilities from time to time (links below).

Cleaning hard drive -

Best utilities for PC cleaning -

Even Anti-Viruses can take up space on your hard drive... First, check their settings, see what is in quarantine, in report logs, etc. Sometimes it happens that many files (infected with viruses) are sent to quarantine, and it is sent to its own queue begins to take up significant space on the HDD.

By the way, in the year 2007-2008, Kaspersky anti-virus on my PC began to significantly “eat up” disk space due to the “Proactive Protection” option being enabled. In addition, antiviruses have various kinds of logs, dumps, etc. It is recommended that, if you have a similar problem, you pay attention to them...

Dear friends, I once encountered a problem - before my eyes it became Lost free space on drive "C". This was quite a long time ago, but an acquaintance reminded me of this the other day, literally shouting for help. There are few programs installed on the computer, and the free space is literally melting before our eyes. He installed the Windows 7 operating system a few days ago; the sellers assured him upon purchase that the system was licensed. But he had already begun to doubt this, thinking that he had been given a defective OS.

Ugly picture? It got to the point where he had 2 GB of 58 GB of free meta on disk (C). I deleted everything I could and moved the rest to disk (D). It didn’t help for long, the next day the same picture happened again. They began to deal with him. For old times' sake, I immediately installed the Free Disk Analyzer program on his computer. The program is easy to configure, the interface is in Russian, and it is free. Free Disk Analyzer quickly analyzed all the disks on your computer. And he produced this picture.

Now you need to click on the disk you need and Free Disk Analyzer will show how much space and which folder is taking up space.

It turned out that the “System Volume Information” folder occupied half of disk space. It is clear that an increase in the volume of the folder also led to a decrease in the volume of disk (C). In general, where did this System Volume Information folder come from and what does it contain?

We all want to take care of protecting our OS; in addition to installing antiviruses, we also set up system recovery. Read more about system recovery (rollback) in my article. When installing some programs and uninstalling them, when installing updates from Microsoft, we create system restore points.

How many of them can be created? But here it all depends on the user settings. By default, when you set new system, you have allocated 3% of disk space for recovery. 3% is not much, so recovery points do not last long. It’s a shame, what if there’s some kind of problem, so I want the restore points to be saved longer. So my unfortunate friend gave as much as 55% to restore the system.

Each restore point captures the state of the system at a specific point in time. All this data remains on the hard drive, thereby filling up a considerable amount of space, and all this information is stored in the System Volume Information folder. Somehow I had to read other people’s very abstruse advice on how to clean out this folder. But I did a simpler thing with a friend’s computer - I entered system restore and deleted all the created restore points.

To do this, you just had to click the “Delete” button. Then I moved the slider, setting the value to 5%.

In the empty line of the window that opens, you can enter any word in Russian or Latin, or a number. Clicked “Create” here too.

Once you have completed creating a manual restore point. I opened the computer.

The problem with disappearing free space on drive C is one of the global ones for all users working in operating systems Windows family. Most owners of personal computers and laptops approach solving the problem rather strangely, giving their equipment for repair to a specialist or service center. The service is not free. But any user who has the Internet and the desire at hand will not have to make much effort to clean it themselves. The purpose of this article is to answer the question “where does the memory disappear from drive C?” Ways to solve the problem are also presented here.

Ignoring additional partitions

In most cases, the user’s laptop or personal computer has a modern hard drive (maybe several drives), which is divided into at least partitions C and D. As often happens, the memory on drive C is reduced, and drive D is empty. All you need to do is transfer music, movies, photos and documents to additional section, and the problem will be solved. It remains to clarify where all the user’s files are hidden on drive C.

1. Desk. In 100% of cases, it contains more than one gigabyte of files. Because of this, memory disappears on the C drive. For ease of access, directories with data can be moved to an additional partition, and then shortcuts can be made from them and placed on the desktop.
2. "Downloads" folder. By default, all browsers store documents and multimedia downloaded from the network into it. It is located in the user’s profile, which can be accessed through “My Computer” - “C:\Users\Profile”.

For torrent lovers

Many computer owners download movies from high quality using Zona or Utorrent programs. After viewing them, users do not delete them, remaining on the distribution. As a result, not only the memory on drive C is clogged, but also the Internet. In the program settings, you need to look at where the files are uploaded, follow the link and delete unnecessary ones. In the future, after watching films, correct deletion is recommended. By right-clicking on the file name in the program, select deleting both the torrent and the downloaded file.

Alternatively, if you want to keep the film in your collection, you should set the path to additional disk, for example "D:\torrents". This solution will eliminate the problem of running out of free space on the C drive.

Windows restore checkpoints

A wonderful feature in the operating system allows all users to restore it to the last successful boot, in case Windows work was damaged by viruses, incorrectly installed software or drivers. But there is also reverse side medals. When writing down points, he stores them in his system folder, accordingly, eats up memory on drive C. Reduce system reserved There is no need for space for recovery points, much less disabling this function altogether. It is enough to clean it every six months.

To login service menu you need to perform the following sequence of actions. “Start” - “Control Panel” - “System” - “ Additional options systems." Select the “System Protection” tab and, placing the cursor on drive C, wait for the “Configure” button to become active and click it. In the window that appears, you can familiarize yourself with the occupied space of the recovery points and, accordingly, delete them using the button of the same name. After liquidation unnecessary files It is recommended to return to the previous menu and click the “Create” button so that there is at least one restore point.

Swap file

One more useful feature Windows is designed to increase system performance. Without going into details, it is used as a RAM assistant. By temporarily dumping unused data onto the hard drive, the system frees up memory for its needs. The paging file size is fixed, set either by the user or by Windows automatically. Due to incorrect

To configure the capacity of this file, you need to go to settings: “Start” - “Control Panel” - “System” - “Advanced system settings”. Select the “Advanced” tab. In the “Performance” section, click the “Options” button. In the window that opens - “Advanced”. Click the “Change” button in the “ Virtual memory" At the very bottom of the window that appears there is information about the current size of the paging file and the recommended size. For drive C you need to specify the recommended setting, and for other drives you need to disable the paging file. Original size and maximum can be the same.

Sleep mode

Many have noticed that when the user is inactive, the monitor screen fades. This way the system goes into sleep mode, from which it can be woken up by moving the mouse. On laptops this feature is useful when running on battery power, but on a personal computer it is not needed. Sleep mode can be disabled, because it causes memory to disappear on the C drive due to the fact that the entire contents of the RAM are written to the hard drive for storage. We go along the path “Start” - “Control Panel” - “Power Options”. Select the item " High performance” and in its settings indicate that the transfer to sleep should never be carried out. After saving and restarting the computer, it is recommended to go to the paging file settings and adjust its size, because it also reserves space for sleep mode, which was disabled.

Clearing cache

When installing everything modern browsers are not configured to independently clear the history of visited pages. Accordingly, the more time a user spends on the Internet, the faster memory disappears from drive C. This is quite natural. Cleaning can be done in two ways. The first is to go to the browser settings and find the section responsible for storing data on the media. In this section of any browser there is a “Clear” button. The more information accumulated during operation, the longer the cleaning will take. You need to be prepared for this, because the process may take more than one minute. During the cleaning process, it may seem that the browser, and the entire system, has frozen. This is not true, it’s just that the cache is written on the hard drive in more than one place and it takes a lot of time for the system to search for this data. The second method is more interesting, since it is produced professional program, which “knows” a lot about unnecessary resources of the Windows system and will find where the memory from drive C goes.

Global from garbage

A software called CCleaner must be installed on every user personal computer and laptop. This wonderful free creation of programmers is designed not only to clean systems of unnecessary files, but also to fully manage operating system resources. The program will give detailed information about where the memory from drive C goes. All actions in the program are designed to improve computer performance. The program is available for download directly from the developer’s website, which eliminates the presence of viruses and spyware in it. After launch, the user will have access to the “Cleaning” menu, from which to start. IN Windows bookmarks and “Application”, the developers have noted the data that needs to be deleted, but it is recommended to uncheck the “Passwords” and “Log” boxes so that after cleaning you do not have to look for login data social media again. After analyzing and cleaning, you can find more than a dozen free gigabytes on the active disk.

Duplicate files also take up space

A fairly popular problem among users is copying, instead of moving, multimedia files and documents. Because of this, the memory on drive C is filled. The CCleaner program allows you to find and delete all duplicate files on your computer. To do this, in the “Service” section there is a “Search for duplicates” item. You need to be very careful with it, because duplicates can be found in the “Windows” and “Windows” system directories. Program Files", which should not be deleted. Get rid of problems with system files The “Exceptions” item will help, where you can specify paths that will be ignored by the program during the search. Duplicate search has fine tuning, for example, you can specify the size of the files you are looking for. By narrowing the search to one gigabyte, you may find the same movie recorded twice. After removing it, the question of where the memory disappears from drive C will be resolved.

Removing unnecessary programs

Over the many years of using the computer, during which the user installed large number software, there may be a dozen applications that have not been used for a long time. Because of them, memory is also lost from the hard drive. Correct removal unnecessary programs With using CCleaner will free up free space on the active media. To do this, just go to the “Service” section and select “Uninstall programs”. Go through the names in the list and delete unused applications. Before uninstalling, it is recommended to clarify the purpose of the program by entering it into the browser search bar. After all, system applications are also reflected in the list.

In conclusion

Having found out where the memory on drive C went and deleted it, you should use the services of applications to clean the registry, or rather its integrity. After all, Windows is for everyone remote file created a shortcut or prescribed some actions for herself to open it. IN CCleaner program A good registry cleaner is built in. They are to be used. By going to the “Registry” menu, the user needs to analyze and correct. During the correction process, the program will prompt you to do backup copy. It is quite reasonable to keep the backup registry on system disk, specifying the path to any directory. But most specialists do not see the need for this, so it is up to the user to decide whether to make a copy.

Here I describe common problems that users encounter. When space on your hard drive disappears, you begin to wonder. You try to do something, delete some unnecessary programs, files, etc., but the space is never freed up. Today there was 50 GB free, and tomorrow it’s already 30 GB; it’s not clear where the disk space goes.

I’ll say right away that it’s not always this problem occurs due to viruses or malware. We will now talk about the reasons why hard drive space is lost.

The first reason is the system functions of the operating system

The loss of free disk space can be caused by any functions of the . These could be:

1. Records of programs, restore points and more.
2. Windows Updates
3. One of known reasons is and , which can take up a lot of space on the hard drive.

Let's look at each of these points and try to free up as much space on your hard drive as possible.

Restore points

Typically, Windows independently allocates a certain amount of disk space in order to record installations of programs, drivers, and other changes in the system. Over time, the space taken up increases.

You can configure recovery point settings as follows:

Go to Control Panel and click on "System and Security", Then "Safety and Service", and then "Recovery". In the window that opens, look for something like "System Recovery Setup".

Now select the desired drive and click "Tune".

Here you can both enable and disable recovery points, and you can also set a certain amount of space occupied by this function.

I'm pretty sure that most users don't use this feature, so those who want it can disable it. Today HDD volumes are very large, so I don’t think that disabling recovery points will somehow increase storage capacity. Sometimes it can even come in handy.

Moreover, you can delete restore points at any time through the appropriate settings.

WinSxS folder

We have already talked about this in one of our articles. This folder can take up to several gigabytes. you can read what you can do with this folder.

Swap file pagefile.sys and hibernation file hiberfil.sys

I also wrote about this in my articles on this site. Files that also take up quite a bit of space. Speaking of the hibernation file, on Windows 8 it will take up a significant amount of space on your hard drive, even if you are not using it. I wrote about him.

The swap file is all useful, and it’s written about how to configure it, be sure to follow the link. I will not write about this in this article, since I already have an article on this topic.

Other reasons for lost disk space

It is possible that the points that we listed above did not help you, or perhaps they did not relate to the problem of missing space, then let’s consider other cases.

Temporary files

When we install programs, temporary files are created, which are not always deleted after removing the program itself.

To delete these temporary files, you can use the built-in utility "Disk Cleanup". To do this we go to "My computer", right-click on to the desired disk, and then press "Properties". In the window that opens, click "Disk Cleanup".

Now we wait a bit for the utility to collect the necessary data.

As you can see, my temporary files took 249 MB, select the checkboxes opposite and click OK.

An alternative could be the program, which I have presented in my articles not for the first time. And for good reason, since it is very useful and helps optimize the system.

Removing programs from your computer

You need to uninstall programs correctly. Standard Manager Uninstaller in Windows is not very suitable for this, since it does not remove entries in the registry and some remnants of the program. For such a case, you can use, for example, Uninstall Tool. Or read here.

And the most important thing is not to clutter your disk with all sorts of garbage. Regularly uninstall apps you no longer use. Take care of your hard drive. That's all.

Comparing the amount of RAM provided by the BIOS and the operating system
with physical volume installed memory, you can almost always see that
There is less memory available than installed. "Missing" is usually units
megabytes, but sometimes reaches larger sizes. In the proposed
The material lists and discusses in detail the reasons for this phenomenon.
Recommendations for optimizing the use of address space are also provided.
and RAM. We will talk exclusively about the amount of memory that the BIOS
tells the operating system why it is smaller than the physical volume.
Memory management within the OS is the topic of a separate article.

First check

Of course, the question of “missing” memory is not always asked solely from
research interest. And the answer does not always lie in the field of architecture and
motherboard circuitry. If after purchasing a new computer or
reinstallation DIMM modules, we see that there is significantly less memory than
stated by the equipment supplier, there is a well-founded desire
check the completeness of our system. There are also cases when the inscriptions on
DIMM labels are not accurate. Labeling analysis
the memory chips themselves installed on DIMMs are also not always effective, so
as not all manufacturers adhere to a regular designation system. That's why,
before moving on to main topic article, let us recall one recipe for identifying
banal forgery. Moreover, you can use it without even opening the case.
computer.

It is known that in modern systems, identification of operational modules
memory is based on the use of the SPD (Serial Presence Detect) protocol. On
Each DIMM module, along with RAM chips, is installed
256-byte read-only memory (EPROM) chip. into her
The module manufacturer has recorded its parameters. When the computer starts, BIOS
reads these parameters and uses them to initialize the memory controller.
Diagnostic programs launched in an OS session (for example, Astra32, Everest),
can also read SPD information, so it is viewable
user. If, according to SPD information, the memory volume (sum of module volumes)
corresponds to the value declared by the supplier, but at the same time, the operating
The system has less memory available, the reason is due to the architecture and
circuit design of the motherboard discussed below, part of the memory is allocated for
use various devices or unavailable due to restrictions
DRAM controller. This article is devoted to considering precisely such situations.
If, however, the amount of memory determined based on SPD is less than expected, then all
much more prosaic - you need to file a claim with the supplier.

Below are the reasons why the operating system has
There is less RAM than is physically installed on the board.
Obviously, each of the reasons belongs to one of three types:

1. Part of the memory is used for internal needs of the BIOS or system devices
   fees.
2. Some memory is physically inaccessible due to limitations of the memory controller.
3. Some memory is physically accessible in the address space, but not
   used due to operating system limitations.

Memory allocation for System Management RAM

System Management RAM is memory used by the BIOS for its own needs.
Physically, it is part of the RAM. It is “cut out” from the address
space using the mapping logic included in the " north bridge"
chipset. This question discussed in detail in a previously published article "and
". How much memory
will be "cut off" for SMRAM depends on the BIOS implementation. On most platforms
this is 128 KB, uses the range 000A0000h-000BFFFFh, shared with video
adapter. Some platforms also use Extended SMRAM,
located above 1MB and its volume reaches several megabytes.

Memory allocation for Shadow RAM

Shadow RAM or “shadow” memory is an area of ​​RAM in which
the contents of the ROM BIOS chip of the motherboard are rewritten or unpacked
fees, as well as additional BIOS peripheral adapters. Initially this
was intended as an option solely to improve performance, since
RAM operating speed is significantly higher than ROM operating speed. Modern
BIOS implementations use packaged storage of the main block, when
At the start it is unpacked into Shadow RAM. Thus, Operation Shadow from
optional has become mandatory. The packaging allows you to use
a smaller ROM chip, therefore cheaper. For correct
ROM emulation, mapping logic included in the “north bridge” of the chipset,
blocks writing to this area RAM. The unpacked BIOS block placed in
Shadow RAM, sometimes called Runtime block.

On most platforms, for Runtime BIOS blocks of peripheral adapters
the range 000C0000h-000EFFFFh is allocated. For the Runtime block of the system BIOS –
range 000F0000h-000FFFFFh. Note that even if the specified ranges
partially used or not used, the entire 256 KB block
000C0000h-000FFFFFh is “cut off” from RAM. Almost everything
modern chipsets allow it to be used only as Shadow RAM.

Note

The statement that RAM (RAM) is significantly faster than ROM (ROM)
valid for a special case - in relation to element base and circuit design
personal computers, since they use slow ROM chips and
fast RAM chips, in addition, the width of the RAM data bus on the motherboard
the fee is significantly higher. To the physical principles of operation of RAM and ROM cells this
statement does not apply.

Memory allocation for ACPI tables

ACPI specification, which is used to transfer information from the BIOS to the OS
about the platform configuration, as well as to optimize energy consumption,
is an alternative approach to the interaction between the BIOS and the OS. Let us remind you that
what's in "classic" BIOS functions, for example, in disk service functions,
available through software interrupt INT 13h, operating system or other
a program must call subroutines to perform a given operation,
included in the BIOS. Interaction between OS and platform via ACPI
is performed fundamentally differently. BIOS at platform startup, before booting
The OS writes into a special memory area a set of tables describing the execution
a number of operations. Simply put, tables contain information about what data
in which register to write to perform a given operation. The OS reads this
information and uses it when interacting with equipment. One of the advantages
This approach is that regardless of the processor instruction system or the current
operating mode (for example, 16-32- or 64-bit), you can use the same
tables, since the construction of ACPI tables, as opposed to executable BIOS procedures,
not tied to processor architecture.

The amount of memory allocated to store ACPI tables is implementation dependent
BIOS. This is usually hundreds of kilobytes; often the BIOS rounds up the size of the reserved
areas up to 1 MB. Note that unlike SMRAM (which is only available in
SMM mode) and Shadow RAM (which has write protection), memory area,
containing ACPI tables does not have special status from the controller's point of view
memory. The fact of its redundancy is only that the BIOS, when transferring the OS
information about the amount of memory, transmits the value minus the size of this area.
ACPI tables use the address range immediately adjacent to
the upper limit of Extended memory. Details in.

Memory allocation for USB RAM

As is known, USB controller is an intelligent device capable of
interact with RAM bypassing the processor (in Bus mode
Master). This interaction consists not only of data transfer between
devices connected to USB and buffers in RAM. For work
A lot of USB controller is required supporting information in memory
for example, transaction schedule. Since the BIOS must communicate with
USB devices before the OS boots (for example, input from USB keyboards, loading from
Flash, etc.), the BIOS, not the OS, should reserve memory. Usually reserved
tens of kilobytes.

Note that devices such as, for example, a controller hard drives, Also
support Bus Master mode and use control information, available
in RAM. But the difference is that the disk controller, unlike
USB controller, can also be used in software exchange mode (PIO
Mode), which is what the BIOS does when transferring control to boot the OS. Switch to mode
Bus Master (synonymous with DMA) and memory reservation for control units, in this
case is the responsibility of the OS, not the BIOS.

Memory allocation for integrated video adapter

If your motherboard has an integrated video adapter,
implemented as part of the "northbridge" chipset, as video memory
Usually part of the RAM is used. Before loading OS, BIOS
reserves a block of one to tens of megabytes for video memory. On
some boards, in BIOS Setup it is possible to control the size of the allocated
block. When the OS starts and the video driver is loaded, initialization occurs
graphics processor and at the disposal of the video adapter can be dynamically
highlighted more memory.

Note that there are boards that have memory reservations for
integrated video adapter occurs even when it is not
used. One of the reasons for this is a poorly written BIOS.

Also note that the integrated video adapter is not always implemented in
part of the "northbridge" chipset. There are motherboards containing
“full-fledged” video adapter in the form of a separate graphics controller chip
with its own memory chips. In this case system memory for video needs
adapter is not reserved.

4GB limit and Memory-Mapped I/O

This factor sometimes takes up more memory than all the others together
taken. Moreover, when we talked about such things as SMRAM, Shadow RAM, ACPI, then
the point was that the memory that the BIOS “hidden” from the operating system
used for internal needs of the platform. Here, part of the memory is just
disappears. When and why does this happen?

Let's take real example. Intel Socket 775 class platform. Intel processor
Pentium 4 650 3.4 GHz (Prescott-2M core), Intel 925XE chipset. Install 4 GB
memory and we see that the operating system has about 3.5 GB available. Where did it go
about 0.5 GB?

Let's start the investigation with the processor. Reading the document and browsing
assignment of signals to Socket 775, we see that the processor supports 36-bit
addressing. The most significant bit of the address is A35# (counting from zero). For reference, this is
contact with coordinates AJ6 on Socket 775. The number of addressable bytes is 2 in
powers of 36, that is, our processor can address 64 GB of memory. Thanks to
paging mechanism, the use of a 36-bit address is possible as in
32- and 64-bit mode. Details in. Thus, in the chain,
which we trace, " weak link" is clearly not a processor.

The next component on the way from the processor to memory is the "northern"
bridge" of the chipset, in our example it is Intel chip 82925XE, described in . From
document it follows that the chipset supports 32-bit addressing,
therefore, the amount of memory address space is (2 to the power of 32) bytes,
that is 4 GB. Moreover, all 4 GB cannot be allocated for RAM, it is required
place a number of devices, which are also accessed through
memory space. That is why the available amount of RAM will be
significantly less than 4 GB. Full list such devices can be found from
documents For the platform in question, videos take up the largest volume
memory and window for accessing configuration registers PCI Express. Let's consider
them in more detail.

Classic VGA adapters, produced back in the days of the ISA bus, use
page-by-page access to video memory through a window whose size does not exceed 128
KB (000A0000h-000BFFFFh). Modern adapters supporting this mode for
compatibility, also support linear access to video memory. At the same time
an adapter with 256 MB of video memory needs to allocate the same amount of address memory
space. Due to unification in the production of video adapters, you can find
and such situations when an adapter with 128 MB of video memory requires the allocation of a window
256 MB in size.

Classic mechanism for accessing the PCI bus configuration space,
described in uses 256 bytes of configuration registers per
device. The PCI Express specification uses 4 KB register blocks,
therefore, there was a need for a new mechanism to access them. New mechanism
uses a 256 MB address space region through which
configuration registers of all devices are addressed as memory cells.
Details in.

Issues regarding the organization of memory-mapped registers (Memory-Mapped I/O)
discussed in the previously published article ",
And
".

Memory Remap Operation

Starting from Intel chipset 955, the 4 GB limit has been exceeded. Of course, in
this happened in the model ranges of chipsets for servers and workstations
much earlier.

The Intel 82955X chip receives a 36-bit address from the processor and
supports 64 GB address space. Maximum amount of RAM
– 8 GB, this time the limitation is not related to the bit size of the address, which
The "north bridge" is capable of receiving from the processor, and with the capabilities of the controller
DRAM.

Typically, when using the Memory Remap operation, the range 0-4 GB is formatted
the same as before. There is RAM, a fragment of which
inaccessible due to the need to accommodate other devices. The innovation is that
the specified fragment does not disappear, but is placed at addresses above 4 GB.
Accordingly, if we have more memory than 4 GB, everything that does not fit in
range 0-4 GB, placed higher.

Of course, the benefit from the physical availability of memory above 4 GB will only be
when the operating system supports addressing above 4 GB. This
provided in 64-bit mode, as well as in 32-bit mode when using
PAE (Physical Address Extension). If the OS does not support addressing above 4 GB,
The relocated memory will no longer be available. Details in.

It should also be remembered that memory accesses are initiated not only
central processor, but also other devices using Bus technology
Master, for example, a hard drive controller. If the controller supports
only 32-bit addressing when reading and writing data, then when placing data
above 4 GB, you will need to additionally use a transit buffer,
located below 4 GB, since the disk controller “does not know how” to address memory
above 4 GB. The transfer between the transit and destination buffer must be performed
CPU. This reduces performance and wastes memory.
Therefore, a platform can be considered a “true 64-bit” only when it is not
Only the processor, but also Bus Master controllers support 64-bit addressing.

Conclusion

The logical continuation of this material is a presentation of methods and
code fragments that allow, for a given platform, "bit-accurate"
determine how memory is used that the BIOS has “hidden” from the operating system
systems. Therefore, if there is reader interest, the author plans
continuation. The task is complicated by the fact that in order to obtain answers to many of
questions posed, you will need to analyze the contents of the system
configuration registers, the architecture of which is not determined uniformly for all
platforms as standard. Such registers are implemented differently in each chipset. TO
Unfortunately, detailed documentation is not available for all chipsets. That's why,
There are no universal recipes here. Revealing this topic, the author outlined
basic principles by which the interested reader can
own research for your specific platform.

Sources of information

developer.intel.com:

1) Intel Pentium 4 Processor 660, 650, 640, and 630 and Intel Pentium 4
Processor Extreme Edition Datasheet. Document Number: 306382-001.
2) TLBs, Paging-Structure Caches, and Their Invalidation. Application Note.
Document Number 317080-001.
3) Intel 925X/925XE Express Chipset Datasheet. Document Number: 301464-003.
4) Intel I/O Controller Hub 6 (ICH6) Family Datasheet. Document Number
301473-001.
5) Intel 955X Express Chipset Datasheet. Document Number 306828-001.
6) Intel I/O Controller Hub 7 (ICH7) Family Datasheet. Document Number
307013-002.
7) AGP V3.0 Interface Specification (no number).

Electronic documents available on the website
developer.amd.com:

8) AMD Functional Data Sheet, 754 Pin Package. Publication #31410.
9) AMD Functional Data Sheet, 939 Pin Package. Publication #31411.
10) AMD Functional Data Sheet, 940 Pin Package. Publication #31412.

Electronic documents available on the website
pcisig.com:

Documents on pcisig.com are available only to PCI members
Special Interest Group. Taking advantage search engines, can be found
These documents are for free download.

11) PCI BIOS Specification. Revision 2.1.
12) PCI Local Bus Specification. Revision 3.0.
13) PCI-to-PCI Bridge Architecture Specification. Revision 1.1.

Electronic documents available on the website
acpi.info:

14) Advanced Configuration and Power Interface Specification. Hewlett-Packard
Corporation, Intel Corporation, Microsoft Corporation, Phoenix Technologies
Ltd., Toshiba Corporation. Revision 3.0.:

Books:

15) V.L. Grigoriev. Microprocessor i486. Architecture and programming.
Moscow LLP "GRANAL" 1993.
16) Yu.M. Kazarinov, V.N. Nomokonov, G.S. Podkletnov, F.V. Filippov.
Microprocessor kit K1810. Structure, programming, application.
Reference book. Moscow "Higher School" 1990.
17) M. Hooke. IBM PC hardware. Encyclopedia. Saint Petersburg,
publishing house "Peter" 2006.