The initial loading of the operating system is carried out using keys. Computer boot process

You turn on the computer, a text loading screen appears on which numbers and letters quickly flash. Usually, the computer works fine and you don't pay attention to them. But this is an important part of the computer’s operation during which the firmware built into the BIOS runs. But then something incomprehensible happened and everything stopped, an error code is displayed on the screen, and sometimes nothing is displayed at all - the cursor blinks and everything is frozen in an incomprehensible dream.

Boot sequence for a standard IBM-compatible personal computer

After turning on the personal computer, its processor does not yet start working.

The first device that starts after pressing the computer's power button is the power supply. If all supply voltages are available and comply with the norm, a special Power Good signal will be sent to the motherboard, indicating successful testing of the power supply and allowing the system board components to start.

After this, the chipset generates a CPU reset signal, which clears the processor registers and starts it up.

The first command to be executed is located at address FFFF0h and belongs to the BIOS address space. This command simply transfers control to the BIOS initialization program and executes the next command (BIOS firmware).

The BIOS initialization program, using the POST program, checks that all computer devices necessary for the BIOS to operate and subsequently load the main operating system are working correctly and initializes them.

Thus, its job is to sequentially read and execute commands from memory.

System memory is configured so that the first instruction the processor reads after a reset will be in the BIOS chip.

By sequentially selecting commands from the BIOS, the processor will begin to perform a self-test, or POST, procedure.

POST procedure

Procedure POST self-test consists of several stages.

• Initial initialization of the main system components;
• Detecting RAM, copying BIOS code into RAM and checking BIOS checksums;
• Initial chipset setup;
• Finding and initializing the video adapter. Modern video adapters have their own BIOS, which the system BIOS tries to detect in a specially designated address segment. During the initialization of the video adapter, the first image formed with using BIOS video adapter;
• Checking the CMOS checksum and battery status. If the CMOS checksum is incorrect, default values ​​will be loaded;
• Testing the processor and RAM. Test results are usually displayed on the screen;
• Connecting a keyboard, testing I/O ports and other devices.
• Initialization disk drives. Information about detected devices is usually displayed on the screen;
• Distribution of resources between devices and displaying a table with detected devices and resources assigned to them;
• Search and initialize devices that have their own BIOS;
• Call software interrupt BIOS INT 19h, which looks for the boot sector on devices specified in the boot list.

Depending on the specific version BIOS order The POST procedure may vary slightly, but the basic steps above are the same when booting any computer.

What are POST codes?

After turning on the computer's power, if the power supply and the main components of the motherboard are working (clock generator, components responsible for the operation of the system bus and memory bus), the processor begins executing the BIOS code.

To be precise, in many modern chipsets, before the system controller transmits commands to the processor, the “smart” system bus is pre-configured. But this does not change the essence of the matter.

The main task of the BIOS at this stage is to check the serviceability and initialize the main hardware components of the computer. First, the internal registers of the chipset and processor are configured, and the integrity of the BIOS code is checked. Then the type and size of RAM is determined, and the video card (integrated into the chipset or external) is searched and initialized. Next, the I/O ports, disk drive controller, IDE/SATA controller and the drives connected to it are configured. And finally, additional controllers integrated on the motherboard are searched for and initialized and installed cards extensions. In total, there are about a hundred intermediate steps, after which control is transferred to the BOOTStrap loader, which is responsible for starting the operating system.

Each POST test step has its own unique number, called a POST code. Before the next procedure starts, its POST code is written to a special port called Manufacturing Test Port. When the device is successfully initialized, the POST code of the next procedure is written to the Manufacturing Test Port, and so on, until all tests are completed. If configuration of the device fails, further execution of POST tests stops, and the POST code of the procedure that caused the failure remains in the Manufacturing Test Port. After reading it, you can clearly identify the problematic device.

Keep in mind that after rebooting the computer using the operating system (soft or warm boot) or exiting power-saving mode, not all steps for testing and configuring hardware components are usually performed, but only the necessary minimum - this is faster. When troubleshooting, you must always perform a “hard” (“cold”) reboot - using the RESET key or turning off the computer’s power. This is the only way to guarantee that all initialization steps will be completed in full.

Award BIOS 6.0: full boot option

This table can be used not only as a list of POST codes, but also as a sequence of actions that are performed when the computer is turned on. It contains POST codes that are displayed during the full POST procedure.

Failure to complete or failure of any step in the test sequence results in the testing stopping and the corresponding POST code being issued. this step failure.

POST codes from other manufacturers can be found on the websites of your motherboard manufacturer or DIOS manufacturer or on the Internet.

Reading POST codes

In workshops or repair specialists, monitoring the execution of BIOS microprograms is carried out using special card extensions. It is inserted into a free slot (most modern models designed for PCI bus) and as it loads, it displays on its indicator the code of the currently executing procedure.

An example would be the BM9222 PCI Post card.

However, the POST card is not a widely used means. Rather, it is a professional computer repairman's tool. Realizing this fact, motherboard manufacturers began to equip models designed for enthusiasts experimenting with computer settings and overclocking with built-in POST code indicators.

An example would be the ECS H67H2-M motherboard, or models X58 Extreme3, P55 Deluxe3 and 890GX Extreme3.

There is also a cheaper solution - during the initial initialization of components, POST codes can be displayed on the screen along with other service information. However, this solution has a significant drawback: if the problem is related to the video card, you most likely will not see anything.

Last opportunity to find out about a failure that occurred during testing Sound signals of error messages.

Sounds and error messages

Even though POST codes are the most powerful tool To identify hardware problems when starting a computer, the BIOS also provides other diagnostic tools. If you do not have a POST card at your disposal, and the motherboard cannot display POST codes, you can rely on sound signals and error messages.

But for this it is necessary that the PC case has a system speaker and it is connected to the motherboard.

Sound signals are especially valuable initial stage, when the video card has not yet been initialized and, as a result, is not able to display anything on the screen. The unique combination of long and short signals will indicate the problematic component.

At later stages, it is easier to navigate by the error message displayed by the BIOS in the event of a hardware problem. In some BIOS versions this message is accompanied by a special sound signal, in others it replaces it. But in any case, the information is usually enough to identify the failing component.

It should be noted that sound signals and error messages are actually a more visual option for displaying certain POST codes, and are not at all additional means diagnostics If you have a POST card at your disposal, or the motherboard is capable of displaying POST codes, you need to focus on the codes - they give a much more accurate and detailed picture. Compare at least the number of POST codes (about a hundred) and the number of different error messages or beeps (several dozen).

Setup procedure

Login to BIOS Setup

Entering BIOS Setup is only possible when the computer is turned on and the initial POST test is successful (one short signal from the system speaker).

To do this, you need to press a specific key or key combination.

Typically, the screen saver during testing displays a message like “Press DEL to enter Setup” - this means that to enter the BIOS Setup you must press the DEL key. You can find out which key is assigned to enter the BIOS from the instructions for the motherboard. If there are no instructions, but screen saver does not display hints, you can try the most well-known combinations:

Delete
Esc
Ctrl + Shift + S or Ctrl + Alt + S
Ctrl + Alt + Esc
Ctrl + Alt + Delete

Safe work with BIOS Setup

Working with BIOS Setup is associated with a certain risk, since if the parameter is changed incorrectly or carelessly, the system may become unstable or not function at all. There are a few simple tips that can help you reduce possible risk to a minimum:

• It is best to experiment with BIOS Setup settings on a new computer that is not filled with information;
• Try not to experiment with the BIOS at all on computers that process or store important or voluminous information. Before setting up your system using the BIOS, be sure to back up your important data. The main thing in such computers is stability. A frozen overclocked computer after several hours of video processing is a waste of time, electricity and work results. An unoverclocked one will cope with this task much more efficiently and will save your nerves;
• Before changing important parameters, always record the set and changed value. This will allow you to return it to working condition in case of unstable operation of the system;
• Do not change parameter values ​​that you do not know. Check their meaning either in the instructions for the motherboard, or on the Internet on the board developer’s resource;
• Do not edit several important unrelated parameters at once. When the system is unstable, it is much more difficult to determine which parameter caused unstable work;
• Do not overclock your computer without proper study and preparation of the system being overclocked;
• Do not use the Hard Disk Utility section, which is designed for low-level formatting of older hard drive models and is found in older BIOS versions, because can damage a modern hard drive;
• If, after setting the parameters and exiting the BIOS, the computer stops starting at all, you can return the system to a working state in several ways:
  • If it is possible to enter BIOS Setup after restarting the computer, you need to set the edited parameters to the previous values. Some BIOS versions themselves roll back changes from the last session.
  • If the changes made are unknown, it is better to use the default parameters using the Load Fail-Safe Defaults command. After this, you will have to configure the system for optimal operation.
  • If the computer does not start at all due to incorrect BIOS settings, then in this case it is necessary to reset the CMOS contents. In this case, all values ​​including date/time will be changed. To do this, reset incorrect settings by simply moving the Flash Recovery (IBM) jumper or the Clearing CMOS jumper to the “clearing CMOS” position. In the latter case, you just need to close the contacts of the corresponding jumper with a jumper for a few minutes.
  • In case of unsuccessful results of Setup BIOS, after resetting the unsuccessful configuration using a jumper in the Setup BIOS procedure, it is necessary to duplicate the return of loading BIOS values ​​ru.Wikipedia.org<< на главную>>

Many users believe that the computer boots using the operating system, but in fact this is only partly true. In this material, you will learn how a PC actually boots and become familiar with such important concepts as BIOS, CMOS, UEFI and others.

Introduction

For many people, working with a computer begins after loading the operating system. And this is not surprising, since the vast majority of the time, modern PCs are actually used using the convenient graphical shell of Windows or any other OS. In this friendly environment for us, we not only launch programs, applications or games, but also carry out settings, as well as configure system parameters to suit our own needs.

But, despite all its multifunctionality, the operating system cannot do everything, and in some key moments, it is simply powerless. In particular, this applies to the initial boot of the computer, which occurs completely without her participation. Moreover, the launch of the OS itself largely depends on the success of this procedure, which may not occur if problems arise.

This may be news to some, but in reality, Windows is not responsible for booting the computer from start to finish; it only continues it at a certain stage and finishes it. The key player here is a completely different firmware - the BIOS, the purpose and main functions of which we will talk about in this material.

What is BIOS and why is it needed?

The key components of any computer device are a combination of processor and RAM, and this is not without reason. The processor is rightly called the heart and brain of any PC, since all the main mathematical operations are entrusted to it. In this case, the CPU can only take all commands and data for calculations from RAM. He also sends the results of his work there. The processor does not directly interact with any other information storage, for example, hard drives.

This is where the main problem lies. In order for the processor to begin executing operating system commands, they must be in RAM. But when the PC is turned on, the RAM is empty, since it is volatile and cannot store information when the computer is turned off. At the same time, on their own, without the participation of the system, computer devices they cannot place the necessary data in memory. And here we are faced with a paradoxical situation. It turns out that in order to load the OS into memory, the operating system must already be in RAM.

To resolve this situation, at the dawn of the era of personal computers, IBM engineers proposed using a special small program called the BIOS, sometimes called the boot loader.

Word BIOS(BIOS) is an abbreviation for four English words Basic Input/Output System, which translated into Russian means: “Basic input/output system.” This name was given to a set of firmware responsible for the operation of the basic functions of video adapters, displays, disk drives, drives, keyboards, mice and other basic input/output devices.

The main functions of the BIOS are initial PC startup, testing and initial setup equipment, resource distribution between devices and activation of the operating system boot procedure.

Where is the BIOS stored and what is CMOS

Considering that the BIOS is responsible for the very initial stage of booting the computer, regardless of its configuration, this program should be available for basic devices immediately after pressing the PC power button. That is why it is not stored on the hard drive, like most regular applications, but is recorded in a special flash memory chip located on the system board. Thus, access to the BIOS and starting the computer is possible even if no storage media is connected to the PC at all.

The very first computers used read-only memory (ROM) chips to store the BIOS, onto which the program code itself was written once at the factory. Somewhat later, they began to use EPROM and EEROM chips, in which it was possible, if necessary, to rewrite the BIOS, but only with the help of special equipment.

In modern personal computers, the BIOS is stored in chips based on flash memory, which can be rewritten using special programs directly to your PC at home. This procedure is usually called flashing and is required to update the firmware to new versions or replace it in case of damage.

Many BIOS chips are not soldered onto the motherboard, like all other components, but are installed in a special small connector, which allows you to replace it at any time. True, this feature is unlikely to be useful to you, since cases requiring replacement of the BIOS chip are very rare and practically never occur among home users.

Flash memory for BIOS storage can have different capacities. In previous times, this volume was very small and amounted to no more than 512 KB. Modern versions of the program have become somewhat larger and have a volume of several megabytes. But anyway in the background modern applications and multimedia files are just minuscule.

In some advanced motherboards, manufacturers can install not one, but two BIOS chips at once - a main one and a backup one. In this case, if something happens to the main chip, the computer will boot from the backup one.

In addition to the flash memory in which the BIOS itself is stored, there is another type of memory on the motherboard that is designed to store configuration settings for this program. It is manufactured using a complementary metal oxide semiconductor or CMOS(Complementary Metal Oxide Semiconductor). This abbreviation is the name given to specialized memory that contains computer startup data used by the BIOS.

CMOS memory is powered by a battery installed on the motherboard. Thanks to this, when you disconnect the computer from the outlet, all BIOS settings are saved. On older computers, CMOS memory functions were assigned to a separate chip. In modern PCs it is part of the chipset.

POST procedure and initial PC boot

Now let's see what the initial process of booting a computer looks like and what role the BIOS plays in it.

After pressing the computer's power button, the power supply starts up first, starting to supply voltage to the motherboard. If it is normal, then the chipset gives a reset command internal memory central processor and its launch. After this, the processor begins to sequentially read and execute commands written in system memory, the role of which is played by the BIOS chip.

At the very beginning, the processor receives a command to perform self-testing of computer components ( POST- Power-On Self-Test). The POST procedure includes several stages, most of which you can watch on the PC screen immediately after turning it on. The sequence of events before the operating system starts loading is as follows:

1. First, the main system devices are determined.

3. The third step is setting up the system logic set, or more simply, the chipset.

4. Then the video card is searched and identified. If an external (independent) video adapter is installed in the computer, then it will have its own BIOS, which the main system BIOS will look for in a certain range of memory addresses. If an external graphics adapter is found, the first thing you will see on the screen will be an image with the name of the video card generated by its BIOS.

5. After finding the graphics adapter, the integrity of the BIOS parameters and battery status begins to be checked. At this moment, those same mysterious white inscriptions begin to appear on the monitor screen, one after another, causing awe inexperienced users due to a lack of understanding of what is happening. But in fact, nothing supernatural happens at this moment, as you will now see for yourself. The first, topmost inscription, as a rule, contains the logo of the BIOS developers and information about its installed version.

6. Then testing of the central processor starts, after which data about the installed chip is displayed: the name of the manufacturer, model and its clock frequency.

7. Next, testing of RAM begins. If everything goes well, the total installed amount of RAM is displayed on the screen with the inscription OK.

8. Upon completion of checking the main components of the PC, the search for the keyboard and testing of other I/O ports begins. In some cases, the computer may stop booting at this stage if the system is unable to detect the connected keyboard. In this case, a warning about this will be immediately displayed on the screen.

9. Next, the detection of storage devices connected to the computer begins, including optical drives, hard drives and flash drives. Information about the found devices is displayed on the screen. In the event that several controllers from different manufacturers, then the procedure for their initialization can be displayed on different screens.

Controller Definition ScreenSerialATA, which has its ownBIOS, with the output of all devices connected to it.

10. At the final stage, resources are distributed between the found internal PC devices. In older computers, after this a summary table with all detected equipment is displayed. IN modern cars the table is no longer displayed.

11. Finally, if the POST procedure is successful, the BIOS begins searching the connected drives Main Boot Area(MBR), which contains data about the operating system startup and the boot device to which further control must be transferred.

Depending on the BIOS version installed on the computer, the POST procedure may take place with slight changes from the order described above, but in general, all the main steps that we have indicated will be performed when booting each PC.

BIOS Setup Utility

BIOS is a configurable system and has own program settings of some PC hardware parameters, called BIOS Setup Utility or CMOS Setup Utility. It is called by pressing a special key during the POST self-test procedure. On desktop computers, the Del key is most often used for this purpose, and on laptops F2.

The graphical interface of the hardware configuration utility is very ascetic and has remained virtually unchanged since the 80s. All settings here are made only using the keyboard - mouse operation is not provided.

CMOS/BIOS Setup has a lot of settings, but the most popular ones that the average user may need include: setting the system time and date, choosing the order of boot devices, enabling/disabling additional equipment built into the motherboard (sound, video or network adapters), controlling the cooling system and monitoring the processor temperature, as well as changing the system bus frequency (overclocking).

For different motherboard models, the number of configurable BIOS parameters can vary greatly. The widest range of settings usually have the most expensive desktop motherboards, aimed at enthusiasts, fans of computer games and overclocking. The meager arsenal, as a rule, is found in budget boards designed for installation in office computers. The vast majority of mobile devices also lack a variety of BIOS settings. We will talk in more detail about the various BIOS settings and their impact on the operation of the computer in a separate article.

BIOS development and update

As a rule, almost every motherboard model has its own BIOS version developed, which takes into account its individual technical features: type of chipset used and types of soldered peripheral equipment.

BIOS development can be divided into two stages. First, a basic version of the firmware is created, which implements all functions, regardless of the chipset model. Today, the development of such versions is mainly carried out by companies American Megatrends(AMIBIOS) and Phoenix Technologies, which in 1998 absorbed the then major player in this market - Award Software (AwardBIOS, Award Modular BIOS, Award WorkstationBIOS).

At the second stage, motherboard manufacturers are involved in the development of BIOS. At this point, the basic version is modified and improved for each specific board model, taking into account its features. At the same time, after a motherboard enters the market, work on its BIOS version does not stop. Developers regularly release updates that can fix found errors, add support for new hardware, and expand the functionality of the program. In some cases, updating the BIOS allows you to breathe new life into a seemingly outdated motherboard, for example, adding support for a new generation of processors.

What is UEFI BIOS

The basic principles of operation of the system BIOS for desktop computers were formed in the distant 80s of the last century. Over the past decades, the computer industry has developed rapidly, and during this time situations have constantly arisen when new device models turn out to be incompatible with certain BIOS versions. To resolve these problems, developers constantly had to modify the code basic system input/output, but in the end a number of software limitations have remained unchanged since the days of the first home PCs. This situation led to the fact that the BIOS in its classic version finally ceased to meet the requirements of modern computer hardware, preventing its spread in the mass personal computer sector. It became clear that something needed to change.

In 2011, with the launch of production of motherboards for processors Intel generation Sandy Bridge installed in the LGA1155 socket, the mass introduction of a new software interface for booting a computer - UEFI - has begun.

In fact, the first version of this alternative to the regular BIOS was developed and successfully used by Intel in server systems back in the late 90s. Then, the new interface for booting a PC was called EFI (Extensible Firmware Interface), but already in 2005 its new specification was called UEFI (Unified Extensible Firmware Interface). Today, these two abbreviations are considered synonymous.

As you can see, motherboard manufacturers were in no particular hurry to switch to the new standard, trying to improve traditional BIOS variations until the last minute. But the obvious backwardness of this system, including its 16-bit interface, the inability to use more than 1 MB of memory address space, the lack of support for drives larger than 2 TB and other constant insoluble compatibility problems with new equipment nevertheless became a serious argument for switching to a new software solution .

What changes did the new boot interface proposed by Intel bring with it and how does it differ from the BIOS? As with BIOS, the main task of UEFI is to correctly detect the hardware immediately after turning on the PC and transfer control of the computer to the operating system. But at the same time, the changes in UEFI are so profound that it would be simply incorrect to compare it with BIOS.

BIOS is a virtually unchangeable program code embedded in a special chip and interacts directly with computer equipment using its own software. The procedure for booting a computer using BIOS is simple: immediately after turning on the computer, the hardware is checked and simple universal drivers for the main hardware components are loaded. After this, the BIOS finds the operating system bootloader and activates it. Next, the OS loads.

The UEFI system can be called a layer between the hardware components of the computer, with their own firmware, and the operating system, which allows it to also perform BIOS functions. But unlike BIOS, UEFI is a modular programmable interface that includes test, work and boot services, device drivers, communication protocols, functional extensions and its own graphical shell, which makes it look like a very lightweight operating system. At the same time user interface in UEFI it is modern, supports mouse control and can be localized into several languages, including Russian.

An important advantage of EFI is its cross-platform and independence from the processor architecture. The specifications of this system allow it to work with almost any combination of chips, be it x86 architecture (Intel, AMD) or ARM. Moreover, UEFI has direct access to all computer hardware and platform-independent drivers, which makes it possible to organize, for example, Internet access or backup disks.

Unlike BIOS, the UEFI code and all its service information can be stored not only in a special chip, but also on partitions, both internal and external hard drives, as well as network storages. In turn, the fact that boot data can be placed on capacious drives makes it possible, due to the modular architecture, to provide EFI with rich functionality. For example, these could be advanced diagnostic tools, or useful utilities, which can be used both at the initial PC boot stage and after the OS starts.

One more key feature UEFI is the ability to work with huge hard drives, partitioned according to the GPT (Guid Partition Table) standard. The latter is not supported by any BIOS modification, since it has 64-bit sector addresses.

Booting a UEFI-based PC, as in the case of BIOS, begins with initializing the devices. But at the same time, this procedure happens much faster, since UEFI can detect several components simultaneously in parallel mode (BIOS initializes all devices in turn). Then, the UEFI system itself is loaded, under the control of which a certain set of necessary actions are performed (loading drivers, initializing the boot drive, starting boot services, etc.), and only after that the operating system is launched.

It may seem that such a multi-step procedure should increase total time boots the PC, but in fact everything happens the other way around. WITH UEFI system starts up much faster thanks to built-in drivers and its own bootloader. As a result, before starting, the OS receives comprehensive information about the computer’s hardware, which allows it to start within a few seconds.

Despite all the progressiveness of UEFI, there are still a number of restrictions that hinder the active development and distribution of this bootloader. The fact is that to implement all the capabilities of the new boot interface, it requires full support from operating systems. To date, only Windows 8 allows you to fully use the capabilities of UEFI. Limited support for the new interface is available for 64-bit versions of Windows 7, Vista and Linux with kernel 3.2 and higher. UEFI capabilities are also used in the BootCamp boot manager by Apple in its own Mac systems OS X

Well, how does a computer boot from UEFI if it uses an unsupported operating system (WindowsXP, 32-bit Windows 7) or file partitioning (MBR)? For such cases, the new boot interface has built-in Compatibility support module(Compatibility Support Module), which is essentially a traditional BIOS. This is why you can see how many modern computers equipped with motherboards with UEFI, boots in the traditional way in BIOS emulation mode. Most often this happens because their owners continue to use HDD partitions with traditional MBR and do not want to switch to GPT partitioning.

Conclusion

It is clear that, unlike traditional BIOS, UEFI interface capable of much more than just the loading process. The ability to launch working services and applications, both at the initial stage of PC boot and after the operating system starts, opens up a wide range of new opportunities for both developers and end users.

But at the same time, it is still premature to talk about a complete abandonment of the basic input/output system in the near future. First of all, you need to remember that until now most computers are running WindowsXP and 32-bit Windows 7, which are not supported by UEFI. Yes, and hard drives marked according to the GPT standard can mostly be found only in new models of laptops on Windows based 8.

So as long as the majority of users, due to their habits or some other reasons, are tied to old versions of the OS and traditional methods of partitioning hard drives, BIOS will remain the main system for booting a computer.

It will not be possible to run from one operating system to another for a long time if there are two of them installed on the computer. After carefully studying both, sooner or later you will have to choose only one of them - main, with which the work will be carried out primarily. If for the most part only one Windows system is used, its other versions or editions located on other disk partitions, does not have to be deleted. Of course, provided that the hard drive space is not limited in size.

The ability to work in the future with other computer systems can be left, but for convenience, it is possible to simplify the entrance to the main one by removing temporarily unused ones from the boot. In this case, starting the computer will be simplified by automatically loading only the required operating system. Another option to make it easier to get started with your computer is not to remove the window for choosing to boot all systems, but to designate the desired version of Windows as the default boot one and reduce the time it takes to select other options in the boot loader window.

How to edit the boot process for multiple operating systems Windows systems installed on one computer - more on this below.

So, in our case we have a computer with installed versions Windows 7 and 8.1. When you turn on the computer, you see a bootloader window with a list of systems to select.

Every time you boot your computer, you can get to the desired system by making the appropriate selection. Otherwise, after a certain time has elapsed - and by default this is 30 seconds– Windows will automatically load, first on the list. In our case it is Windows 7, since it is the last one installed on the computer, and it is its bootloader, as we see, that greets us after the computer starts.

Well, let's change that. Let's set up automatic loading of the main system - Windows 8.1. To do this, of course, you need to enter it.

We need a settings section, and in Windows 8.1 you can get to it using the context menu on the button.

In the system window select additional options.

You can also get to the settings section in Windows 7 using the context menu, but called up on the icon "Computer" in Explorer. Among the commands you must select .

In Windows 7 we also select additional options.

The further steps in both systems are identical.

In the system properties window that appears, in the tab "Additionally" Click the parameters button in the last section.

Now you can start editing the boot of multiple systems. Changing the boot software Windows default from the options in the drop-down list. In our case, we change the pre-installed Windows 7 to Windows 8.1.

As mentioned, by default the Windows boot loader waits half a minute so that the user can select the operating system.

If work is primarily carried out in only one system, there is no point in leaving half a minute waiting for it to automatically load. Another operating system may not be prevented from starting, but the preset time for selecting boot options may be reduced. In displaying the list of bootable systems, in our case we will install 5 second Waiting before Windows 8.1 main system boots automatically. This time will be more than enough to make a choice if you ever need to log into Windows 7.

To completely remove another system from the boot list, you need to uncheck the option display system list. In this case, only the system selected for booting by default will boot without any time delay.

If a second operating system is ever needed, you can enter it by making this option active again.

After making changes, click "OK" at the bottom of this window, as well as at the bottom of the system properties window.

That's it - the list of loading operating systems has been edited.

Above we looked at editing the boot of existing operating systems. But often, when starting a computer, we can see a list of operating systems that are already on the computer No. This is a natural development after the second operating system was removed by normal formatting disk partition or destroying system files manually, but at the same time The entry about the possibility of loading it in the system configuration was not removed. The boot loader may also display the option to start a non-existent main Windows after the system has been reinstalled. This, by the way, is not the main one, but one of the reasons why system specialists advise implementing the so-called clean Windows installation– without saving files previous system and formatting the disk partition.

It is better to completely remove the existing operating system from the boot options so that it does not delay the process of starting the main Windows.

In the main system we call the command. On Windows 8.1 quick access it is implemented in the context menu on the button.

We need system configuration section. Enter the value in the command field:

Click "OK".

In Windows 7, you can launch the system configuration window more easily by entering a key query in the menu search field.

The system configuration window will appear, go to the tab. Select the entry about loading a non-existent system and delete it.

In our case, the download list contained different versions of Windows, and deciding which one to remove "Seven" It obviously wasn't difficult for us. But if the download list contains entries about two identical Windows versions, descriptions of the systems will help in orientation with the one that needs to be deleted. The Windows we are actually in will be designated as current.

Save the changes made with the button. After clicking "OK" the system will offer reboot.

After restarting the computer, we can observe immediate startup of the main system.

After turning on the computer, there is no operating system in its RAM. By itself, without an operating system, computer hardware cannot perform complex actions such as loading a program into memory. Thus we are faced with a paradox that seems insoluble: in order to load the operating system into memory, we must already have the operating system in memory.

The solution to this paradox is to use a special small computer program called bootloader, or commands located in permanent memory (for example, on an IBM PC - reboot commands without any help). This software can detect devices suitable for booting and load the OS bootloader from a special partition of the selected device itself (most often the boot sector) of these devices.

Bootloaders must comply with specific restrictions, especially regarding volume. For example, on IBM PC first level loader must fit in the first 446 bytes of the master boot record, leaving room for 64 bytes of the partition table and 2 bytes for the AA55 signature needed for the BIOS to detect the bootloader itself.

Story

Early computers had a set of switches that allowed the operator to place the boot loader in memory before the processor started. This bootloader then read the operating system from an external device, such as a punched tape or hard drive.

The pseudo-assembly bootloader code can be as simple as the following sequence of instructions:

0: write the number 8 to register P 1: check that the punched tape reader can start reading 2: if it can’t, go to step 1 3: read the byte from the punched tape reader and write it to the battery 4: if the punched tape runs out, go to step 8 5: write the value stored in the accumulator into RAM to the address stored in register P 6: increase the value of register P by one 7: go to step 1

This example is based on the bootloader of one of the minicomputers released in the 1970s by Nicolet Instrument Corporation.

0: write the number 106 to register P 1: check that the punched tape reader can start reading 2: if it can’t, go to step 1 3: read the byte from the punched tape reader and write it to the battery 4: if the punched tape runs out, go to step 8 5: write the value stored in the accumulator to RAM at the address stored in the P register 6: decrease the value of the P register by one 7: go to step 1

The length of the second-level bootloader was such that the last byte of the bootloader changed the command located at address 6. Thus, after step 5 was completed, the second-level bootloader started. The second-level loader was waiting to load the punched tape reader with the length of the punched tape containing the operating system. The difference between the first level loader and the second level loader were checks for errors in reading from punched tape, which were common at that time, and, in particular, on the ASR-33 teletypes used in this case.

Some operating systems, the most typical of which are older (pre-1995) operating systems Apple computers Computer are so closely tied to the computer hardware that it is impossible to load any other operating system on these computers. In these cases, it is common to develop a boot loader that acts as the boot loader for the standard OS and then transfers control to the alternative operating system. Apple used this method to run the A/UX version of Unix, and then it was used by various free operating systems.

Devices initialized by BIOS

A boot device is a device that must be initialized before the operating system boots. These include input devices (keyboard, mouse), base output device (display), and the device from which production will be made - floppy drive, hard drive, flash drive, PXE).

Boot sequence of a standard IBM-compatible personal computer

The personal computer is loading

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Starting a computer is not just turning it on. Powering up is an event, and launching is a process. It is extended over time and occurs under external control. Depending on who is the controlling party, there are three stages in starting a computer.

First stage

At the first stage, the launch is controlled by a person. First, he must make sure that the keyboard - the main control device - is available and connected, and that the power supply is supplied. To initialize the launch, just press the button on the front panel - then the process develops automatically.

If in fact automatic start is not required, and this happens when carrying out repair and restoration work, the first stage is the best time to seize control from the automation and take it over. This is done using the keyboard. Details are below.

Second stage

At the second stage, the devices control the startup of the computer. More precisely - the motherboard. Even more precisely, the read-only memory (ROM) chip located on it. Exactly - a package of built-in programs called BIOS. You can read how to configure the Boot menu in BOIS in another instruction.

Third stage

The computer approaches the third stage after the BIOS system launches programs that allow you to read data written on internal and external disk media. The purpose of the third stage is to load the operating system. In fact, this stage itself is divided into several stages, but we won’t dive that far.

As in the second stage, the controlling side of the third stage of launch is the program. Only now it is not “hardwired” into the ROM of the motherboard, but is taken from the disk that is designated as the system one. This program is the bootloader of the operating system.

If for some reason a person is not satisfied with which operating system the initial bootloader loads and in what mode it launches it, the bootloader can be interfered with. That is, a person can take control of the initial loading. This is usually not done, but if you need to perform some specific actions or troubleshoot detected problems, the ability to control the boot process can be very useful.

Intervention to control the boot should occur immediately after the recognized disk drives are displayed on the screen.