Clean installation of macOS, or how to reinstall (restore factory settings) Mac. Installing Mac OS X from a USB flash drive

And its update. Before you begin, it is important to decide what exactly you need to do. That is, it will be necessary to understand whether a complete reinstallation of the operating system or a simple update is required. You will also need to prepare the device for reinstallation (for example, if you are going to sell your device).

Additionally, you can restore from a TimeMachine backup if you have configured this. So, first things first:

If you want to update your Mac OS, you can create a backup copy just in case, so that in case of unforeseen circumstances, you can restore the system.
If you are going to restore the operating system, then no action is required. However, you can check for backups if you want to install one of them.
For a complete reinstallation, you will need to create a copy, just as in the first point. Then be sure to deauthorize your computer or laptop from iTunes. To do this, launch the program, open the “Account” tab, select the authorization item, and then open the deauthorization item. Please note that your Apple ID password may be required. Next, sign out of iCloud after disabling Find My Mac if it was previously enabled. Also log out of your iMessage and FaceTime account. At this point, your preparation ends. Let's move on, friends.

Reinstallation

First of all, please note that the following instructions provide for reinstallation with the installation of the version of the operating system that was installed when you purchased the device. That is, if you purchased a Macbook with OSX Mavericks, and then upgraded it to ElCaptain, then after reinstallation the laptop will have Mavericks again. It is also worth remembering that all your data will be deleted from your computer. This method is suitable for those who want to sell their device, give it to someone, or simply receive the device “out of the box.” If this method does not suit you, then go to the “Recovery” paragraph.
So, let's get started: immediately after turning on the computer, hold down the key combination Option+Command+R.

Once you see the Apple logo, you can release the buttons.
If you did everything correctly, Disk Utility will launch, with which you will need to clean up the built-in hard drive. Please note that Extended journal format must be used. After this you can close the window.
Now click on “Reinstall mac OS”. Follow the prompts on your computer or laptop screen to complete the steps indicated.
When your device restarts, you'll see the Setup Assistant that opens when you turn on macOS computers for the first time. If you don't want to configure it (for example, as mentioned above, when selling the device), then use the Command+Q combination to turn off the Mac. This way, you will give the opportunity to configure the settings to another user, your future buyer. Ready! This completes the reinstallation.

Update

Updating macOS is much easier than any other operating system on your computer. This process is accompanied by fewer problems and questions. This will be especially noticeable by those people who have updated Windows at least once. In order to update your Mac computer or laptop, you only need an Internet connection and a little time.

Launch the Mac AppStore.
In shopping or in other sections of the store, find the new version of the operating system. Most often it is in the first places of the “Top Chart” or in the “Selection”.
Click the “Download” button or “Install” if the system has already been downloaded previously. Wait for the operation to complete and continue using the now updated mac OS.

Recovery

Recovering with Time Machine

If you have a Time Machine backup, you will need to boot the device from the recovery partition using Command+R when you turn on the computer. In the mac OS Utilities window, select the item of the same name. Please note that all data from the disk will be cleared and replaced with the information and files from your backup. The recovery itself is easy to do using the instructions on the computer screen.

With its own pre-installed operating system Mac OS. Like all the company's products, it claims to be of exclusive quality and the use of advanced technologies. The following varieties are currently on sale:

MacBook;
MacBook Air;
MacBook Pro.

Find out how to update your Mac's OS in the article below.

MacBook Pro is available in 13-inch and 15-inch sizes and in different specifications. All Mac models are equipped with Intel processors, the battery life without recharging is up to 10 or up to 12 hours.

The newest operating system currently used on Mac computers is Mac OS Sierra. Older versions of the OS can be updated for free via the Internet. The company's main advantage of the system is that it was created specifically for Mac equipment. Unlike Windows, which is installed on computers from a variety of manufacturers. By the way, now MacBook Pro and other models support the ability to install Windows.

MacBook Pro and others are sold with the system already installed. However, in some cases, you may need to install or reinstall Mac OS on your MacBook. It is necessary to distinguish between the terms:

The installation is otherwise called a “clean” installation, which is performed on a blank (formatted) hard drive or on a new one.
Reinstallation is when a new system is installed over the old one without full formatting and preserving user data.

The need to install and reinstall the Mac OS arises when there are serious problems with its operation or an unsuccessful update. Like Windows, it still leaves behind garbage, which over time leads to slowdowns, freezes and other troubles. We will consider these processes using the example of the latest operating system, namely Mac OS Sierra. For previous versions, such as Mac OS X, there will be essentially no differences, but it is still recommended to update to the latest version if your device supports it.

Operating system installation

A clean installation may be necessary if you decide to sell your laptop and need to permanently remove all data and Apple ID from it, or if there is a serious system problem. The installation algorithm on a MakBook Pro looks like this:

Data backup.
Creating a bootable USB flash drive.
System installation.

To back up your data, use an external drive and the Time Machine program, which automatically launches when you connect a removable drive. The utility will ask whether to use an external drive for backup, click “Use.” as a backup drive."

After the backup is complete, you need to make a bootable USB flash drive using disk utility:

The MacBook Pro itself will find the desired image on the flash drive and begin installing the Mac operating system. You just need to follow the instructions on the screen.

Reinstalling the operating system

You can reinstall the system from the OS recovery menu on Mac OS, which is called up by a key combination during boot:

Command+R - reinstalls the latest version of the OS installed on the Mac, without updating to the latest.
Option+Command+R - update to the latest compatible Mac OS.
Shift+Option+Command+R - if macOS Sierra 10.12.4 or a newer version is already installed on your Mac, then pressing the combination will allow you to reinstall the OS that came with your Mac laptop.

After pressing these key combinations, a menu will appear in which you need to select “Reinstall Mac OS”. Next, do the following:

When the name Mac OS Sierra is displayed, click Next.
Select the drive on which you will install the system (usually called Macintosh HD).
The system reinstallation will begin, after which the Mac laptop will boot as usual.

All data, including passwords and Apple IDs, will be saved, as well as user data. But still create a backup copy before reinstalling, just in case. Reinstallation is also sometimes called recovery, as it often helps solve performance and performance problems. If the problems have not been corrected, then you can already try installing a system with formatting the boot disk on your MacBook, not forgetting to copy all the data to an external drive, because after this procedure they will all be deleted.

Sooner or later the day comes when you need to reinstall the Mac OS operating system on your MacBook PC. This task is no more difficult than reinstalling Windows. This is what we will talk about.

Why and how to reinstall the operating system on a MacBook

The reasons for reinstalling the MacOS operating system on a Mac computer are as follows:

Damage or wear of the built-in storage device (HDD);
selling or donating a MacBook to another person;
“moving” to another MacBook (a newer model, but maintaining the previous version of the MacOS system);
transferring data to Apple gadgets or to another computer.

What happens when reinstalling MacOS:

Cleaning the boot volume if necessary

Then check out the articles from this article. You will be asked to select a boot volume, select the volume and click Install. . This way, you can restore your system from the recovery partition if anything goes wrong. Some users may find it helpful to take note of the contents of the Applications folder for later reference. A screenshot may be sufficient, but if not, the following steps describe an easy way to create an app list.

The process will take a few minutes to complete, so leave it running. And it's especially helpful for the new user to have a nice, clean machine that is back to its original factory condition. Most people do not have this feature enabled.

“from scratch”, including formatting the built-in disk;
reinstallation “on top”, preserving personal data and applications (macOS update).

For example, using the MacAppStore, you can upgrade your version of OS X Lion and OS X Mountain Lion to a newer version - OS X Mavericks.

Here are the steps to follow when selling or transferring your Mac to someone else. It deserves special mention.

But it's always better to check. But you are allowed to allow up to 5 computers. Don't worry, you don't lose any content and nothing is deleted from your computer. When you deactivate a computer, you prevent it from accessing protected content. And if necessary, you can authorize your computer later.

Don't save this step later. If you sell or give away a computer that still has one of your five authorizations, you need to deauthorize all of your computers and then reauthorize any that you are still using. That's a hell of a lot of hassle and time for something you can do now before you give it away or sell it.

Backup personal data from a MacBook to a separate media or cloud service.
Disabling special services and functionality that manage data copying and transfer.
Erase all personal information from the disk.

Attention! Before you start reinstalling MacOS on your MacBook PC, take the trouble to save all your data on an external drive!

This will be discussed first.

Here you see the number of computers you have allowed in the past. Unfortunately, it does not list the names of these computers. So if this number doesn't agree with you, try de-authorizing your computer several times until it is no longer allowed.

Additionally, select "Deauthorize all computers" to clear five permissions. Then re-authorize all your computers one by one. Many third-party applications include authorization and activation of the machine, such as image, audio, and video editing programs. Application activation is the process of connecting a specific application to a valid user license.

Backing up your data using Time Machine

The Time Machine application is designed to backup personal files from a MacBook and restore them back to it. But it requires external USB drives (HDD, SDD drives) formatted in MacOS Extended or Xsan - FAT/NTFS file systems designed for Windows and Android are not supported. If the disk was previously formatted in FAT/NTFS formats, the MacBook will not accept it if you refuse to reformat it “for yourself.”

You must activate your application before you can use it. On the other hand, deactivation disconnects the application from a valid user license. Once deactivated, you can reactivate this license at any time on any computer.

Therefore, check the list of applications, look for programs that require activation keys. Once you are there, go to the program menu bar and find the deactivation or deauthorization link. Its utilities allow you to completely erase your internal hard drive.

Reinstalling Mac OS X and Apple programs

Once posted, download and install it from this product page. We install a lot of applications, updates and maybe even think about operating system software using terminal applications or third party developers.

The Time Machine application is launched from the MacOS system preferences in the Apple menu. When you connect an external hard drive, a corresponding notification will appear.

Do you really want to destroy all data recorded on this drive in a different format?

If the external drive has already been formatted, the Time Machine application will give the go-ahead for its use. Confirm your request.

This is the actual and expected use. This is the value and price of experience. And the new owner gets a fresh start - without the clutter left over from all your previous applications, preferences, etc. Important! We have a workaround that should allow you to back up and restore your desktop message history, however we cannot guarantee that it will work. Type "Terminal" and open the application.

Copy and paste the phone number folder to another location. Follow the cleaning instructions below, reinstall. Don't forget to empty your trash afterwards. Still experiencing the same problems? So far, the malware has been fairly well described and is not viral in nature, so for any given variant it is installed in one location and launched from there to affect the system. As a result, once a variant has been identified, you must remove it from your system by following detailed instructions.

Do you really want to copy your data to this drive?

If Time Machine does not show disk selection, do the following.

How to reinstall Mac OS from an installation flash drive

The preliminary steps are as follows.

Update from App Store

This is the recommended approach; however, it relies on malware definitions that have been defined for malware, which may lag behind the original malware results. If you decide that it would be better if you played it safely and wiped your system and started over by following this procedure, you should be able to do so while retaining your data.

Sync and Backup First, make sure your system is properly synced with your cloud services to ensure that items such as contacts and calendars are preserved. Doing so will allow you to restore some of these items without relying on sync services to manage them for you. When you are done with the backup, unmount and disconnect the external hard drive that you used for the backup. Do not select the restore from backup option. Restoring data from a backup. The next step is to copy the data into the system from backups. If your contacts and calendars are missing, you can re-import them from previously created backups manually. Once you've installed your apps, be sure to update them completely, then open and customize them according to your preferences. At this point, your system should be back in working order and you should be able to continue your workflow as you did before the reinstallation. In addition to syncing, make sure your system is backed up. . The final step in this process is to protect against further infection.

Download the Mac OS X installation image from the Mac App Store or third-party sites.
Once the download is complete, right-click on the downloaded file and select “Show package contents.”
Go to the /Contents/SharedSupport/ folder, copy the InstallESD.dmg file to a safe location on your disk, and mount it to your MacOS desktop.

We will need the Disk Utility application included with MacOS. The next steps are as follows.

Install a reverse firewall to help detect and block programs from calling home on remote servers and consider installing an antivirus utility. While you don't need to set up your antivirus tool to thoroughly scan all files on demand, you can set it up to scan only shared folders for downloads and then have it scan the entire system once a week or perhaps once a month. For now, despite the latest malware news, this should be enough to prevent malware and provide you with sufficient protection.

Disk Utility will create an installation flash drive automatically, and it does this operation quite reliably. When copying is complete, Disk Utility will notify you.

Congratulations! The MacOS installation flash drive has been created! You can restart your MacBook. Preparing to install MacOS is as follows.

Feel like you need a clean slate? This means you delete all your data, everything you do on the computer, and put it back just like it was when you took it out of the box. But there are scenarios where a full cleaning and recovery session can be valuable.

No buyer wants a computer with a hard drive to fill up with someone else's data, so resellers usually work to reset the computer. But another important part is restoring factory settings. Erasing a hard drive is quite simple, but you'll need to access the factory settings again when you're done. During the reboot process, your computer will display a gray slate screen before going to the login screen. Select the reinstall option, confirm that you really want to do this, and continue.

All! MacOS installation has started. The MacOS operating system will install automatically - this will take 30-100 minutes, depending on the performance of your MacBook. After it, your PC will be immediately ready for use.

How to install the system without formatting the internal drive

Installing MacOS without erasing the disk means downloading and installing MacOS updates directly from the MacAppStore. An installation flash drive is not needed here. This is reminiscent of updating iOS on smartphones and tablets over the air. This method is good for those who once bought a MacBook - and are not going to change it, but, on the contrary, will work on it for many years, because MacBook computers, like Apple iDevice gadgets, are very high quality, reliable and convenient.

Here you must connect your computer to the Internet.

Once you've been collecting data and applications for over a year, the performance differences start to show. It just doesn't run as smoothly as it once did. There are many tricks to get it back into action.

Many users are hesitant to reinstall their entire operating system. There are many benefits to a new setup, especially in terms of performance, but it's a much bigger undertaking to start from scratch. Although it's work, it's definitely worth it in the long run, and here we'll walk you through the process from start to finish. This is a three-step event: backup, installation, and migration.

Before updating, check whether your MacBook meets the hardware requirements of the new version of MacOS - otherwise it will slow down.

Not every previous version of MacOS can be updated to the desired version. So, if your MacBook is running macOS Snow Leopard (10.6.8) and your MacBook will run macOS Sierra, first upgrade to macOS X El Capitan.

Start with cleaning

It might be best to add a hidden fourth step before we begin. Using your computer for a long time, you probably have a lot of things you don't need on your hard drive. Applications you installed but didn't continue to use and files that became redundant months ago. Take this time to sort through your data and throw out anything you don't want to keep.

If your files are disorganized, take this time to sort things out. Separate working documents from game installers and family photographs. Categorize and organize files in multiple categorized folders. Of course, this is completely optional, but it will help speed up the backup process and get you up and running on your next installation faster and faster.

The version of MacOS Sierra is taken as an example. Other copies are searched for and “installed” in exactly the same way. Your actions are as follows.

If you have OS X El Capitan 10.11.5 (or more recent), the macOS Sierra version downloads silently. You will then be prompted to install this version.

There is a difference between starting with a clean slate and starting completely from scratch. Before you reinstall your computer, make sure your data is secure. The easiest way to back up your data is to move it to an external drive. This is a good option if you only want to move a certain number of folders between two installations, or if the drive is not large enough to accommodate all your data and needs to be split into multiple parts.

You can find these app libraries in the Music and Pictures folders located in your Home folder, respectively. You can choose which folders to return after reinstalling your system. The first backup may take a maximum of an hour. Also check your settings to ensure that important folders are not missing. Alternatively, you can install the latest version right away.

Click on the install button

During the installation of MacOS, the PC restarts several times. If this version does not suit you (the performance of the MacBook has dropped), “roll back” to the previous one (for example, OS X El Capitan), with which the PC performance was very satisfactory.

Restoring MacOS from a backup

For example, we take a “rollback” from MacOS Sierra (10.12) back to OS X El Capitan (10.11) or OS X Yosemite (10.10). Let's say there are backups made in the Time Machine application before installing MacOS Sierra.

Important! You can only restore a MacOS system from a backup to the same MacBook. Trying to transfer your copy of the MacOS system with data to another PC in this way is useless. Use other methods.

Connect your external drive to your MacBook and save your existing files to Time Machine, naming the new copy MacOS Sierra.
Open your previous copy of OS X Yosemite with Time Machine on a different drive after connecting it to your MacBook.
Restart your MacBook while holding Command+R on your keyboard. The familiar MacOS recovery menu will open.
From the OS X Utilities menu, select Restore from Time Machine Backup.
Once in the “Recover from Time Machine” recovery window, click on “Continue”, and then specify the source - the disk with the OS X El Capitan “backup”.
The saved copy should be: In the case of OS X El Capitan, the MacOS version should be 10.11.x. Click the Continue button. Specify the installation disk to restore from a copy, click on “Restore”.

Ready! The OS X El Capitan version will be reinstalled.

Transferring a copy of the operating system and your data to another MacBook

Go to Programs/Utilities and open Migration Assistant. The structure of your files and folders will be preserved.

Click to continue

When running, the application requires closing all other running programs.

If both computers are working, but you still want to duplicate your version of MacOS and all data on the second computer, connect the computers to each other using a LAN cable via a Wi-Fi wireless network. Connecting directly using a Thunderbolt or FireWire cable will require running your previous Mac in backup mode, which will make the Assistant experience a little more complicated. However, both methods work clearly. You can connect an external disk with a backup copy to the new PC instead of the previous PC - in this case, the operation of the Assistant on the new PC will not change significantly.

So, the procedure is as follows. As an example, we take the normal operating mode of a previous PC with “Assistant”.

All! The copy session has started. This can take anywhere from 30 minutes to two hours, depending on the amount of data and the performance of both Macs.

Problems encountered when reinstalling MacOS

Problems when updating or “rolling back” may be as follows.

No recent backups. You once disabled backup yourself. Copy your files now to avoid losing them by starting the process manually. Enable backup.
An error occurred during the next backup or when restoring personal data from a previous copy. The external drive that has been recorded so far is unsuitable for further use. Contact an Apple service center or certified computer repair shop to restore your data. This procedure is not free.
Error during the next MacOS update. Your Mac PC may no longer be supported. This happens once every few years. You will continue to use the current version of MacOS until you replace your Apple PC.
The computer began to work noticeably slower than before the update. The minimum system requirements of the next new version are equal to or exceed the technical specifications of your PC. “Roll back” to any previous version of MacOS. Typically, Apple tries to prevent this from happening - it simply stops supporting older computers, just as it is no longer possible to install iOS 10.x on iPhone 4x devices.
After several active years, your PC suddenly began to freeze despite the fact that you did not update MacOS. Maybe it's time to replace the internal HDD/SSD drive? Try making a backup copy of your important data before replacing the internal drive - while something is still being read from it.
It is impossible to “roll back” to one of the previously installed versions of MacOS. The “rollback” must be done gradually. If there are no previous backups, download a new “image” and “roll back” to this version first, and then repeat the “roll back” to an even earlier version of MacOS.

Video on the topic

Reinstalling MacOS - “on top” or “from scratch” - is not difficult. It is only important to secure your data. This is a real way to extend the life of your beloved MacBook for another number of years. You will succeed!

Mac OS X Yosemite is a system introduced by Apple in 2014. This is the most current and advanced Mac OS among the systems offered by the manufacturer of Apple technology. We invite you to find out how it is done installation from scratch. We will also look at the issue of reinstalling the Yosemite system itself to restore factory settings.

What is the best way to install the system?

Mac OS X Yosemite is available in the Appstore. There are two options for installing it:

On top of the old system;
Clean installation from scratch.

You have the option to install Mac OS X Yosemite directly on top of the old OS X Mavericks. This is advisable if you value the current state of the file system, installed programs and their settings. All data will remain in the same place, changes will only affect the operating system. But the performance of many programs may be impaired. Compatibility and update issues can cause a lot of inconvenience.

Installing from scratch eliminates many system problems. Factory settings will be completely restored. This will help get rid of unnecessary installed applications, unnecessary data, etc. Let's look at this process in more detail.

Installing Mac OS X Yosemite from scratch

Creating a USB flash drive

After downloading the update from the Appstore, proceed as follows:

Launch Disk Utility;
In the left panel, select the drive, on the right, go to the “Disk Partition” tab;
In the "Partition Scheme" menu, select "Section 1". The disk name is "Yosemite", the format must be "Mac OS Extended (Journaled)".
Go to "Options", select the GUID partition scheme. Click "Apply".
Disk Utility begins formatting the flash drive.
From the "Utilities" folder, launch "Terminal".
To create a flash drive, run the following command:

Enter the administrator password.
It will take 10-15 minutes to create a bootable USB flash drive.
After the procedure is successfully completed, reboot the Mac. When loading, hold down Alt.
You are ready to install Mac OS X Yosemite.

Installing Yosemite

After creating a flash drive and rebooting the Mac, follow the instructions:

Go to the "Downloads" menu and select "Mac OS X Installer".
You need to open Disk Utility and select the disk with the system to format. Go to the "Erase" tab.
In the "Format" menu, "Mac OS Extended (Journaled)" must be selected, and the name of the disk is written.
Click "Erase", thereby starting the disk formatting process.
Close Disk Utility and open the Install Mac OS X section.
We specify the Yosemite boot disk and start the installation process.

Starting the installation process involves following the installer's instructions. Select the necessary parameters, the system will soon be ready for use. After installing Mac OS Yosemite, you can start using the system from scratch or transfer files from Time Machine.

Reinstalling Mac OS X Yosemite

If OS X Yosemite is already installed, you may need to reinstall it in the following cases:

System failures;
Errors when installing updates;
Disk cleaning;
The need to restore factory settings.

So, let's answer the question, how to reinstall Mac OS X Yosemite. To do this, you need to erase your Mac data and reinstall the system. Don't forget to back up your valuable files. To restore factory settings, you need to use the built-in recovery disk. To reinstall the system, an Internet connection is required, as well as a connected power adapter.

The procedure is simple:

Restart your Mac. During boot (gray screen), press Command+R.
Select "Disk Utility" and click "Continue".
Select the disk and click "Erase".
In the "Format" section, select Mac OS Extended (journaled), enter a name, and click "Erase".
The disk will take some time to clear.
Select "Disk Utility" and click "Finish".
Go to "Reinstall OS X", click "Continue".
Select the disk to use. In most cases it is the only one available.
We follow the installer's instructions and finish.
The system has been reinstalled!

Most Mac users upgrade to the next generation of operating system with a simple click of the " Update» in the Mac App Store, although a clean install of OS X is believed to be the most reliable method. In this material we will tell you how to do this.

In contact with

How to do a clean install of OS X El Capitan on a Mac by first formatting the disk?

1 . Restart your Mac and hold down the keys while turning on the computer ⌘ Cmd And R.

2 . In the loaded application, select the menu item " Disk Utility" and click the " Continue».

3 . In the left side menu, select the system drive (by default it is called " Macintosh HD") and in the main window go to the " Erase" and format it by specifying the format " Mac OS Extended (Journaled)».

Attention! All data will be deleted from the Mac.

4 . After finishing the formatting process, close " Disk Utility».

5 . Select an item Install OS X in the window " OS X Utilities", if you need to download a copy of OS X El Capitan from the Internet and click the " Continue».

6 . If you plan to use a bootable USB flash drive (by creation), then close the “ OS X Utilities».

7. In the window that appears, click Boot disk...

8 . In the window that appears, select a bootable USB flash drive with OS X El Capitan that was previously connected to your computer and click Reboot.

The computer will reboot and offer installation of the system from the USB flash drive.

It is worth noting that you can also press a button ⌥Option (Alt) on the keyboard when you turn on the computer. A list of available drives will appear from which you must select a bootable USB flash drive.

MAC OS, like Windows, sometimes requires reinstallation. This may be due to your MAC device being slow or due to it being sold (I don't think you'll be happy with a MAC being sold with your personal information on it). Or, on the contrary, buying a MACBOOK (PRO, AIR) or iMAC with a bunch of incomprehensible files or unnecessary programs. In general, there can be many reasons to reinstall MAC OS. In this article I will describe in detail how to reinstall MAC OS and get a “clean” operating system.

So, before you start, you need to transfer all the necessary information to external media, since after reinstalling MAC OS, it will be almost impossible to restore anything.

In order to reinstall MAC OS you will need:

1 MACBOOK (PRO, AIR) or iMAC connected to a power source;

2 Internet access from MACBOOK (PRO, AIR) or iMAC;

3 This article and about an hour of time.

To reinstall MAC OS using the method described below, you must be using OS 10.7 or higher (10.8, 10.9). In order to check what version of the operating system you have installed, click on the apple in the upper left corner and select "About this MAC". The window that opens will contain information about the installed version of MAC OS.

If you are using a version older than 10.7, you need to update it.

You should load "OS X Utilities", if this does not happen, repeat the procedure by rebooting and pressing the "COMMAND" + "R" key combinations.

Select Disk Utility.

IMPORTANT!!! The following steps will delete all data on your drive, so you need to be sure that the necessary files are not on the MAC.

Then select the disk with the system, open the “Erase” tab on the right and click the “Erase” button.

Confirm deletion by clicking the "Erase" button.

After that, close the Disk Utility window and select Reinstall MAC OS.

After this, confirm the installation, click the "Continue" button. With the release of the new OS X 10.10, OS X Yosemite will be installed.

In the next information window, click “Continue”.

The next step is to read the license agreement and accept it.

Then select the installation drive. In this case, the choice is obvious. Click the "Install" button.

After this, the MAC OS download process will begin.

After this, the MAC will automatically reboot and MAC OS installation will begin.

After the installation is complete, you will receive a “clean” MAC OS operating system; all that remains is to set some settings.

The next step is to select the country where you plan to use MACBOOK (PRO, AIR) or iMAC.

Select your keyboard layout.

You can connect to a Wi-Fi network (you can skip this step if you wish).

If you want to restore data made earlier using Time Machine or from a Windows computer, select the appropriate option; if you do not plan to restore anything, select “Do not transfer any information” and click “Continue.” The data that you transferred to external storage can be transferred later.

The next step is to sign in with your Apple ID. In this example I won't do that.

Then read the license agreement and accept it.

After this, provide your credentials (username and password) and click “Continue.”

The last step is to register your MAC (this step is optional).

And in the end you will get a "clean" MAC OS.

Video of reinstalling the MAC OS operating system on iMAC/MACBOOK PRO/AIR.

In my opinion, installing MAC OS is incredibly simplified, you don’t even need disks with the operating system - pressing a few keys + an hour of time and you have a “clean” MAC OS.