I purchased a used 2018 Mac mini desktop and wanted to put a fresh installation of the latest macOS 10.15 Catalina on it. Below are the steps I took.

Note: The instructions below are the same for macOS 10.13 High Sierra and macOS 10.14 Mojave.

Download macOS Catalina

If you want to archive the installer file for later use, or use it to create a bootable USB drive, this file might not be sufficient. Luckily, there is a utility called macOS Catalina Patcher. Presumably because quite reasonably it would not make sense to install on top of a later version of the OS. However in this case I want to create a boot USB drive for an installation on another Mac. I am stuck in a chicken and egg situation where I need another machine running El Capitan or earlier to create and El Capitan boot installer.

You will need a Mac to download macOS Catalina; you can download Catalina from The Mac Go. (The Mac mini came with macOS 10.14 Mojave so I used it to download Catalina.)

Go to the Mac App Store, search for “macOS Catalina”, and download it. It will be saved to the “/Applications/Install macOS Catalina” location. If the installer automatically launches, just close it.

Note: If you plan to run the installer first to update your current macOS version to Catalina, you will want to move the “Install macOS Catalina” application out of the “/Applications” directory; otherwise, the installer will delete itself from the “/Applications” directory when the upgrade completes. For example, you can move the “Install macOS Catalina” application to the “~/Downloads” directory and run it from there.

Format USB Flash Drive

Because macOS Catalina is 8.4GB in size, you will need a 16GB USB flash drive. You don’t need to delete the existing content on the drive because we will blow it all away in a subsequent step.

If the USB flash drive is not already formatted as “Mac OS Extended (Journaled)”, format it like so:

1. Plug the USB flash drive into your Mac.
2. Launch the “Disk Utility” application.
3. On the left-hand pane, select the USB drive (not the partition under it, if any).
4. Click on the “Erase” tab (or button at the top).
   1. Input a name like “Catalina” (this name will be overwritten later).
   2. Select “Mac OS Extended (Journaled)” for “Format”.
   3. If available, select “Master Boot Record” for “Scheme”.
   4. Click the “Erase” button at the bottom. Click the “Erase” button in the warning popup dialog if you get one.
5. The format operation may take several minutes to complete. (USB 2.0 and large capacity drives may take longer.) After the format completes, the partition will be mounted under “/Volumes/Catalina” (or whatever name you selected above).
6. Close the “Disk Utility” application.

Write macOS Catalina to USB Flash Drive

To create a bootable USB macOS Catalina installer, run the “Terminal” application and this command:

Note: If the createinstallmedia command returns a “Failed to start erase of disk due to error (-9999, 0)” error, then your current Mac OS X version does not fully support the createinstallmedia tool. Use a more recent macOS version (at least Mac OS X 10.11 El Capitan) or manually create the USB installation drive using instructions from Bootable USB Flash Drive to Install Mac OS X 10.10 Yosemite.

The “createinstallmedia” program will erase the USB flash drive, create a new partition named “Install macOS Catalina”, and copy the installation files to that partition. The output will look like:

The above process took 20-30 minutes using my Kingston USB 2.0 flash drive.

Boot From USB Flash Drive

Note: Apple’s How to create a bootable installer for macOS page suggest using the “Startup Disk” configuration (under “System Preferences”) to select the USB flash drive as the startup drive. Then on restart, the Mac should boot from the USB flash drive. Unfortunately, the “Startup Disk” did not list my USB flash drive as a startup option, so I was not able to use this method.

To boot a Mac with the USB flash drive:

1. Insert the USB flash drive.
2. While holding the “option” key down, turn on the Mac to display the Startup Manager.
3. You should see one or more icons, one of which should be called “Install macOS Catalina” for the USB flash drive. (The internal hard drive may not be visible if it does not have a valid, bootable partition installed.)
   • Note: If you don’t see the USB flash drive’s “Install macOS Catalina”, try removing and re-inserting the USB flash drive while viewing the Startup Manager screen. The USB flash drive should then appear after a few seconds.
4. Select the “Install macOS Catalina” (with left/right arrow keys) and hit the “return/enter” key to boot from the USB flash drive.

It may take 5-10 minutes to load the installer from the USB flash drive. Sometimes the progress bar may appear to be frozen or the screen will go black for a minute or two. Be patient.

External Startup Disk Not Allowed Bluestacks ios version.

On a newer Mac with the T2 security chip, booting from an external drive may be disallowed by default. Attempting to boot from a USB flash drive will result in a “Security settings do not allow this Mac to use an external startup disk” warning message.

To allow booting from the USB flash drive, do the following:

1. Hold down “Command-R” (hold down both the “Command ⌘” and “R” keys) when you start the Mac to launch macOS Recovery. You can release the keys when you see the Apple logo.
   • Tip: An easier alternative is to hold the “Option/Alt” key on boot to launch the Startup Manager. Then just click and release “Command-R” keys to launch macOS Recovery.
2. The macOS Recovery screen contains a top-level “macOS Utilities” menu.
3. Click on the “Utilities” menu and select “Startup Security Utility”. Input your administrator password when prompted.
4. In the Startup Security Utility, under “Allowed Boot Media”, select the “Allow booting from external or removable media” option.
5. If the Mac won’t have access to the Internet (either by wire or wirelessly) when installing macOS Catalina, make sure to select either the “Medium Security” or “No Security” option under the “Secure Boot” section. (You can change the option back to the default “Full Security” afterwards.)
6. Quit the macOS Utilities to restart the Mac.
7. On restart, follow the directions in the previous section to boot from the USB flash drive.

Erase the Internal Hard Drive

When the installer finishes loading, you will see a “macOS Utilities” screen appear. It looks the same as the “macOS Recovery” screen with one difference. In the “macOS Utilities” window, the second option will say “Install macOS” instead of “Reinstall macOS”. In “macOS Recovery”, the “Reinstall macOS” option would just re-install the same version of macOS. The “Install macoS” option will install the macOS Catalina version on the USB flash drive.

Before installing macOS, I wanted a clean slate so I erased the internal hard drive like so:

1. Select the “Disk Utility” option and click the “Continue” button on the bottom to launch the “Disk Utility” application.
2. On the left-hand pane, select the internal hard drive (not the partition under it, if any).
3. Click on the “Erase” button at the top.
   1. Keep the default “Macintosh HD” name or input a new one.
   2. Select “APFS” for “Format”.
   3. Click the “Erase” button at the bottom. The SSD (Solid State Drive) format took less than a minute to complete.
4. Close the “Disk Utility” application.

Install macOS Catalina

Warning: If your Mac has a T2 security chip and you left the “Full Security” option configured in the Startup Security Utility, make sure that Internet access (wired or wireless) is available before starting the macOS Catalina installation. You can configure the wireless network by clicking on the wireless icon at the top-right corner of the macOS Utilities screen.

Back at the “macOS Utilities” window, do the following to start the macOS Catalina installation:

1. Click on the “Install macOS” option and click the “Continue” button.
2. The “macOS Catalina” installer’s splash screen will appear. Click the “Continue” button.
3. Click on the “Agree” button to agree to the license. A popup confirmation window will appear; click on the popup’s “Agree” button.
4. Select the internal hard drive and click the “Install” button.

My Mac mini took 20-30 minutes to complete the macOS Catalina installation. I think there were a couple of reboots in-between. And a few times, the screen would go black for a minute or two. Be patient and give the process an hour or more to complete.

If you run into problems installing macOS Catalina, check the “What Does Giving Up Mean?” section (at the bottom) of Install macOS Sierra Using Bootable USB Flash Drive for possible solutions.

Note: macOS Catalina seems to have an issue with my Dell 24in U2410 monitor. During the initial bootup screen, the monitor shows a blank screen with a message, “The current input timing is not supported by the monitor display”. Thankfully, the monitor works correctly after the bootup completes. And later, this warning message no longer appeared on bootup.

Enjoy your fresh installation of macOS 10.15 Catalina.

In previous tutorial, we wrote a post about creating macOS Catalina bootable USB on Mac, which is a simple tool and there are a couple of free tools to complete the task. You can even use the built-in tool Disk Utility and dd command to do it without installing any third-party apps. However, the situation is much different on Windows 10 because macOS install file (end with .dmg) is not supported by Windows OS. Unlike ISO image, there are few tools on Windows that can handle .dmg files. That's the most challenging part!

So in this article, we will show you how to create macOS bootable USB on Windows 10 and targets macOS Catalina specifically, which is the latest version of Apple macOS and it is easy to download the install file. This will be a great help if there were something wrong with your Mac and a fresh install was demanded. Also if you were a Mac enthusiast and can not afford the price, then it is not a bad choice to build a hackintosh with Catalina.

Before heading to the details of each method, please make sure you have downloaded a copy of Catalina OS dmg file and a working USB drive with more than 12GB storage.

Method 1: Create macOS Catalina Bootable USB on Windows 10 via DMG Editor

There are more than one solutions to create macOS Catalina Bootable USB on Windows 10 and we will go with easy one first. DMG Editor, a popular app developed by UUByte, is a multi-functional and cross-platform image burning tool that works on Windows, Linux and macOS. It supports creating bootable USB from popular image files, including dmg, iso, zip, img. And it has full support for Linux distros and old versions of Windows OS. macOS support was not available in previous versions. But now, the latest version of DMG Editor adds better support for macOS dmg file. Let's get a try first.

Step 1.Go to UUByte official website and download Windows version of Etcher from there.

Step 2. Run the executable file and complete the installation process. After that, insert an USB drive in Windows 10.

Step 3. Open the installed UUByte DMG Editor by double-clicking on the icon shown on your home screen. Click on the 'Burn' option then. After that, add Catalina .dmg file to the software and click on 'Change' button to choose the inserted USB device.

Step 4. Finally, click on the 'Burn' button to start the dmg burning process. At this time, a progress bar is displayed on the screen and it gives you an estimated calculation for the time remaining.

Step 5. Wait about 10 minutes. It will show you a pop-up message after completing the task successfully.

The process is very quick and easy to execute. But you might have issues running Etcher app on old computers with low profile hardware. Etcher GUI is built primarily on a new Javascript framework called Electron , which consumes a lot of computing resources. So if you were going to use Etcher to create macOS Catalina bootable USB, make sure testing it on a high-profile Windows 10 PC or laptop.

Method 2: Convert .dmg to .iso and Create macOS Catalina Bootable USB

macOS Catalina install image is distributed in .dmg format and Windows 10 has no support. Hen it is almost impossible to read such files in conventional ways. So in this part, we will convert macOS Catalina dmg file into ISO and create a bootable installer by burning the ISO file to USB. This can be done with the help of third-party software.

To execute the method, you need two software. First, you need a special software to convert dmg to ISO. Second, an ISO to USB burning software to make bootable USB from ISO file. To demonstrate, we have used 7 PowerISO & UUByte ISO Editor to create macOS Catalina bootable USB from Windows 10.

Step 1: Download and install PowerISO on Windows 10.

Step 2: Insert your USB drive. Right-click on this peripheral device and choose the option to format it. After a few seconds, you will get the notification of completing the format process.

Step 3: Now, open PowerISO and navigate to Tool menu. From the pop-up list, please click the 'Convert' option.

Step 4: In a pop-up window, click the folder icon to add macOS Catalina dmg file in Source file field. And set an output file name under Destination file section. Next. choose Standard ISO Images (.ISO) from Output image file format.

Step 5: When the ISO file is created successfully. Download and install UUByte ISO Editor. Then click Burn button to open ISO burning Window. Next, add ISO file to the program and select the USB name. Wait for 7 minutes, and a bootable USB is ready!

Step 6: After getting a task completion message on screen, eject the USB and then start installing macOS Catalina from the USB drive.

The solution is simple but may need to purchase a couple of tools for executing the steps. But if you will search smartly on the internet, chances are there that you can get the required tools without paying any cost. However, if you want to bypass using any of the third-party tools, you can create the Catalina OS bootable USB by accessing macOS in a virtual machine.

Method 3: Use TransMac to Create macOS Catalina Bootable USB in Windows 10

TransMac is a single-purpose utility to open Mac disk image from a Windows PC. It's one of the quickest methods to create macOS bootable USB drive from dmg file. However, the support for Catalina is not good as Mojave and High Serrira. Plus, you have to pay for 59 USD to use the burn feature. That's why we mention this app at the end of this post.

Step 1: Download TransMac from the official site and run the .exe file to complete the installation process.

Step 2: Now plug in a USB device into the port. Now right-click on TransMac icon shown on the home screen and then choose to Run as administrator.

Create Bootable Catalina Installer

Step 3: After landing inside the tool's window, all disk drives will be displayed on the left side automatically. Click File -> Open Disk Image to load macOS Catalina dmf file into the program.

Step 4: Before proceeding further, you need to format your USB device to make it compatible with Mac HFS or APS partition. For doing the same, click on the 'Format Diks for Mac' option. Wait for 30 seconds to complete the process.

Step 5: Right-click on the selected USB disk. From the shown list, click on 'Restore with Disk Image'. If it shows any warning message, just click on the OK button to accept.

Step 6: After that, select the location of saved Mac OS Catalina DMG file and then click on the OK button. Now stay back and look after 20 minutes. You will get ready with a bootable Catalina USB.

TransMac is one of the easiest method to create a bootable macOS Installer USB on a Windows PC. You can use this application to burn any version of macOS operating system file to USB.

Conclusion

How To Create A Bootable Catalina Installer

To conclude, we would recommend going with either the first or the second method to create bootable macOS Catalina USB. Both are super easy to follow because you don't need to install multiple tools and go through a multi-layer process to meet your requirement.