Numerous mini computers, due to their compact size, often lack a DVD ROM to save space. This design choice eliminates the need for an external USB DVD ROM. If you find yourself using such a mini computer and don't have an external USB DVD ROM, your go-to solution is to utilize a USB drive for installing operating systems like Windows, Linux, or macOS. Additionally, you can transform a bootable USB flash drive into a diagnostic tool for your PC. This guide outlines the steps for creating a USB bootable device. It's important to note that this guide is compiled based on information from wikihow.com.
Method 1 of 5: Making a USB Drive to Install Any PC Operating System
1.Open the Command Prompt. You will need to run Command Prompt as an Administrator. Right-click on it and select Run as Administrator. You may need to enter the Administrator password. This method will create a USB drive that is bootable. You can then copy the contents of an operating installation disc onto the drive to create a portable installation drive. This method only works in Windows Vista, 7, and 8.
2. Open the disk management utility. This can be opened by entering the command disk part.
3. Display the connected disks. Type the command list disk to show a list of all the drives connected to your computer. Your USB drive should be listed here as well. Make note of the number next to your USB drive.
4. Select the USB drive. Enter the command select disk #, replace “#” with the number from the previous step.
5. Clean the flash drive. Enter the command clean to have the disk management utility verify the integrity of the USB drive, and erase all data.
6. Create a bootable partition. Once the USB drive is clean, type in create partition primary. You will see a message saying that the operation was successful.
7. Select the new partition. Enter the command select partition 1 and press Enter. Once you receive a confirmation message, type active and press Enter. This will activate the partition.
8. Format the USB drive. Enter the command format fs=fat32. After pressing the Enter key, the program will work for a few minutes (in the case of small USBs, such as 32Gb USBs, a slow format may take several hours) and the progress will be displayed as a percentage.
9. Assign a drive letter to the USB. Enter the assign command to assign a drive letter to the USB drive. Enter exit to end the Disk Management program.
10. Copying an Operating System Once the USB drive is bootable, you can copy the installation files for the operating system you want to install. You can drag and drop the files using your favorite file manager/browser.
Copying any drivers that may be needed during the installation of the operating system makes the installation process smoother.
Method 2 of 5: Making a Windows 7/8 Install Drive
1. Create or Obtain a Windows 7/8 ISO: Install a free burning program capable of creating ISO files. If you have a Windows 7 ISO file from Microsoft, skip to Step 2.Insert your Windows 7 DVD, open the burning program, and choose an option like "Copy to Image" or "Create Image," selecting your DVD drive as the source.
Save the ISO file with an easy-to-remember name and location. Note that the ISO size equals the disc size, requiring ample storage on your hard drive.
The creation process duration depends on your computer and DVD drive speed.
2. Download Windows 7 USB/DVD Download Tool: Obtain this free tool from Microsoft, applicable for Windows Vista ISOs as well. It's compatible with various Windows versions.
3. Select the Source File: Choose the ISO created or downloaded in the first step and click Next. 
4. Select USB device. You are given the option to either burn to a DVD or create a USB device. For this guide, click USB Device. 
5. Choose Your USB Device: Ensure your flash drive is correctly connected, with at least 4GB of available space for the Windows installation.
6. Wait for the Program: The tool formats the USB drive for proper booting and copies the ISO file, a process taking up to 15 minutes based on your computer speed.
Method 3 of 5: Making a Windows XP Install Drive
1. Prepare your software and hardware: Gather USB_Prep8 and bootsect.exe, both freely available online developer tools. Additionally, have a flash drive with a minimum capacity of 1GB and a Windows XP installation CD or DVD. Insert the USB drive and Windows XP disc, closing any Autoplay windows that appear.
2. Extract and run USB_Prep8: Extract the USB_Prep8 .zip file, open the resulting folder, and run usb_prep8.cmd. This action launches a command prompt. Press any key to format the USB drive using PeToUSB. Note: For Windows 7, open a cmd prompt as an administrator and run usb_prop8.cmd from the prompt.
3. Initiate the format: Maintain the default settings in the PeToUSB window. After the format completes, keep both windows open and start a new command prompt by pressing Windows key + R, typing "cmd," and pressing Enter.
4. Extract bootsect: Navigate to the bootsect folder in the new command window. In the bootsect directory, type "bootsect.exe /nt52 Z:" and replace "Z" with your USB drive letter. Close any windows displaying USB drive contents to avoid operation failure. Bootsect copies necessary files for USB booting, and when done, you'll see the message "Bootcode was successfully updated on all targeted volumes." Close Bootsect and PeToUSB, but keep the usb_prep8 command window open.
5. Adjust Prep8 settings: After bootsect completes, the usb_prep8 command window displays a numbered menu for settings adjustment. Change the first three settings:
Press 1 and Enter. In the Browse for Folder window, choose the drive with your Windows XP disc and press OK. 
Press 2 and then Enter. If you have a drive on your computer that is already assigned to the letter T:, then change this option to a free letter. Otherwise, you can leave this as is.
Press 3 and then Enter. Enter the drive letter for your USB flash drive.
6. Start the copy process. To do this, press 4 and then Enter. You will be notified that proceeding will format the virtual disk from the earlier menu. Press Y to continue. Once the format is complete, press any key to continue.
Files will scroll up the screen as the copy process progresses. You will be prompted to press any key to continue again. After a few moments, a window will open confirming that you want to copy TempDrive Files. Press Yes, and wait around 15 minutes, then press Yes for the next two windows that open.
7. Start Windows XP setup. The USB drive is now installed. Insert it into the computer where you want to install Windows XP. You will need to set the BIOS to boot from the USB drive. See our guide on how to set up the BIOS properly.
Once the boot menu opens, select option 1 for a text mode installation. The Windows XP installation will now begin normally.
After the text mode portion is complete and the computer reboots, select option 2 to begin the GUI (Graphical User Interface) portion of the installation.
Keep the USB drive plugged in throughout the installation process.
Method 4 of 5: Creating a USB PC Repair Toolkit
1. Download the Ultimate Boot CD (UBCD) ISO file. This file is available for free from the developer here.UBCD is a set of diagnostic tools that run before the operating system is loaded. Having these tools on a single USB flash drive makes it easy to use as a PC repair tool. You will also need the Universal USB Installer, which can be found here. Place the Universal USB Installer in the same folder as the UBCD .iso file. 
2. Run the Universal USB Installer. Select Ultimate Boot CD from the menu. make sure the directory in the field is correct. Select the correct drive letter for the USB flash drive. Click the Create button.
3. Boot from the USB drive. once USB creation is complete, you are ready to boot from the drive and run the diagnostic tools.
Method 5 of 5: Making a Mac OS X 10.7 or 10.8 USB Install Drive
1. Prepare the required hardware and software. You'll need an 8GB or larger USB flash drive. You'll also need the OS X installer from the Mac App Store. Download the application and insert it into your USB drive.
2. Launch the Disk Utility. It can be found in the Utilities folder inside the Applications folder. The Disk Utility will allow you to manipulate the USB drive. In the left frame, select your USB drive and then open the Partition tab. Under Partition Layout, select 1 Partition.
3. Select the format. From the Format drop-down menu, select Mac OS Extended (Journaled). This will allow any Mac OS computer to read the drive. Click the Options button and select GUID Partition Table.
4. Locate the installation Mac OS X file. This is the .app file downloaded from the Mac App Store. It is installed in the Applications folder by default. Right-click the file and select Show Package Contents. Open Contents and then Shared Support. You will see a file named InstallESD.dmg. Drag this file to your desktop. 
5. Open the Disk Utility again. Click on the USB drive in the left frame. Open the Restore tab and click the Image… button next to the Source box. Select the InstallESD.dmg file. For Destination, drag the newly created partition into the field.
6. Click the Restore button. You will be asked for confirmation before the copy process begins. Press Erase to continue. The process can take up to an hour to complete, depending on the speed of your Mac. Once it is finished, you can boot from the USB drive and install Mac OS X as if you were using a disc.
