How To: Boot a Mac into FreeDOS for Bootable, SpinRite or ReadSpeed (Part 2 of 3 - Media Creation)

  • SpinRite v6.1 Release #3
    The 3rd release of SpinRite v6.1 is published and may be obtained by all SpinRite v6.0 owners at the SpinRite v6.1 Pre-Release page. (SpinRite will shortly be officially updated to v6.1 so this page will be renamed.) The primary new feature, and the reason for this release, was the discovery of memory problems in some systems that were affecting SpinRite's operation. So SpinRite now incorporates a built-in test of the system's memory. For the full story, please see this page in the "Pre-Release Announcements & Feedback" forum.
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  • BootAble – FreeDOS boot testing freeware

    To obtain direct, low-level access to a system's mass storage drives, SpinRite runs under a GRC-customized version of FreeDOS which has been modified to add compatibility with all file systems. In order to run SpinRite it must first be possible to boot FreeDOS.

    GRC's “BootAble” freeware allows anyone to easily create BIOS-bootable media in order to workout and confirm the details of getting a machine to boot FreeDOS through a BIOS. Once the means of doing that has been determined, the media created by SpinRite can be booted and run in the same way.

    The participants here, who have taken the time to share their knowledge and experience, their successes and some frustrations with booting their computers into FreeDOS, have created a valuable knowledgebase which will benefit everyone who follows.

    You may click on the image to the right to obtain your own copy of BootAble. Then use the knowledge and experience documented here to boot your computer(s) into FreeDOS. And please do not hesitate to ask questions – nowhere else can better answers be found.

    (You may permanently close this reminder with the 'X' in the upper right.)


Well-known member
Sep 18, 2020
This How To is in Three Parts:
  1. Part 1 - Intro
  2. Part 2 - Media Creation - How to make a bootable USB on your Mac for Bootable, ReadSpeed, or SpinRite - this post
  3. Part 3 - Booting your Mac - How to get your Mac to boot from external media instead of the internal hard drive

Note: If you have access to a Windows machine, you may just want to run the Windows-based GRC media prep program for each of the utilities and prepare your flash drive there. It's easier than doing it on the Mac. If that's the case, prepare your media and move on to Part 3 of this How To.

Media Creation - How to make a bootable USB on your Mac for Bootable, ReadSpeed, or SpinRite​

This post describes how to create bootable flash drives for the GRC DOS-based utilities on a Mac, before attempting to boot them. Once the bootable flash drive is created, you can refer to part 3 noted above to learn how to boot your Mac from the flash drive to run the GRC software. If you're unsure if your Mac can natively boot these utilities, well, that's what Bootable is for -- to confirm one way or the other if your system can boot FreeDOS natively (and if not, you can take a look at the instructions for How To Run SpinRite on a UEFI-only Machine).

You can use just about any flash drive of 128 MB or greater.

You should download and try booting and running both of the "test" utilities, Bootable and ReadSpeed, before committing to purchase SpinRite.


If you are unsure if your Mac can natively boot FreeDOS in order to run SpinRite, you should try and download and run the Bootable utility. If you can get that to boot and run, you can get SpinRite to boot and run. The instructions on the Bootable home page are pretty good; nonetheless, it's worth putting them in a generalized context with media creation instructions for all of the GRC utilities


ReadSpeed is a utility designed to discover and benchmark the drives on your system. As a general rule, if ReadSpeed can discover and benchmark the drive, then SpinRite should be able to discover and work on the drive as well. As noted below, there may be drives that SpinRite can access through the Mac's BIOS emulation, using the SpinRite's "forcebios" switch, that ReadSpeed simply can't see and benchmark.


SpinRite is GRC's disk maintenance and bad sector refresh / repair tool.

Media Creation Instructions​

  1. For each of the three utilities, you'll download an .IMG files which will be written to a USB Flash Drive. Decide how you'd like to write that image to the flash drive:
    1. Using Balena Etcher
    2. Using the Raspberry Pi imager software
    3. Using the internal Mac dd command
  2. You should probably download the .IMG files for each of the utilities in the following order, ensuring the prior application works before moving on:
    1. Bootable
    2. ReadSpeed
    3. SpinRite
  3. Getting the .IMG file for:
    1. Bootable
      1. Download the Bootable.ZIP file from the Bootable home page
      2. Unzip the folder, you'll see three files; you're interested in the BootAble.img file
      3. Note the name and location of the .IMG file
    2. ReadSpeed
      1. As of 4/29/2024, the following should work but does not. The downloadable .IMG file is not valid. This page will be updated when the ReadSpeed .IMG download is functional.
        1. Download the readspeed-img.ZIP file directly from the ReadSpeed home page
        2. Unzip the folder, you'll see one file, called ReadSpeed.img
        3. Note the name and location of the .IMG file
    3. SpinRite
      1. After purchasing SpinRite, or entering the information to get an upgrade, you will be brought to the SpinRite download page.
      2. Click on your custom link in the section "For users without any access to Windows" and download the file
      3. Unzip the folder and you'll see one file called spinrite.img
      4. Note the name and location of the .IMG file
  4. Write the image using the method of your choice:
    1. Insert the USB drive that will be erased and overwritten with the .IMG file
    2. If using Balena Etcher:
      1. Select the .IMG file that you downloaded
      2. Select your flash drive
      3. Flash the file
      4. Once you get a notification that flashing was successful, close the program
      5. Eject the USB drive, then reinsert the drive
    3. If using Raspberry Pi Imager:
      1. Raspberry Pi Device: Select No Filtering
        1. Operating System: Select Use custom
      2. Select the .IMG file that you downloaded
      3. Storage - Choose Storage: Select the USB drive
      4. Click Next
      5. Would you like to apply OS customisation settings? Select No
      6. All existing data will be erased? Select Yes
      7. The image will be written to the drive
      8. You can now eject the SD card: Select Continue
      9. The image has now been written to the USB drive
      10. Close the program
      11. Eject the drive, then reinsert the drive
    4. If using the ddcommand
      1. Open a Terminal session
      2. List all of the devices
        1. diskutil list
      3. Note the name of the USB drive (will be something like /dev/disk2). BE ABSOLUTELY SURE that you have identified the drive correctly
      4. Unmount the disk, for example (again, use YOUR device name):
        1. diskutil unmountDisk /dev/disk2
      5. Use the dd command (elevated via sudo) to write the .IMG of interest to the device.
      6. For example, if the spinrite.img file is in the user's Downloads folder, AND the device of interest is /dev/disk2, you would:
        1. cd ~/Downloads
        2. sudo dd if=spinrite.img of=/dev/disk2
      7. exit from the Terminal
      8. Eject the drive, then reinsert the drive
  5. Boot the newly created flash drive using the instructions noted in Part 3 of this How To:
    1. Booting your Mac - How to get your Mac to boot from external media instead of the internal hard drive
  6. Runtime notes for: Bootable
    1. The created Bootable drive, labeled 'BOOTABLE R1' has 5 files on it, but all have the DOS attributes of Hidden, System, and Read-Only
    2. You can OPTIONALLY make the files visible and editable:
      1. Determine the mount point for the drive
      2. On the Terminal:
        1. df -h
      3. If the mountpoint is /Volumes/BOOTABLE R1:
        1. cd /Volumes/'BOOTABLE R1'
        2. ls -lO (That's a capital O at the end of that; you'll see the attributes for the files
      4. Remove the Hidden attribute from all files:
        1. chflags nohidden *
      5. Remove the Read-Only attribute from all files:
        1. chflags nouchg *
      6. You should now be able to see the files in the MacOS finder and they will not show the Read-Only "lock" icon
      7. NOTE: I am unable to determine if there is a way in MacOS to change the "System" attribute on the files.
    3. NOTE: On my Mac, the Bootable "Splash Screen" would show stating that booting was successful, and to press any key to drop to the DOS command prompt. My Mac would not respond to any key press to drop to the DOS prompt, yet when running SpinRite it would respond to a keypress. Therefore, the fact that you can see the "Success" image means your Mac should be able to run any DOS program including ReadSpeed and SpinRite.
  7. Runtime notes for: ReadSpeed
    1. ReadSpeed should see IDE and AHCI / SATA drives
    2. It will not see drives that may be accessible to SpinRite by using the ForceBIOS switch
    3. So in essence, ReadSpeed may only see a subset of the drives that SpinRite can access
  8. Runtime notes for: SpinRite
    1. None so far
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