🔧 Reinstall macOS on an old Mac from Windows: Create a bootable USB stick easily! 🚀
This guide explains how to create a bootable macOS USB drive from an ISO image on a Windows PC, using only TransMac. It is designed for older MacBook Pro models up to 2015 and covers macOS versions 10.6, 10.8, 10.12 and 10.13.6.
🛠 Hardware and software required
📌 Windows PC
📌 USB drive (16 GB minimum)
📌 macOS ISO image:
📥MacOS 10.8 (Mountain Lion)
📥MacOs 10.12.6 (Sierra)
📥MacOS 10.13.5(High Sierra)
📌 TransMac (to create the bootable drive, free 15-day trial version))
📥 1. Install TransMac on Windows
✅ Download TransMac
1️⃣ Go to the official Acute Systems website
2️⃣ Download TransMac (15-day trial version available)
3️⃣ Install the software on your PC
✅ Run TransMac as administrator
1️⃣ Right-click the TransMac icon
2️⃣ Select Run as administrator
💾 2. Format the USB drive for macOS
⚠️ Warning: This step will erase all data on the USB drive!
✅ Format the USB drive with TransMac
1️⃣ Insert your USB drive into the PC
2️⃣ Open TransMac and find your USB drive in the left-hand column
3️⃣ Right-click the USB drive ➝ Format Disk for Mac
4️⃣ Confirm and wait for the formatting to finish
📂 3. Copy the macOS ISO to the USB drive
✅ Restore the ISO to the USB drive with TransMac
1️⃣ In TransMac, right-click the USB drive
2️⃣ Select Restore with Disk Image
3️⃣ Click Yes to confirm
4️⃣ Select the macOS ISO file you downloaded
5️⃣ Start the process and wait 20 to 30 minutes
🚀 4. Boot the Mac from the USB drive and install macOS
✅ Boot the Mac from the USB drive
1️⃣ Shut down your Mac completely
2️⃣ Plug in the bootable USB drive
3️⃣ Switch on the Mac while holding down the Option (⌥) key
4️⃣ In the startup menu, select the USB drive containing macOS
✅ Start the macOS installation
1️⃣ In the installer, open Disk Utility
2️⃣ Select your internal disk and click Erase
- Format: Mac OS Extended (Journaled)
- Scheme: GUID Partition Map
3️⃣ Close Disk Utility and click Install macOS
4️⃣ Follow the on-screen instructions to complete the installation
🎯 Conclusion
🎉 Your bootable macOS USB drive is ready!
You can now reinstall macOS on an older MacBook Pro, up to 2015, with TransMac, without using Rufus.
If you run into a problem:
🔹 Boot error?
Check that the ISO is correct or try another one. Sometimes you need to start with the lowest ISO version in order to move up to the higher ones, finishing with 10.13.5 (High Sierra).
🔹 USB drive not detected?
⚠️ Here is how to fix the problem!
If your bootable macOS USB drive does not appear in the Mac's startup menu, here are the steps to follow to fix the problem.
1️⃣ Check the USB drive connection
✔️ Unplug the USB drive and plug it into another port
✔️ Try a different USB adaptor (if you are using a hub)
✔️ Try another USB drive (some are not compatible)
2️⃣ Reformat the drive and recreate the bootable USB drive
If the drive is detected in Windows but not on the Mac, repeat the process with TransMac:
✔️ Reformat the USB drive with "Format Disk for Mac"
✔️ Recreate the bootable drive with "Restore with Disk Image"
✔️ Try another ISO image if possible
3️⃣ Reset the Mac's NVRAM and SMC
An internal memory problem can prevent the Mac from booting from a USB drive.
🔄 Reset the NVRAM
1️⃣ Shut down the Mac completely
2️⃣ Switch it on while holding down Option (⌥) + Command (⌘) + P + R
3️⃣ Keep holding the keys for 20 seconds, then release them
🔄 Reset the SMC (Intel Macs only)
1️⃣ Shut down the Mac completely
2️⃣ Hold down Shift + Control + Option + Power for 10 seconds
3️⃣ Release everything and switch the Mac back on
4️⃣ Check the USB drive with Terminal
If you have access to macOS (via another Mac or in Recovery mode):
1️⃣ Open Terminal
2️⃣ Type the following command:
diskutil list
3️⃣ Check whether your drive appears in the list
4️⃣ If it is visible but does not boot, reformat it as Mac OS Extended (Journaled) with Disk Utility, then recreate the bootable drive
If your USB drive is still not detected:
🔹 Try another port or another USB drive
🔹 Recreate the drive with TransMac
🔹 Reset the Mac's NVRAM and SMC
🔹 Check with Terminal in macOS
⚠️ Need help? Ask your questions on the website www.e-med-cyber.fr! 😊