: Inside, you will see a file named InstallMacOSX.pkg . Double-click it.
Once your bootable media is ready, you can perform a clean installation or upgrade an older system. Shut down the target Mac completely. Insert your bootable USB drive into a USB port.
Select the USB drive and format it as with a GUID Partition Map . Name the drive YosemiteUSB . Open Terminal (Applications > Utilities). Paste the following command into Terminal and press Enter:
You can download the OS X Yosemite 10.10 DMG directly through Apple Support.
Select from the main menu and follow the prompts to complete configuration. Troubleshooting Common Installation Errors
: Follow the on-screen prompts. This process does not install Yosemite yet; instead, it extracts the official app named Install OS X Yosemite directly into your Applications folder.
: Packages critical backend security updates designed to shield older machines from vulnerabilities. Technical Specifications & System Requirements
Double-click the downloaded .dmg file to mount it on your desktop.
2 GB Required free storage: 8 GB for the installer + ~12 GB for the OS itself.
Downloading the installer once allows you to update multiple offline Macs without consuming internet bandwidth each time.
The OS X Yosemite 10.10.5 update includes the new Photos app and improves the stability, compatibility, and security of your Mac. Apple Support
