4 official macOS installers of the last decade on one single 32Gb USB flash drive. Most recently updated versions (however updates may be available) Some older Mac OS will only be compatible with older hardware and some newer will only be compatible with newer macs. Please refer to Apple website for compatibility with your machine. El Capitan 2015 High Sierra 2017 Mojave 2018 Catalina 2019 Does not require WiFi Internet recovery. Install any of these 4 OS and keep USB as emergency Recovery tool. Includes general instructions. Attention! If you get ANY error, please First check the system bios date! Open Utilities > Terminal and enter “date” press Enter. It will show current date. If the year is not 2020 (usually after power interruption it is reset to default date to something like 1996) run command “date” (instructions included) then close terminal and repeat installation. For some OS the date may be needed to set back, for example for El Capitan (that was released in 2015) change the year to 2016 and repeat installation. 10-in-1 mac OS USB Catalina Mojave High Sierra El Capitan Yosemite Mavericks Etc. Shipped with USPS first class Mail.