Before you download and install Mac OS X Yosemite 10.10.5, make sure to:
Before Yosemite, OS X was distinctly separate from iOS in look and feel. Yosemite introduced "Continuity," blurring the lines between the Mac and the iPhone/iPad. It introduced the "Dark Mode" for the first time and revamped system fonts (introducing Helvetica Neue to the Mac). mac os x yosemite 1010 5 download dmg link
Released in August 2015, the 10.10.5 update focused on improving the stability, compatibility, and security of your Mac. It addressed specific issues with Mail, Photos, and VoiceOver, making it the most polished iteration of Yosemite. For many users, this version represents the "sweet spot" between the classic Mac aesthetic and the modern flat design language introduced with the 10.10 launch. System Requirements for Yosemite Before you download and install Mac OS X Yosemite 10
** Official Apple Link: **