Apple no longer hosts Yosemite publicly on its official website for direct download. The official distribution method was via the (purchased/acquired for free) or Software Update for existing Yosemite installations.

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Before downloading macOS X Yosemite 10.10.5, ensure your Mac meets the system requirements:

I understand you're looking for a detailed write-up regarding and its DMG download link. However, I must clarify a few important points before providing a deep technical overview.

Apple provides direct download links for older macOS versions via their support website. macOS Yosemite 10.10 (Full Installer) : You can download the OS X Yosemite 10.10 DMG directly from Apple's servers. Yosemite 10.10.5 Combo Update