OS X Yosemite продолжает направление, которое было задано с запуском прошлогодней OS X Mavericks, предлагая пользователям ещё более ясный дизайн и ещё больше функций, воодушевлённых iOS. Если в Mavericks появились привычные iOS-приложения Maps и iBooks, то на этот раз Apple обещает, что обе системы созданы для максимально удобной совместной работы.
Плоский дизайн, полупрозрачные панели, уход от градиентов и текстур в iOS 7 хорошо просматриваются и в OS X 10.10, благодаря чему настольная платформа выглядит гораздо современнее. Иконки приложений получили новый минималистический и более плоский дизайн, панель приложений и окна — более резкие грани.

Переработке подвергся Safari, получивший более ясный, понятный дизайн и улучшенную интеграцию поиска. Apple заявляет, что браузер теперь исполняет код jаvascript быстрее, чем любой другой присутствующий на рынке браузер — на стандартных веб-сайтах разница по сравнению с Firefox может быть шестикратной, а с Chrome — пятикратной. Apple расширила и поддержку веб-стандартов Safari, в том числе WebGL, SPDY и HTML5.

Реализована поддержка работы AirDrop между OS X и iOS — пользователи могут обмениваться изображениями и другими данными между своими мобильными устройствами и настольными системами без использования шнура.

OS X 10.10 Yosemite DP 5 для Разработчиков. Является предварительным и не предлагается для массовой установки.
Поэтому, настоятельно рекомендуется перед обновлением создать резервную копию в Time Machine.
Обновление вы устанавливаете на свой страх и риcк

Notes and Known Issues
Installation Known Issues
- Migrating from a user account encrypted with legacy FileVault may not restore files.
- You cannot restore from a Time Machine backup of OS X Yosemite using the system restore utility on earlier versions of OS X. Doing so will prevent your Mac from booting. To fix the issue, boot into your OS X Yosemite Recovery Partition and run “Repair Disk” on the un-bootable volume.
- Alternatively you can run the following from a pre-OS X Yosemite partition:
- /Volumes//usr/bin/afscexpand /Volumes//usr/sbin/kextcache
- /Volumes//usr/sbin/kextcache -u /Volumes/

Family Sharing Known Issues
- Shared purchase history page on Mac App Store and iOS App Store are disabled.
- Items already owned by family members must be re-downloaded from the Purchased page (not Store pages) to get them free of additional charge.

Gatekeeper Note
- Signatures created with OS X v10.8.5 or earlier ("v1 signatures") are obsoleted and will no longer be recognized by Gatekeeper. To ensure your apps will run on updated versions of OS X they must be signed using the codesign tool on OS X v10.9 or later ("v2 signatures"). For more information see OS X Code Signing In Depth.

Handoff Known Issues
- NSUserActivity payloads may not transfer successfully between apps using Handoff if running on two machines without an active internet connection.
- App icons may stay in the Dock after you have stopped using the corresponding app on another device.
- Handoff will not work on systems configured with multiple user accounts.
- Handoff icons may not appear in the Dock after using the corresponding app on another device. Trying another Handoff-supported app may resolve this issue.

iCloud Drive Notes
- iCloud Documents & Data created with OS X Yosemite Developer Preview will be deleted from the servers during this beta period. Information downloaded and not deleted from your Mac will remain on your Mac and will re-sync after the data wipe occurs.
- Migrating to iCloud Drive will disable Documents & Data syncing for your iCloud account on OS X Mavericks and earlier Macs, as well as iOS 7 and earlier devices.

iCloud Known Issue
- Some account password prompts may request the same login information several times before dismissing.

Aperture Note
- Only Aperture 3.5.1 will run on OS X Yosemite Developer Preview 5. Older versions of Aperture will not launch.

Aperture Known Issues
- It may not be possible to enable My Photo Stream or iCloud Photo Sharing if both iPhoto and Aperture are present on the system.
- Text and other UI elements, such as checkboxes and radio buttons, may be clipped or not display properly.
- Importing and exporting images, adjustments, and book PDF generation may be slower.
- Thumbnails and images may occasionally be out of sync when in Split Browser mode.
- Printing a book to Preview from the local printing dialog may result in an error.
- Thumbnails of newly imported PDFs may temporarily show incorrect color.
- Adjustment and zoom sliders may not respond to single clicks and need to be dragged to operate.
- Leica Monochrom RAW images are not supported.
- The Auto-stack slider may be slow to respond.

iPhoto Note
- Only iPhoto 9.5.1 will run on OS X Yosemite Developer Preview 5. Older versions of iPhoto will not launch.

iPhoto Known Issues
- It may not be possible to enable My Photo Stream or iCloud Photo Sharing if both iPhoto and Aperture are present on the system.
- Text and other UI elements, such as checkboxes and radio buttons, may be clipped or not display properly.
- Application window may not be restored to its original size after exiting Full Screen view.

Markup Known Issue
- The Color Picker may not allow color selection.

Safari Notes
- Subpixel rendering is now on by default for all web content. Web sites or in-app web views with extremely tight design constraints may render differently.
- In OS X Yosemite Developer Preview 5, CSS object model getters Element.client{Left,Top,Width,Height} and Element.offset{Left,Top,Width,Height} will return rounded double values based on subpixel layout and rendering metrics instead of fractional values. Element.scroll{Left,Top,Width,Height} will return integral values.

Safari Known Issues
- Date & Size limits set in Safari are not enforced in Developer Preview 5.
- Safari may stop responding while loading video when playing Netflix content.
- On certain machines, some forms of protected content, such as Netflix, may fail to play back. To resolve, hold down Option during the next reboot and select your OS X Yosemite partition.

Tools Notes
- In Developer Preview 5, unsigned or improperly signed kexts will not be loaded. To use unsigned kexts during development, this strict check can be disabled by adding a “kext-dev-mode=1” boot arg.
- AVFoundation changes the way some ID3 metadata values are represented as AVMetadataItems for binaries that are linked with the Developer Preview 5 SDK.
- Installing kernel extensions on systems running Developer Preview 5 may make your system un-bootable. To fix the issue, boot into the Recovery Partition and run the following:
- touch /Volumes//System/Library/Extensions
- kextcache -u /Volumes/
- In OS X Yosemite Developer Preview 5 and iOS 8.0 beta 5, the NSURLSessionTask class provides a new priority property. Complete usage details are available in the NSURLSession.h header file, provided by the Foundation framework.
- URLForUbiquityContainerIdentifier: might return nil when running your application in Xcode. If so, open System Preferences, navigate to iCloud > iCloud Drive, and enable Xcode.
- Developer Preview 5 includes new APIs to create CIContext objects that use the second GPU on Mac Pro hardware.

Other Known Issues
- Some text may not be localized to the selected system language.
- Some languages may have clipped or misaligned layout.
- The login window may not display users. Reboot the system to resolve this problem.
- All Sharing settings in System Preferences may be disabled when migrating to OS X Yosemite Developer Preview 5 from earlier versions of OS X.