OS X Mountain Lion InstallESD.dmg

Overview

InstallESD.dmg is usually used for making bootable installers or creating virtual machines. This is an original InstallESD.dmg ejected directly from OS X Mountain Lion Installer. 

About OS X Mountain Lion

First developer release: June 2012
First final release: September 2012

Requirements

App can be opened in: Mac OS X Tiger, Mac OS X Leopard, Mac OS X Snow Leopard, Mac OS X Lion. 

New in OS X Mountain Lion

Notifications

Drag two fingers to the left and you'll see your notifications arranged along the right of the screen. Notifications will incorporate a whole bunch of programs, from email and iMessage, to Twitter mentions and direct messages to event reminders.

If you own an iOS device running , you'll be familiar with these bleeping reminders -- now you have them on your computer.

AirPlay Mirroring

This new feature will let you send a 720p stream of whatever's on your Mac's screen to a telly that's hooked up to Apple TV, turning your telly into a massive monitor that's connected over Wi-Fi. Handy if you want to give hilarious cat videos the big-screen treatment they deserve.

Apple TV isn't that popular, but with the company rumoured to be working on building a (craftily dubbed iTV, ), this might be a more intriguing feature in the future.

Gatekeeper

This one's likely to prove divisive -- it's a new security feature that controls what kind of software is installed on your Mac, with owners able to choose between installing software from any source, or only allowing downloads from the Mac App Store, and Apple-approved developers.

Developers will have a unique Developer ID, which they'll get from Apple, that marks their software as safe.

A third option for the really security conscious will be to only install apps from the Mac App Store.

A helpful extra bit of security? Possibly, but the idea of Apple regulating software outside its own App Store is something new. Security-conscious Mac owners will likely choose the 'safer' Apple-approved option, putting pressure on software developers to make sure they have the Apple stamp of approval to get their programs downloaded.

While it increases security, it also gives Apple more control -- something I feel not everyone will be keen on.

Game Center

Apple's bringing its mobile gaming hub app to OS X. I'm not sure how often you'd end up using this, but the ability to setup multiplayer games, even if your competitors are using an iPhone, iPod touch or iPad, is intriguing.

Apple's promising to let you 'personalise your Mac gaming experience'. Could this mean we'll get Game Center avatars to dress up in fancy virtual clothes? Here's hoping.

Notes and Messages

Yes, I've gone mad with power and bundled these two new features under one heading, for your convenience. OS X Mountain Lion introduces a Notes app that looks just the same as the iOS version, and Messages replaces iChat, working just like iMessage on mobile devices, with the ability to drag photos or videos into the conversation. You'll be able to hold chats between an iOS device and a computer running Mountain Lion. Handy.

So Apple is definitely trying to squish its mobile and computer-based operating systems into each other, with most of the new OS X features being taken wholesale from iOS. Are you excited about this upgrade? Tell me what you think in the comments below, or over on our Facebook wall.

Want to install older macOS/OS X?

Read this article by Apple Support to know whether how to downgrade your Mac.