Dans une doc (Core Technology Overview) qui est plus technique que ce que je n'aurais cru:

Compressed Memory
Compressed Memory keeps your Mac fast and responsive by freeing up memory when
you need it most. When your system’s memory begins to fill up, Compressed Memory
automatically compresses the least recently used items in memory, compacting them
to about half their original size. When these items are needed again, they can be
instantly uncompressed.
Compressed Memory improves total system bandwidth and responsiveness, allowing
your Mac to handle large amounts of data more efficiently. Through use of the dictionary-
based WKdm algorithm, compression and decompression are faster than reading and
writing to disk. If your Mac needs to swap files on disk, compressed objects are stored
in full-size segments, which improves read/write efficiency and reduces wear and tear
on SSD and flash drives. The advantages of Compressed Memory include the following:
• Shrinks memory usage. Compressed Memory reduces the size of items in memory
that haven’t been used recently by more than 50 percent, freeing memory for the
applications you are currently using.
• Improves power efficiency. Compressed Memory reduces the need to read and write
virtual memory swap files on disk, improving the power efficiency of your Mac.
• Minimizes CPU usage. Compressed Memory is incredibly fast, compressing or
decompressing a page of memory in just a few millionths of a second.
• Is multicore aware. Unlike traditional virtual memory, Compressed Memory can
run in parallel on multiple CPU cores, achieving lightning-fast performance for bothreclaiming unused memory and accessing seldom-used objects in memory.

Power Efficiency
The power technologies in OS X Mavericks were built with the capabilities of modern
processors and the demands of modern apps in mind. The new power technologies
work together to achieve substantial power savings, while maintaining—and in some
cases even improving—the responsiveness and performance of your Mac.
These technologies are rooted in a few key principles:
• Just work for existing apps. No changes to applications should be needed, though
small changes may facilitate additional power savings.
• Keep as many processor cores idle as possible given the demand for CPU.
• When on battery power, only do work that the user is requesting or that is absolutelyessential.

App Nap
App Nap puts applications that you’re not using into a special low-power state that
regulates their CPU usage as well as network and disk I/O. App Nap can be automati-
cally triggered if an app’s windows are not visible and the app is not playing audio,
though developers can explicitly make an app ineligible for App Nap by using the
existing IOKit IOPMAssertion API (used today in OS X to prevent the system from
sleeping while an app is busy). App Nap triggers a number of power-saving measures,
including:
• Timer throttling—Reduces the frequency with which an app’s timers are fired. This
can mean significant improvements in CPU idle time when running applications that
frequently check for data.
• I/O throttling—Assigns the lowest priority to disk or network activity associated
with a napping app. The rate at which an application can read or write data from a
device is significantly reduced. In addition, I/O throttling reduces the chances that a
background process will interfere with the I/O activity of an app that you are actively
using.
• Priority reduction—Reduces the UNIX process priority of an app so that it receives asmaller share of available processor time.

J'en conseille la lecture si vous etes interessé.

http://images.apple.com/osx/preview/docs/OSX_Mavericks_Core_Technology_Overview.pdf