Adobe 12040118 - After Effects Standard Tutorial page 541

Cached frames are restored after an undo/redo.
Cached frames are restored when a composition or layer is returned to a previous state, such as turning a layer's visibility off then back on.
Reusable frames are recognized anywhere on the timeline (e.g., when using loop expressions, time remapping, or copy/paste of keyframes),
not just adjacent frames.
Reusable frames are recognized on duplicated layers or duplicated compositions;
Cache is not automatically destroyed by a render queue render at anything other than Current Settings.
In After Effects CS5.5 and later, Disk Cache is enabled by default. For disk cache preferences, and to enable, or disable disk caching:
Choose Edit > Preferences > Media & Disk Cache (Windows) or After Effects > Preferences > Media & Disk Cache (Mac OS), and select, or
deselect Enable Disk Cache.
Disk cache preferences allow you to select a folder to contain your cache.
Click the Choose Folder button, and then click OK (Windows) or Choose (Mac OS).
To empty the disk cache:
Click the Empty Disk Cache button.
Note: Even when disk caching is enabled, each frame must be able to fit into a contiguous block of RAM. Enabling the disk cache doesn't help
with limitations regarding inadequate RAM to hold or render a single frame of your composition.
For the best performance with disk caching, select a folder that's on a different physical hard disk than your source footage. If possible, the folder
should be on a hard disk that uses a different drive controller than the disk that contains your source footage. A fast hard drive or SSD with as
much space allocated as possible is recommended for the disk cache folder. The disk cache folder can't be the root folder of the hard disk.
As with the RAM cache, After Effects only uses the disk cache to store a frame if it's faster to retrieve a frame from the cache than to rerender the
frame.
The Maximum Disk Cache Size setting specifies the number of gigabytes of hard disk space to use. In After Effects CS6, the default disk cache
size is set to 10% of the volume's total size, up to 100 GB. In After Effects CS5.5, this amount is 20 GB, by default. Because of this, many more
frames are eligible for disk caching than in previous versions.
Note: In After Effects CS5.5, and later, the application checks to make sure that you have 10 GB free above what is set in Preferences > Media &
Disk Cache. After Effects warns you if there is not enough room for the disk cache.
Global RAM cache
In After Effects CS6, RAM caching is vastly improved over previous versions. Global RAM Cache, offers these advantages:
Cached frames are restored after an undo/redo.
Cached frames are restored when a composition or layer is returned to a previous state, such as turning a layer's visibility off then back on.
Reusable frames are recognized anywhere on the timeline (e.g., when using loop expressions, time remapping, or copy/paste of keyframes),
not just adjacent frames.
Reusable frames are recognized on duplicated layers or duplicated compositions;
Cache is not automatically destroyed by a render queue render at anything other than Current Settings.
In this video by Learn by Video
background so that you don't need to wait for a preview to be rendered before you can resume work.
Persistent disk cache
Once you save a project in After Effects CS6, frames in the disk cache will be retained even after you close the project or quit After Effects. This
protocol is called persistent disk cache.
In After Effects CS6, the disk cache is no longer emptied at the end of a session. With the persistent disk cache feature, frames stored in the disk
cache is retained between sessions. This saves rendering time as you work on a project or other projects that use the same cached frames.
Upon opening a project, the disk cache is scanned looking for frames matching those in the project, and makes them available for use. The disk
cache contains frames from all projects you've opened in the same or earlier sessions, so disk-cached frames from one project will be retrieved for
reuse in other projects that need those same frames. As the cache is scanned, blue marks gradually fill in on your timeline.
Note: Because previous versions of After Effects didn't store everything on disk needed for this feature, resave CS5.5 and earlier projects in CS6
to experience persistent caching.
Note: Roto Brush frames are not persistently cached.
Cache work area in background
you'll see how the RAM and disk caches are used to save time, and how you can render compositions in the