Out-of-core rendering for textures unloads the memory used by textures to hard drive by using a lower resolution version of them, depending on how far from the camera they appear in the scene. Think of it as “Level of Detail” for textures, which lowers RAM usage without affecting the appearance of the final image. 

Out-of-core rendering for textures can be found and enabled in Render Settings > Performance: 

Parameters for Out-of-core textures can be found in: 
Render Settings > System > System Settings > Out-of-core textures: 

You can set the Cache size (GB), and the percentage of the HDD to be left free. If any of those limits are reached, no more offloading of textures to the HDD will take place. 

The default texture cache path is: C:\Users\”YourUsername”\AppData\Local\Temp\CoronaRenderer\ImageTextureCache
and it can be modified to any custom directory. 

Note: Out-of-core textures work only with Corona Bitmaps.

How it works

The texture cache is generated for each scene, when the textures are loaded, and is deleted on scene closure. It is used always (when enabled), not only when the system is running low on RAM. The best savings in memory are when the textures have higher resolution compared to what is needed for their placement in the scene – textures viewed from distance will likely be partially offloaded to the hard drive.

The renders below show up to 30% saving in peak memory used by Corona:

Out-of-core textures: OFF, Memory used by Corona: 4.6GB

Out-of-core textures: ON, Memory used by Corona: 3.4GB

Source: Chaos