Thumbnail Images (Thumbnail View) are stored normaly in a cache by
your Operating System.Disabling this function can free up memory
but can cause delays when opening folders:

- HKEY_CURRENT_USER\Software\Microsoft\Windows
\CurrentVersion\Explorer\Advanced

Create or modify in the right pane the entry below:

DisplayThumbnailCache

If you need to create it do a rightclick in the right pane , new ,
REG_DWORD [Dword Value] and name it like above.

Doubleclick now this entry and set it's value to:

0 = DisplayThumbnailCache disabled
1 = DisplayThumbnailCache enabled


Restart your PC!