It is a registry entry not a file, that may be added or modified in the "Taskband"
registry hive under the following registry path:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Taskband
In the right-hand pane, see if there is a "NumThumbnails" DWORD line.
If it is not there, you must add it as a DWORD (32-bit) string value,
and you must also enter 0 or 1 in the "Value data" blank provided.
Next to the right of that blank, tick the radio button "Decimal"
click OK and exit the registry editor.
A restart or signing out and signing back in may be required.
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