If you're on Windows, you want a codec pack for showing the various image formats as thumbnails. Adobe does not provide this, and there are both free and inexpensive packages to do it. I use and like the FastPictureViewer Codec Pack myself.
Note that codecs enable thumbnails and previews all across Windows via Explorer, not just in Photoshop, and the best ones provide not only thumnbnails/previews for PSD files but also things like raw files from cameras.
Since you brought this up, and since I long ago got into killing any kind of thumbnail generation from Windows itself because it always wants to thumb every drive connected to it (with TBs of BIG image files) thus paralyzing the system - what do these codecs do in terms of rampant thumb generation and thus killing system performance? Can you restrict their activities to only x sized images like in Bridge?
I don't find thumbnail generation happens at all unless I'm looking at the folder, and the view is in one of the thumbnail modes (e.g., Large Icons, etc.).
I guess all my storage is fast enough that I don't see any practical impact. My default view for folders I haven't looked in yet and haven't set to another mode is Details View, so no thumbnail generation activity occurs unless I want it to.
That said, I just browsed to a folder I had never been to before containing raw files on my external backup drive, connected via USB 2.0, switched the view to Large Icons to see the thumbnails, and it only took about 1 second to fill in all the 27 thumbnails in the Explorer window... All the while I have a 3D rendering going on in Photoshop. On my SSD array thumbnail generation for any given folder is virtually instantaneous.
In answer to your question - the impact of generating thumbnails is a non-issue in every way I can see. I'll be happy to try something specific if you'll let me know what you want to see.
Note that there is a COMPLETELY DIFFERENT thing that Explorer is by default configured to do - generation of Thumbs.db files. Since Windows 7 this has been enabled for compatibility purposes only, and can be turned off via the Local Policy Editor. I've had this turned off for years. How to do that, excerpted from my popular "Configure the Windows 7 'To Work' Options" book:
Turn Off Caching of Thumbnails in Thumbs.db Files
People sometimes report that they cannot manipulate their folders as they want to because Explorer has a Thumbs.db file open. Windows 7 generates these files for compatibility with older software that may expect such files to exist in folders with, for example, photos in them.
Unless you're running such old software (which is uncommon at this point), you can just turn this off without consequences, and with a benefit: You'll no longer be blocked from manipulating folders because of Thumbs.db file conflicts.
The good news is that (with Windows 7 Professional and above) you can disable this through the Group Policy Editor:
- Click Start, type gpedit.msc into the search box, and hit Enter.
- When the Local Group Policy Editor comes up, navigate into:
> User Configuration
> Administrative Templates
> Windows Components
> Windows Explorer
- Right-click the entry Turn off the caching of thumbnails in hidden thumbs.db files and choose Edit.
- Enable the setting.
- Log off Windows and back on.
Note: If you have a version of Windows that does not provide the Group Policy Editor, the change can be done through a registry modification:
[HKEY_CURRENT_USER \ Software \ Policies \ Microsoft \ Windows \ Explorer]
DisableThumbsDBOnNetworkFolders REG_DWORD 0x00000001
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