The module of the ErgoSoft RIP responsible for creating the Preview images in the JobComposer. It is generally a background module that is automatically started with the RIP and just runs and does its Job without requiring user interaction.
If you do need to access the Preview Server directly, you can find it in the Taskbar (Usually bottom right next to the clock on windows systems). Double click the Icon to open the Preview Server window.
In the Preview Server Window, you can see the current status (Idle/Busy) at the top. The Update Queue shows the queue of images that the preview server is currently working on and lets you see what will be processed in what order.
The bottom segment of the window displays the log file for the preview servers activities and lets you see the history of processed image previews and their status.
If you want immediately update an image preview, you may drag and drop it directly into the Preview Server in order to make it process that file (But of course you can also simply right-click the image in the JobComposer and select Update Snapshot).