The PSB format is next to the more commonly used psd format, the second native graphics format of the image editing software Adobe Photoshop. The PhotoShop big file is a lossless graphics format that stores much more information besides pure image data.
Among other things, information about layers, masks, paths as well as alpha channel information and vector elements are stored. Adobe Photoshop is the standard program for professional image editing.
The difference to a normal psd file is the increased maximum resolution and the removal of file limits (Windows 4GB, Mac 2GB). Images in psd format can have a maximum of 30,000 x 30,000 pixels, whereas PSB can have up to 300,000 x 300,000 pixels. Such large pictures are made for example by some professional cameras or are produced in panoramic or satellite images.
The PSB format was introduced with the CS series and therefore can not be processed by older Photoshop versions. Opening a PSB file can cause problems, since the PSB format is not 100% downwards compatible. Each new version of Photoshop has new features that result in new data that will be stored in the PSB file.
In order to be able to save the PSB format, it usually has to be activated via the file handling in the settings. Psb files can only be used by Photoshop CS. Photoshop is available for Windows and Mac OSX.