What is a PSB file?
Adobe Photoshop has two file extensions. If you are saving a file up to 30000*30000 pixels, it will use the PSD format. If you are storing anything exceeding than that and up to 300000*300000, the PSB (Photoshop Big) file extension comes into play. It can range up to 4 EB (i.e. exceeding 4.2 billion GB).
Being so massive in size, it supports all the Photoshop features that a user would generally require, such as effects, filters, and layers. If you so desire, these files can be converted to PNG, JPG, GIF, and other formats. PSB is nothing but a large version of PSD files and is compatible with only Photoshop CS or higher.
You cannot save files in this format by default. You must activate the PSB file format option in the File Handling pane found under the Photoshop Preference box by tapping on the Enable Large Document Format option.
How to Open PSB Files
How to Make PSB Files
Exact steps for creating PSB files will vary by program and operating system. Download one of the above listed programs and you should be able to follow typical procedure for opening files or creating files from the File menu. Typically you will select File > Open or File > New and continue through the prompts. Some programs may follow a different procedure for either creation or opening of files.