Before we dive into custom builds, we must understand the stock version. stands for iPod Software Update (though it now applies to iPhones, iPads, and Apple TVs). It is the file format Apple uses to distribute firmware.
| Tool | OS | Purpose | |------|----|---------| | | Windows | Creates custom IPSW from stock Apple IPSW | | PwnageTool | Mac (old) | Creates custom IPSW (older iOS) | | iFaith | Windows/Mac | Dumps SHSH, builds signed custom IPSW | | Odysseus | Mac/Linux | Advanced downgrade with blobs | download custom ipsw