This string refers to a for the iPhone 3G (internal model number iPhone1,2). Specifically, it targets iOS 4.2.1 (build 8C148) — the final, semi-functional operating system for that device. The phrase "Custom Restore" implies a build that bypasses Apple’s official signing checks, often created using tools like sn0wbreeze , PwnageTool , or iFaith .
Today, this is purely a collector/researcher item. You can’t activate it normally (activation servers for iOS 4 are long gone unless you hacktivate it). But if you’re into , an IPSW like this might contain custom root filesystem changes, kernel patches, or bundled unofficial tools. -iPhone1-2 4.2.1 8C148 Custom Restore.ipsw-
To the uninitiated, the filename looks like a jumble of numbers and letters. However, to an iOS technician or historian, it is a precise label that tells a complete story. Let's break it down component by component. This string refers to a for the iPhone