.IMG

Introduction

A raw disk image is an exact copy of a disk, a memory card or a floppy, byte for byte, with nothing added. It is the simplest disk image there is, and the one written by tools such as dd. Operating systems for small computers, such as Raspberry Pi OS, are usually distributed as .img files, often compressed as .img.xz or .img.zip.

Because there is no header, the file is exactly the size of the disk, unused space included. The extension .img is also used for other, unrelated formats, so the contents decide what a particular file is.

Structure

Byte n of the file is byte n of the disk. Whatever the disk held at its start is what the file starts with. A hard disk or memory card image usually begins with a master boot record, whose last two bytes, at offsets 510 and 511, are 55 AA; a disk with a GUID partition table also has the text EFI PART at offset 512. A floppy disk image starts with the floppy’s boot sector, and a 1.44 MB floppy gives a file of exactly 1,474,560 bytes.

Also used for

• GEM Image .img

Links