This book is Volume 3 of the series, FYSOS: Operating System Design, and will show the reader how to detect, initialize, and communicate with three of the most common media hardware devices, the Floppy Disk Controller, the IDE Hard Disk Controller, and the SATA (AHCI) Hard Disk Controller. The reader will learn how to detect the controller, what type of controller it is, initialize it to default values, detect attached devices, and then communicate with those devices, such as reading and writing to the attached media. All of this is done without any outside help, such as operating system calls or the help of the BIOS. The reader will learn how to communicate with the hardware directly, reading and writing to the system bus to achieve these tasks. The companion CD-ROM contains complete source code of each example within the book, showing how to accomplish these tasks. This book, and its companion series of books, does not expect you to build the next great wonder of the computer world. It simply will help you with your interest in controlling the computer's hardware, from the point the BIOS releases execution to your boot code to the point of a fully working Graphical User Interface. It is not required that you know much about operating system design, though a good knowledge of C Programming Language and a moderate knowledge of an Intel(r)/AMD(r) x86 computer's hardware is expected to use this book