tailieunhanh - Writing Your Own Toy OS By Krishnakumar R. Raghu and Chitkala Assembled by Zhao Jiong

This article is a hands-on tutorial for building a small boot sector. The first section provides the theory behind what happens at the time the computer is switched on. It also explains our plan. The second section tells all the things you should have on hand before proceeding further, and the third section deals with the programs. Our little startup program won't actually boot Linux, but it will display something on the screen. Bài viết này là một thực hành hướng dẫn cho việc xây dựng một khu vực khởi động nhỏ. Phần đầu tiên cung cấp các lý thuyết sau. | Writing Your Own Toy OS By Krishnakumar R. Raghu and Chitkala Assembled by Zhao Jiong gohigh@ 2002-10-6 Writing Your Own Toy OS Writing Your Own Toy OS Part I By Krishnakumar R. This article is a hands-on tutorial for building a small boot sector. The first section provides the theory behind what happens at the time the computer is switched on. It also explains our plan. The second section tells all the things you should have on hand before proceeding further and the third section deals with the programs. Our little startup program won t actually boot Linux but it will display something on the screen. 1. Background The Fancy Dress The microprocessor controls the computer. At startup every microprocessor is just another 8086. Even though you may have a brand new Pentium it will only have the capabilities of an 8086. From this point we can use some software and switch processor to the infamous protected mode . Only then can we utilize the processor s full power. Our Role Initially control is in the hands of the BIOS. This is nothing but a collection of programs that are stored in ROM. BIOS performs the POST Power On Self Test . This checks the integrity of the computer whether the peripherals are working properly whether the keyboard is connected etc. . This is when you hear those beeps from the computer. If everything is okay BIOS selects a boot device. It copies the first sector boot sector from the device to address location 0x7C00. The control is then transferred to this location. The boot device may be a floppy disk CD-ROM hard disk or some device of your choice. Here we will take the boot device to be a floppy disk. If we had written some code into the boot sector of the floppy our code would be executed now. Our role is clear just write some programs to the boot sector of the floppy. The Plan 2 Writing Your Own Toy OS First write a small program in 8086 assembly don t be frightened I will teach you how to write it and copy it to the boot .