The OSloader will enable protection mode and paging machism ("enable" is actually a legacy conception, nowadays these behaviours should usually boot as default).And the last 64 bytes before magic number is used to store disk partition table(DPT), to denote where does the disk start or end. the magic number means that this sector(or disk, MBR is located in the first sectors) is bootable, in order to be located by BIOS routine. MBR is directly written in assemble code (fixed format), and there's another conventions.We will call the new area the OSloader anyway. Since our system is actually designed from here, and this size of MBR is limited in 1 sector (512MB), we will only implement a loader on it, which load another large area of disk into memory, then jump to it (like what BIOS does, this process is often know as link load, though low efficient.).MBR is most well known as its address 0x7c00 (btw, we can only at most 20 bit address by combining register cs and register ip, before goto protection mode).That's actually where you can hack start from. At the end of BIOS execution, it will load a disk area called MBR then jmp to it.(However, we will see goodbye to him, when we enter protection mode.) ![]() In a word, IVT is a basic abstract, which get you rid of directly manipulating device port or viewing tons of register manual. In the past time, DOS as a system run on real mode, is basically built on such interface. After BIOS, you will also get an interrupt vector table (IVT).During this process, the CPU will scan your hardware and execute some necessary check. It's usually in the ROM of motherboard, which is rarely changed or even unchangable, designed as a hardcode by hardware vendor. BIOS is simply the first program to run.Then, the CPU will read the code from that address, which is ( jmp far f000:e05b), then it will execute it to goto BIOS.After initialization, all thing will be done automatically in the deterministic hardware rules.You may be able to run bochs and select the bochsrc file to read (provided with the project code template) immediately. The first does not support debugging and the latter, bochsdbg, has an internal debugger. This will install bochs and bochsdbg, under C:\Program Files. BTW, the magic number 0xf000:fff0 is just a initial status, which is a common conception of any state machine. Download and run the pre-built installer. ![]()
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