First page Back Continue Last page Summary Graphic
History and Technical info
PC ROM boot programs:
changed around the time 386 appeared
is mapped (with other BIOS code) into
the area of memory just under 4gb
starts in real mode (backwards compatible)
loads 512 bytes from boot device at 0x7c00
jumps to this address
Notes:
The PC boot process changed slightly
about the time the 386 was introduced.
The BIOS, including the ROM boot
program, is mapped onto very high
memory, but the machine starts in real
mode, so that it looks at boot time like
a pre-386 machine. After selecting
the boot device, the ROM program
transfers 512 bytes from it to address
0x7c00 (31744). Then it jumps to this
address.