GRUB

http://mirror.href.com/thestarman/asm/mbr/GRUB.htm
http://en.wikipedia.org/wiki/Master_boot_record

As stated in the article, when you install the grub, it will prompt a message asking where you want to install the grub(MBR or VBR). But usually, the installation will further write 8K code after section 0, and it's not clearly explained by installer. Look into Ubuntu grub, it does have a 8056 bytes stage 1.5 code.

GRUB(MBR) will be loaded onto 0000:7C00 to execute. It will further jump into 7C4A, before that, it's some data(such as stage2 address) called BIOS Parameter Block (BPB). The works of stage1 code are,
1. setup disk(LBA mode)
2. load stage2(or 1.5) code onto 0000:8000
3. jump to 0000:8000