"No operating system. [...] Just [...] BIOS". Hmm. Out of interest, is there a difference in environment between running a COM executable for MS-DOS versus run

"No operating system. [...] Just [...] BIOS". Hmm. Out of interest, is there a difference in environment between running a COM executable for MS-DOS versus running a bootblock? I know there's the whole of MS-DOS, but a typical size-coded demo (http://www.sizecoding.org/wiki/DOS http://www.sizecoding.org/wiki/DOS) will only use int 10h to switch mode, and that's it. Everything else is IO mapped (e.g. the keyboard) or memory mapped (e.g. screen memory). Could these equally run as a bootblock, and vice-versa? One difference I know of is that DOS maintains an ever-increasing timer that it writes to 0:046C... is that available at bootblock execution time?