I need to read first sector of removable media with bios function. How to do this?

i believe that when doing it through bios, it depends what kind of media it is

I mean a pen drive

You do that by trying the following, first you need a BIOS, that can boot USB, second when you put the pen drive in and boot, go to the Bios and see if it emulates it as a floppy or hdd, if its emulates a floppy then you read it like you would a floppy or if a hdd you read it as a hdd.
The reading of both these are the same for first sector, but differ from there on.
Note: If it floppy emultion, it will useally be as a fat16 floppy, not fat12.
The easist way to boot from a pen drive is to format it and sys file it to make it bootable, then make your OS bootable from dos.

thx I will check it immediately.

ok it works. I set boot from usb-hdd in bios, because when I booting from usb-fdd does't work.

I format usb using far16 then I sys it with win98, put autoexec and config and some useful programs and small app written by me in bc.exe and finally I read this first sector and it's fat16. Thanks again for quick help.

Your welcome, You can read/write from usb pen drive from pmode, by switch to and from realmode and using int 13h for read/write, thats what i do in my OS, its got 2 drivers for both floppy and hdd.
One a pmode driver, the other a BIOS driver, it works well, but is slow .