GNU Info

(nasm.info)Section 7.3

---

Next: Section 7.4 Prev: Section 7.2.2 Up: Chapter 7

---

Enter node , (file) or (file)node

7.3. Producing `.SYS' Files
===========================

   MS-DOS device drivers - `.SYS' files - are pure binary files,
similar to `.COM' files, except that they start at origin zero rather
than `100h'. Therefore, if you are writing a device driver using the
`bin' format, you do not need the `ORG' directive, since the default
origin for `bin' is zero. Similarly, if you are using `obj', you do not
need the `RESB 100h' at the start of your code segment.

   `.SYS' files start with a header structure, containing pointers to
the various routines inside the driver which do the work. This
structure should be defined at the start of the code segment, even
though it is not actually code.

   For more information on the format of `.SYS' files, and the data
which has to go in the header structure, a list of books is given in the
Frequently Asked Questions list for the newsgroup
`comp.os.msdos.programmer'.