Well, more than likely, these functions are either implemented in assembly, use inline assembly, or call some special generic syscall functions written in assembly.
Accessing a hard disk using the BIOS calls involves raising the software interrupt 13h. This includes setting the CPU registers to the needed values to communicate the desired action, which are then interpreted by the interrupt handler.
Here's a list of the services that int 13h provides:
http://en.wikipedia.org/wiki/INT_13absread and abswrite, even though I've never used them, more than likely refer to interrupts 25h/26h (absolute disk read/absolute disk write). These services are provided by the DOS kernel (IO.SYS), but I believe they are a very thin wrapper around INT 13h services.
If you're wondering if you can access the disks directly in modern operating systems in this way, the answer is usually no. They can be accessed directly, but usually through some other interface of sorts (a device / hardware abstraction layer). It's not that you can't trigger interrupts (and software interrupts are still the primitive here), but it's just that the OS does not provide a specific interface for reading/writing disks... it provides an interface for reading and writing to devices in a generalized manner, and device specific functionality is implemented through IOCTLs upon handles issues by the OS.
This post has been edited by perfectly.insane: 2 Jun, 2008 - 03:52 PM
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