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Direct Disk Access (Bypassing the BIOS)
As I mentioned in the section on the role of the BIOS, one of its traditional responsibilities is acting as a "middleman" between the operating system and the hard disk. Well, there's a problem with middlemen: they may be convenient in some situations, but they are inefficient. Having the BIOS in the middle of every transaction can hurt performance, and make more advanced transfer methods difficult to implement.
As a result, many more advanced operating systems take responsibility for data transfer between themselves and the hard disk away from the BIOS. For example, modern versions of Windows employ their own 32-bit protected mode access routines for the hard disk, which are faster and more efficient than using the default BIOS code. This has now in fact become pretty much the standard way of doing things.
Unfortunately, bypassing the BIOS does not mean that we are able to avoid its problems or limitations. :^) Traditional BIOS routines are still needed for compatibility with DOS and older programs. The BIOS is also responsible for compatibility with older hardware, and also for its other roles. And unfortunately, all that means that we still have to deal with the BIOS's capacity barriers.