32 Bit Data Transfer - Dilema

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Ukratko to se odnosi na stari DOS pristup HDDu kao i SmartDRV-doublebuffer itd. (nevažno kao BIOS opcija na novijim OSevima, zato nisi pronašao podatak osim za NT4)

edit: konkretnije pronađen primjer;

The second advantage of 32-bit disk access is that it saves two (relatively slow) switches between virtual and protected mode per disk I/O call. Take, for instance, a disk read performed by a DOS application. In the absence of 32BDA, each such call causes the following sequence of events:

1 Application calls INT21 to read from disk

2 Windows traps the call, switches to protected mode

3 Windows switches to real mode, returns to DOS

4 DOS makes int13 call to BIOS disk routines

5 Windows traps the call, switches to protected mode

6 Windows switches to real mode, returns to BIOS

7 BIOS acts upon int13 call and does the read

8 Windows traps the return from int13, switches to PM

9 Windows switches to RM, returns the result to DOS

10 DOS receives the result, passes on to application

11 Windows traps the return from DOS, switches to PM

12 Windows switches to RM, returns result to application

13 Application receives the result from the INT21 call

Using 32-bit disk access replaces steps 6 to 8 by a single call to the FastDisk VxD. This removes two mode switches, resulting in a usually small disk performance improvement. (Steps 3-11 also apply to native Windows applications).