INT 21h

09h [E]DX instead of DX

0Ah [E]DX instead of DX

0FH – 17H not supported; use corresponding file handle function.

1Ah [E]DX instead of DX

21h – 24h not supported; use corresponding file handle function.

25h [E]DX instead of DX. Protected mode vector will be set.

26h – 29h not supported; use corresponding file handle function.

2Fh [E]BX instead of BX

31h No value is required in DX

35h [E]BX instead of BX. Protected mode vector will be returned.

38h [E]DX instead of DX

39h [E]DX instead of DX

3Ah [E]DX instead of DX

3Bh [E]DX instead of DX

3Ch [E]DX instead of DX

3Dh [E]DX instead of DX

3Fh [E]DX instead of DX

40h [E]DX instead of DX

41h [E]DX instead of DX

43h [E]DX instead of DX

44h subfunction 02h, use [E]DX instead

44h subfunction 03h, use [E]DX instead

44h subfunction 04h, use [E]DX instead

44h subfunction 05h, use [E]DX instead

47h [E]SI instead of SI

48h Protected mode memory will be allocated

49h Protected mode memory will be released

4Ah Protected mode memory will be resized

4Bh [E]DX & [E]BX instead of DX & BX; Parameter block offset entries are [d]word

4Eh [E]DX instead of DX

56h [E]DX & [E]DI instead of DX & DI

5Ah [E]DX instead of DX

5Bh [E]DX instead of DX

62h Protected mode selector will be returned

6Ch [E]SI instead of SI

In DOS/4G mode, a few parameters change:

3Fh ECX instead of CX. Return value in EAX instead of AX.

40h ECX instead of CX. Return value in EAX instead of AX.

48h EBX instead of BX

4Ah EBX instead of BX

4Bh environment segment/selector in parameter block (ES:EBX) becomes a FWORD (6 bytes)

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