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Format of kernel entry jump table for DR DOS 5.0-6.0

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Offset Size Description

00h

5 BYTEs

far jump to kernel entry point for CP/M CALL 5

05h

5 BYTEs

far jump to kernel entry point for INT 20

0Ah

5 BYTEs

far jump to kernel entry point for INT 21

0Fh

5 BYTEs

far jump to kernel entry point for INT 22 (RETF)

14h

5 BYTEs

far jump to kernel entry point for INT 23 (RETF)

19h

5 BYTEs

far jump to kernel entry point for INT 24

1Eh

5 BYTEs

far jump to kernel entry point for INT 25

23h

5 BYTEs

far jump to kernel entry point for INT 26

28h

5 BYTEs

far jump to kernel entry point for INT 27

2Dh

5 BYTEs

far jump to kernel entry point for INT 28

32h

5 BYTEs

far jump to kernel entry point for INT 2A (IRET)

37h

5 BYTEs

far jump to kernel entry point for INT 2B (IRET)

3Ch

5 BYTEs

far jump to kernel entry point for INT 2C (IRET)

41h

5 BYTEs

far jump to kernel entry point for INT 2D (IRET)

46h

5 BYTEs

far jump to kernel entry point for INT 2E (IRET)

4Bh

5 BYTEs

far jump to kernel entry point for INT 2F

Note:

All of these entry points are indirected through this jump table to allow the kernel to be relocated into high memory while leaving the actual entry addresses in low memory for maximum compatibility.
Some of these entry points (22h,23h,24h,2Eh,2Fh) are replaced as soon as COMMAND.COM is loaded, and return immediately to the caller, some returning an error code (the original handler for INT 2F returns AL=03h [fail]).