Internal flags: (read DIF)
00_0001 Int25/Int26 packet method available
00_0002 Int21.7305 packet method available
00_0004 VDD registered and usable
00_0008 internal flag for paged output
00_0010 DEBUG's input isn't StdIn
00_0020 DEBUG's input is a file
00_0040 DEBUG's output isn't StdOut
00_0080 DEBUG's output is a file
00_1000 state of debuggee's A20
00_2000 state of debugger's A20 (not implemented: same as previous)
00_4000 debugger booted independent of a DOS
00_8000 CPU is at least a 386 (32-bit CPU)
01_0000 internal flag for tab output processing
02_0000 running inside NTVDM
10_0000 internal flag for paged output
40_0000 in TSR mode (detached debugger process)
0100_0000 running inside dosemu
0400_0000 T/TP/P: while condition specified
0800_0000 TP: P specified (proceed past string ops)
1000_0000 T/TP/P: silent mode (SILENT specified)
2000_0000 T/TP/P: silent mode is active, writing to silent buffer
