INT 2A CU - NETWORK - BEGIN DOS CRITICAL SECTION                                
	AH = 80h
	AL = critical section number (00h-0Fh) (see #02555)
Notes:	normally hooked to avoid interrupting a critical section, rather than
	  called
	the handler should ensure that none of the critical sections are
	  reentered, usually by suspending a task which attempts to reenter
	  an active critical section
	the DOS kernel does not invoke critical sections 01h and 02h unless it
	  is patched.  DOS 3.1+ contains a zero-terminated list of words
	  beginning at offset -11 from the Swappable Data AreaThe portion of the DOS data segment containing all of the variables used internally by DOS to record the state of a function call in progress.  See also INT 21h Function 5D06h and INT 21h Function 5D0Bh.
	  (see #01687 at INT 21/AX=5D06h); each word contains the offset within
	  the DOS data segment of a byte which must be changed from C3h (RET)
	  to 50h (PUSH AX) under DOS 3.x or from 00h to a nonzero value under
	  DOS 4.0+ to enable use of critical sections.	For DOS 4.0+, all
	  words in this list point at the byte at offset 0D0Ch.
	MS Windows patches the DOS kernel's calls to INT 2A/AH=80h-81h into
	  far calls to its own handler, and does not reflect the calls back
	  to INT 2A unless SYSTEM.INI contains ReflectDOSInt2A=1 or
	  ModifyDOSInt2A=0 in the [386Enh] section
	Novell NETX does not issue INT 2A/AH=80h and INT 2A/AH=81h calls when
	  it intercepts INT 21 calls and processes them itself
SeeAlso: AH=81h,AH=82h,AX=8700h,INT 21/AX=5D06h,INT 21/AX=5D0Bh


(Table 02555)
Values for DOS critical section number:
 01h	DOS kernel, SHARE.EXE, DOSMGR
	apparently for maintaining the integrity of DOS/SHARE/NET
	  data structures
 02h	DOS kernel, DOSMGR
	ensures that no multitasking occurs while DOS is calling an
	  installable device driver
 05h	network redirector
 06h	DOS 4.x only IFSFUNC
 08h	ASSIGN.COM
 0Ah	MSCDEX, CORELCDX
 0Fh	IBMInternational Busiuness MachinesInternational Busiuness Machines) A hardware, software and other service technology company founded in 1911. PCIBM PC LAN server (while intercepting INT 10/AH=06h,07h,0Eh)