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)