diff --git a/mps/code/ssw3i6.asm b/mps/code/ssw3i6.asm
index a81828c285b..4589147758f 100644
--- a/mps/code/ssw3i6.asm
+++ b/mps/code/ssw3i6.asm
@@ -1,11 +1,27 @@
-; @@@@ FIXME: W3I6MV add copyright and license
+; ssw3i6.asm : WIN32/x64 STACK SCANNER
+;
 ; $Id$
+; Copyright (c) 2012 Ravenbrook Limited.  See end of file for license.
+; Portions copyright (C) 2002 Global Graphics Software.
+
+; For register usage see 
+; MSDN -> x64 Software Conventions -> Register Usage
+; <http://msdn.microsoft.com/en-us/library/9z1stfyw>
 
 .CODE
 EXTERN TraceScanArea : PROC
 
 StackScan PROC FRAME
-
+   ; Prolog follows.  See 
+   ; MSDN -> x64 Software Conventions -> Prolog and Epilog
+   ; <http://msdn.microsoft.com/en-us/library/tawsa7cb>
+   ; Also see 
+   ; MSDN -> Microsoft Macro Assembler Reference -> Directives Reference
+   ; <http://msdn.microsoft.com/en-us/library/8t163bt0>
+   ; for the use of .pushreg and other directives.
+   ; Push the callee-save registers.   
+   ; Stack must be 16-byte aligned; the return address is on top of the stack;
+   ; after pushing another register it will be 16-byte aligned again.
    push rdi
 .pushreg rdi
 
@@ -26,15 +42,20 @@ StackScan PROC FRAME
    
    push r15
 .pushreg r15
-   
+   ; An odd number of qwords have been pushed on the stack (including the
+   ; return address) so we need to subtract an extra 8 bytes on top of the
+   ; 4 qwords we need for to reserve for the register parameter stack area.
+   ; See
+   ; MSDN -> x64 Software Conventions -> Stack Usage -> Stack Allocation
+   ; <http://msdn.microsoft.com/en-us/library/ew5tede7> 
    sub rsp, 40 
 .allocstack 40
 .endprolog
-
+   ; for convenience set up arguments in reverse order.
    mov r8, rdx     ; stackBot
    mov rdx, rsp    ; top of stack
-   add rdx, 40     ; where last callee saved register stored
-   ; mov rcx, rcx  ; ss
+   add rdx, 40     ; where last callee-save register stored
+   ; mov rcx, rcx  ; ss already in the right register.
    call TraceScanArea
    add rsp, 40
    pop r15         ; pop the callee-save registers
@@ -49,4 +70,44 @@ StackScan PROC FRAME
 
 StackScan ENDP
 
-END
\ No newline at end of file
+END
+; C. COPYRIGHT AND LICENSE
+;
+; Copyright (C) 2001-2012 Ravenbrook Limited <http://www.ravenbrook.com/>.
+; All rights reserved.  This is an open source license.  Contact
+; Ravenbrook for commercial licensing options.
+; 
+; Redistribution and use in source and binary forms, with or without
+; modification, are permitted provided that the following conditions are
+; met:
+; 
+; 1. Redistributions of source code must retain the above copyright
+; notice, this list of conditions and the following disclaimer.
+; 
+; 2. Redistributions in binary form must reproduce the above copyright
+; notice, this list of conditions and the following disclaimer in the
+; documentation and/or other materials provided with the distribution.
+; 
+; 3. Redistributions in any form must be accompanied by information on how
+; to obtain complete source code for this software and any accompanying
+; software that uses this software.  The source code must either be
+; included in the distribution or be available for no more than the cost
+; of distribution plus a nominal fee, and must be freely redistributable
+; under reasonable conditions.  For an executable file, complete source
+; code means the source code for all modules it contains. It does not
+; include source code for modules or files that typically accompany the
+; major components of the operating system on which the executable file
+; runs.
+; 
+; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+; IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+; TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+; PURPOSE, OR NON-INFRINGEMENT, ARE DISCLAIMED. IN NO EVENT SHALL THE
+; COPYRIGHT HOLDERS AND CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+; NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+; USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+; ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+; THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+