The Software Control Word is a Tag 6 Word which is used as a Block Marker.

 The Algol Compiler defines the fields below with the BE.. prefix at 10083362,

Tag 6 - SWCW
Field	Name	Description
[47:2]	SWCW_TypeF	SW_MarkerV = 2. (BSET 47)
[45:1]	SW_MarkerF	Block_MarkerV = 0
[42:1]	Block_MarkerF	Block_ExitV = 0
[44:1]	BEOnGoPastF	Exception Procedure.
[43:1]	BEGoPastNoDSF	DMAlgol Protected Exception Procedure.
[26:1]	BEIsolatedF	Isolated Procedure
[24:1]	BECheckPointF	CheckPoint
[22:1]	BECBTogF	Structure or Connection Block Declaration
[21:1]	BEEpilProcF	Epilog Procedure
[20:1]	BELastChanceF	Processing after being DSED
[19:1]	BELibTemplateF	Library Template or Directory
[17:1]	BEBadGoToF	Non Local GOTO
[16:1]	BEDirectArrayF	Direct Array Declaration
[15:1]	BEEventF	Event or InterLock Declaration
[14:1]	BEInterruptF	Interrupt Declaration
[13:1]	BEFileF	File Declaration
[12:1]	BE2DimF	Multi Dimension Arrays (ArrayDec Calls)
[11:1]	BE1DimF	Single Dimension Arrays (Non ArrayDec Calls)

These Flags are used by BlockExit to determine what types of Objects are included in the Block and therefore should be deallocated.

The MCP Defines these fields in Struct_SWCW at 1022500 and Struct_Block_Exit_Marker at 24502948,

Tag 6 - SWCW
Field	Name	Description
47:2]	SWCW_TypeF	SW_MarkerV = 2. (BSET 47)
45:1]	SW_MarkerF	Block_MarkerV = 0
42:1]	Block_MarkerF	Block_ExitV = 0
[44:1]	OnGoPastF	On GoPast Procedure in Block.
[43:1]	GoPastNoDSF	Give Kangaroo protection to GoPast.
41:1]	DefunctBlockF	Block being BlockExited
40:13]	BlockStartF	MSCW relative start of partial block.
[26:1]	IsolatedF	Isolated environment.
25:1]	CheapBlockF	Cheap Block, Don't turn off RCW BlockExit bit in BlockExit.
[24:1]	NoCPBitF	Compiler says can't checkpoint.
23:24]	BlockSearchF	BlockSearch uses these Bits
23:1]	DBSBlockF	Top DBS Block of ACR Task
[22:1]	CBTogF	Connection Block Declaration
21:1]	DBSBlockF	Top DBS Block of ACR Task
[21:1]	AlgolEpiF	AlgolEpiF = 1 Call Epilog Algol
[20:1]	PLIEpiF	PLIEpiF = 1 Call Epilog (PL & Statistics)
[19:1]	LibTemplTogF	Library Template or Directory
18:1]	FmtBTogF	Format Pseudo Buffer FIB-Locked.
[17:1]	LabelF	Non Local GOTO
[16:1]	DirTogF	Direct Array Declaration
[15:1]	EventTogF	Event Declaration
[14:1]	IntTogF	Interrupt Declaration
[13:1]	FileF	File Declaration
[12:1]	MDTogF	Multi Dimension Array Declaration
[11:1]	SDTogF	Single Dimension Array Declaration
10:1]	ProcRefF	Procedure Reference Provider or Owner
9:1]	ProcessFlagF	Critical Block has Dependent Tasks
9:10]	LoWorderF	Used by BlockExit