<s>
Command	B-Application
CICS	I-Application
or	O
Command-CICS	O
is	O
a	O
software	O
product	O
that	O
allows	O
organizations	O
to	O
migrate	O
from	O
"	O
Macro	O
level	O
"	O
CICS	B-Application
to	O
"	O
Command	O
level	O
"	O
CICS	B-Application
without	O
any	O
re-programming	O
so	O
that	O
companies	O
could	O
migrate	O
to	O
later	O
versions	O
of	O
CICS	B-Application
that	O
did	O
not	O
support	O
macro	O
level	O
application	O
programs	O
.	O
</s>
<s>
The	O
later	O
versions	O
of	O
CICS	B-Application
offered	O
many	O
advantages	O
over	O
previous	O
versions	O
yet	O
tens	O
of	O
thousands	O
of	O
application	O
programs	O
were	O
effectively	O
locked	O
out	O
of	O
the	O
new	O
version	O
unless	O
they	O
were	O
prepared	O
to	O
operate	O
two	O
completely	O
different	O
versions	O
of	O
CICS	B-Application
on	O
the	O
same	O
Operating	B-General_Concept
Systems	I-General_Concept
,	O
creating	O
both	O
operational	O
and	O
maintenance	O
problems	O
.	O
</s>
<s>
Two	O
different	O
,	O
simultaneous	O
,	O
CICS	B-Application
Licenses	O
were	O
also	O
required	O
.	O
</s>
<s>
When	O
CICS	B-Application
was	O
first	O
released	O
by	O
IBM	O
in	O
the	O
late	O
1960s	O
,	O
it	O
used	O
IBM	O
Assembler	O
macros	O
to	O
generate	O
the	O
API	B-General_Concept
system	B-Operating_System
calls	I-Operating_System
to	O
the	O
CICS	B-Application
teleprocessing	B-General_Concept
monitor	I-General_Concept
kernel	B-Operating_System
.	O
</s>
<s>
This	O
was	O
also	O
true	O
even	O
if	O
programs	O
were	O
written	O
in	O
COBOL	B-Application
or	O
PL/1	B-Language
.	O
</s>
<s>
Ken	O
Dakin	O
an	O
independent	O
programmer	O
and	O
CEO	O
of	O
APT	O
Ltd	O
.	O
in	O
the	O
U.K.	O
,	O
realized	O
that	O
by	O
creating	O
a	O
middleware	B-General_Concept
product	O
,	O
the	O
problem	O
could	O
be	O
solved	O
for	O
almost	O
all	O
situations	O
.	O
</s>
<s>
Ken	O
Dakin	O
approached	O
IBM	O
to	O
market	O
his	O
product	O
but	O
received	O
no	O
interest	O
at	O
the	O
time	O
,	O
despite	O
the	O
fact	O
that	O
tens	O
of	O
thousands	O
of	O
their	O
clients	O
application	O
programs	O
would	O
need	O
to	O
be	O
converted	O
or	O
rewritten	O
for	O
the	O
new	O
versions	O
of	O
CICS	B-Application
,	O
costing	O
many	O
millions	O
of	O
dollars	O
.	O
</s>
<s>
Command-CICS	O
intercepted	O
macro	O
level	O
applications	O
via	O
a	O
Link-edited	O
(	O
static	O
)	O
"	O
stub	O
"	O
positioned	O
ahead	O
of	O
the	O
Load	O
module	O
(	O
MVS	B-Application
)	O
or	O
Phase	O
(	O
DOS/VSE	B-Application
)	O
.	O
</s>
<s>
On	O
gaining	O
control	O
from	O
the	O
CICS	B-Application
Program	O
Control	O
Program	O
(	O
PCP	O
)	O
,	O
a	O
"	O
pseudo	O
macro	O
level	O
"	O
environment	O
was	O
established	O
consisting	O
of	O
a	O
pointer	O
to	O
a	O
(	O
unique	O
)	O
pseudo	O
"	O
Common	O
System	O
Area	O
"	O
(	O
CSA	O
)	O
,	O
a	O
pointer	O
to	O
a	O
Transaction	O
Control	O
Area	O
plus	O
Transaction	O
Work	O
Area	O
(	O
TCA+TWA	O
)	O
and	O
a	O
pseudo	O
Terminal	O
Control	O
Terminal	O
Entry	O
(	O
TCTTE	O
)	O
and	O
other	O
artifacts	O
of	O
a	O
macro	O
level	O
environment	O
.	O
</s>
<s>
Before	O
passing	O
control	O
directly	O
to	O
the	O
original	O
program	O
entry	O
point	O
,	O
Command-CICS	O
set	O
up	O
the	O
actual	O
general	O
purpose	O
registers	O
,	O
R13	O
and	O
R12	O
to	O
point	O
to	O
the	O
pseudo	O
control	O
blocks	O
.	O
</s>
<s>
The	O
CSA	O
was	O
the	O
principal	O
control	O
block	O
holding	O
pointers	O
to	O
the	O
CICS	B-Application
kernel	B-Operating_System
programs	O
(	O
File	O
Control	O
Program	O
,	O
Storage	O
Control	O
Program	O
etc	O
.	O
)	O
</s>
<s>
in	O
a	O
real	O
macro	O
level	O
CICS	B-Application
environment	O
.	O
</s>
<s>
The	O
Command-CICS	O
CSA	O
had	O
alternative	O
pointers	O
to	O
Command-CICS	O
entry	O
points	O
instead	O
.	O
</s>
<s>
It	O
was	O
possible	O
to	O
use	O
CEDF	O
to	O
debug	O
the	O
application	O
program	O
calls	O
when	O
Command-CICS	O
was	O
used	O
.	O
</s>
<s>
The	O
application	O
program	O
proceeded	O
to	O
execute	O
normal	O
machine	O
code	O
instructions	O
right	O
up	O
to	O
its	O
first	O
macro	O
level	O
API	B-General_Concept
call	O
,	O
thus	O
adding	O
zero	O
overhead	O
to	O
the	O
program	O
until	O
that	O
point	O
.	O
</s>
<s>
As	O
soon	O
as	O
the	O
API	B-General_Concept
call	O
left	O
the	O
application	O
program	O
,	O
Command-CICS	O
code	O
would	O
gain	O
control	O
and	O
replace	O
the	O
original	O
linkage	O
with	O
its	O
own	O
,	O
equivalent	O
,	O
Command-level	O
call	O
.	O
</s>
<s>
In	O
original	O
earlier	O
command	O
level	O
CICS	B-Application
versions	O
(	O
that	O
supported	O
both	O
Macro	O
and	O
Command	O
level	O
programs	O
)	O
,	O
the	O
CICS	B-Application
"	O
Exec	O
Interface	O
Program	O
"	O
(	O
DFHEIP	O
)	O
converted	O
the	O
Command	O
level	O
call	O
to	O
an	O
'	O
actual	O
macro	O
level	O
call	O
.	O
</s>
<s>
This	O
would	O
add	O
a	O
very	O
small	O
additional	O
overhead	O
only	O
during	O
CICS	B-Application
calls	O
.	O
</s>
<s>
Later	O
versions	O
of	O
CICS	B-Application
,	O
however	O
,	O
executed	O
the	O
CICS	B-Application
API	B-General_Concept
directly	O
,	O
imposing	O
no	O
additional	O
"	O
backward	O
compatibility	O
"	O
overhead	O
.	O
</s>
<s>
Command-CICS	O
was	O
initially	O
sold	O
by	O
APT	O
Ltd	O
in	O
the	O
U.K.	O
and	O
APT	O
International	O
in	O
mainland	O
Europe	O
and	O
the	O
rest	O
of	O
the	O
world	O
.	O
</s>
<s>
CICS/COMET	O
for	O
z/OS	B-Application
-	O
a	O
similar	O
product	O
from	O
UNICOM	O
Systems	O
Inc	O
.	O
</s>
