Why we prefer level no 77 for defining elementary item

Yogesh_agarwal · New User Joined: 15 Feb 2006 Posts: 5 Location: Noida

Hi all,
We can use level number 01 and 77 both for elementary item.but why it is always recommended to use 77 instead of 01.

Thx in advance

Yogesh

Nirmala · New User Joined: 13 Feb 2006 Posts: 3

Hi,
Any item declared in Level 01 will have Duble Word boundary set by the system .. which will occupy more space.

Regards
Nirmala

nuthan · Posted: Wed Feb 15, 2006 7:42 pm

Hai,
If u mentioned as 01 item, in future it can be sub grouped. But if u mentioned as 77 item it will be remained as elementary item only.

priyesh.agrawal · Posted: Wed Feb 15, 2006 10:17 pm

http://ibmmainframes.com/viewtopic.php?t=1239

Regards,

Priyesh.

Yogesh_agarwal · New User Joined: 15 Feb 2006 Posts: 5 Location: Noida

Hi,
Thanks a lot to all of you.

kanak · Moderator Joined: 12 Mar 2005 Posts: 252 Location: India

Earlier versions of COBOL had a difference in the way the data was stored/accessed when you use a 77 and 01 level.

77 level was boundary aligned and 01 level was not boundary aligned .

Boundary alignment used to dictate the number of bytes used for actual storage, addressability and fetching.
The minimum fetch unit used to be a word and so even if your character size is less than a word all the bytes in the word would be used for storing the value. There was no impact on the fetch time for the character variables .

In addition to the storage , when the declaration is for numeric values and if the numeric values are used in any kind of intensive computation , the declaration types would have an impact on the CPU time if they were declared at 01 level because of the non-alignment .

In MVS COBOL and VS COBOL II 01 level variables are also boundary aligned and have been hence there is no difference .

Let me know if i am wrong.