RSLogix 5000 "compact"

[cmschleich]

RSLogix5000 -> File -> Compact

What does this do exactly, or do you know of where I can read about it? I can't find reference to it in the help, literature library, knowledge base, or PLCS.net; at least witht he words I'm searching for.

Thank you

 

[zankorel]

My understanding is that it just purges all unreferenced descriptions/comments in the file. if you change/delete tags and routines a lot, these unreferenced comments can add up.

 

[cmschleich]

Just found this in help, but your description tells me more than theirs.

"Choose this command to compact the project file to improve performance. Normal editing of your project can cause fragmentation that results in increased file size and degraded performance. We recommend that you periodically compact your project file to eliminate this fragmentation."

 

[jimbo3123]

It appears to make the program file smaller.
I just shrunk an ACD file from 707KB to 574KB using the command.

 

[cmschleich]

I did a RSLogix compare on an original vs compacted logix file I have, it noted several differences, and they are all with function block IRef/Oref connections to blocks. When I look at the two routines side by side, visually I can't see any difference. Must be removing something in the database or L5K file.

 

[dmroeder]

Wowsurs, I never noticed that. I like to tinker too... I must be slipping.

 

[jimbo3123]

I did a RSLogix compare on an original vs compacted logix file I have, it noted several differences, and they are all with function block IRef/Oref connections to blocks. When I look at the two routines side by side, visually I can't see any difference. Must be removing something in the database or L5K file.

I just compared my apps too, but the compare tool reported no differences. My program has no function blocks though (all ladder).

 

[pandersen]

I think when you delete code it leaves a gap in the binary file, fragmenting the project. Compacting would remove those gaps. I've had 10mb+ files compact to 200kb, usually when I take a very large project and gut it for a new project.

 

[OkiePC]

Also, when you add tags, and delete them, you can end up with gaps. When you compact, I believe the order of the tags in memory is optimized and gaps are removed...much like defrag for a hard drive.

 

[zankorel]

If you do an export, you will see descriptions like 'UNUSED_COMMENT', and similar. If you compact them, they will disappear.

 

[mordred]

if it follows the normal rules of file storage in the RFFMML encoding for drive storage files will typically have the " 1 "s seperated by 4 to 8 zero's this is to prevent the 1's in storage from wanting to migrate to each other. zip compression removes these extra zero's used to seperate the 1's. The flip side is that a zipped file will self degradate faster than normal storage. The compact feature may also be doing this as well.

 

[rdrast]

if it follows the normal rules of file storage in the RFFMML encoding for drive storage files will typically have the " 1 "s seperated by 4 to 8 zero's this is to prevent the 1's in storage from wanting to migrate to each other. zip compression removes these extra zero's used to seperate the 1's. The flip side is that a zipped file will self degradate faster than normal storage. The compact feature may also be doing this as well.

(Blink)
Care to back that one up?

 

[mordred]

http://www.storagereview.com/guide2000/ref/hdd/geom/dataRequirements.html

here is a little info on the subject the book I learned this from was much older than this article and explained it a little differently but its essentially for the same reasons please note there are different schemes of coding on a hard drive and compression software often switches from one to the other as well as a couple of other things it does. I was incorrect on the abbreviations above its been a few years since I had to study this

 

[mordred]

http://en.wikipedia.org/wiki/Modified_Frequency_Modulation


http://www.lintech.org/comp-per/09PRML.pdf

the second link provides a very detailed explanation of PRML probably more than we really need to know LOL
here is some other links
and an expalnation from one of them

RLL definition - computer


(Run Length Limited) An encoding method commonly used on magnetic disks, including RLL, IDE, SCSI, ESDI, SMD and IPI interfaces. The actual number of bits recorded on the disk is greater than the data bits. Earlier drives inserted extra bits into the data stream so there was more space between signals when reading the data back. As electronics improve, fewer extra bits are inserted, and the ratio of data bits to recorded bits becomes greater.


The "run length" is the number of consecutive 0s before a 1 bit is recorded. For example, RLL 1,7 means there must be at least one 0 between every 1, and the 7 means a maximum of eight time periods between flux transitions. See hard disk.

 

[rdrast]

All of that has nothing to do with the various zip or other compression formats though. All of that has to do only with physically dropping a pattern of bits on a magnetic platter.

Compression formats don't "Strip out" the interspacial guard bits at all. In fact, the on-disk, or in-memory, or on-tape DATA is identical, irregardless of the physical storage method chosen.