Bool[32]: Memory size?
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Ron Beaufort
Lifetime Supporting Member
here's a little Boot Camp lesson in memory usage ...
start up a brand new "junk" program ... go to the Controller Properties feature – to the Memory tab ... (different software versions might have this in different locations – you might have to hunt around) ...
write down the value of Max Used (31,880 bytes in the example shown below) ....
now go and set up just one BOOL tag named X ... note that's just ONE character for the name ...
now go back to the Memory tab – press the Estimate button to update the values ... now write down the current Max Used ... (31,960 in my experiment) ....
do the math ...
so in my example, we used up 80 bytes (that's 640 bits) of our processor's memory just so that we will be able to store a single bit value of ONE or ZERO ...
now go back and delete that BOOL tag – then recheck the memory used ... you should be back to 31,880 again ...
next go and set up just one DINT tag named X ... note that's just ONE character for the name ...
now go back to the Memory tab – press the Estimate button to update the values ... now write down the current Max Used ... (another 31,960 in my experiment) ....
again - do the math ...
so in my example, we used up 80 bytes of our processor's memory so that we will be able to store 32 bit values – a double integer ... (personally, I find this kind of weird) ...
and so on – and so on ...
play around with longer tagnames ... try creating Arrays of BOOLS and DINTS ...
have fun ... stay safe – stay well ...
.
start up a brand new "junk" program ... go to the Controller Properties feature – to the Memory tab ... (different software versions might have this in different locations – you might have to hunt around) ...
write down the value of Max Used (31,880 bytes in the example shown below) ....
now go and set up just one BOOL tag named X ... note that's just ONE character for the name ...
now go back to the Memory tab – press the Estimate button to update the values ... now write down the current Max Used ... (31,960 in my experiment) ....
do the math ...
so in my example, we used up 80 bytes (that's 640 bits) of our processor's memory just so that we will be able to store a single bit value of ONE or ZERO ...
now go back and delete that BOOL tag – then recheck the memory used ... you should be back to 31,880 again ...
next go and set up just one DINT tag named X ... note that's just ONE character for the name ...
now go back to the Memory tab – press the Estimate button to update the values ... now write down the current Max Used ... (another 31,960 in my experiment) ....
again - do the math ...
so in my example, we used up 80 bytes of our processor's memory so that we will be able to store 32 bit values – a double integer ... (personally, I find this kind of weird) ...
and so on – and so on ...
play around with longer tagnames ... try creating Arrays of BOOLS and DINTS ...
have fun ... stay safe – stay well ...
.
Last edited:
Thank you Ron, This is extremely useful for the memory-scrooge-Mc.Duck inside me. I will try as soon as I get to work Monday and see what the sizes actually are
Ron Beaufort
Lifetime Supporting Member
my advice is to get over that "memory saving" attitude - sooner rather than later ...
you'll go crazy trying to trim off any "wasted" space with the RSLogix/Studio 5000 platform ... in simple terms, if you need to worry about conserving memory, then you didn't buy a big enough processor to begin with ...
for some reason this reminds me of a new customer looking over one of those great big fancy bus-sized motor homes in a dealer's showroom ... he asked, "What kind of gas mileage does this thing get?" ... the dealer said, "Sir, if you've got to ask that kind of question, then you can't afford one of these." ...
party on ...
I have always been told that the Compact and Control Logix were built so that a DINT is the minimum the Processor will allocate for memory. So if you create a BOOL tag the Processor will allocate the same amount of memory as it would for a DINT. So if saving memory is what you are after it is better to create a DINT and use the bits of that DINT for your BOOL's. I really hate doing that because it can become very hard to read the program. You end up with tags that have very "general" names like ALARM.0, ALARM.1, Alarm.2 and so fourth. I like to use Tag names with better descriptions like Tank_1_Hi_Level, Low_Pressure_Alarm , Ect. I feel that tags with better discriptions help with reading the program and knowing what is going on even-though the use up more memory.
I was pretty curious so I just did Ron's experiment using a L30ER as the Processor and here is what I found:
Creating a Bool named X
Used 88 Bytes of Memory
Creating a Bool named THIS_IS_A_VERY_LONG_TAG_NAME_FOR_X
Used 120 Bytes of Memory
Creating a DINT named X
Used 88 Bytes of Memory
Creating a DINT named THIS_IS_A_VERY_LONG_TAG_NAME_FOR_X
Used 120 Bytes of Memory
So what I have been told is correct. The Tag name's length seemed to have a big difference on the memory used.
As Ron has said if you need to be this cautious on your memory usage you don't have the correct processor. Get one with more memory and program so that is makes sense and is easy to read and understand. That will end up saving money in the long run.
I was pretty curious so I just did Ron's experiment using a L30ER as the Processor and here is what I found:
Creating a Bool named X
Used 88 Bytes of Memory
Creating a Bool named THIS_IS_A_VERY_LONG_TAG_NAME_FOR_X
Used 120 Bytes of Memory
Creating a DINT named X
Used 88 Bytes of Memory
Creating a DINT named THIS_IS_A_VERY_LONG_TAG_NAME_FOR_X
Used 120 Bytes of Memory
So what I have been told is correct. The Tag name's length seemed to have a big difference on the memory used.
As Ron has said if you need to be this cautious on your memory usage you don't have the correct processor. Get one with more memory and program so that is makes sense and is easy to read and understand. That will end up saving money in the long run.
Then they'd want to get in the habit of using UDTs.
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