Compare hardware of S7-projects

I did a test with two projects starting with the same hardware and I compared the SDB-folder. Result : no differences. Then in one project I added a digital input card and compiled the project. After comparison : no differences. How is this possible. How can I reliably compare the hardware of two projects? Then I download the first project completely in plc-sim, opened the hardware config and went online. I could look online without problems or warnings (logic). When I opened the hardware config of the second project and went online I got a warning that online and offline are different.
What is the exact relation beween the SDB-folder and the hardware of an S7 controler????
On the other hand I was confronted several times in the past with comparing online offline the hardware of a project and the comparison reported differences. But when comparing manually in detail all part numbers there was no differences (also not in connection etc.) This situation makes it really difficult to do service on machines.
Please advice me, thanks.

If I compare the system data blocks after changing the HW, I get "Differences".
Try to post the two projects that reports no differences despite that you have different hardware configs.

Projects are in the download section : test compare.zip.
I use Step 7 v5.5

My STEP7 says that there are differences.

Edit: And the size of the SDB is different in the two projects. 886 bytes and 864 bytes.

have you tried exporting the profiles to text files and doing a text compare, using a tool like Beyond Compare.

Hi there,
What I found is that even if you change the MPI address only checksum of SDB wont be same.

Press alt+Enter after selecting blocks to see checksum.

It also happen for me. I am told that you SHOULD save and compile the HW config to show the differences. But even doing that:

I added a new TCP/IP connection in Netpro, compiled it and downoaded it to the CPU. But when comparing it to the original project it created NO differences.

I am really confused. Because when my colleague does the same procedure, it DOES create differences for him!!!

No idea why.

Thanks,
Sam