I see that all documentation is talk about the blocks size.

How far did the blocks are used for performance use the database - like similar pages on MS SQL SERVER.

it is for performance or just for calculating disk space?

Yes, there are performance implications as well, probably less on OpenSystems,
more on the mainframe, due to the disk architecture (for example larger block sizes better utilize disk space).

Block sizes come into play almost everywhere, for example for RABNs in the buffer pool,
during buffer flushes, there is a performance implication when it comes to block splits
due to inserts, the number of descriptor values found in a single ASSO RABN, etc. etc.

And the standard block size
is very different for these windows?

in mainframe is very different ?

Yes, very different, as I said, mainframe DASD architecture is totally different,
this is why there is a Device And File Considerations section in the Adabas for mainframes documentation.

was now reading about checkpoints

checkpoints are the list of commands in PLOG
that can be used to retrieve data?

Start PLOG------------------------
— CheckPoint
— CheckPoint
— CheckPoint
End PLOG-------------------------

no, checkpoints are records of specific markers Adabas had recorded. They can be used for recovery to specify points in time to roll forward to or roll back to (when applying PLOGs)

but specifically

what types of commands / situations are recorded at checkpoint

if possible tell me some example command that is registered.

I’ve read the REPORT / CHECKPOINT most still do not understand