Dont understand why these different Partitions-Designations

Have two HDDs of the same size. Old ones. Partitioned this way. Dont understand why on the second one(B) where i associated remaining space to a volume is Primary and not logical. no data there yet.
A) C: Primary D: Primary same size E: Primary -just allocated remaining Space after a long time. Why couldnt i turn it as logical? whats the difference now for daily work if its not logical.
maybe D it was logical and because i made a systempartition-backup to D it turned to Primary.

B) second drive
C: Primary D: Logical(remaining space used)
They are two of multiples i am using with winxp on GA-7N400 Pro 2
maybe troubles are also because Systempartition is not set that big.
could now free more space, remaining 9gb free space. not much.
BTW: where do i find the rubbish which is accumulating on systempartition? Thanks

To be honest, this is drive partitions basics.... considering you are doing all this partitioning you should have learned a bit about this, but here we go...

An MBR disk can have up to 4 primary partitions. This is why logical partitions exist. You can create an extended partition and then you can create any number of logical partitions inside this space. Extended partition can be created as any partition but you need to have a first primary partition.
If you do it manually, you can select what sort of partition you create. If you use a program that automates it for you, then its up to the program to decide what kind of partition it will use.
Other than a little overhead creating the extended and logical partitions there should be no performance difference to either way.