Thanks Barracuda, that makes a lot more sense now, the IT person that setup my PC did a good job and this is the HDD setup:
First drive has 4 partitions The last partition (sda4) is virtually 1Gb the other 3 are windows recovery, EFI system FAT 32 and reserved (only 17Mb).
The second drive has 3 partitions, the first 686Gb is Basic data sdb1 NTSF - Not mounted, sdb2 Linux swap (version 1) - Active, sdb3 Linux File System Ext4 - Mounted. Don't ask me what they all are but I assume I should make use of the first partition, it is only used by Win 10 for 3 Virtual Machines, 640Gb free.
Good to know that I can just upgrade my version when needed.
