Hello... Your one physical Drive was Logically Partitioned... into two areas... they are now seperate memory locations, on your one physical drive.
All plater type hardrives, will give you a WEI of 5.8-5.9.
I have not ever owned or tested a hybrid drive and you can GOOGLE or WIKI more information about them... maybe there is a setting in Windows to increase your performance or WEI.
Most pre-loaded, store bought computers, Partition the hardrives, because your Backup/Restore information, and OS, will be put there... So they don't have to give you any Physical Disks... It's up to you to make your own Backup OS Disks for future use... DID YOU SEE any warnings or Read any Printed media to advise you of this? Most people ignore and start computing...
When Loading new programs... choose "Custom install" option... to Load/Use, your Data D: Drive space.