Two OS in Windows 10 - is this slowing the laptop?

Last time I had to do I hard restart I noticed I seem to have two OS's (both Windows 10) and I was given a choice about which one to use when restarting. Not sure how this came about, but when I go to This PC in Windows Explorer I see a drive called OS (D:). The usage bar is red and shows only 15 GB available of 185 GB.

First question is whether this situation is likely to be slowing the computer, which has been running lately like a relic from the '90s.

Second question is how to determine which OS is unecessary and how to remove the unecessary OS, or if doing this is even necessary.

The laptop is a low-end Asus about 3 years old.

The D Drive sounds like an external or 2nd drive connected. Hit Win + R then msconfig then OK Go to Boot tab and post a screenshot, like below.

mrgeek said:

The D Drive sounds like an external or 2nd drive connected. Hit Win + R then msconfig then OK Go to Boot tab and post a screenshot, like below.

It's not an external drive. I don't know where it came from. Is it what's called a "virtual" drive or a partition?

Can I delete it? Or is there a procedure for getting rid of it?

Is it likely it's affecting performance?

Now a screenshot of disk management would help. We need where the mystery D: drive is:
Disk Management - How to Post a Screenshot of | Tutorials

NavyLCDR said:

Now a screenshot of disk management would help. We need where the mystery D: drive is:
Disk Management - How to Post a Screenshot of | Tutorials

From the looks of disk management, this is the scenario that I could see have happened in the past. The computer was originally set up with Windows 10 installed on the partition which now contains D: drive (185 GB). The partition that now has C: drive was a data partition at that time (278.69 GB). That's a fairly common setup.

I would guess that at some point a clean install of Windows 10 was done, at which point the Data partition was selected as the partition to install Windows 10 to. This did not wipe the 185 GB partition, it just left it there. At some point, Windows 10 did a version upgrade of itself, though Windows update, and this is where the last partition came from, which is the 782 MB (OEM Partition). There have been reports in the past of Windows upgrades in the past picking partitions without drive letters and assigning drive letters to them, this may or may not have happened with the Windows upgrade that also created the last 782 MB (OEM Partition).

If you are absolutely sure there is nothing on the 185 GB "OS" D: drive partition that you need to keep, then I would suggest you install MiniTool Partition Wizard Free:
Best Free Partition Manager for Windows | MiniTool Partition Free

Delete the OS (D:) 185 GB partition. Delete the 499 MB Recovery partition after it. Resize the DATA (C:) drive partition to fill in the empty space. I would also rename (relabel) the DATA partition to something other than DATA as it is really now your OS (Windows 10) partition.

You still might be left with a dual boot menu when Windows starts up. Run MSCONFIG, select the boot tab, and you can delete the extra boot menu entry there.

Thanks! I'll probably do as you suggest anyway, but the original question(s) was, is there a reason to do it? Is it likely to be affecting performance, other than confusing me during a restart?

It won't affect performance at all.

Keeping it the way it is won't affect performance, or removing the extra OS won't?