Rene Lamontagne wrote:

Just noticed yesterday a new drive in Disk management, Don't know how
long it has been there but only since 1903.

It is called "portablebasedlayer" 8.00 GB NTFS healthy primary
partition, 400 MB used, it is *read only* and has no drive letter.

I can't do anything to it as all options are greyed out except property's.

It only shows up there and not in "this PC" . It does not seem to do
anything and not causing any problems, Just wondering how and why it got
there.

Rene

Without a drive letter, it won't show up in File Explorer.

You did not mention how large is the disk in which the 8GB partition
exists. You did not mention if the disk is an SSD or HDD. For example,
if the disk is an SSD, a reserved area is allocated for overprovisioning
to allow the SSD to have a spare sector pool for remapping bad blocks of
sectors. The default spare pool size varies by the size of the SSD. I
recall seeing my 256GB SSD had about a 7% spare pool size. My 1 TB SSD
(an NVMe in an m.2 motherboard slot) has a lot bigger spare pool
partition, by default, so I didn't bother using Samsung's Magician to
increase the spare pool space. If I did want more overprovisioning
space (than the difference in terabytes and tibibytes), Magician would
resize my Win10 partition (make it smaller) to create unallocated space
for use as overprovisioning space.

If your SSD is 120GB in size then 8GB is about right for a 7% spare pool
partition; however, as I said, the spare pool size is variable, usually
depends on the size of the SSD, and users can use tools (like Samsung
Magician for Samsung SSDs) to change the overprovisioning. The larger
the overprovisioning, the longer the SSD will last. It mitigates write
amplification in SSDs.

Consumer-grade SSDs have a small overprovisioning than do SSDs in an
enterprise configuration. Longevity and reliability are more important
for enterprise usage.

View:
https://www.youtube.com/watch?v=Q15wN8JC2L4
and read:
https://searchstorage.techtarget.com...erprovisioning
https://www.kingston.com/us/ssd/overprovisioning
https://www.seagate.com/tech-insight...its-master-ti/
https://en.wikipedia.org/wiki/Write_amplification

That's just a guess because you did not identify to us the brand and
model of the disk where is the mystery partition. I don't remember the
partition on my SSD having a partition name. The overprisioning uses
unallocated space on the disk.

However, when I added more overprovisioning space in my Win7 setup that
had a 256 GB SSD (which reduced the Win7 partition to create some
unallocated space on the SSD), I don't recall that the space had a name.
In fact, since it is unallocated space, it isn't in a partition, so it
cannot have a name. Only partitions get names.

Using the "portablebaselayer" string in a search found:

https://www.tenforums.com/tutorials/...ws-10-a-3.html

You didn't mention which edition of Windows 10 that you are using (Home,
Pro) or which build of it. I am using the Home edition of Windows 10.
When I went into Control Panel - Uninstall a program, and picked
Windows features in the left pane, I didn't see a feature named
"sandbox".

https://www.techrepublic.com/article...test-software/

I'm still back on the 1809 build. According to the article, the sandbox
is a new feature in the 1903 build; however, I just have the Home
edition and the sandbox feature is available only in the Pro editions,
and up.

You didn't say the brand and model of the disk with the mystery
partition, so one guess was it is an SSD and you increased its
overprovisioning size. Yet, that creates unallocated space on the disk,
not a partition. My next guess based on a lack of your Windows edition
and its build is that maybe it has to do with the new sandbox feature.