Desktop: Dell XPS 8700, Windows 10 Pro, 64 bit, version 1803. Laptop: Dell Inspiron 5537, Windows 10 Home, 64 bit, version 1803. Both are running Avast Premier and Malwarebytes 3 Premium, fully updated.
Night before last the April features update arrived on my laptop computer and was installed uneventfully (it had reached my desktop a couple of weeks earlier). The laptop now has a brand new "local drive" with drive letter E: that shows up on the File Explorer screen. The system is constantly notifying me that I am running out of space on Local Drive E: and need to do something about it. A "Low Disk Space" warning icon is almost continuously present in the system area of the toolbar. When I try to open Drive E: in File Explorer to see what it contains, it shows only "This folder is empty".
To try to find out what was going on here, I first ran Speccy, and then Macrium Reflect. There are (at present) no external drives connected to either computer.
Speccy reports the hard disk partitions as follows:
Hard drive WDC WD10JPVX-75JC3T0 Capacity 931 GB
Partition 0, FAT32, size 496 MB, used 54 MB (11%)
Partition 1, 40.0 MB
Partition 2, NTFS, size 489 MB, used 290 MB (59%)
Partition 3, C:, NTFS, size 918 GB, used 164 GB (17%)
Partition 4, E:, NTFS, size 501 MB, used 470 MB (93%)
Partition 5, NTFS, size 11.7 GB, used 11.1 GB (94%)
Macrium Reflect 7.1.3196 (UEFI) reports them as follows:
GPT Disk 1 WDC WD10JPVX-75JC3T0 931.51 GB
1. ESP (None) FAT32 (LBA) Primary 54.8 MB used out of 500 MB
2. DIAGS (None) FAT32 (LBA) Prinary 2 KB used out of 40.0 MB
3. (None) Unformatted Primary 128.0 MB used out of 128.0
4. WINRETOOLS NTFS Primary 290.7 MB used out of 490.0 MB
5. Windows (C:) NTFS Primary 164.18 GB used out of 918.14 GB
6. (E:) NTFS Primary 470.8 MB used out of 502.8 MB
7. PBR Image (None) NTFS Primary 11.05 GB used out of 11.75 GB
The used space of the last two is shown in RED, indicating (I gather) that they are both over 90% full.
If it is relevant, the laptop had Windows 8 installed when originally purchased. Shortly before the deadline for the free Windows 10 upgrade expired, I upgraded the laptop first to Windows 8.1, and then immediately (the next day) to Windows 10. The desktop, purchased considerably later, had Windows 7 Professional installed when originally purchased. I upgraded it directly to Windows 10 at about the same time as the laptop upgrade. Both upgrade experiences were uneventful (once I had figured out how to do them) and my Windows 10 experience has since then been remarkably free of trouble. In the context of the Meltdown/Spectre flap, I installed the software mitigations as soon as the dust settled, and the BIOS/UEFI firmware mitigations provided by Dell a few weeks after they became available. Those upgrades were also basically uneventful.
Having started life with Windows 8, the laptop boots in UEFI mode; having started life with Windows 7, the desktop boots in Legacy (BIOS) mode, and has fewer hard drive partitions.
Can someone explain what is going on here? It looks to my untutored eye as if a drive letter (E:) had been mistakenly assigned to the next-to-last partition, whose contents are not meant to be accessible to the ordinary daily operations of the Windows system. A drive E: was definitely NOT there before the features update.