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Interesting 1809 Disk Layout Changes

Yesterday, MS released Windows 10 1809. It took them a while to get the release pushed out through all channels. I was able to get to it first through the Media Creation Tool on the Download Windows 10 page. But within an hour, the Update Assistant and Windows Update also proved viable as upgrade sources. After all the dust settled on this latest release, I noticed some Interesting 1809 disk layout changes for the OS boot/system disk. Here is a before and after shot (from 2 different PCs):

Disk layout before upgrade above, after below. Note the new, 498 MB OEM partition that appears at right.
[Click either image for full-sized view.]

About Those Interesting 1809 Disk Layout Changes

Looks like the minimum or allowable size of the WinRE partition has gone up again, with the 1809 release. Both before and after shots feature a 450 MB OEM partition at the head of the disk. However, use of the reagenct /info command on before and after machines shows different WinRE locations. On the before PC, the partition is number 1 (first place from top figure above): a 450 MB NTFS partition. On the after PC, the partition is number 5 (immediately following the OS partition): a 498 MB NTFS partition.

Message traffic on TenForums also tells me that users who upgraded with WinRE partitions of 498 MB or larger  in size found their disk layouts unaltered. That tells me the existing WinRE partition was preserved and its contents replaced during the upgrade process. Those PCs, like mine, who had the “old standard” 450 MB WinRE partition will find a new and bigger (498 MB) WinRE partition in their disk layouts as well. Most likely, it will be positioned immediately following the OS partition (from which the installer steals the space necessary to accommodate the 498 MB disk extent).

Why Use Two Different Tools to Show Disk Layouts?

I used the MiniTool Partition Wizard (MTPW) to show the disk layout on an already-upgraded machine. I did that to confirm that the reagentc /info output was correct. It read:


Because diskmgmt.msc does not show the 16MB Microsoft Reserved (MSR) partition, but MTPW does, you can count from left to right yourself, and confirm that the new 498 MB NTFS WinRE partition does indeed occur in position 5 on that drive. That’s why I highlighted (bolded) “partition5” in the preceding output string.

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