“TPM is ready for use, with reduced functionality” message when the BIOS is in legacy mode with TPM 2.0
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Applies to: Windows Server version 1803Windows Server Datacenter CoreWindows Server Standard CoreWindows Server 2016Windows Server 2012 R2 StandardWindows Server 2012 R2 PreviewWindows Server 2012 R2 FoundationWindows Server 2012 R2 for Embedded SystemsWindows Server 2012 R2 EssentialsWindows Server 2012 R2 DatacenterMore
On a Windows Server-based operating system, you have the operating system installed in Legacy MBR mode (PC/AT) with Trusted Platform Module (TPM) version 2.0. In this situation, you receive a message in the TPM user interface stating that "The TPM is ready for use, with reduced functionality."
On the operating systems that are listed in the Applies To section, TPM 2.0 is supported in UEFI mode only.
TPM 2.0 is designed to be fully functional in UEFI mode. Systems must be in UEFI mode with TPM enabled and secure boot configured and enabled in order to attain the security status that's described in the following TechNet article:
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