AMD Radeon R9 M370X not recognized by Windows 8 partition. Mid 2015 15 inch Macbook Pro

Can you post the output of diskutil list? The MSR partition exists only if your Windows was installed using EFI boot. The output will show what your installation type is - BIOS or UEFI? You can get the same information using MSInfo.

It shows UEFI:

OS Name Microsoft Windows 8 Pro

Version 6.2.9200 Build 9200

Other OS Description Not Available

OS Manufacturer Microsoft Corporation

System Name CHRISTOPHERW

System Manufacturer Apple Inc.

System Model MacBookPro11,5

System Type x64-based PC

System SKU Unsupported

Processor Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz, 2501 Mhz, 4 Core(s), 8 Logical Processor(s)

BIOS Version/Date Apple Inc. MBP114.88Z.0172.B00.1503301047, 3/30/2015

SMBIOS Version 2.7

BIOS Mode UEFI

BaseBoard Manufacturer Apple Inc.

BaseBoard Model Not Available

BaseBoard Name Base Board

Platform Role Mobile

Secure Boot State Unsupported

PCR7 Configuration Binding Not Possible

Windows Directory C:\Windows

System Directory C:\Windows\system32

Boot Device \Device\HarddiskVolume1

Locale United States

Hardware Abstraction Layer Version = "6.2.9200.16384"

User Name ChristopherW\Christopher

Time Zone Pacific Daylight Time

Installed Physical Memory (RAM) 16.0 GB

Total Physical Memory 15.9 GB

Available Physical Memory 13.9 GB

Total Virtual Memory 21.4 GB

Available Virtual Memory 19.3 GB

Page File Space 5.50 GB

Page File C:\pagefile.sys

Hyper-V - VM Monitor Mode Extensions Yes

Hyper-V - Second Level Address Translation Extensions Yes

Hyper-V - Virtualization Enabled in Firmware Yes

Hyper-V - Data Execution Protection Yes

What does diskutil list from OS X Terminal show?

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *500.3 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_HFS Macintosh HD 418.4 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3

4: Microsoft Basic Data BOOTCAMP 81.1 GB disk0s4/dev/disk1

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *31.5 GB disk1

1: DOS_FAT_32 UNTITLED 31.5 GB disk1s1

Can you post the output of sudo fdisk /dev/disk0 ? There is a MSR partition for EFI-based installations. You do not have it, yet your installation is UEFI according to the output you posted.

Is it possible to clean install W8.1 rather than a W8 -> W8.1 upgrade?

Funny you should say that. I am actually downloading the W8.1 iso right now. I'll have to switch over to the mac book to do the sudo command. Will post that in a moment.

Here is the output of the sudo command:

Disk: /dev/disk0 geometry: 60821/255/63 [977105060 sectors]

Signature: 0xAA55

Starting Ending

#: id cyl hd sec - cyl hd sec [ start - size]

------------------------------------------------------------------------

1: EE 1023 254 63 - 1023 254 63 [ 1 - 977105059] <Unknown ID>

2: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

3: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

4: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

Assuming that checks out - and now that I have the W8.1 iso - should I start over with BCA, delete the current windows partition and just start from scratch?

Problem solved! I followed the Boot Camp instructions and did a clean install using the W8.1 iso image. The installer updated the boot camp drivers without a hitch and the screen resolution looks great. Thanks for all your help!

Can you verify that the drivers for the GPU are the Apple BC drivers?