Level 1

4 points

Why can I only use 2.48 GB RAM in Boot Camp (Win 8.1 Pro, 64-bit)?

Hello, I am fairly new to the iMac and I have to use some programs in Windows that are not available for Mac so I set up Boot Camp and installed Windows 8.1.

My iMac is a I7-2600 CPU @ 3.4GHz with 16 GB RAM, system type-bit. Under system in Windows it shows Installed memory (RAM) 16 GB (2.48 GB usable).

I read about this problem and most answers are related to people using 32-bit. So what is wrong in my case, where is the problem?

Thank you in advance for help and suggestions.

iMac, OS X Yosemite (10.10.3)

Posted on May 3, 2015 11:52 AM

Top-ranking reply

Loner T

Level 9

59,536 points

Posted on May 4, 2015 8:04 PM

Your 2011 iMac is a preUEFI Mac (all Macs prior to Late 2013 models are). The preUEFI Macs support varying degrees of EFI boot capability, but do not fully comply with UEFI specifications. This causes various BC drivers to work, not work, or partially work, depending the year of the Mac and the OS used.

There are two methods that have been "successful" in working around broken Optical drives (apart from replacing it).

1. http://forums.macrumors.com/showthread.php?p=20584499#post20584499

2. Bootcamp without Optical disc drive

My recommendation is to remove Windows using BC Assistant (only, nothing else), and then try either of these two methods. You want a legacy BIOS installation (aka Hybrid MBR method). The CSM-BIOS layer correctly exposes hardware for preUEFI machines. It will also address your memory visibility issue.

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195 replies

Loner T

Level 9

59,536 points

May 7, 2015 3:45 AM in response to Mortandos

Can you boot using Command+Opt+R (Internet Recovery) or Command+R (Local Recovery)?

Loner T

Level 9

59,536 points

Jun 3, 2015 11:38 AM in response to Mortandos

We can remove the MBR and force an EFI installation, or leave the MBR and retry the BIOS mode installation.

Loner T

Level 9

59,536 points

May 5, 2015 2:46 PM in response to Mortandos

BCA is confused between the Startup Disk (SSD) and the 1TB disk. Is there data on the 1TB disk that you want to save? If the whole disk will be used, would you be willing to reformat it as an MBR disk for Windows after you save your data?

Loner T

Level 9

59,536 points

May 7, 2015 7:37 PM in response to Mortandos

I was referring to differences between EFI Boot and MBR (BIOS mode). Your Mac supports the BIOS mode, EFI Mode will cause problems. If your Mac has an Optical drive, you cannot use a USB to boot and install Windows. It has to be done using DVD.

Loner T

Level 9

59,536 points

May 7, 2015 9:39 PM in response to Mortandos

Any Mac which does not have a built-in Optical drive, will support installing Windows from a USB and/or an external Optical drive.

With the exception of a couple of models, a Mac with a built in Optical drive

a. will not support USB booting, and,

b. will not support EFI boot. If it is forced to use EFI mode, there are numerous issues, like black screens, audio, gpu, BSODs, etc. As you get closer to 2013, the issues get fewer. Late 2013 and newer models support EFI fully.

c. W7 is very buggy about EFI support, W8.1 is much more stable with EFI boot. Sleep/Hibernation are issues with either method of installation.

Your 2011 iMac will work best using a legacy BIOS installation. BCA provides two main features, partitioning and booting. Partitioning is relatively easier and can also be achieved manually. Booting is also possible, if you have an external Apple SuperDrive, the chances of success are much better. There are utilities like Rufus USB or UnetBootin or Microsoft's diskpart on a USB, that can be used to achieve booting.

Loner T

Level 9

59,536 points

Jun 3, 2015 8:24 PM in response to Mortandos

The following method is worth a test, if you can get your friend's external Optical drive.

1. Manually partition your internal disk.

2. Manually create an MBR using this FAT partition.

3. Connect the external DVD/Optical drive.

4. Power cycle the iMac and hold the Alt Key. Select the Windows DVD.

5. If the installer comes up, point it to this FAT partition which will be formatted to NTFS.

You may run into Boot Camp: iMac displays a black screen during installation of Windows 7 - Apple Support, because of your AMD GPU.

Loner T

Level 9

59,536 points

Jun 9, 2015 5:49 PM in response to Mortandos

The disk0s1 partition boots. Your Fdisk commands are correct. You can post the output of Fdisk for disk1 again for validation if you like.

sudo /usr/sbin/bless --verbose --device /dev/disk0s1 --setBoot --legacy --nextonly

The bless should be as shown.

The black screen could be because of two reasons.

1. The disk0s1 does not have appropriate Video drivers for you GPU, which is an issue with AMD GPUs and Windows installers.

2. The boot device is unreadable or cannot be found.

In my case I am trying on a 2008 MBA with W7, which may have additional issues. I will try to find an AMD GPU machine and test, if possible.

My suggestion is to build the USB on a USB2 flash drive as recommended in the link and try your installation again.

Loner T

Level 9

59,536 points

May 3, 2015 4:25 PM in response to Mortandos

What does this screen show on your iMac?

Please also see Will Windows 7 Pro run with 16GB of Ram in Macbook Pro Early 2011 13-inch?.

Loner T

Level 9

59,536 points

Jun 4, 2015 9:22 AM in response to Mortandos

Can you see the 1TB drive in DU? Is it an exFAT format? Can you post the output of diskutil list?

Loner T

Level 9

59,536 points

Jun 11, 2015 5:03 PM in response to Mortandos

One option to test is to convert disk0s1 to NTFS and test booting.

Loner T

Level 9

59,536 points

Jul 12, 2015 8:30 AM in response to Frederic Stark

The EFI method will cause problems because it does not expose devices via CSM-BIOS, which is the correct method in preUEFI Macs.

Mortandos Author

Level 1

4 points

May 3, 2015 5:01 PM in response to Loner T

@Loner T, it looks like yours except my processor is different and it says "Pro" after Windows 8.1 and the restriction: Installed memory (RAM) 16.0 GB (2.48 GB usable). The system type is identical, 64-bit so it's not the 32-bit limitation (I read about that).

Mortandos Author

Level 1

4 points

May 3, 2015 6:10 PM in response to Loner T

My Mac: iMac (27-inch, Mid 2011), 3.4 GHz Intel Core i7, 16 GB 1333 MHz DDR3, AMD Radeon HD 6970M 2048 MB.

The result of the command is hw.cpu64bit_capable: 1

I'm not sure what I'm looking for when executing the msconfig command in Windows.

Mortandos Author

Level 1

4 points

May 3, 2015 7:37 PM in response to Loner T

That part is like in your picture, unchecked and with a zero. I changed it, checked the box and set it to 16 GB, applied it and restarted and there was no change (showing the system configuration). However, running msconfig again showed zero and and the box unchecked (again).

Mortandos Author

Level 1

4 points

May 4, 2015 2:18 PM in response to Loner T

I did both following the provided instructions but nothing has changed. Isn't it strange that when I use MSCONFIG as you suggested and then check MAXIMUM MEMORY and choose 16384 and then click ok and then immediately check again it's back to "0" ?

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Why can I only use 2.48 GB RAM in Boot Camp (Win 8.1 Pro, 64-bit)?