Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

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

195 replies

Mortandos Author

Level 1

4 points

Jun 6, 2015 9:51 PM in response to Loner T

Here is the output of the fdisk command:

Disk: /dev/disk0 geometry: 121601/255/63 [1953525168 sectors]

Signature: 0xAA55

Starting Ending

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

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

*1: 07 1023 254 63 - 1023 254 63 [ 2 - 19793400] HPFS/QNX/AUX

2: 07 1023 254 63 - 1023 254 63 [ 19793403 - 1933731765] HPFS/QNX/AUX

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

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

Mortandos Author

Level 1

4 points

Jun 6, 2015 9:58 PM in response to Loner T

Ok, I will try this again but do I create the second (big partition) after step 2 or 3 or later after the reboot?

The bless command - the disk0s is 1 (small) or 2 (big partition)?

1. Disk is GPT.

2. Create a 4GB exFAT partition.

3. Copy the contents of W7 ISO to this partition. The installer should not have files larger than 2GB.

4. Use Fdisk to make this partition bootable.

5. Use bless

sudo /usr/sbin/bless --verbose --device /dev/disk0s3 --setBoot --legacy --nextonly

6. Restart (first time I had no bootable device which was corrected with steps 4 and 5).

Is that the correct use of the fdisk command (if not please advice):

Setting Your Partition "Active" Using Fdisk

Words in bold below are things you must type (followed by Enter).

1. Boot your Mac OS X install dvd

2. Once the installer is running, go to the Utilities menu and open Terminal

3. Determine which disk your MacOSX partition is on

Type diskutil list

Verify which disk number holds your partition (disk0, disk1, etc.)

4. Start using Fdisk

Assuming the MacOSX disk is the first disk ("disk0"), then
type fdisk -e /dev/rdisk0 <== use "rdisk" with your disk number here !!

Ignore the error "fdisk: could not open MBR file ..."

5. Determine which partition for MacOSX needs to be set "Active"

Type p

Verify which partition is for MacOSX (1, 2, 3, etc.)

6. Set the partition "Active"

Assuming it is partition 1, then
type f 1 <== use your partition number here !!

7. Save and exit

Type write

Type y (yes you are sure)

Type exit (to quit)

8. Remove the install DVD and reboot

Mortandos Author

Level 1

4 points

Jun 9, 2015 2:07 PM in response to Loner T

the output of the bless command was like in your example, however the reboot resulted in the error message with the underscore cursor

Loner T

Level 9

59,477 points

Jun 9, 2015 4:17 PM in response to Mortandos

Mortandos wrote:

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

You seem to have another issue - Boot Camp: iMac displays a black screen during installation of Windows 7 - Apple Support .

Mortandos Author

Level 1

4 points

Jun 9, 2015 4:53 PM in response to Loner T

But you also had the same error message and the underscore cursor, I'm not sure whether the link regarding Windows 7 applies to my problem. Can you look at my previous post please and tell me the correct use of the bless and the fdisk command? The boot partition is disk0s1 (exFat) and the partition for the installation of Windows is disk0s2 (Tuxera NTFS), the hard disk is MBR.

Loner T

Level 9

59,477 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.

Mortandos Author

Level 1

4 points

Jun 9, 2015 6:07 PM in response to Loner T

I started with the USB stick in the first place (that's how I did the EFI boot and that's (probably) why I only had 2.48 GB RAM available). So in case I want to use the USB stick the Fdisk command is for the USB stick and the bless command also?

Loner T

Level 9

59,477 points

Jun 9, 2015 6:24 PM in response to Mortandos

Your USB-related issue is because of the choice of EFI boot, not due to the USB itself.

The USB will only contain BC drivers, not the Windows installer. You have the following step in the link.

After partitioning has completed, click "Start the installation" and insert your Windows 7 install DVD. Your computer will restart.

In your case you will use the blessed disk0s1 instead of the Windows DVD. You can remove the '--nextonly' qualifier so you do not have to run this command multiple times.

Mortandos Author

Level 1

4 points

Jun 9, 2015 6:42 PM in response to Loner T

I'm not sure whether I understand this right, how is the USB stick supposed to help me in case I'll get the underscore cursor again?

Loner T

Level 9

59,477 points

Jun 9, 2015 6:59 PM in response to Mortandos

If you download the package, there is a file called AutoUnattend.xml. It sets up the Windows PE (Pre-boot Environment). It has the correct AMD drivers so the installer can be displayed. You can edit the file in a text editor and see how the drivers are loaded. These drivers are not bootable, but your disk0s1 is being marked bootable.

Mortandos Author

Level 1

4 points

Jun 9, 2015 7:31 PM in response to Loner T

so putting it on the bootable partition is not recommended?

Jun 10, 2015 3:04 AM in response to Mortandos

This quickly turned into a Windows installation thread, was the original available RAM problem solved? Is it something specific to this/these Macs or affecting all Macs runnings BootCamp?

Loner T

Level 9

59,477 points

Jun 10, 2015 3:21 AM in response to Mortandos

You need to put the contents of the .zip file at the root of disk0s1. It is kept separate to allow the Installer and the PE to be separate.

Loner T

Level 9

59,477 points

Jun 10, 2015 3:25 AM in response to improwise

improwise wrote:

This quickly turned into a Windows installation thread, was the original available RAM problem solved? Is it something specific to this/these Macs or affecting all Macs runnings BootCamp?

No. All Macs should work and recognize the available physical memory. Windows 32-bit cannot go beyond 3.84/4GB limit.

The issues discussed in this thread are

1. UEFI v BIOS booting

2. Lack of a functional Optical drive

3. iMacs with AMD GPUs not booting correctly due to lack of drivers

There is a separate PAE discussion which may become part of this discussion.

Mortandos Author

Level 1

4 points

Jun 10, 2015 8:10 PM in response to Loner T

Just to clarify this, you said "You need to put the contents of the .zip file at the root of disk0s1. It is kept separate to allow the Installer and the PE to be separate." but disk0s1 is the small boot partition. So BC drivers and Win install on the small partition?

Because in an earlier post you said "The USB will only contain BC drivers, not the Windows installer" - so WHERE do you want me to put the BC drivers?

I tried it with the BC drivers on the USB stick and got something new: This time I got the black screen with the message "Insert DVD or CD and press any key to return". So why did it want to boot from the super drive now?

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