Virtual machine memory limits and hardware versions

Details

This article provides information about virtual machine memory limits and hardware versions.

Solution

Virtual machines that use hardware versions earlier than 7 do not account for reserved memory. Virtual machines using more than 4 GB of memory actually used 0.25 GB or 0.5 GB less memory, because the additional memory size was used to specify the highest space available as system RAM, ignoring the space occupied by PCI devices.

To determine the current hardware version of a virtual machine in the vSphere Client:

1. Click the virtual machine.
2. Click the Summary tab.
3. Find the hardware version in the VM Version field.

Due to this, the guest recognizes less physical memory than you configured for the virtual machine. For example, if you configured 4 GB (memsize = 4096 in the .vmx configuration file) of memory, the guest only sees or recognizes 3.75 GB.

This behavior is expected and does not negatively affect the operation of the guest. Physical Address Extension (PAE) will not enable the guest to recognize all 4 GB of memory.

When you configure the virtual hardware to have 4 GB of physical memory, the virtual machine monitor (VMM) provides it to the guest as a single contiguous block of virtual physical memory. The guest also maps other devices in its address space, some of which must be at addresses less than 4 GB. As a result, this also makes some of the physical memory inaccessible. Therefore, the guest can only use 3.75 GB of physical memory from the 4 GB you originally configured.

Note: This does not waste 0.25 GB of memory. The VMM does not need to allocate the memory that the guest cannot access. There is only a slight difference between the size of memory you specify and the memory the guest recognizes. This also happens natively on some systems.

With hardware version 7 and later, VMware products reserve 1 GB for PCI devices. As a result, all the memory specified in the virtual machine configuration is available to the guest operating system. Memory settings now specify the amount of memory available, not the highest address available as system RAM, which is now 1 GB higher for virtual machines with more than 3 GB of memory.

Memory limits for VMware products

ESXi/ESX

ESXi/ESX virtual machines	Hardware version	Memory limit
5.1	9	32-bit and 64-bit virtual machines: 1011 GB All specified memory is accessible to the guest. The guest accounts for space obscured by PCI devices.
5.0	8	32-bit and 64-bit virtual machines: 1011 GB All specified memory is accessible to the guest. The guest accounts for space obscured by PCI devices.
4.x	7	32-bit and 64-bit virtual machines: 255 GB All specified memory is accessible to the guest. The guest accounts for space obscured by PCI devices.
3.5	4	32-bit and 64-bit virtual machines: 65532 MB
3.x	4	32-bit and 64-bit virtual machines: 16384 MB
2.x	3	32-bit and 64-bit virtual machines: 3600 MB

Workstation

Workstation virtual machines	Hardware version	Memory limit
9.x	9	64 GB for systems with 64-bit host operating systems 8 GB for systems with 32-bit host operating systems
8.x	8	64 GB for systems with 64-bit host operating systems 8 GB for systems with 32-bit host operating systems
7.x	7	32 GB for systems with 64-bit host operating systems 8 GB for systems with 32-bit host operating systems
6.5	7	32-bit and 64-bit virtual machines: 8 GB All specified memory is accessible to the guest.
6.x	6	32-bit and 64-bit virtual machines: 8 GB
5.x	3 and 4	32-bit and 64-bit virtual machines: 3600 MB All specified memory is accessible to the guest.
4.x	3 and 4	32-bit and 64-bit virtual machines: 3600 MB All specified memory is accessible to the guest

Fusion

Fusion virtual machines	Hardware version	Memory limit
5.x	9	32-bit and 64-bit virtual machines: 8 GB
4.x	8	32-bit and 64-bit virtual machines: 8 GB
3.x	7	32-bit and 64-bit virtual machines: 8 GB
2.x	7	32-bit and 64-bit virtual machines: 8 GB
1.x	4	32-bit and 64-bit virtual machines: 8 GB

Player

Player virtual machines	Hardware version	Memory limit
5.x	9	64 GB for systems with 64-bit host operating systems 8 GB for systems with 32-bit host operating systems
4.x	8	64 GB for systems with 64-bit host operating systems 8 GB for systems with 32-bit host operating systems
3.x	7	32 GB for systems with 64-bit host operating systems 8 GB for systems with 32-bit host operating systems
2.5	7	32-bit and 64-bit virtual machines: 8 GB All specified memory is accessible to the guest.
2.x	6	32-bit and 64-bit virtual machines: 8 GB
1.x	3 and 4	32-bit and 64-bit virtual machines: 3600 MB All specified memory is accessible to the guest.

The PC architecture reserves a portion of the address space that is below 4 GB for PCI devices. This space cannot be used for system memory. Also note that this is one of the main reasons for guests not recognizing all allocated physical memory.

For more information on the reservation for PCI devices, see PCI Hole.

Note: The information provided in this link is provided as-is and VMware does not guarantee the accuracy or applicability of this information.

This table lists the address space size available for system memory under 4 GB for each hardware version:

Hardware version	Reserved memory	Supported memory
9	1024 MB	3 GB (3072 MB)
8	1024 MB	3 GB (3072 MB)
7	1024 MB	3 GB (3072 MB)
6	512 MB	3.5 GB (3584 MB)
4	256 MB	3.75 GB (3840 MB)
3	496 MB*	3.52 GB (3600 MB)

* Hardware version 3 does not support virtual machines larger than 3600 MB. As a result, the restrictions listed in this article do not apply to these virtual machines.

Source:-

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1014006