topic Re: Why does my CPU only support 32GB RAM when it has 39 address bits? in Mobile and Desktop Processors

Why does my CPU only support 32GB RAM when it has 39 address bits?

BLohr — Fri, 08 Jul 2016 20:46:20 GMT

The following is the output of cat /proc/cpuinfo

user@localhost:~$ cat /proc/cpuinfo

processor : 0

vendor_id : GenuineIntel

cpu family : 6

model : 60

model name : Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz

stepping : 3

microcode : 0x12

cpu MHz : 800.000

cache size : 3072 KB

physical id : 0

siblings : 4

core id : 0

cpu cores : 2

apicid : 0

initial apicid : 0

fpu : yes

fpu_exception : yes

cpuid level : 13

wp : yes

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 fma cx16 xtpr pdcm pcid sse4_1 sse4_2 movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid

bogomips : 6784.48

clflush size : 64

cache_alignment : 64

address sizes : 39 bits physical, 48 bits virtual

power management:

Now, 39 bits should get me 512GiB addressable physical memory. However, the http://ark.intel.com/products/77480/Intel-Core-i3-4130-Processor-3M-Cache-3_40-GHz Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz only supports 32GiB. Why is this? How can I reconcile this calculation?

I am not asking about the number of slots in the motherboard, maximum ram / DIMM cards etc. I am looking for how the physical bits, address lines, and the maximum amount of physical RAM fit. I understand that the mother board designer does not need to use all the the RAM that the CPU can take. But it seems that the CPU can only take 32GiB of RAM while the 39 bits physical should let it take 512GiB. Why did Intel allot 39bits physical when it could do with 35 physical bits.

Also, 48 bits should account for 256TiB of virtual address space. Is this true?

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

idata — Tue, 12 Jul 2016 21:47:27 GMT

Hi lordloh,

Please let me investigate about this, as soon I get an answer I let you know.

Regards,

Hellen.

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

Ronny_G_Intel — Wed, 20 Jul 2016 17:19:06 GMT

Hello lordloh,

Theoretically yes but there are instructions set on the processor to allow a maximum amount of memory to 32GB.

Details are available here: https://www-ssl.intel.com/content/www/us/en/processors/core/4th-gen-core-family-desktop-vol-1-datasheet.html Desktop 4th Gen Intel® Core™ Processors Datasheet, Vol. 1 page # 18

I hope this helps,

Ronny G

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

idata — Mon, 25 Jul 2016 17:21:34 GMT

Hi Lordloh,

Could you please let me know if Rguevara's information helps you?

Regards,

Hellen.

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

BLohr — Tue, 26 Jul 2016 03:09:36 GMT

I think it makes a few things clear.

My understanding is that the processor supports a certain type of DRAM technology viz. - 4Gb / DIMM. This allows a maximum of 32GiB.

I am not well versed with DRAM technology and therefore may have gaps in my understanding here. Let me know if any of these are wrong -

The DRAM controller in the processor supports certain kind of DRAMs
The DRAM controller supports a maximum of 4GiB / DIMM and supports a maximum of 8 DIMMs - thus 32GiB.

What I am not able to reconcile is that I am using a 8GB DDR3 card and have 2 of these as my MotherBoard only supports 16GB RAM. I would be grateful if someone could point me some easy to understand DRAM resource. I am trying to figure this from various pages on wikipedia.

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

idata — Wed, 27 Jul 2016 22:14:14 GMT

Hi Lordloh,

Please let me investigate this.

Regards,

Hellen.

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

idata — Thu, 04 Aug 2016 18:14:34 GMT

Hi Lordloh,

The memory controller in the processor can handle different RAM device Technology (1Gb, 2Gb & 4Gb) with a specific DRAM organization.

Here you can get more information about:

http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-desktop-vol-1-datasheet.html http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-desktop-vol-1-datasheet.html

Page 19

Regards,

Hellen.

Re: Why does my CPU only support 32GB RAM when it has 39 address bits?

idata — Sat, 10 Sep 2016 17:52:40 GMT

Hi Lordloh,

Thought I would just check in and find out if the information provided helps you.

Regards,

Hellen.