intel 桌面平台， e3 i7 等，应该是36位地址线，总共可以描述64G 的地址空间。
其中pcie 设备一般要占据1-2个G，这样系统可用空间就少两个G。
32G 无影响， 64 g 就无法编址了。
processor : 7
vendor_id : GenuineIntel
cpu family : 6
model : 58
model name : Intel(R) Xeon(R) CPU E3-1265L V2 @ 2.50GHz
stepping : 9
cpu MHz : 2500.055
cache size : 8192 KB
physical id : 0
siblings : 8
core id : 3
cpu cores : 4
apicid : 7
initial apicid: 7
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 rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms
bogomips : 5000.11
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:
Mar7 16:14:46 localhost kernel: BIOS-e820: 0000000000000000 - 0000000000099c00 (usable)
Mar7 16:14:46 localhost kernel: BIOS-e820: 0000000000099c00 - 00000000000a0000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 0000000000100000 - 00000000cdd2b000 (usable)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000cdd2b000 - 00000000cdddb000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000cdddb000 - 00000000cdef8000 (ACPI NVS)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000cdef8000 - 00000000cf04d000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000cf04d000 - 00000000cf04e000 (usable)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000cf04e000 - 00000000cf091000 (ACPI NVS)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000cf091000 - 00000000cf800000 (usable)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000fed00000 - 00000000fed04000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000fed1c000 - 00000000fed20000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
Mar7 16:14:46 localhost kernel: BIOS-e820: 0000000100000000 - 0000000130000000 (usable)
从linux 比较好看这个。 我这个超威的主板，pcie 地址空间大概是800m
想新出的， xeon-d， 也就是Broadwelll de， pcie 空间大概2个G。
地址表中间usable 才是内存的地址，所以会损失掉一些。
