引用:
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作者arnan
snipped....
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<<能完全支持4GB RAM的電腦組合? >>>
結論是....一般User用的板子...插四G都只能用到3.5G左右
不管你晶片組寫最大支援到8G還是16G都一樣
跟OS支不支援也無關
要插多少用多少...請買Server用版本的主機板
這樣沒錯吧???
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以下貼一下32bit linux分別開HIGHMEM4G/HIGHMEM64G及X86-64 linux在同一台機器(4GB,其中256MB暫時分配給onboard VGA)上看到記憶體的狀況....
1:HIGHMEM4G
/proc/mtrr
reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
reg03: base=0x100000000 (4096MB), size= 512MB: write-back, count=1
/proc/meminfo
MemTotal: 3357656 kB
MemFree: 3247604 kB
Buffers: 2580 kB
Cached: 88196 kB
SwapCached: 0 kB
Active: 18756 kB
Inactive: 74704 kB
HighTotal: 2490304 kB
HighFree: 2398160 kB
LowTotal: 867352 kB
LowFree: 849444 kB
2:HIGHMEM64G
/proc/mtrr
reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
reg03: base=0x100000000 (4096MB), size= 512MB: write-back, count=1
/proc/meminfo
MemTotal: 3876308 kB
MemFree: 3765348 kB
Buffers: 2564 kB
Cached: 88220 kB
SwapCached: 0 kB
Active: 18756 kB
Inactive: 74680 kB
HighTotal: 3014592 kB
HighFree: 2922108 kB
LowTotal: 861716 kB
LowFree: 843240 kB
3:X86-64
/proc/mtrr
reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
reg03: base=0x100000000 (4096MB), size= 512MB: write-back, count=1
/proc/meminfo
MemTotal: 3790632 kB
MemFree: 3630120 kB
Buffers: 4536 kB
Cached: 122820 kB
SwapCached: 0 kB
Active: 27696 kB
Inactive: 103520 kB
由1-3的MTRR可知其實CPU都有將3.25G-4G間的RAM mapping到4G以後,只要OS support應該還是能用到的,但一般32bit OS(ex XP或鵝config成HIGHMEM4G時)無法存取4GB以後的部份,以至於比config成HIGHMEM64G時損失約512MB的RAM,而 X86-64雖然還是要做mapping才不會浪費RAM,不過不像32bit時須要做PAE(所以記憶體被分成low/high memory兩部份),對須要大量記憶體的AP應該有一定程度的優勢吧
....