可能重复：
64 位系统上仅使用 3.2 Gb 内存
我一直在运行 64 位版本的 11.10，它是从 11.04 升级而来，并非全新安装。我之前有 2GB 的 RAM，今天我又添加了 4GB 的 RAM，总内存为 6GB，但只有 3.2GB 可用。
BIOS 检测正常，显示 6GB。即使 lshw 显示 6GB 内存，但不知何故只有 3.2GB 可用。
输出uname -a
ashfame@ashfame-desktop:~$ uname -a
Linux ashfame-desktop 3.0.0-13-generic #22-Ubuntu SMP Wed Nov 2 13:27:26 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
输出free -m
ashfame@ashfame-desktop:~$ free -m
total used free shared buffers cached
Mem: 3268 2304 963 0 134 969
-/+ buffers/cache: 1201 2066
Swap: 2027 0 2027
输出lshw
ashfame-desktop
description: Desktop Computer
product: ()
width: 64 bits
capabilities: smbios-2.4 dmi-2.4 vsyscall64 vsyscall32
configuration: boot=normal chassis=desktop uuid=95649FA0-34EF-11DC-B2FF-000EA6292A3D
*-core
description: Motherboard
product: DG965RY
vendor: Intel Corporation
physical id: 0
version: AAD41691-301
serial: BTRY728008RN
slot: Base Board Chassis Location
*-cpu
description: CPU
product: Intel(R) Core(TM)2 CPU 4400 @ 2.00GHz
vendor: Intel Corp.
physical id: 0
bus info: cpu@0
version: Intel(R) Core(TM)2 CPU 4400 @ 2.00GHz
slot: LGA 775
size: 2GHz
capacity: 4GHz
width: 64 bits
clock: 200MHz
capabilities: fpu fpu_exception wp 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 x86-64 constant_tsc arch_perfmon pebs bts rep_good nopl aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm lahf_lm cpufreq
*-cache:0
description: L2 cache
physical id: 1
slot: Unknown
size: 2MiB
capacity: 2MiB
capabilities: asynchronous internal write-back unified
*-cache:1
description: L1 cache
physical id: 3
slot: Unknown
size: 32KiB
capacity: 32KiB
capabilities: asynchronous internal write-back data
*-cache
description: L1 cache
physical id: 2
slot: Unknown
size: 32KiB
capacity: 32KiB
capabilities: asynchronous internal write-back instruction
*-firmware
description: BIOS
vendor: Intel Corp.
physical id: 4
version: MQ96510J.86A.1687.2007.0510.0258
date: 05/10/2007
size: 64KiB
capacity: 960KiB
capabilities: pci upgrade shadowing cdboot bootselect edd int9keyboard int14serial int17printer int10video acpi usb zipboot biosbootspecification netboot
*-memory
description: System Memory
physical id: 17
slot: System board or motherboard
size: 6GiB
*-bank:0
description: DIMM DDR2 Synchronous 667 MHz (1.5 ns)
product: OCZ2N800SR1G
vendor: 0x7F7F7F7FB0000000
physical id: 0
serial: 0xFFFFFFFF
slot: J6H1
size: 1GiB
width: 64 bits
clock: 667MHz (1.5ns)
*-bank:1
description: DIMM DDR2 Synchronous 667 MHz (1.5 ns)
product: NT2GT64U8HD0BY-AD
vendor: Nanya Technology
physical id: 1
serial: 0xCB901004
slot: J6H2
size: 2GiB
width: 64 bits
clock: 667MHz (1.5ns)
*-bank:2
description: DIMM DDR2 Synchronous 667 MHz (1.5 ns)
product: OCZ2N800SR1G
vendor: 0x7F7F7F7FB0000000
physical id: 2
serial: 0xFFFFFFFF
slot: J6J1
size: 1GiB
width: 64 bits
clock: 667MHz (1.5ns)
*-bank:3
description: DIMM DDR2 Synchronous 667 MHz (1.5 ns)
product: NT2GT64U8HD0BY-AD
vendor: Nanya Technology
physical id: 3
serial: 0x1B911003
slot: J6J2
size: 2GiB
width: 64 bits
clock: 667MHz (1.5ns)
*-pci
description: Host bridge
product: 82P965/G965 Memory Controller Hub
vendor: Intel Corporation
physical id: 100
bus info: pci@0000:00:00.0
version: 02
width: 32 bits
clock: 33MHz
*-pci:0
description: PCI bridge
product: 82P965/G965 PCI Express Root Port
vendor: Intel Corporation
physical id: 1
bus info: pci@0000:00:01.0
version: 02
width: 32 bits
clock: 33MHz
capabilities: pci pm msi pciexpress normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:40 ioport:2000(size=4096) memory:e0200000-e02fffff ioport:d0000000(size=268435456)
*-display
description: VGA compatible controller
product: RV770 [Radeon HD 4850]
vendor: ATI Technologies Inc
physical id: 0
bus info: pci@0000:01:00.0
version: 00
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
configuration: driver=fglrx_pci latency=0
resources: irq:50 memory:d0000000-dfffffff memory:e0200000-e020ffff ioport:2000(size=256) memory:e0220000-e023ffff
*-multimedia
description: Audio device
product: HD48x0 audio
vendor: ATI Technologies Inc
physical id: 0.1
bus info: pci@0000:01:00.1
version: 00
width: 64 bits
clock: 33MHz
capabilities: pm pciexpress msi bus_master cap_list
configuration: driver=HDA Intel latency=0
resources: irq:49 memory:e0210000-e0213fff
*-communication
description: Communication controller
product: 82P965/G965 HECI Controller
vendor: Intel Corporation
physical id: 3
bus info: pci@0000:00:03.0
version: 02
width: 64 bits
clock: 33MHz
capabilities: pm msi bus_master cap_list
configuration: driver=mei latency=0
resources: irq:16 memory:e0326100-e032610f
*-network
description: Ethernet interface
product: 82566DC Gigabit Network Connection
vendor: Intel Corporation
physical id: 19
bus info: pci@0000:00:19.0
logical name: eth1
version: 02
serial: 00:19:d1:93:ad:2f
size: 100Mbit/s
capacity: 1Gbit/s
width: 32 bits
clock: 33MHz
capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=1.3.10-k2 duplex=full firmware=1.1-0 ip=192.168.1.2 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
resources: irq:47 memory:e0300000-e031ffff memory:e0324000-e0324fff ioport:30e0(size=32)
*-usb:0
description: USB Controller
product: 82801H (ICH8 Family) USB UHCI Controller #4
vendor: Intel Corporation
physical id: 1a
bus info: pci@0000:00:1a.0
version: 02
width: 32 bits
clock: 33MHz
capabilities: uhci bus_master
configuration: driver=uhci_hcd latency=0
resources: irq:16 ioport:30c0(size=32)
*-usb:1
description: USB Controller
product: 82801H (ICH8 Family) USB UHCI Controller #5
vendor: Intel Corporation
physical id: 1a.1
bus info: pci@0000:00:1a.1
version: 02
width: 32 bits
clock: 33MHz
capabilities: uhci bus_master
configuration: driver=uhci_hcd latency=0
resources: irq:21 ioport:30a0(size=32)
*-usb:2
description: USB Controller
product: 82801H (ICH8 Family) USB2 EHCI Controller #2
vendor: Intel Corporation
physical id: 1a.7
bus info: pci@0000:00:1a.7
version: 02
width: 32 bits
clock: 33MHz
capabilities: pm debug ehci bus_master cap_list
configuration: driver=ehci_hcd latency=0
resources: irq:18 memory:e0325c00-e0325fff
*-multimedia
description: Audio device
product: 82801H (ICH8 Family) HD Audio Controller
vendor: Intel Corporation
physical id: 1b
bus info: pci@0000:00:1b.0
version: 02
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list
configuration: driver=HDA Intel latency=0
resources: irq:48 memory:e0320000-e0323fff
*-pci:1
description: PCI bridge
product: 82801H (ICH8 Family) PCI Express Port 1
vendor: Intel Corporation
physical id: 1c
bus info: pci@0000:00:1c.0
version: 02
width: 32 bits
clock: 33MHz
capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:41 ioport:7000(size=4096) memory:e1200000-e13fffff ioport:e1400000(size=2097152)
*-pci:2
description: PCI bridge
product: 82801H (ICH8 Family) PCI Express Port 2
vendor: Intel Corporation
physical id: 1c.1
bus info: pci@0000:00:1c.1
version: 02
width: 32 bits
clock: 33MHz
capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:42 ioport:1000(size=4096) memory:e0100000-e01fffff ioport:e1000000(size=2097152)
*-ide
description: IDE interface
product: 88SE6101/6102 single-port PATA133 interface
vendor: Marvell Technology Group Ltd.
physical id: 0
bus info: pci@0000:03:00.0
logical name: scsi0
version: b1
width: 32 bits
clock: 33MHz
capabilities: ide pm msi pciexpress bus_master cap_list emulated
configuration: driver=pata_marvell latency=0
resources: irq:17 ioport:1018(size=8) ioport:1024(size=4) ioport:1010(size=8) ioport:1020(size=4) ioport:1000(size=16) memory:e0100000-e01001ff
*-cdrom
description: DVD-RAM writer
product: DVD RW AW-G170A
vendor: SONY
physical id: 0.0.0
bus info: scsi@0:0.0.0
logical name: /dev/cdrom
logical name: /dev/cdrw
logical name: /dev/dvd
logical name: /dev/dvdrw
logical name: /dev/scd0
logical name: /dev/sr0
version: 1.62
serial: [
capabilities: removable audio cd-r cd-rw dvd dvd-r dvd-ram
configuration: ansiversion=5 status=nodisc
*-pci:3
description: PCI bridge
product: 82801H (ICH8 Family) PCI Express Port 3
vendor: Intel Corporation
physical id: 1c.2
bus info: pci@0000:00:1c.2
version: 02
width: 32 bits
clock: 33MHz
capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:43 ioport:6000(size=4096) memory:e0c00000-e0dfffff ioport:e0e00000(size=2097152)
*-pci:4
description: PCI bridge
product: 82801H (ICH8 Family) PCI Express Port 4
vendor: Intel Corporation
physical id: 1c.3
bus info: pci@0000:00:1c.3
version: 02
width: 32 bits
clock: 33MHz
capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:44 ioport:5000(size=4096) memory:e0800000-e09fffff ioport:e0a00000(size=2097152)
*-pci:5
description: PCI bridge
product: 82801H (ICH8 Family) PCI Express Port 5
vendor: Intel Corporation
physical id: 1c.4
bus info: pci@0000:00:1c.4
version: 02
width: 32 bits
clock: 33MHz
capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
configuration: driver=pcieport
resources: irq:45 ioport:4000(size=4096) memory:e0400000-e05fffff ioport:e0600000(size=2097152)
*-usb:3
description: USB Controller
product: 82801H (ICH8 Family) USB UHCI Controller #1
vendor: Intel Corporation
physical id: 1d
bus info: pci@0000:00:1d.0
version: 02
width: 32 bits
clock: 33MHz
capabilities: uhci bus_master
configuration: driver=uhci_hcd latency=0
resources: irq:23 ioport:3080(size=32)
*-usb:4
description: USB Controller
product: 82801H (ICH8 Family) USB UHCI Controller #2
vendor: Intel Corporation
physical id: 1d.1
bus info: pci@0000:00:1d.1
version: 02
width: 32 bits
clock: 33MHz
capabilities: uhci bus_master
configuration: driver=uhci_hcd latency=0
resources: irq:19 ioport:3060(size=32)
*-usb:5
description: USB Controller
product: 82801H (ICH8 Family) USB UHCI Controller #3
vendor: Intel Corporation
physical id: 1d.2
bus info: pci@0000:00:1d.2
version: 02
width: 32 bits
clock: 33MHz
capabilities: uhci bus_master
configuration: driver=uhci_hcd latency=0
resources: irq:18 ioport:3040(size=32)
*-usb:6
description: USB Controller
product: 82801H (ICH8 Family) USB2 EHCI Controller #1
vendor: Intel Corporation
physical id: 1d.7
bus info: pci@0000:00:1d.7
version: 02
width: 32 bits
clock: 33MHz
capabilities: pm debug ehci bus_master cap_list
configuration: driver=ehci_hcd latency=0
resources: irq:23 memory:e0325800-e0325bff
*-pci:6
description: PCI bridge
product: 82801 PCI Bridge
vendor: Intel Corporation
physical id: 1e
bus info: pci@0000:00:1e.0
version: f2
width: 32 bits
clock: 33MHz
capabilities: pci subtractive_decode bus_master cap_list
resources: memory:e0000000-e00fffff
*-firewire
description: FireWire (IEEE 1394)
product: TSB43AB22A IEEE-1394a-2000 Controller (PHY/Link) [iOHCI-Lynx]
vendor: Texas Instruments
physical id: 3
bus info: pci@0000:07:03.0
version: 00
width: 32 bits
clock: 33MHz
capabilities: pm ohci bus_master cap_list
configuration: driver=firewire_ohci latency=32 maxlatency=4 mingnt=2
resources: irq:19 memory:e0004000-e00047ff memory:e0000000-e0003fff
*-isa
description: ISA bridge
product: 82801HB/HR (ICH8/R) LPC Interface Controller
vendor: Intel Corporation
physical id: 1f
bus info: pci@0000:00:1f.0
version: 02
width: 32 bits
clock: 33MHz
capabilities: isa bus_master cap_list
configuration: latency=0
*-storage
description: SATA controller
product: 82801HB (ICH8) 4 port SATA AHCI Controller
vendor: Intel Corporation
physical id: 1f.2
bus info: pci@0000:00:1f.2
logical name: scsi1
version: 02
width: 32 bits
clock: 66MHz
capabilities: storage msi pm ahci_1.0 bus_master cap_list emulated
configuration: driver=ahci latency=0
resources: irq:46 ioport:3408(size=8) ioport:3414(size=4) ioport:3400(size=8) ioport:3410(size=4) ioport:3020(size=32) memory:e0325000-e03257ff
*-disk
description: ATA Disk
product: ST3160215AS
vendor: Seagate
physical id: 0.0.0
bus info: scsi@1:0.0.0
logical name: /dev/sda
version: 3.AA
serial: 5RX16VWR
size: 149GiB (160GB)
capabilities: partitioned partitioned:dos
configuration: ansiversion=5 signature=00090294
*-volume:0
description: EXT4 volume
vendor: Linux
physical id: 1
bus info: scsi@1:0.0.0,1
logical name: /dev/sda1
logical name: /
version: 1.0
serial: 6c158778-6562-40f5-9f4f-1d49d9d68b13
size: 147GiB
capacity: 147GiB
capabilities: primary bootable journaled extended_attributes large_files huge_files dir_nlink extents ext4 ext2 initialized
configuration: created=2011-05-01 10:12:11 filesystem=ext4 lastmountpoint=/ modified=2011-11-26 20:37:01 mount.fstype=ext4 mount.options=rw,relatime,errors=remount-ro,user_xattr,acl,barrier=1,data=ordered mounted=2011-11-26 20:37:47 state=mounted
*-volume:1
description: Extended partition
physical id: 2
bus info: scsi@1:0.0.0,2
logical name: /dev/sda2
size: 2028MiB
capacity: 2028MiB
capabilities: primary extended partitioned partitioned:extended
*-logicalvolume
description: Linux swap / Solaris partition
physical id: 5
logical name: /dev/sda5
capacity: 2028MiB
capabilities: nofs
*-serial UNCLAIMED
description: SMBus
product: 82801H (ICH8 Family) SMBus Controller
vendor: Intel Corporation
physical id: 1f.3
bus info: pci@0000:00:1f.3
version: 02
width: 32 bits
clock: 33MHz
configuration: latency=0
resources: memory:e0326000-e03260ff ioport:3000(size=32)
输出cat /proc/meminfo
ashfame@ashfame-desktop:~$ cat /proc/meminfo
MemTotal: 3346872 kB
MemFree: 1152164 kB
Buffers: 22152 kB
Cached: 871740 kB
SwapCached: 320 kB
Active: 1355716 kB
Inactive: 407872 kB
Active(anon): 695948 kB
Inactive(anon): 183108 kB
Active(file): 659768 kB
Inactive(file): 224764 kB
Unevictable: 248 kB
Mlocked: 248 kB
SwapTotal: 2076668 kB
SwapFree: 2075652 kB
Dirty: 4 kB
Writeback: 44 kB
AnonPages: 869668 kB
Mapped: 195364 kB
Shmem: 9360 kB
Slab: 88080 kB
SReclaimable: 61084 kB
SUnreclaim: 26996 kB
KernelStack: 3712 kB
PageTables: 36956 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 3750104 kB
Committed_AS: 3551040 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 195492 kB
VmallocChunk: 34359536360 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 189440 kB
DirectMap2M: 3217408 kB
输出sudo dmidecode-http://pastebin.com/85VBDYmC
尝试使用 11.04 和 11.10 的可启动 USB 并从中启动，显示仅 3.2GB 可用。
根据与 fossfreedom 的聊天，我尝试移除 1GB 内存条，只保留新的 2GB 内存条并从中启动。系统仍然显示 3.2GB 内存。我甚至将它们移至单个通道，它仍然显示 3.2GB 内存。
如果有帮助的话，1GB 内存条来自同一制造商 - Corsair（实际上是双通道内存套件），而较新的 2GB 内存条来自同一制造商 - Kingston。
我还被建议升级 BIOS，但由于它检测到 6GB 的 RAM，我怀疑这与此无关。BIOS 发行说明没有提到任何修复该问题的内容。以下是 PDF -http://downloadmirror.intel.com/17520/eng/MQ_1761_ReleaseNotes.pdf（我的 BIOS 版本 - 1687）
我在 BIOS 中看到的唯一选项是更改 RAM 运行的频率和延迟。屏幕截图如下：
知道这里发生什么事了吗？
答案1
您的 RAM 模块与主板兼容，但内存频率是限制因素 - 这就是为什么只有 3.2GB 可用于操作系统，而 800MB 保留用于主板系统图形。
两个品牌的 RAM 模块的产品编号NT2GT64U8HD0BY-AD和OCZ2N800SR1G输出中列出的lshw表明它们是 800MHz 的 PC2-6400 模块。
从您的屏幕截图可以看出，您的 BIOS 将内存频率限制为 667MHZ，并且显示它们是 800MHz 模块。
你之所以能看到通过安装的 6GB RAM，lshw是因为 Ubuntu 列出了所有硬件安装在您的系统上 - 而不是正在使用的内容。
为了让你的主板使用更多的 RAM，你需要购买额定频率为 533 或 667MHZ 的模块 - 然后你将能够使用高达 8GB 的 RAM。