目前我的电脑内存只有512M，想加根内存条。机器主板是nVidia Corporation MCP61,看了下主板说明
书发现系统内存支持双通道内存技术。配置了4个DDRII DIMM插槽，支持DDRII 800/667/533内存，
最大支持8G容量。
为了尝试下双通道内存技术，打算买根跟原来一样的内存条。发票的电脑配置上只写了kingston DDRII
512M。剩下的事情就是确定内存的工作频率。上网google发现有个工具dmidecode(DMI table
decoder)。它可以全面的显示你系统的信息，包括bios、cpu、内存等信息。
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[ray@localhost testcase]$ sudo dmidecode --help
Usage: dmidecode [OPTIONS]
Options are:
-d, --dev-mem FILE     Read memory from device FILE (default: /dev/mem)
-h, --help             Display this help text and exit
-q, --quiet            Less verbose output
-s, --string KEYWORD   Only display the value of the given DMI string
-t, --type TYPE        Only display the entries of given type
-u, --dump             Do not decode the entries
-V, --version          Display the version and exit
[ray@localhost testcase]$ sudo dmidecode -t memory
# dmidecode 2.7
SMBIOS 2.4 present.
Handle 0x0007, DMI type 5, 24 bytes.
Memory Controller Information
        Error Detecting Method: 64-bit ECC
        Error Correcting Capabilities:
                None
        Supported Interleave: One-way Interleave
        Current Interleave: One-way Interleave
        Maximum Memory Module Size: 2048 MB
        Maximum Total Memory Size: 8192 MB
        Supported Speeds:
                70 ns
                60 ns
        Supported Memory Types:
                DIMM
                SDRAM
        Memory Module Voltage: 3.3 V
        Associated Memory Slots: 4
                0x0008
                0x0009
                0x000A
                0x000B
        Enabled Error Correcting Capabilities:
                None
Handle 0x0008, DMI type 6, 12 bytes.
Memory Module Information
        Socket Designation: DIMM0
        Bank Connections: 0 1
        Current Speed: Unknown
        Type: ECC DIMM
        Installed Size: 512 MB (Single-bank Connection)
        Enabled Size: 512 MB (Single-bank Connection)
        Error Status: OK
Handle 0x0009, DMI type 6, 12 bytes.
Memory Module Information
        Socket Designation: DIMM1
        Bank Connections: None
        Current Speed: Unknown
        Type: Unknown
        Installed Size: Not Installed
        Enabled Size: Not Installed
        Error Status: OK
Handle 0x000A, DMI type 6, 12 bytes.
Memory Module Information
        Socket Designation: DIMM2
        Bank Connections: None
        Current Speed: Unknown
        Type: Unknown
        Installed Size: Not Installed
        Enabled Size: Not Installed
        Error Status: OK
Handle 0x000B, DMI type 6, 12 bytes.
Memory Module Information
        Socket Designation: DIMM3
        Bank Connections: None
        Current Speed: Unknown
        Type: Unknown
        Installed Size: Not Installed
        Enabled Size: Not Installed
        Error Status: OK
Handle 0x0010, DMI type 16, 15 bytes.
Physical Memory Array
        Location: System Board Or Motherboard
        Use: System Memory
        Error Correction Type: None
        Maximum Capacity: 8 GB
        Error Information Handle: Not Provided
        Number Of Devices: 4
Handle 0x0012, DMI type 17, 27 bytes.
Memory Device
        Array Handle: 0x0010
        Error Information Handle: Not Provided
        Total 64 bits
        Data 72 bits
        Size: 512 MB
        Form Factor: DIMM
        Set: None
        Locator: DIMM0
        Bank Locator: BANK0
        Type: DDR2
        Type Detail: Synchronous
        Speed: 533 MHz (1.9 ns)
        Manufacturer: Manufacturer0
        Serial Number: SerNum0
        Asset Tag: AssetTagNum0
        Part Number: PartNum0
Handle 0x0014, DMI type 17, 27 bytes.
Memory Device
        Array Handle: 0x0010
        Error Information Handle: Not Provided
        Total Unknown
        Data 64 bits
        Size: No Module Installed
        Form Factor: DIMM
        Set: None
        Locator: DIMM1
        Bank Locator: BANK1
        Type: Unknown
        Type Detail: Unknown
        Speed: Unknown
        Manufacturer: Manufacturer1
        Serial Number: SerNum1
        Asset Tag: AssetTagNum1
        Part Number: PartNum1
Handle 0x0016, DMI type 17, 27 bytes.
Memory Device
        Array Handle: 0x0010
        Error Information Handle: Not Provided
        Total Unknown
        Data 64 bits
        Size: No Module Installed
        Form Factor: DIMM
        Set: None
        Locator: DIMM2
        Bank Locator: BANK2
        Type: Unknown
        Type Detail: Unknown
        Speed: Unknown
        Manufacturer: Manufacturer2
        Serial Number: SerNum2
        Asset Tag: AssetTagNum2
        Part Number: PartNum2
Handle 0x0018, DMI type 17, 27 bytes.
Memory Device
        Array Handle: 0x0010
        Error Information Handle: Not Provided
        Total Unknown
        Data 64 bits
        Size: No Module Installed
        Form Factor: DIMM
        Set: None
        Locator: DIMM3
        Bank Locator: BANK3
        Type: Unknown
        Type Detail: Unknown
        Speed: Unknown
        Manufacturer: Manufacturer3
        Serial Number: SerNum3
        Asset Tag: AssetTagNum3
        Part Number: PartNum3
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在Memory Controller Information中，可以看到最大的内存大小是8G，支持内存种类为DIMM和SDRAM。
有四个Memory Slots。对应接下来的4个Memory Module Information。DMI type 16 (man
dmidecode里面有DMI TYPES specification)的意思是 Physical Memory Array。 这里也可以看出来，
最大支持内存为8G， 有4个内存设备。最后则列出具体的4个内存设备，其中发现了一个内存设备为512M，
类型Type：DDR2， 工作频率Speed: 533 MHz (1.9 ns)。这个就我目前电脑上的那根内存条。