背景
老 IBM X3650 （2009前后）机型（12条内存槽）的内存极限是48GB。
该机一共12条内存槽，其中：
1，4
7，10
2，5
8，11
3，6
9，12
分别组对。如果在某一对内存槽中插入不同容量的内存，比如插入2G，4G，则以容量小的为实际容量。
那么可以推理得到，如果一对内存槽中只插入1条内存，另一个对应的插槽空闲（No Module Installed），则以容量小的为实际容量，也就是0GB。
1. 据官方文档记载，老 IBM X3650 （2009前后）机型（12条内存槽）的内存极限是48GB。
- 常规模式就是这样：
hw.model: Intel(R) Xeon(R) CPU X5450 @ 3.00GHz
Signature: Type 0, Family 6, Model 7, Stepping 10
Signature: Type 0, Family 6, Model 7, Stepping 10
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB 官方文档推荐
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Range Size: 48 GB
- 官网手册：41Y5718.System.x3650.安装指南.pdf 第25页/页面编码11末段提到：
安装内存模块
以下注意事项描述服务器支持的双列直插式内存模块（DIMM）类型和安装DIMM 时必
须考虑的其他信息：
v 服务器支持多达12 个Fully Buffered DIMM，频率PC2-5300，容量为512 MB、1
GB、2 GB 和4 GB 不等，系统内存最大可达48GB。有关服务器可用的内存模块
的列表，请参阅http://www.ibm.com/servers/eserver/serverproven/compat/us/
- 官网英文手册：44r5190.System.x3650.Type.7979.Installation.Guide 第26页/页面编码12末段提到：
Installing a memory module
The following notes describe the types of dual inline memory modules (DIMMs) that
the server supports and other information that you must consider when installing
DIMMs:
v The server supports up to 12 Fully Buffered DIMM PC2-5300 512 MB, 1 GB, 2
GB, and 4 GB DIMMs, for a maximum of 48 GB of system memory. See
[url]http://www.ibm.com/servers/eserver/serverproven/compat/us/[/url] for a list of memory
modules that you can use with the server.
Note: Because some memory is reserved for system operation, the actual
usable memory size that is reported by the operating system is less than the total
installed size.
v The server comes with a minimum of two 512 MB DIMMs, installed in slots 1 and
4. When you install additional DIMMs, you must install two identical DIMMS at a
time, in the order shown in the following table, to maintain performance.
- 另有：老外的内存升级指南网站
https://www.memorystock.com/memory/IBMSystemx3650Type7979Server.html
- 上述url不能算官方文档吧，只是老外的内存升级指南网站。
The IBM System x3650 (Type 7979) Server Computer takes the PC2-5300 DDR2 240-pin Fully Buffered ECC SDRAM DIMMs. Must be installed in matching pairs. memory type, and comes installed with 1GB (Removable) memory.
How much memory does the IBM System x3650 (Type 7979) Server Computer take?
You can upgrade your IBM System x3650 (Type 7979) Server Computer to up to a maximum memory capacity of 48GB Memory.How many total memory slots to install memory?
The Computer has 12 Sockets (6 banks of 2) to install memory, already with 1GB (Removable) standard memory installed. For best System x3650 (Type 7979) Server Computer performance use the maximum amount of 48GB, fill all the slots with the max allowed memory per slot for your Computer.
以上手册中的链接均已失效。但pdf 仍可搜到/下到。
2. 经本人实测。该机型启动过程可以识别高达72GB内存。未测试更多，是因为手头没有这么多8G单条内存了）。
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
8
8
8
8
8
8
8 实测可识别并完成自检，系统无法正常工作
8
4
4
4
4
Range Size: 72 GB
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
3. 但上述第2部分提及的容量只是启动过程识别，实际并不能进入系统正常工作。包括后来测试了64GB也未能成行。
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
8
8
8
8
8
8
4 实测可识别并完成自检，系统无法正常工作
4
4
4
4
4
Range Size: 64 GB
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
个人猜测原因是：如果插入了大量的8GB单条内存，则必须保留最后2个编号为9，12 的插槽空闲。
否则主板bios 虽然能过检，但是在FreeBSD 内核加载完瞬间崩溃。
4. 本次实测该机型可以支持56GB 的FreeBSD系统正常运行。
实际插入内存组合方式排列如下：
hw.model: Intel(R) Xeon(R) CPU X5355 @ 2.66GHz
Signature: Type 0, Family 6, Model 15, Stepping 7
Size: 4 GB
Size: 4 GB
Size: 1 GB
Size: 1 GB
Size: 2 GB
Size: 2 GB
Size: 4 GB 实测可正常工作
Size: 4 GB
Size: 1 GB
Size: 1 GB
Size: 2 GB
Size: 2 GB
Range Size: 28 GBhw.model: Intel(R) Xeon(R) CPU X5355 @ 2.66GHz
Signature: Type 0, Family 6, Model 15, Stepping 7
Size: 4 GB
Size: 4 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Size: 4 GB 实测可正常工作
Size: 4 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Range Size: 32 GBhw.model: Intel(R) Xeon(R) CPU X5450 @ 3.00GHz
Signature: Type 0, Family 6, Model 7, Stepping 10
Signature: Type 0, Family 6, Model 7, Stepping 10
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB 官方文档推荐
Size: 4 GB 实测可正常工作
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB
Range Size: 48 GBhw.model: Intel(R) Xeon(R) CPU X5355 @ 2.66GHz
Signature: Type 0, Family 6, Model 15, Stepping 7
Size: 8 GB
Size: 8 GB
Size: 4 GB
Size: 4 GB
Size: No Module Installed
Size: No Module Installed
Size: 8 GB 实测可正常工作
Size: 8 GB
Size: 4 GB
Size: 4 GB
Size: No Module Installed
Size: No Module Installed
Range Size: 48 GBhw.model: Intel(R) Xeon(R) CPU X5355 @ 2.66GHz
Signature: Type 0, Family 6, Model 15, Stepping 7
Size: 8 GB
Size: 8 GB
Size: 8 GB
Size: 8 GB
Size: 4 GB
Size: 4 GB
Size: 8 GB 实测可正常工作
Size: 8 GB
Size: 4 GB
Size: 4 GB
Size: No Module Installed
Size: No Module Installed
Range Size: 64 GB
如果不购买单条8GB内存，并尽量利旧手头已有的单条4GB、2GB内存，得到的最佳性价比配置如下：
hw.model: Intel(R) Xeon(R) CPU X5450 @ 3.00GHz
Signature: Type 0, Family 6, Model 7, Stepping 10
Signature: Type 0, Family 6, Model 7, Stepping 10
Size: 4 GB
Size: 4 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB 实测可正常工作
Size: 4 GB 不采购单条8GB内存前提下的最佳性价比配置
Size: 4 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Size: 2 GB
Range Size: 32 GB
5. 最后实际运行的最佳性价比内存模型如下：
hw.model: Intel(R) Xeon(R) CPU E5405 @ 2.00GHz
Signature: Type 0, Family 6, Model 7, Stepping 6
Signature: Type 0, Family 6, Model 7, Stepping 6
Size: 8 GB
Size: 8 GB
Size: 4 GB
Size: 4 GB
Size: 4 GB 花最优化的费用（尽量少购买单条8GB内存）
Size: 4 GB 并尽量利旧手头已有的单条4GB内存
Size: 8 GB 实测可正常工作
Size: 8 GB
Size: 4 GB
Size: 4 GB
Size: No Module Installed
Size: No Module Installed
Range Size: 56 GB
此处所谓最佳性价比，指的是花最优化的费用（尽量少购买单条8GB内存），得到较大的内存容量，并尽量利旧手头已有的单条4GB、2GB内存。
