IBM System x3755 M3 7164 Installation And User Manual page 26

The server supports up to 512 GB of system memory when registered DIMMs
are installed. The server supports up to 128 GB of system memory when
unbuffered DIMMs are installed. The memory controller supports error correcting
code (ECC) for up to 32 industry-standard PC3-10600, registered or unbuffered,
DDR-3, synchronous dynamic random access memory (SDRAM) dual inline
memory modules (DIMMs).
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IBM System x3755 M3 Type 7164: Installation and User's Guide