Memory
See 
“Memory module installation rules and order” on page 39 for detailed information about memory configuration and 
setup.
•  Slots: 24 dual inline memory module (DIMM) connectors that support up to: 
–  24 RDIMMs
•  Memory module types: 
–  TruDDR5 RDIMM: 16 GB (1Rx8), 32 GB (2Rx8), 64 GB (2Rx4 10x4)
•  Speed: Operating speed depends on processor model and UEFI settings. 
–  Maximum speed: 4800 MT/s
•  Minimum memory: 16 GB
•  Maximum memory:  
–  RDIMM: 1.5 TB: 24 x 64GB RDIMMs
For a list of supported memory options, see 
https://static.lenovo.com/us/en/serverproven/index.shtml. 
Internal drives
Front:  
•  Up to eight 2.5-inch hot-swap SAS/SATA drives
•  Up to ten 2.5-inch hot-swap AnyBay (SAS/SATA/NVMe) drives
Inside:  
•  Up to two internal SATA M.2 drives
Expansion slots
Depending on the model, your server supports up to three PCIe slots in the rear. 
•  PCIe x16, low-profile
•  PCIe x16/x16, low-profile + low-profile
•  PCIe x16/x16, low profile + full-height
Integrated functions and I/O connectors
•  Lenovo XClarity Controller (XCC), which provides service processor control and monitoring functions, video 
controller, and remote keyboard, video, mouse, and remote drive capabilities. 
–  The server supports Lenovo XClarity Controller 2 (XCC2). For additional information about Lenovo XClarity 
Controller 2 (XCC2), refer to 
https://sysmgt.lenovofiles.com/help/topic/lxcc_frontend/lxcc_overview.html.
•  One XCC system management port on the rear to connect to a systems-management network. This RJ- 
45connector is dedicated to the Lenovo XClarity Controller functions and runs at 1 GB speed.
•  A group of two or four Ethernet connectors on OCP 3.0 module
•  Up to four USB 3.2 Gen1 (5 Gbps) ports:
–  Three on the rear of the server
–  One on the front of the server
note
.
•  One USB 2.0 port on the front of the server
note
.
•  Up to two VGA connectors
–  One on the rear of the server
–  (Optional) One on the front of the server
note
.
Note: Available when the front I/O module is installed in the server.
Network
OCP 3.0 module on the rear of the server
4 ThinkSystem SR645 V3 User Guide