How many DIMM slots are available and what type of memory does it support?

The motherboard has 4 DIMM slots (2DPC) and supports DDR5 ECC UDIMM.

What type of processors does the ASRock rack EC262D4U-2L2T support?

The ASRock rack EC262D4U-2L2T supports Intel® Xeon® 6300-series, Xeon® E-2400 series, and Pentium® Gold G7400/G7400T processors.

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ASRock rack EC262D4U-2L2T Micro-ATX Server Motherboard, Intel® Xeon® 6300-series, Xeon® E-2400 series, and Pentium® Gold G7400/G7400T processors

Micro-ATX (9.6" x 9.6")
Supports Intel® Xeon® 6300-series, Xeon® E-2400 series, and Pentium® Gold G7400/G7400T processors
4 DIMM slots (2DPC), supports DDR5 ECC UDIMM
1 PCIe5.0 x16, 1 PCIe4.0 x4, 1 PCIe4.0 x1
2 OCuLink
Supports 1 M.2 (PCIe4.0 x4)
Up to 8 SATA 6Gb/s
2 RJ45 (10GbE) by Intel® X710
2 RJ45 (1GbE) by Intel® i210
Remote Management (IPMI)