How much memory and storage does this desktop include?

It comes with 8 GB DDR4-2666 MHz RAM and a 256 GB PCIe NVMe TLC M.2 SSD.

What processor does this HP ProDesk 600 G6 desktop use, and how fast can it go?

It uses an Intel Core i5-10500T 10th Gen processor with a 2.3 GHz base frequency and up to 3.8 GHz with Intel Turbo Boost Technology.

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HP ProDesk 600 G6 Intel Core i5-10500T 2.3 GHz up to 3.8 GHz 8GB DDR4 256GB SSD Intel UHD Graphics 630 Windows 11 Pro Desktop, Black - 2F0Z2UP

Intel Core i5-10500T (2.3 GHz base frequency, up to 3.8 GHz with Intel Turbo Boost Technology, 12 MB L3 cache, 6 cores)
Intel UHD Graphics 630
8 GB DDR4-2666 MHz RAM
256 GB PCIe NVMe TLC M.2 SSD
Windows 11 Pro