How much memory and storage does this desktop include?

It comes with 16 GB DDR5 memory in a 1 x 16 GB configuration running up to 4800 MT/s, and a 256 GB SSD TLC drive.

What processor does this Dell Pro Slim Essential QVS1260 Desktop use, and how powerful is it?

It uses an Intel Core i5-14500 vPro processor with 14 cores and a maximum turbo speed of up to 5.0GHz.

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Dell Pro Slim Essential QVS1260 Desktop - Intel Core i5-14500 - 16GB - 256GB SSD - Windows 11 Pro - Intel UHD Graphics 730 - 180W - GK4HK