Memory for Servers DDR4

Memory for Servers - DDR4 ECC 16gb
Memory for Servers - DDR4 ECC 8gb
Memory for Servers - DDR4 ECC Registered 16gb
Memory for Servers - DDR4 ECC Registered 32gb
Memory for Servers - DDR4 ECC Registered 64gb
Memory for Servers - DDR4 ECC Registered 8gb

What is the difference between a Windows / Dos / Ubuntu Laptop ? Which One Should I Buy ?

Windows, Dos or Ubuntu are basically operating systems, software part of the laptop. It is just that Genuine Windows Come at a Price ( say around Rs.5000) So Laptops with Windows Pre-loaded are a few thousands more expensive than the laptops which do not come with windows pre-loaded.