A very basic question on RAM

Sets are supposed to have been tested together in a system and proved to work without errors and met the manufacturer's stated specifications.

+1^
Also, manufacturers are free to change the components and chips used to manufacture their ram. Over time, it is possible for two sticks with the exact same part number to be manufactured entirely differently. Some motherboards, particularly older ones can be very sensitive to this.

A ram vendor will only guarantee the performance and functioning of kits, not a mix of separate purchases.

In most cases there is no issue, but be forewarned to buy kits when you can.

Thats very helpful .
Thanks for the info.