8 GB of RAM is highly recommended. If you only have 4 GB of RAM there are serious limitations: you cannot always run multiple engines (this depends on which engines and their settings), you cannot run Scan with 6 piece endgame databases (Scan loads endgames into memory which requires 2 GB), and you sometimes cannot use the 8 piece endgame databases.

SSD is recommended, especially if you are using 7 and 8 piece endgame databases.

Core i5 (or higher) is recommended. Fast processor is needed to run multiple engines, and to enjoy the new instant analysis option.