The original PS3 release is roughly in size. Because of the way the PS3 handles digital installations, you generally need at least 16 GB of free space to download and install the digital version simultaneously. How to Play Demon's Souls (PS3) on PC - RPCS3 Guide

For fans of the "Soulsborne" genre, the original on the PlayStation 3 remains the definitive starting point. Whether you are looking for the original PKG file for a jailbroken console or setting it up for high-definition emulation, this guide covers the essential technical details for the classic that started it all. 1. Demon’s Souls PS3 : Technical Specifications