Boy, Cyberspace is basically more or less of a sanctuary for "dead reploids" (See Phantom).
The ability to live in Cyberspace is unique to Phantom and Cyber Elves. A regular Repliroid soul has no existence outside of a body, it is simply becomes part of the data stream, like a Cyber Elf that runs out of energy and dies.
It's been used for troop transfer, quick shortcuts, and epic battles because of the such large space.
What ARE you talking about?
Its the same as the one from X4.
The opposite. It's completely different. ZERO4 emphasized the difference quite clearly. ZERO3's Cyberspace is the program world that encompasses all substance world phenomena in the form of a program. What you see in Xtreme, X4, X7, ZERO4 is instead a manmade program world, accessible through teleportation.
And that's where data of old bosses is stored (
This data is simply stored in the Mother Computer.
if Reploid souls are data
A Repliroid soul is a Repliroid's operational DNA program. It is synonymous to a personality program, to a Cyber Elf.
And how come reploids still living can enter it?
The ZERO3 Cyberspace is accessible thanks to the resonance between Omega and Dark Elf causing the appearance of those doors. The other Cyberspace is accessible by teleportation, as teleportation turns the user into data.