what do you mean no swapping? so your saying you cant stream off the cd/dvd/gd? this is how its done in most modern games. the trick is to make the sections overlap enough so that while your loading the new data, the player can still see stuff. just look at shenmue2, they had TONS of npcs most with different textures and models (yes even the generic ppl). shenmue''s engine handled this by fading them in. distracting yes, but effective. the world data on the other hand (also quite detailed) never had the fading problem, but you knew the dc was always loading stuff due to the drive noise. though at many points shenmue required load screens (which were not too long). this was acceptable because the chunks were large and the next area ussually used an entirly different texture set and npcs. though i am ranting abit (shenmue2 is such a grand view of the power of the dc).

now on to things to consider. in a racing game, you can do this (gta3 does it) as well, just a bit more complex. in gta3, you will notice the change form high detail from lower detail when you transition through certain blocks. its very difficult to make it completly transparant. you have to deal with the dirve seek time and read speed. also you will have to stream the data while you render. the best way would be to break up the sections by visiblity. try to have obsticales that will hide some of the next section so that while your loading it, the player wont notice. also try to orgainze your sections so that they have the data close to a section transition at the begining. you may have to duplicate your data on the disc for optimal reading. which wont be much of a problem when dealing with dvds on ps2 or gamecube.

rolling yoru own level mangemnet system will probally be faster then relying on an os level one (mainly because you KNOW what data will be needed next and can premptivly start a load when the player gets close). i suggest testing these ideas on a pc with the data on a cdrom or with file functions that artifical mimick the read speed you will have (dont make it a perfect read speed either). this will help work out the bugs.

btw when you split the data you dont have to use seperate files. just ensure that things are ordered nicely. you could theorectically stream the level at all times, and only have some problems if the player does a quick 180 (like in gta3). basically you need some priority for the data. for instance npc models behind the player, that cant harm the player, should be unloaded if the player is moving forward for a certain amount of time. this will help keep down watsed ram on things that dont need to be kept track of. now in gta3, the level never faded in too much (ie from a 180) but at times it was noticable when turing at certain sections. lower quality textures and models may be used to reduce this. ie use the lower quality stuff when you begin caching the level so you progressivly load things like a progressive jpg. low->med->full detail.

Just one comment, if you are going to be streaming stuff in and out, you need to consider dynamic objects in your world that get initialised before they are actually visible, or if your game is such that you will be leaving locations and returning to them, objects that need to correctly react with the world in the interem.

Gibberish explained by example: Say you have an object that does collision detection with the world, and you go and (literally) stream the world out from under it''s feet, is it gonna get stuck somewhere rediculous when the geometry gets streamed back in, or maybe fall through the world while it''s geometry is unavailable for collsion tests?

Not a problem if your game world consists purely of static physical objects, but if you are trying to simulate a slightly more lively world it may be.

Well, we had the problem that objects just ''disappeared'' out of the world, and we realised that this was the problem.. solution, make them inactive while their block is not streamed into mem.