(This is my neck of the woods)
To understand PSX file formats you kind of have to know how the PSX was designed. Waaay back when Nintendo wanted to make a cheap CD-ROM add on to the SNES, the asked Sony, one of the biggest manufactures of CD-ROMs at the time to come up with a *low cost* soultion to thier problem. What came out of Sony's R&D was a cd-rom based off of thier sony diskman technology. It was low-cost, worked well, and had perks for being very compact. Sony did something a little different, they added a microcontoller to the actulal "drive" part thereby making an interface card unneccasary, and making the thing even cheaper to produce. When the big N screwed Sony by creating a secret bidding war against the american company Phillips (makers of CD-i) and the fact sony wanted say on what games would be published for the SNES CD system. N dropped the idea of a CD-ROM system and payed dearly with the N64.
Meanwhile. Sony had this really cool CD-ROM system with no seller. So they decided to make thier own game system. Now the PSX didn't come out of thin air. Sony was actully already making the pre-PSX system board for Namco's "Tekken" arcade systems. It was called a "System 11 board" and already had the MIPS R3000, a primitive MDEC, GPU and the GTE (an older one with some opcodes missing) It used hard ROM chips for programs. Because the new Sony CD-ROM didn't require a controller card, they basicly opened a memory address in the hardware resisters, plugged in the CD-ROM, added memcards, did a little magic with DMA and did an all-around chipset upgrade and *POW* instant PSX. That's why it looked like it came out of nowhere.
Now This is where file formats come in. You see, tekken (The ROM arcade version) used the TMD file format models and TIM for textures (TMD stands for Tekken MoDel and TIM is Tekken Image Map or Texture Image Map) Because it was already in use with the arcade it bacame the de-facto standard for PSX devopment. When Psynogsis made PSY-Q they incorperated those formats into the dev kit. Sometimes the format needs to be changed to 1) make it harder for hackers such as ourselves to easly extact the models and 2) improve upon the functionality that the TMD/TIM formats offer. In the case of metal gear solid, Konami had to toss a good 90% of the dev libs because they simply were too differnt than what they needed. MGS, by the way, moves vertexs around a bone structure, not whole polygons, like the TMDs.
I might as well add this. I guess you guys are wondering how on earth I know so much about things like this. Might was well tell you guys now. I used to work for Namco. Nothing glorous, just arcade repair. So I know of the PSX's humble beginnings. (And so much about it now) If you think I'm pulling a Joey, feel free to think that. This is the last time I'm going to mention my employment with them. (Due to the fact that the Namco part that makes games and the Namco part that does arcades only share the name and the bank account, Namco doen't want arcade dudes such as myself to use the term "I work for namco" to get them in places where they shouldn't be)
