How Rockstar fit an entire city into PlayStation 2 memory

TL;DR

Rockstar used real-time asset streaming to load only nearby city sectors into the PS2's 32MB RAM, creating the illusion of a full open world.

Key Points

• 1.The core problem was fitting 130MB of city data into 32MB of RAM. Liberty City's models and textures totalled ~130MB across three islands, with even one island (Portland) requiring 40–50MB alone — far exceeding the PS2's memory chip.
• 2.Technical lead Adam Fowler invented a streaming system that loads only nearby sectors. An invisible square around the player defines which assets are held in memory; as the player moves, new assets stream in from the DVD while old ones are silently deleted.
• 3.LOD (level of detail) solved pop-in by using low-polygon stand-ins for distant structures. Far-away buildings, bridges, and even other islands render as simplified imposters that fade into full models as the player approaches, saving significant memory.
• 4.A strict pool of only eight vehicle types in memory at once explains GTA 3's repetitive traffic. Cars not in those slots are ejected; whichever car you're hunting suddenly seems everywhere because it now occupies one of those eight slots.
• 5.Adam Fowler wrote a custom memory manager to combat fragmentation. He also standardised hundreds of asset file sizes (500+ files at exactly 2KB, 416 at exactly 4KB) so assets could slot into vacated memory gaps without leaving unusable holes — and stress-tested it by running dev kits overnight on the Portland train loop.
• 6.DVD seeking was a major bottleneck, so assets were physically arranged on the disc by city location. The disc reader prioritises assets near its current laser position rather than queuing order; common models like lampposts were even duplicated at multiple disc locations to reduce seek travel — a technique still used in Spider-Man on Blu-Ray.
• 7.To prevent players outrunning the streaming system, Rockstar secretly slowed the game down. Cars had a speed cap, air resistance was quietly increased in some areas, flying vehicles were banned, and a large building was placed in Portland's main drag — with GTA IV later using roadworks on Algonquin's longest road for the same reason.