[ryanfx]

1). 20GB has no chrome trim, no memory card reader and no wi-fi. Not manufactured anymore. Has the best backwards compatibility with PS2 games due to Emotion Engine (PS2's CPU) and Graphics Synthesizer (PS2's GPU) installed.
2). NTSC 60GB has the same backwards compatibility as 20GB version, also has memory card reader and wi-fi. Has a chrome trim. Not manufactured anymore.
3). 80GB - extended memory, but reduced backwards compatibility with PS2 games, it has only Graphics Synthesizer (PS2's GPU). Around 60-80% of PS2 games can be played. Available only in NTSC regions.
4). 40GB - can't play PS2 games at all (all PS2 chips were removed), has 2 USBs instead of 4, no memory card reader, has wi-fi. Avalable in black and white colors. White is on sale only in Japan. Uses 65nm technology (lower power consumption). Improved cooling system. It's the latest version. 40GB doesn't support SACD (Super Audio Compact Disc).
5). PAL 60GB - reduced backwards compatibility with PS2 games. it has only Graphics Synthesizer (PS2's GPU). Around 80% of PS2 games can be played.
Wi-fi included in all models, except 20GB.
They are all based on Blu-ray. They all play PS1 games.