[quote name='galvatron2k1']480p DVDs... ok, I can see that for some people. But the phat came out before the slim. So, the upgrade removed some features. But if you bought it initially, there would be no reason to upgrade.[/QUOTE]
The PS2 went through 10 different revisions. Each one improving from the last.
"Three of the original PS2 launch models were only sold in Japan, and lack the Dev9 expansion port of current PS2 models. These versions were SCPH-10000, SCPH-15000 and SCPH-18000. These included a PCMCIA slot instead of the Expansion Bay (DEV9) port of newer models. A PCMCIA to Dev9 adapter was made available for these models. SCPH-10000 and SCPH-15000 did not have a built-in DVD player and instead relied on an encrypted player that was copied to a memory card from an included CD-ROM (normally, the PS2 will only execute encrypted software from its memory card, but see PS2 Independence Exploit). V3 has a substantially different internal structure from the subsequent revisions, featuring several interconnected printed circuit boards. As of V4 everything was unified into one board, except the power supply. V5 introduces minor internal changes and the only difference between V6 (sometimes called V5.1) and V5 is the orientation of the Power/Reset switch board connector, which was reversed to prevent the use of no-solder modchips. V7 and V8 are also similar. Assembly of the PS2 moved to People's Republic of China with the V9 (model number SCPH-50000/SCPH-50001), which added the Infrared port for the optional DVD Remote control, removed the FireWire port, added the capability to read DVD-RW and +RW discs, added progressive-scan output of DVD movies, and a quieter fan. V10 and V11 have minor changes."