PlayStation 2 Expansion Bay

The PlayStation 2 Expansion Bay is a 3.5" drive bay introduced with the model 30000 and 50000 PlayStation 2 (replacing the PCMCIA slot used in the models 10000, 15000, and 18000, and no longer present as of the model 70000) designed for the network adaptor and internal hard disk drive (HDD). These peripherals enhance the capabilities of the PS2 to allow online play and other features that were shown at E3 2001.
Network Adaptor.
The Network Adaptor was released together with the launch of the PlayStation 2 Network Play service. Two models of the adapter were available - one with a dial-up modem and an Ethernet jack for broadband Internet connection (sold in North America), and one with only an Ethernet interface (sold in Europe and other regions). A start-up disc ("Network Access Disc") is included with the Network Adaptor and installs a file on the memory card for connection settings which are accessible by all but one Network Adaptor compatible game. "Tony Hawk's Pro Skater 3" was released in November 2001 and supported the Network Adaptor hardware, but not the software as it was not finalized until much later.
The Network Adaptor also provides a Parallel ATA interface and a Molex disk drive power connector to allow installation of a 3.5 in IDE hard disk drive in the expansion bay. As the two disk connectors are on separate circuit boards from the main Network Adapter one, third party connector replacements including a SATA connector and SATA to IDE converter are available.
Slimline PlayStation 2 models have an ethernet port built-in, but no official hard disk drive interface. However, the first slimline model (SCPH-70000) has a complete Network Adapter onboard (including an analog modem in the earliest North American models), and may be modified to add an external IDE connector board.
From the SCPH-75000 series onwards, Ethernet functionality was integrated into the I/O Processor (which was completely internally redesigned), completely removing the disk interface.
The maximum supported rate is 100Mbit/s, at full duplex. It is also backwards compatible with 10Mbit/s hardware and configurations.
Hard disk drive.
The PlayStation 2 Hard Disk Drive (PS2 HDD) was released on July 19, 2001 in Japan (together with the Network Adaptor) and on March 23, 2004 in North America. It requires the Network Adaptor to connect to the PlayStation 2 and to receive power. The HDD has a 40 GB capacity that can be used by games to reduce load time by putting data on the hard drive temporarily, or back up memory card data. Due to MagicGate copyright protection, programs that are bootable directly from the HDD (e.g. PlayStation Broadband Navigator, PlayOnline Viewer, Pop'n Music Puzzle-dama Online) are keyed to the system when that system installs them. The HDD can be transferred to another PlayStation 2 system and files on the HDD can be accessed, but those specific programs cannot be booted without being reinstalled. Contrary to popular belief, a complete reformat of the HDD is not necessary upon transfer of the HDD between consoles, or else it would not be useful to have the HDD be preformatted and have preinstalled software, as is the case with the North American HDD unit. An HDD Utility Disc is included to allow maintenance of the HDD (including defragmentation, disk repair and formatting utilities, along with a file manager browser) and in North America, "Final Fantasy XI" is also included. There are 35 North American games that support the HDD.
Maxtor and Seagate Technology produced hard drives used in these kits.
Unofficial software called HD Loader (later also HD Advance and Open PlayStation Loader) allow users to copy entire games to the HDD and run them without the discs. They also allow using some standard consumer hard drives in the PS2, however they will not be compatible with software that is expecting the standard PS2 hard drive. This software combined with a hard drive allows one to play games without using the original disc. This is desirable as it protects the fragile and perhaps rare game discs from harm, in some cases it may improve performance. However, the practice is not without controversy. HDLoader bypasses the usual copy protection mechanisms built into the console, allowing for piracy.
Linux kit.
The Linux Kit for PlayStation 2 was released in 2002 and included the PlayStation 2 Linux software, keyboard, mouse, VGA adapter (which requires an RGB monitor with sync-on-green), Network Adaptor (Ethernet only) and a 40 GB hard disk drive. It allows the PlayStation 2 to be used as a personal computer.
Hacking and modding.
As of mid 2010, it is possible to install and use the PlayStation BB Navigator (PS-BBN) and the HDD-OSD (HDD Utility-Disc) on every PlayStation 2 Console from every region. This can be achieved with the use of special "patched" files for the HDD-OSD, PS-BBN, and a modified version of "uLaunch" (a well known piece of PlayStation 2 homebrew software) called "hacked-ule". It is now also possible to install homebrew software to the HDD and make it launchable through the HDD-OSD and PS-BBN's "Game-Channel", just like any other official HDD game. However, installing such homebrew software to the HDD still requires much work in a Hex-Editor. PS-BBN can now also be fully translated into any given language; the translation process involves the use of the "Beta-linux" release for PlayStation 2 and a specially compiled kernel which gives access to the "APA-ReiserFS" partitions.
As of 2013, most (if not all) games that use the HDD to install data (to decrease load time) and/or to save/load (instead of using a Memory Card) can be used on any PlayStation 2 console from any region and on any HDD by using a Hex-Editor (or ATADPatcher v0.02) and some type of booting software "ESR" (a well known piece of homebrew software for the PS2). If a "patched" copy of HDD-OSD and/or PlayStation BB Navigator (PS-BBN) is used, users can see all the data currently installed in the same way as with the official "SONY 40 GB HDD" (SCPH-20401).