Xfrom

XFROM was a DEV9 subsystem that consisted of a memory card flash memory attached to the SPEED chip.

It was only seen in a functional state inside the PSX. It used the same chip brand and model than normal memory cards. However, the driver for XFROM has code for handling chips of 8, 16, 32, 64 and 128mb. As seen on the following Driver based on reverse engineering

SCPH-5xxxx also have the drivers to access it (rom0:XFROMMAN & rom0:XFLASH) and the OSDSYS was updated to upload these drivers to the IOP and look for updates on XFROM following the same path convention that memory card updates.

yet there was never found a compatible SPEED chip inside any of the network adapter versions