NIC is the abbreviation for Number In a Can. Dallas Semiconductor which today is part of Maxim Integrated Products chose this perhaps not very fortunate name to describe the iButton 1-wire devices used for hardware identification on Origin, Octane and later systems. Most later "NICs" are not really metal cans, but small 6-pin SMD chips, usually DS2505 ones (the exceptions are MAC NICs on IP27 systems and IOC3 MENET and PCI cards, which use DS1981U NICs and IP30 systems which use a DS2502).
A NIC contains a 64-bit unique address that is used to identify it inside a system and possible some OTP (One-Time Programmable) EPROM. The unique address is not used for anything by SGI software. However, the OTP memory contains important information on the device containing the particular NIC:
- 6 bytes at 0x05: serial number in ASCII
- 9 bytes at 0x15: part number in ASCII (xxx-xxxx-)
- 3 bytes at 0x23: revision in ASCII (xxx)
- 10 bytes at 0x34: readable name of the device (in ASCII, naturally)
Each 32-byte page of the device is protected by a 16-bit CRC in accordance with Dallas recomendations. Also, the page redirection table is used by SGI to keep track of hardware revision updates (very prominent on early IP30 system boards, as there is a hand-soldered wire running over the whole board).