The EFI technology component that allows the full utilization of drives greater than 2.2TB is called the GPT, or the GUID (Globally Unique IDentifier) Partition Table. GPT replaces the older MBR (Master Boot Record) scheme (which is subject to the 2.2TB limit) and allows partitions of up to 9.2 zettabytes (2^70)--a large, barely comprehensible number. Windows XP and later versions of the OS support GPT, but, again, only 64-bit Vista and 7 support it during the boot process.
While Windows systems suffer from the MBR's constraints, Macs and 64-bit Linux machines have no issues using or booting from 3TB drives. Apple has supported EFI/GPT since it switched to Intel CPUs. Most 32-bit Linux distributions also support 3TB drives, without requiring an EFI/UEFI BIOS.
You can use the full capacity of a 3TB drive via USB--with a drive enclosure that supports it. The SATA-to-USB bridge chip inside the enclosure takes care of any addressing issues. This is why the first 3TB drive shipped last summer as an external model--a switch from the usual pattern of internal units shipping first.
Although you shouldn't have any issues attaching a prepackaged 3TB external drive, you may have problems if you buy a 3TB internal drive and try to add it to a USB-connected enclosure yourself. Read the fine print: Many of the bare enclosures say they support 3TB, but not all of them do.
Installing a 3TB Drive
If you have 64-bit Vista, 64-bit Windows 7, a Mac, 64-bit Linux, or in some cases 32-bit Linux, check to see if your system's BIOS supports 3TB. If doesn't, you'll need to obtain a BIOS update or to buy a newer motherboard that supports 3TB.
If you already have a 3TB drive, you can check to see whether that drive is being properly recognized by booting up the system and looking in the BIOS to verify that the capacity is correctly reported. For operating systems that don't support booting from 3TB, you'll need to boot from a smaller drive and use the 3TB drive as auxiliary storage. Perform the same BIOS check, and then download and employ any required drivers and/or partitioning software the drive maker supplied. If you use third-party partitioning software, make sure to use the GPT, not MBR, partitioning scheme.