If you have a laptop an external is your only option, but they are slower than internals (unless it's an eSATA or USB 3.0) and have more latency issues. It only stands to reason. An internal sound card's speed is dictated by the type of card (a PCI utilizing the IDE or SATA) which is connected directly to the motherboard on one of the internal slots and will have a minimum of 133 MBs speed, much better than USB 2.0 or Firewire 800.
Almost all new computer desktops are now utilizing SATA or SATA 2 connections to the motherboard, rather than the old IDE, which is still faster than Firewire 800 or USB 2.0.
Anyways, the facts are these, from slowest to fastest:
* USB 1.1 = 12 Mbs (which is the same as 1.5 MBs)
* Firewire 400 = 400 Mbs (50 MBs)
* USB 2.0 = 480 Mbs (which is the same as 60 MBs)
* Firewire 800 = 800 Mbs (100 MBs)
* Conventional internal IDE, now known as Parallel ATA or PATA => 133 MBs, but can go higher if SATA connections on motherboard go to internal slots (see below).
* Serial ATA (SATA 1) = 150 MBs
* SATA 2 = 3 Gbs (300 MBs)
* Ultra SCSI = 320 MBs
* USB 3.0 = 3.2 Gbs (realistically achieving 400 MBs) theoretically higher up to 5 Gbs.
* SATA 3 = 6 Gbs (600 MBs)
* Firewire's future 6.4 Gb/s (768 MB/s)
NOTE: To turn Megabits/second (Mbs) into MegaBytes/second (MBs), divide by 8.