But I'm not using a NIC, soundcard, modem, video capture card or in fact *anything* else while doing these tests. Neither will IBM be. So what's soaking up the remaining bandwidth?
Also, you'll notice that hard drive rotation speeds are increasing. Most are (or used to be) 5400rpm, now we're seeing 7000rpm or so, even 10000rpm on some. The increased rotation speed gives faster data transfer. If the hard drives were already being throttled by the bus, why on earth would they bother to rotate them faster? After all, the bus is already maxed out, so they can't send any more data! Conclusion: The bus *isn't* maxed out, it's still the hard drive that's the limitation.
As for not quoting theoretical specs - why not, everybody else does. I could quote CDROM drives for a start. Technically, a 50X drive can transfer 7.5MB/sec, but it won't. The only time it's ever come near to that is in the manufacturers labs.
BTW, if you look at SCSI drives they bear out the same story. Ultra2 SCSI offers 80MB/sec transfer rate. The Ultra2 SCSI hard drive I looked at transfers data at 40MB/sec. Now, SCSI has its own bus - you can copy data from one SCSI device to another without the data ever touching the PCI bus or the CPU. So if hard drives are throttled by the bus, why on earth can't the SCSI drives (which in basic physical construction are the same as their IDE equivalents) max out at the bus maximum?