PCI 속도에 대하여 질문드립니다.

Gigabit Ethernet
1000^3 bits/sec = 1,000,000,000 bits/sec
1,000,000,000 bits/sec / 8 = 125,000,000 bytes/sec
125,000,000 bytes/sec / 1024 = 122070.3125 Kilobytes/sec
122070.3125 Kilobytes/sec / 1024 = 119.20928955078125 Megabytes/sec

Fast Ethernet
100,000,000 bits/sec / 8 = 12,500,000 bytes/sec
12,500,000 bytes/sec / 1024 = 12207.03125 Kilobytes/sec
= 11.920928955078125 Megabytes/sec

Bus bandwidth < 여기서 나오는 속도들은 도대체 어떤 수식에 의해서 계산되는거죠?
32-bit/33 Mhz PCI ---> 127.2 MB/sec
64-bit/33 Mhz PCI ---> 254.3 MB/sec
64-bit/66 Mhz PCI ---> 508.6 MB/sec
64-bit/133 MHz PCI-X ---> 1017.3 MB/sec

Single disk transfer rates
SCSI Seagate X-15.3 (15,000 RPM) STR --> beginning: 76.4MB/s end: 51.1MB/s
SCSI Seagate X-15 - 36 LP (15,000 RPM) STR --> beginning: 60.5 MB/sec end: 45 MB/sec
ATA Western Digitial's Caviar WD1000JB (7200 RPM) STR --> begginning: 43.8 MB/s end: 27.9 MB/sec