computer bus speeds explained
how fast is your system bus?

Published: 18-Nov-2000 (updated 6/1/2001)

Now that you have learned about network speeds (see article) we can examine the common ways network interfaces and other devices link into the computer.  By examining the maximum throughput of various interfaces like ISA, PCI, and USB, we can determine what network interfaces are inappropriate for certain bus's.  By comparing the speeds in this article with the network speeds article, you will get a good idea of how fast devices talk to your computer.

Bus Speed Chart

BusName	Width	Speed*/Sec
SCSI-1		5 Mbytes
ISA	8bit, 8Mhz	8 Mbytes
SCSI-2		10 Mbytes
PCMCIA	16 bit, 10 Mhz	20 Mbytes
IDE DMA33		33 Mbytes
Ultra2 SCSI		40 Mbytes
IDE DMA66		66 Mbytes
PCCard	32 bit, 33 Mhz	132 Mbytes
PCI 2.0	32 bit, 33 Mhz	132 Mbytes
PCI 2.1	64 bit, 33 Mhz	264 Mbytes
PCI 2.2	64 bit, 66 Mhz	528 Mbytes
Serial	1 Bit	115 kbit
Parallel Port	8 Bit	115 kbit
USB 1.0  (standard USB)	1 Bit	1.5 MBytes 12 Mbits
Firewire (IEEE 1394)	Serial	12.5-50 MByte 100-400 Mbit
USB 2.0	Serial	60 MBytes 480 Mbit
Firewire (IEEE 1394b)	Serial	25-100 MBytes 200-800 Mbit

Ethernet NIC's and the ISA bus :  Some manufacturers actually sell 100Mbps Ethernet cards for an ISA BUS.  As you can see from the chart above, the ISA bus will max out at 8MBytes/sec.  8MBytes/sec is the theoretical maximum you could ever get from a 100Mbps LAN card plugged into the ISA bus! 

computer bus speeds explained
how fast is your system bus?