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How can a serial interface be faster than a parallel one?

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Newbie level 5
Feb 19, 2003
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Serial vs Parallel.


I'm wondering how could a serial interface be faster than a parallel one. For example, the USB 2.0 supports a high speed of 480Mb/s which is much faster than the Parallel port transfer rate, although logically transfering the data in parallel should be faster than in series.


The reason that newer faster bus designs use serial is the cable cost. It costs less overall for the cable to have one high quality set of wires and have the silicon at each end run faster. Another aspect hs the small size of the connetctors which is a big aspect of makng portable computers smaller.

The lesson was learned in the old days on the SCSI bus system.

The trick is in differential mode. The faster serial buses like USB, firewire, ethernet etc all use differential pairs for data. Differential mode offers a lot more noise rejection besides cancelling rise / fall time delays.

If a parallel bus is designed with differential signal, it would be too expensive. But you can get very high data speeds. But as Flatulent said, serial means cheaper cable and cheaper connector. With speeds ever rising, I double we will revert back to parallel buses soon.

Re: Serial vs Parallel.

All of the newer high speed serial interfaces employ low voltage differential signals. This, combined with high current drive, enables reliable operation at very high data rates.

As data rates keep increasing, it becomes critical to match the conductor lengths within a parallel bus to prevent skewing between bus signals due to differences in propagation delays. At some point it is no longer practical to try to match the conductor lengths, and the only way to reliably get higher data rates is via serial bus.

Serial vs Parallel.

USB uses a much faster clock frequency than the traditional parallel port.

Re: Serial vs Parallel.

Will anybody plz indicate useful sites for usb programming..

Re: Serial vs Parallel.

yousafzai said:
Will anybody plz indicate useful sites for usb programming..

This is a bit offtopic but look here:

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