how different USB standards manage different speed

[titan_amit]

I know this may be a stupid question but i am unable to find an answer to this.I wanted to know what is the reason that different versions of USB have different speed though they more or less follow the same protocol(by protocol i mean that they have effectively same overhead). For example in the case of full speed and high speed USB max data that can be transmitted in a frame are 1023 and 1024 respectively but they have a considerable difference in their speed(which are 12 Mbps and 480 mbps respectively). Can you also please tell me the reason for the dramatic increase in speed of super speed USB.

[Jan Axelson]

Low speed is for peripherals such as mice and keyboards that don't need anything faster and might benefit from the more flexible cable allowed for low speed (though the requirements were tightened with USB 2.0.)

Full speed was designed to compete with the existing serial and parallel interfaces of that era (mid 1990s).

As demand grew for a faster interface, USB 2.0 was developed to use the highest speed possible while keeping the same connectors and cables as USB 1.x.   

SuperSpeed uses a different hardware interface and low-level protocols, much of it borrowed from the existing PCI Express interface.

[titan_amit]

Thanks sir for your reply but i think i was not very clear in explaining what i intended to ask.
I wanted to know whats the protocol difference that allows later versions of USB to act at faster speed.
for e.g. A frame in full speed USB is allowed to transfer maximum of 1023 data whereas a frame in high speed is allowed to transfer 1024 bits of data and they have same frame frequency so how come high speed has 40 times the speed of full speed.

[Jan Axelson]

High-speed bits are 40x narrower than full-speed bits so more of them fit in a frame.

The 1023/1024 limit is per transaction, not per frame.

The USB spec also defines limits on how much bandwidth a single transfer can use.

Jan 

[titan_amit]

thanks sir  one  more question-- does the same principle applies to super speed USB also or some other technology have been applied there.

[Jan Axelson]

Yes, SuperSpeed has a different hardware interface and different maximum rates for the transfer types, but the same principles apply.

One more thing, please call me "Jan," or "ma'am" if you must, not sir.

Jan