I need help with the following question A PCI Express system has 10 Mbps links (

Question

I need help with the following question

A PCI Express system has 10 Mbps links (gross capacity). How many signal wires are

needed in each direction for 16x operation? What is the gross capacity each way?

What is the net capacity each way?

Answers:

For 16x operation, 16 wires are needed each way for a gross capacity of 80

Mbps. The net capacity is then 64 Mbps.

Note, 16 wires in each direction means 8 for data and 8 for ground

Can someone explain to me how to get the gross capacity and net capacity

Thanks

Explanation / Answer

Buddy this is a simple problem:
We know that the bus is Pci x16
     so the bus contains 16 lines, 8 of which are data connection, 8 are gound.

To transmit data we always need a pair of such line (i.e. one data is paired with one ground) so we have effectively 8 lines.

It is given that bandwidth is 10Mbps, so having 8 lines, ideally the bandwidth would be 8*10 Mbps = 80Mbps

But you ideal cased are only theoritical case, and not practical. In practical situations, there are always some overhead related, and in case of PCI and other bus, we consider to be 20% overhead

So out of 80Mbps 20% of 80Mbps or 16Mbps is overhead and cannot be used

So the gross is (80 - 16) Mbps or 64Mbps

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