Hi guys

i know that the clock speed of CPU must be faster than data transfer to make synchronization and
as we know that maximum clock speed of CPU is 4 GHZ

there was 10 gigabit Ethernet,
which mean that it faster than CPU clock about 2.5 times if we have CPU has a 4 GHZ clock

how transfer data(bit rate) can be faster than CPU clock?

if the CPU is a 128 bit CPU, the processor is writing 128 bits to the data bus at a time.

I think you are mixing up Gigahertz and Gigabits

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no i know they different



if CPU can read or write(send/receive) 128 bit per cycle
that mean the CPU can send or receive maximum [4 *(10^9)*128] bit=512 Gbps
but this only can happen when the data( send or receive) in parallel(sending 128 bit at same time)


but when the data send in serial(bit by bit) as in Ethernet,
the CPU can maximum receive [4 *(10^9)*1] bit=4 Gbps

Why does the cpu need to get involved?

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ok let talk about network interface card(NIC) this also need clock to synchronous its operation
any logic circuit need clock for synchronization except combinatorial circuit(not use in network communication)

in Ethernet 10Mb, the NIC is writing ~10 million bits to the wire per second.
in Fast Ethernet 100Mb, the NIC is writing ~100 million bits to the wire per second.
in Gig Ethernet 1000MB, the NIC is writing ~1000 million bits to the wire per second

_________________
"If you're good at anticipating the human mind. It leaves nothing to chance."
-Jigsaw

in 10 Gig Ethernet 10Gb, the NIC is writing ~10 billion bits to the wire per second
that mean at least we need 10 GHZ clock in the NIC

Do you hint at 'asic'?

asic or fpga also need clock for synchronization when dealing with network

Since when do CPU's deal with one bit per clock cycle? Last time I checked it was either 32 or 64 bits per cycle for most architectures.

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yes that right
but in this case the CPU send 32 bit at one time(parallel) to memory for example

but in network CPU(or NIC) send data bit by bit(serial)

the CPU isn't sending anything, the NIC does the sending and serializes the data onto the transmission medium (copper wire|fiber)

the CPU clock speed has nothing to do with access rate of the physical medium of the NIC... there is a bus between the NIC and the chipset/cpu/memory controllers

Basically. I was hinting at the fact that the CPU itself is not the thing doing the sending of packets onto the wire.

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is NIC has a clock or not?

if NIC don't have clock,
then how can synchronize its operation?

actuaZly there are two clocks

here
http://en.wikipedia.org/wiki/Media_Inde ... _Interface

scroll down to section Gigabit Media Independent Interface

"implemented using an eight bit data interface clocked at 125 MHz:

_________________
"If you're good at anticipating the human mind. It leaves nothing to chance."
-Jigsaw

The clock is recovered from the line code so synchronisation is not necessary.

NO
i think the NIC need clock for synchronization regardless the type of coding.




that right the 1 Gigabit & 10 Gigabit Ethernet use Multi_level coding instead of using line coding(like in fast Ethernet)
so i think 10 Gbps can obtain by using clock 1250 MHZ(8*1250=10000 Mbps)

the NIC(by using Memory Buffer ) may send data to CPU or to memory as 16 or 32 bit at one time

Tell that to a professional overclocker
Also, ASICs do it in hardware, and the CPU, which can read 32, 64, perhaps 128 bits at a time, doesn't need to examine the entire packet. Just IP headers. So theoretically, an IPv4 destination address is read in one clock cycle on a x86 platform. Even if it takes two clock cycles, one +2Ghz CPU core may perhaps do 1Gbps of routing in software. But I'm no expert.

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