# The meaning of speed (processors)

Discussion in 'Electronic Basics' started by species8350, Sep 15, 2003.

1. ### species8350Guest

My pc runs at 600MHz. I presume that this means that my processor runs
at this speed.

If I have a 600MHz processor does this mean that the processor will
calculate 600 million calculations per second - sounds a bit on the
high side.

What is the difference between 600MHz and 600MIPS

Wile I am here what does pipelining mean?

Thanks

S

2. ### Mark LittleGuest

600MHz refers to the clock speed that is applied to the processor. 600MIPS
refers to doing 600 Million Instructions Per Second. As processors often
take more than one clock cycle to complete and instruction, the number of
MIPS is likely to be lower than the clock speed.

A Reduced Instruction Set Computer (RISC) attempts to up the MIPS by
simplifying the instruction set so that the instructions can be completed
in one clock cycle.
It is actually not practical to create a processor that can complete all of
its instructions in a single clock cycle, so pipelining is used to give an
effective throughput of one clock cycle.

Image that an instruction has four phases. The first is fetch the
instruction, followed by reading the data, working on the data and writing
back the result.

If I have four streams operting on the instructions and stagger the start of
each stream by one clock cycle, it still takes 4 clock cycles to complete
an instruction, but an instruction is completed every clock cycle. This
works if each instruction is done sequentially, but breaks down if the
program does a jump, sub-routine call or similar.

regards,
Mark

3. ### species8350Guest

Thanks Mark,

What is a clock cycle. In the case of a 600MHz processor is it
600cycles, what does this mean in terms of instrctions.

Thanks

S

4. ### Mark LittleGuest

A 600MHz processor would generally have 600 million clock cycles per second.
How many instructions gets executed per second depends on quite a number of
factors. The first in the complexity of the instruction. In "clear
register", it will generally execute in less time than it read a memory
location, do an operation on the data and write it back.

One of the other factors is the method by which the processor executes the
instruction. Some processors have hard coded logic, while others have
micro-code which operates like a mini-program for each instruction.

regards,
Mark

Thank you

S