Re: what is the meaning of registers,internal memory?
From: Homosapien (spamtrap_at_crayne.org)
Date: 12/27/04
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Date: Mon, 27 Dec 2004 20:37:52 +0000 (UTC)
Hi!
They aren't stupid questions at all. Everyone has to start somewhere.
Some people act as if everyone should be born with a Ph.D in comp sci,
but that's not the case.
Registers inside the CPU are little scratch pads that are on the CPU
die, right on the silicon. They are like RAM, in that they are
volatile. You switch the machine off and the contents disappear.
Unlike RAM, these little scratch pads as I mentioned are tucked away
deep inside the CPU itself. RAM on the other hand is a chip or bunch of
chips that are separate components, in a slot or slots on the
motherboard. The CPU must reach out over the bus to get the contents of
RAM or to put stuff into RAM. RAM is much slower than internal CPU
registers. Much, much slower.
ROM = Read Only Memory. Actually, nowadays it is usually a flashable
chip, i.e. EEPROM. So strictly speaking it's not ROM, but it's treated
as if it were. It's read only, never written to. Normally it contains
some startup code for the system board to check the devices and run
tests, then look for an operating system to boot.
RAM = Random Access Memory, readable and writable. You say mp, you mean
multiprocessor? In any case, most MP systems today share RAM, and there
is a lot of contention for the memory. NUMA systems are different. In
SMP systems, that are normally used today (or have been before NUMA
anyway) all the CPUs share the same "link" or bus between them and the
memory. A lot of processor time is wasted on competing for access to
the memory bus.
NUMA = Non Uniform Memory Access. It means that there is a limit on the
number of CPUs on a memory bus, and eliminates the bottlenecks with many
CPUs competing for access to the memory. With NUMA it is possible to
have "remote memory" where all the CPUs and their busses are connected
by a high speed link. This is rather like a cluster that is connected
by a gigabit ethernet, or something like that. It can of course mean a
huge motherboard with many busses, containing perhaps several groups of
4 CPUs or whatever, and lots of different groups of RAM chips.
NUMA systems are not clusters however, and it's a rough analogy. In
NUMA systems it would be a big board with each group of CPUs and their
local memory all residing on the same board. A cluster links separate
(perhaps uniprocessor) machines by a network.
Hope this helps.
yogesh wrote:
> Dear all!
> I have just started learning the assembly language and getting
> confused.
> I have following doubts/confusions.
>
> What is the registers inside the microprocessor?(Well, it may seem a
> very infant type of question but believe me I have not come across any
> concise definition and relation between the register and
> microprocessor ..)
>
> while referring to the memory(RAM/ROM),is it external to mp or do mp
> have its own internal memory? as many times the internal memory terms
> is also used.
>
> I will be very much grateful if someone gives answeres to my stupid
> doubts..:)
>
> regards,
> Yogesh Joshi
>
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