[sclug] Cheap'n'nasty Tesco Linux machines

Dickon Hood sclug at splurge.fluff.org
Fri Mar 14 11:33:58 UTC 2008

On Fri, Mar 14, 2008 at 09:40:11 +0000, Jason Rivers wrote:
: On Fri, Mar 14, 2008 at 9:28 AM, Phillip Chandler <
: phillip.chandler at ntlworld.com> wrote:

: > My understanding of Dual Core (pretty slim actually, but here goes) is
: > that both are only used for things like multitasking and gaming etc. So
: > theoretically if your a home user just wanting to do basic stuff like
: > check email, surf, write letter to auntie Mildred in Australia, then
: > dual core is a waste of money because to do the basics you would only be
: > using one core. Therefore the 2nd core is redundant, the first one has
: > to be running at 100% for other work to be transferred over to the send
: > core.

That's not how modern OSes schedule threads.  A thread is the fundamental
unit of execution these days (it used to be processes); the OS's job is to
schedule the execution of these in the most optimal way possible.  That's
likely to mean that a long-running process at 100% CPU will have a core to
itself, and everything else (and better-behaved) gets to share the other.
At other times, both cores will be in use running processes that are
awakened on such things as IRQs, packets arriving, users doing annoying
things with the keyboard and mouse, and simple clock ticks; that sort of

: > Dual core would also be perfect for places like NASA or a
: > university doing vast computations.

You want a farm at that sort of level.  Two cores isn't going to help
much.  Google for 'compute cluster'.

: > If your using one for burning a dvd and the second for playing doom 3,
: > then dual core kicks in and works great. But who would be burning a dvd
: > and playing doom while their waiting ?

: urm.... me? - I do that alot - not Doom - but any game really, and they're
: normally high end demanding games - but few of them support multi thredding
: so are useless (effectively) on a dual core.

Not entirely true.  Most modern games are threaded these days as dual-core
chips have been mainstream for a couple of years now, and the games
consoles have been multicore for longer than that.  In particular, you'll
find threads dedicated to sound, graphics display, and engine, if nothing
finer-grained than that.

: > So my thinking here is that when they advertise a machine as dual core
: > with a speed of "X" which is based on both cores working, then
: > technically if your only going to be a home user (as described above)
: > then in my mind your not going to be getting the speed stated, your only
: > going to get the speed of one core, ie half the speed.

: > So the questions here are, do I sort of understand the concept of Dial
: > Core ? Do I even sound like I know what Im going on about ? Is the idea
: > above have some credibility ?

Multiple cores can help in a number of situations: anything multithreaded
(so media playing, for example; a modern libavcodec (VLC and mplayer) will
thread H.264 playback).  Also, where you have something like X handling
your display, one core can be managing that, whilst the other is running
the application you're interacting with.  That reduces latencies quite
substantially.  Chances are you won't notice the difference, however.

So there are advantages for the average end user in having multiple cores,
but users aren't always going to make use of them all of the time.

For about 98% of the time, the cores will be equally busy, at almost
completely idle.  I keep mine busy running xsnow.

: almost - the dual core systems don't top one core before using the second -
: if I open application X - that kicks in and uses 60% of one core, then I
: fire up application Y, depending on the Operating System - this will most
: likely go over to Core 2, (and I don't mean an intel chip)

: until games start using multiple threads - really there's no actual reason
: to have a multi core CPU - as an end user at least.

They started threading a couple of years ago.

Dickon Hood

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