Re: FN-FORUM: Mac mini - Ok for web dev?

date posted 8th October 2007 15:48

On Monday 08 October 2007 15:59:53 Ian Piper wrote:
> On 8 Oct 2007, at 2:24 pm,
>
> [EMAIL REMOVED] wrote:
> > Does this explain why my MacMini (Intel Core Duo, 2GHz, 1Gb RAM)
> > performs rather slower than I had expected; is a big chunk of the
> > RAM being eaten up by the graphics as soon as I turn it on?
>
> I'm no expert, but yes, from what I have read the integrated graphics
> controller chip uses a chunk of your installed RAM - how much of it,
> and how tenaciously it holds onto it, are beyond my knowledge I'm
> afraid.

[Disclaimer: the following is to the best of my knowledge...]

Yes, it takes a chunk, but it's a small chunk; I think 64MB for the Mac Mini.

On the PC architecture this is often a BIOS option. It's permanently
reserved at boot time. Losing a few percent of your RAM at boot is
neither here nor there in terms of overall performance (particularly
if you've got "enough" - see below). The real performance hit comes
from having to share the RAM at all - only one processor at a time
can use the bus and if the CPU is busy with it the graphics chip has
to wait its turn.

Other performance hits come from the fact that the integrated GPU
chips are simply not as fast as their stand-alone cousins, and provide
less hardware support for things like texture mapping so they get
done by the CPU instead.

A third factor, which I believe no longer applies, was that dedicated
graphics cards would have faster RAM than the mainboard did.

What is "enough" RAM?

At any particular time there is, in theory at any rate, a quantifiable amount
of memory that a system needs; if you are in the middle of a routine that
creates a 64 byte buffer, then that's another 64 bytes, and so on.

If you have less RAM than you need, then virtual memory comes into play;
RAM contents that are not currently in use are paged out to disk.

If you have more RAM than you need, then you can cache the files that
you are accessing.

In real terms, a system will typically be doing both at the same time.

Many years ago, RAM was expensive and the typical Windows system was
desperately short of it. I'd regularly see systems where the disk light
simply never went off, as it was continuously swapping stuff between
disk and RAM. At this time, though, most users seemed to think that
their CPU speed was all-important.

Over the years the message seems to have got out there - make sure
you've got enough RAM. On the other hand the performance gains from
having "more than enough" are really very slight. Having 4GB instead of
2GB in your LAMP server will not make it twice as fast - at least, not until
you've got many thousands of users...