Thanks for that, David. But I meant that you are now able to fit more RAM, and
have the CPU use it, than was the case when some Macs were sold.
Chris
On 7 Apr 2012, at 10:52, David Thatcher wrote:
> On Fri, Apr 06, 2012 at 09:22:31PM +0100, Chris Barker wrote:
>> I gather that the limitations initially placed on computers have been
>> made void by improvements in the RAM. But I might have got the wrong
>> end of the stick there . . .
>>
>> Chris
>
> To comment on this general non-OS-specific statement: Yes, more RAM is
> better - up to a point. Modern operating systems use a 'protected paged
> virtual' memory model. As applications start up, they request some
> pages/blocks of memory from the operating system, can ask for more as
> they need it, and -if the OS & app are properly written- can return it
> to the free pool when they are finished with it (if not done properly it
> is one form of 'memory leak' and why some systems need a 'maintenance
> reboot' periodically (pronounced 'often' or 'daily' :) ).
>
> If there is no free ram when an application asks for it, the OS will
> make decisions about what applications are idle & will 'swap' those
> applications' memory pages out into a hard disk 'swapfile'. When swapped
> pages are required for use (the application wakes up for some reason),
> they are swapped back in, and other pages are swapped out. All of this
> swapping in/out takes enormous amounts of time, as disk input/output is
> thousands to million times slower than memory accesses - and if swapping
> is happening a lot, the machine seems to grind to a halt.
>
> Basically by stuffing your machine full of RAM, you are minimising the
> swapping, and thus the machine appears to run faster - until you run out
> of free RAM again!
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