On Tue, 14 Jan 2014 12:07:21 -0000, The Natural Philosopher wrote:

On 14/01/14 08:52, Ian Jackson wrote:
In message om,
"dennis@home" writes
On 13/01/2014 23:02, Uncle Peter wrote:


Given that commercial stuff is NOt enigeneered tpo 'worst case' but
generally engineered to 99.99% chance' level, it's surprsng that stuff
works as well as it does.

You could always buy RAM rated much faster than you're going to run it.


Not always..
sometimes the designer will use the minimum hold time for the ram to
allow them to change the address to start the next cycle early.
If the ram is too fast the output will change too soon and put the CPU
into a metastable state.
Then anything could happen.

This disagrees with what Mike Tomlinson has just said when I asked the
specific question as to whether 'faster than motherboard spec' memory
could screw up your computer. A couple of weeks ago I replaced a pair of
512MB PC2-4200 (533MHz) with a pair 1GB PC2-6400 (800MHz). After a week
of faultless operation, the PC suddenly started to play up. Another 1GB
PC2-6400 pair (different make) also gave problems. [As Mike advises,
I'll be carrying out more memory tests.]

I have to say that despite extensive Googling, I have found it very
difficult to find any definitive and authoritative statements about
using 'too fast' memory. When the subject is raised, most discussions
rapidly veer away from the original question, and your are left
wondering whether the answer was 'yes', 'no', 'maybe' - or, more often,
'nobody here knows the answer, so we'll answer a question that no one
asked'.

I will concede the possibility that fast DRAM relies on - say - being
refreshed more often than slower, and might leak charge away at a slower
clock rate.

I will also concede that it may be possible to rely on a propagation
delay to achieve the desired result and getting rid of it could cause
problems, though I am not so clear that anyone actually does this.

So, whilst I will concede a possibility, I am pretty sure (and most
people writing on the subject agree) that the actuality is that faster
RAM wont do any harm *on account of being faster*.

I suspect what dennis is hinting at is an incomplete understanding of
how SDRAM works...

http://en.wikipedia.org/wiki/Synchro..._access_memory

it is in fact pretty complicated. Quite a long way from 'here's an
address, give me some data'

And if you read it its pretty clear that there is plenty of room for
'one manufacturers implementation of the spec != another manufacturers
implementation', with possible results being less than ideal.

So I'd be inclined to lay that at the door of 'instant incompatibility'
rather than speed.

AFAIK RAM is designed to work UP TO the rated speed, so should be able to handle the lower spec being used.

--
Landing: A controlled mid-air collision with a planet.