Re: Cube G4 ram into eMac 700

Curmudgeon <leave@xxxxxxxx> writes:

Ram Speed doesn't "Switch" it is a HARDWARE Propagation Time designed
into the Ram chips when they are built. If you have PC100 Chips
they WILL function at PC100 Speeds. If you have PC133 Chips, they will
function at PC133 speeds, as well as ANY Slower Speed. What the Module
says it is, is programmed into a separate memory location, on board
the module, and read during Memory Initialization.

Well, thanks for your ever-so-pleasant reply, You, but these modules do
say PC133 on them, but according to my friends at OWC fail to report it
to the System Profiler application, reporting instead to have "toggled"
down to PC100. If they were really running at 100 MHz, I'd expect that
I'd see the sort of system crashes others have predicted (or at least a
noticeable sluggishness in general) but the machine is solid as a rock.

If You would like to take it up with the folks at OWC, please feel free
to give them a call.


That's not how it works. First of all, RAM does not care about "Megahertz"
at least not directly. They are concerned about time.

Take this oversimplifed example..

You need to read a byte of data at address 00FFAA23BAD.

Step 1) Push 00FFAA23BAD to the address bus handling such. [Systems can
have more than one such bus...]

2) Wait

3) Read the data bus at that address..


You wait, because the address bus takes some time to quiet down, the chip
then takes some time to find that data and put in on the data bus, then
you want that bus's noise to die down, etc...

Better RAM does not take as long for its step; its data is up sooner.
So, if your CPU can read it sooner, it's "faster". Now, if you don't
read it as fast as you could, but wait a while, as a slower system would,
that's OK too. If you waited long enough, the data would eventually bleed
away except for refresh...

[Dynamic RAM is a series of tubes no wait... it's millions of little
capacitors holding a [un]charge. Keeping them correctly [un]charged over
time is another aspect called "refresh".......

We talk memory bus speed for the benefit of the humans designing systems.
Somewhere there's a spec that gives times for the dozen-plus access
times on PC100 vs PC133.

I've used PC133 in PC100 systems with no difficulties, but that does
not mean it's universally true.




--
A host is a host from coast to coast.................wb8foz@xxxxxxx
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
.

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