Hardware Updrage (again)

Richard Smith rdls
Fri Nov 26 23:57:31 GMT 1999


Paul Richards wrote:
> 
> Richard Smith wrote:
> 
> > Andrew Boothman wrote:
> > >
> > > I need to pick your collective brains on a related issue though. My new
> > > motherboard-to-be says that it will take DIMMs, nothing more specific. A visit
> > > to the manufacturer's web site reveals that it takes "PC/100, EDO, SDRAM"
> > > (http://www.mycomp-tmc.com/tmc/TI5VGPds.htm). It also states "Data Integrity :
> > > ECC/Parity Checking". So does thet mean that I need ECC SDRAM?
> >
> > The motherboard chip set should autodetect what type of DIMM is fitted.
> > ECC DIMMs are significantly more expensive than your regular DIMM, and
> > are only neccesary for mission critical applications.
> >
> > > Looking in an advert for computer memory, they list PC100 SDRAM coming in
> > > normal, ECC and C 2 vareties. So which do you think is right for me?
> >
> > Normal SDRAM DIMM for a home system, I would say.
> 
> I'd say the opposite :-)

OK, ECC DIMMs for a home system and normal DIMMs for a mission critical
system then ;-)

> There are no applications that are so "uncritical" that memory integrity is not
> important. A bad memory register can cause hidden corruption throughout your
> filesystem, subtly modifying the contents of documents you may have. More likely,
> it'll corrupt something less sutbly, like a directory pointer. Memory never (hardly
> ever) fails catastrophically, usually it develops bad memory locations and you'll
> see unusual things happening, mysterious reboot, unexpected signals when doing
> compiles etc. Without ECC you may not realise that you've got bad memory for quite
> some time.

A few years ago, you couldn't get 30-pin SIMMs without parity checking,
because IBM was paranoid about memory integrity and wired the parity
checker to the NMI. When memory prices went through the roof, all of a
sudden, clone manufacturers started fitting 8-bit modules instead of
9-bit modules.

The situation persists today. Most mother boards are capable of
accepting ECC memory, but it's rarely fitted as standard.

I recently bought several SBCs for a mission critical application
(running FreeBSD of course), and the supplier had to get the ECC DIMMs
in specially for my order. Which implies to me that not a great
proportion of memory sales are ECC.

> For the sake of around 30 I'd strongly recommend ECC memory.

Go for it.

Richard.






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