[kwlug-disc] Refurb laptops & monitors - Eco-Tech Recycling?

[Cedric Puddy]

It all depends on what the memory controller is designed for. 

Some memory controllers are happy to use one stick of ram; others are set up to require sticks in pairs (usual reason, as I understand it, is so that the reads and writes are split between the two chips, allowing double the memory bandwidth by allowing to read/write memory in blocks twice as wide as a single stick could handle). (Another reason would be if you are running your memory in a "RAID" configuration, where the contents of sticks are simultaneously mirrored, and each have ECC; if a stick goes bad, this allows you to potentially correct an arbitrary number of corrupted bits. This is not generally done on home computers, but is certainly done on critical servers.) 

There are a number of systems that require sticks to be added, or at least support, memory installed in sets of three sticks. Most of these systems, such as I've encountered, will allow memory to be added in single sticks, but you miss out on some memory bandwidth, just as some can enable extra memory bandwidth with sticks installed in pairs, but will still work with single sticks. 

There are other things as well -- for example, very high memory density chips often don't support the same speeds, or multi-rank features as lower density ram. 

I am not a motherboard designer, so press me on the details and you'll get a increasing amounts of guesswork, but the generalities above 

-Cedric 


----- Original Message -----

From: "John Johnson" <jvj at golden.net> 
To: "KWLUG discussion" <kwlug-disc at kwlug.org> 
Sent: Thursday, 24 April, 2014 6:11:57 PM 
Subject: Re: [kwlug-disc] Refurb laptops & monitors - Eco-Tech Recycling? 

On 2014-04-24 10:37, unsolicited wrote: 

It's long been known to install memory in pairs. 


"It is known" is not the same as "knowing why". 

I was trying to explain the "why" memory is installed in pairs, at least on older machines. 
I am not sure, but I think the "pairing" is now done in the modules themselves (or, at least, in some types of memory modules). 

JohnJ 

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