[CVALE] Question about computer memory.

[Rob johnston]

Terry wrote:
> Greetings !
> 
> I have a follow up question ...
> 
> Years ago ECC for RAM or Disk required CPU power.  This was typically turned off to improve 
> application performance.
> 
> Is this the case these days?

Not sure about disks, but I think these days the performance impact of 
memory ECC is fairly negligible.

Does calculation of disk or RAM error correcting code require cycles
> from the main CPU or has the calculation been moved elsewhere?

It's part of the function of the memory controller.  On some (mostly 
older) x86 systems this would be a separate ASIC (part of the 
motherboard chipset).  AMD processors (I think since K8) and the newest 
Intel processor have an integrated (on-chip) memory controller.

Also, your on-chip caches - l1, l2 (some chips have l3), instruction and 
data caches are also ecc-protected (which is a good thing).  After all, 
  not having ECC means not detecting memory (or cache) errors, which can 
lead to silent data corruption.

rob

-------------------------
Robert Johnston
Solaris Core OS
robert.johnston at sun.com
http://blogs.sun.com/robj
-------------------------

> Terry
> 
> 
> 
> Landon Blake wrote:
>> I was looking at a Dell workstation that listed the following items for
>> memory:
>>
>>  
>>
>> *	Up to 24GB1 <javascript:void(0)>  of DDR3 ECC or non-ECC memory
>> for true workstation-level tasks.
>> *	1GB, 1066MHz, DDR3 SDRAM, NECC (1 DIMM)
>>
>>  
>>
>> I was wondering what the difference was between these two (2) types of
>> memory. I think the 1GB of SDRAM is the memory I am most familiar with
>> as a programmer. Is the other memory listed some sore of paging
>> mechanism on the hard drive? Or is it something else?
>>
>>  
>>
>> Thanks,
>>
>>  
>>
>> Landon   Memory
>>
>>  
>>
>>  
>>
>>  
>>
>>
>>
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