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Old September 29th 14, 09:58 PM posted to alt.comp.periphs.mainboard.gigabyte
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Default memory timing setting

Haines Brown wrote:
My 16 Gb Skill RAM says to set tCL to 9, tRCD to 9, tRP to 9 and tRAS to
24. When I boot a new board the BIOS by default has timing set
automatically. But I see that it is setting tCL at 11, tRCD at 11, tRP
at 11, and tRAS at 28.

Which set of timings should I accept? Is the difference in these values

Haines Brown

If your RAM features "XMP", your GA-H97-DH3 has XMP in the BIOS.
(Not all RAM has an XMP profile stored in the SPD chip.)

The SPD EEPROM on each DIMM contains timing information.
The standard portion, has several timings, for different clocks.
The timings may not represent the actual module rating, if
the actual module rating falls outside JEDEC values. There are
lots of RAM products, which are faster than the JEDEC standards,
and the true timings are not recorded in the SPD.

In cases like that, you enter the BIOS and manually set
DRAM clock (via a divider), all the timings, and VDimm voltage.
For example, maybe your memory does CAS9 at 1.65V or
CAS11 at 1.5V. You paid for CAS9, so you set the voltage
to 1.65V (the limit for some of the Intel processors), set
the other stuff, save and exit.

There are also a couple less-official memory standards, XMP
being one of them. The XMP profiles are also stored in the
SPD chip. They may not be covered in the most general JEDEC
spec on how to put info in the SPD.

The profiles can cover one DIMM per channel or two DIMMs per
channel configurations. Usually, only the one DIMM per channel
profile is set up.

If you enable XMP, it automatically sets VDimm to 1.65V and
CAS0 timings. So with one BIOS setting, you get the "rated"
RAM specification.

After running memtest86+, doing some Prime95 on Linux, you
can head back to Windows and run CPU-Z.

(Non-install version)

It shows the "standard timing" section of the SPD EEPROM on
the DIMM. The standard timings do not have to match the
"rated" speed of the module. By doing this, the motherboard
uses slower timings on the first application. This allows
the "enthusiast" user, to dial in the actual values via
the BIOS setup screen. If it was not done this way,
some users would experience a crash on their first POST,
and lots of RAM would be returned to the seller. By
making the standard timings "slow", it encourages
successful bootstrapping.

The XMP information should be in there as well. But perhaps
the screenshots have not been updated to match the current
version of the software.

You can only use CPU-Z, if the machine is stable enough to
install or connect a Windows drive. Don't connect the Windows
C: to the computer, until the memory has had some error
testing. As otherwise, the Registry can become corrupted.
Even after memtest86+ gives the memory a pass, it's
still possible to corrupt the registry. Someone I was
giving this recipe to, had Windows fall over on him, even
after memtest86+ said things were fine. That's why the
Prime95 stress test is necessary, and it can be
done from a Linux LiveCD (and you cannot corrupt an
already-burned CD by using bad RAM). If you could run
Windows in a read-only mode, this sort of thing
would not be necessary.