memory timing setting

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
significant?

Haines Brown

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
significant?

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)
http://www.cpuid.com/softwares/cpu-z.html

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.

http://www.cpuid.com/medias/images/e...es-cpuz-05.jpg

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.

HTH,
Paul

Paul writes:

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
significant?

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.)

Your kind reply rather goes over my head. My Skill RAM does support XMP,
but it sounds like it is used for overclocking, which I don't wish to
do.

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.

Are you saying that the higher timings (slower?) reported by BIOS are
acceptable and not to worry? That is, are you saying that the Skill
specs simply accommodate overclocking?

You can only use CPU-Z, if the machine is stable enough to install or
connect a Windows drive.

Windows drive? I've never had one of these. After leaving DOS, my hard
disks are always set up for Linux only. But if the higher timing values
reported by BIOS are not problematic, I probably need not worry about
CPU-Z.

Haines

Haines Brown wrote:
Paul writes:

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
significant?

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.)

Your kind reply rather goes over my head. My Skill RAM does support XMP,
but it sounds like it is used for overclocking, which I don't wish to
do.

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.

Are you saying that the higher timings (slower?) reported by BIOS are
acceptable and not to worry? That is, are you saying that the Skill
specs simply accommodate overclocking?

You can only use CPU-Z, if the machine is stable enough to install or
connect a Windows drive.

Windows drive? I've never had one of these. After leaving DOS, my hard
disks are always set up for Linux only. But if the higher timing values
reported by BIOS are not problematic, I probably need not worry about
CPU-Z.

Haines

You need some sort of utility that can report *current* settings.

There have been cases (I have a motherboard here), where the
values shown in the BIOS are incorrect. Using CPU-Z, it was possible
to verify the settings when the machine was booted into Windows.
It's not the OS that matters, merely the OS chosen by the author
of the utility.

The standard timings are capable of a great many things, but
they typically are not coded for higher than JEDEC values.
This is to ensure the computer always boots (on first installing
the RAM product). You can then manually set the BIOS to the
enthusiast values used by the DIMM. Or for a XMP motherboard
and XMP RAM DIMMs, set the BIOS to XMP profile, and both the
enthusiast timing and VDimm required operating voltage, are
dialed in for you.

I don't paint this as a set of absolutes, and this is just
a general picture of the landscape. If you accept the
automatically derived BIOS timing ("leave all settings on
Auto"), there is still a need to use CPU-Z and verify the
actual operating conditions. Such information is necessary
even if you're doing memory testing with memtest86+ (memtest.org).

I have a new machine here, where memtest86+, when it was running,
reported the RAM as "DDR3-3100" or so, when in fact the setting
wasn't anything like that. Testing in CPU-Z later, showed the
settings as being the same as the BIOS selected values.

You're very much working in the dark on this stuff, and
CPU-Z is the closest thing to an "impartial witness"
we've got. While the author could have compiled for Linux,
I've not heard of such a version.

Many of the Windows OSes, you can install them "for free" for
a limited number of days of testing. On Windows 8, you
use the circulating "install-only" keys. On Windows 7 or WinXP,
you press "Next" at the key input step (25 character input field).
The OS will run anywhere from 3 days to 30 days, after such
an install. All you really need is media. And Windows 7 was
available for download from digitalriver website.

X17-24208.iso (32-bit Windows 7 Home Premium x86 SP1 (bootable) iso)
X17-24208.iso (64 bit...)

You could try the 32 bit, and a copy of CPU-Z, if you're curious.

The BIOS manual settings should also have some way of indicating
what the BIOS thinks are normal values, as well as
overclocked values. I don't really think of your setup as
overclocked, but it's easier to view and comment on this
stuff, with CPU-Z tables at hand. As it shows the standard
profiles, XMP profile, plus the currently used settings.

Paul