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My motherboard is based on Intel Z68 chipset and supports up to 32GB RAM. I wanted to upgrade my current RAM (2*8GB + 2*4GB) to (2*8GB + 2*8GB), so I have 32GB in total.

Original (Working) 24 GB Configuration:

Northbridge         Intel Ivy Bridge rev. 09
Southbridge         Intel Z68 rev. B3
Memory Type         DDR3
Memory Size         24 GBytes
Channels            Dual
Memory Frequency        802.1 MHz (1:6)
CAS# latency (CL)       9.0
RAS# to CAS# delay (tRCD)   9
RAS# Precharge (tRP)        9
Cycle Time (tRAS)       27
Command Rate (CR)       2T


DIMMs #1 & #3
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Kingston (7F980000000000000000)
    Size            4096 MBytes
    Max bandwidth       PC3-10700 (667 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         yes
    XMP revision        1.2
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-17-23 @ 457 MHz
    JEDEC #2        7.0-7-7-20-27 @ 533 MHz
    JEDEC #3        8.0-8-8-22-30 @ 609 MHz
    JEDEC #4        9.0-9-9-24-33 @ 666 MHz
XMP profile         XMP-1600
    Specification       PC3-12800
    Voltage level       1.650 Volts
    Min Cycle time      1.250 ns (800 MHz)
    Max CL          9.0
    Min tRP         11.25 ns
    Min tRCD        11.25 ns
    Min tWR         15.00 ns
    Min tRAS        33.75 ns
    Min tRC         45.00 ns
    Min tRFC        160.00 ns
    Min tRTP        7.50 ns
    Min tRRD        6.00 ns
XMP timings table       CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
    XMP #1          6.0-6-6-18-24-n.a @ 533 MHz (1.650 Volts)
    XMP #2          7.0-7-7-21-28-n.a @ 622 MHz (1.650 Volts)
    XMP #3          8.0-8-8-24-32-n.a @ 711 MHz (1.650 Volts)
    XMP #4          9.0-9-9-27-36-n.a @ 800 MHz (1.650 Volts)

DIMMs #2 & #4
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Corsair (7F7F9E00000000000000)
    Size            8192 MBytes
    Max bandwidth       PC3-10700 (667 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         yes
    XMP revision        1.3
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-17-22 @ 457 MHz
    JEDEC #2        7.0-7-7-20-26 @ 533 MHz
    JEDEC #3        9.0-9-9-24-33 @ 666 MHz
XMP profile         XMP-1600
    Specification       PC3-12800
    Voltage level       1.500 Volts
    Min Cycle time      1.250 ns (800 MHz)
    Max CL          9.0
    Min tRP         11.25 ns
    Min tRCD        11.25 ns
    Min tWR         15.00 ns
    Min tRAS        30.00 ns
    Min tRC         50.63 ns
    Min tRFC        260.00 ns
    Min tRTP        7.50 ns
    Min tRRD        7.50 ns
    Command Rate        2T
XMP timings table       CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
    XMP #1          6.0-6-6-16-27-2T @ 533 MHz (1.500 Volts)
    XMP #2          9.0-9-9-24-41-2T @ 800 MHz (1.500 Volts)

When I put the 2 new 8GB DDR3 SP DIMMs in place of the 2 old 4GB DIMMs, BIOS detects them and reports total memory correctly as 32GB. However, when I try booting up either Windows from the hard drive, or even the installation disk/USB flash drive, it appears to "hang". After running MemTest software, I realized that it is not hanging, but rather dramatically slows down (probably by a factor of 100!) at certain memory address ranges (i.e. MemTest slows down dramatically at certain places, but reports no errors).

The same thing happens regardless of:

  • Where I insert the DIMMs (tried all kinds of combinations)
  • What channel/rank interleaving settings I select in BIOS
  • Whether I run at 1333MHz or at 1600MHz.

Not Working 32GB Configuration

Northbridge         Intel Ivy Bridge rev. 09
Southbridge         Intel Z68 rev. B3
Memory Type         DDR3
Memory Size         32 GBytes
Channels            Dual
Memory Frequency        802.1 MHz (1:6)


2 DIMMs in any 2 slots
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Corsair (7F7F9E00000000000000)
    Size            8192 MBytes
    Max bandwidth       PC3-10700 (667 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         yes
    XMP revision        1.3
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-17-22 @ 457 MHz
    JEDEC #2        7.0-7-7-20-26 @ 533 MHz
    JEDEC #3        9.0-9-9-24-33 @ 666 MHz
XMP profile         XMP-1600
    Specification       PC3-12800
    Voltage level       1.500 Volts
    Min Cycle time      1.250 ns (800 MHz)
    Max CL          9.0
    Min tRP         11.25 ns
    Min tRCD        11.25 ns
    Min tWR         15.00 ns
    Min tRAS        30.00 ns
    Min tRC         50.63 ns
    Min tRFC        260.00 ns
    Min tRTP        7.50 ns
    Min tRRD        7.50 ns
    Command Rate        2T
XMP timings table       CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
    XMP #1          6.0-6-6-16-27-2T @ 533 MHz (1.500 Volts)
    XMP #2          9.0-9-9-24-41-2T @ 800 MHz (1.500 Volts)


2 other DIMMs in any 2 remaining slots
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Silicon Power (7F7F7F7F7F7FD3000000)
    Size            8192 MBytes
    Max bandwidth       PC3-12800 (800 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         no
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-16-22 @ 457 MHz
    JEDEC #2        7.0-7-7-19-26 @ 533 MHz
    JEDEC #3        8.0-8-8-22-30 @ 609 MHz
    JEDEC #4        9.0-9-9-24-33 @ 685 MHz
    JEDEC #5        10.0-10-10-27-37 @ 761 MHz
    JEDEC #6        11.0-11-11-28-39 @ 800 MHz

What works, i.e. the speed is as it should be, and everything boots up is if I replace only 1 of the 4GB DIMMs with the new 8GB DIMM. Of course, with this arrangement I end up with 28GB and not 32GB that I hoped for.

Current ("Compromise") (Also Working) 28GB Configuration:

Northbridge         Intel Ivy Bridge rev. 09
Southbridge         Intel Z68 rev. B3
Memory Type         DDR3
Memory Size         28 GBytes
Channels            Dual
Memory Frequency        802.1 MHz (1:6)
CAS# latency (CL)       9.0
RAS# to CAS# delay (tRCD)   9
RAS# Precharge (tRP)        9
Cycle Time (tRAS)       24
Command Rate (CR)       2T


DIMMs #1 & #3
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Corsair (7F7F9E00000000000000)
    Size            8192 MBytes
    Max bandwidth       PC3-10700 (667 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         yes
    XMP revision        1.3
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-17-22 @ 457 MHz
    JEDEC #2        7.0-7-7-20-26 @ 533 MHz
    JEDEC #3        9.0-9-9-24-33 @ 666 MHz
XMP profile         XMP-1600
    Specification       PC3-12800
    Voltage level       1.500 Volts
    Min Cycle time      1.250 ns (800 MHz)
    Max CL          9.0
    Min tRP         11.25 ns
    Min tRCD        11.25 ns
    Min tWR         15.00 ns
    Min tRAS        30.00 ns
    Min tRC         50.63 ns
    Min tRFC        260.00 ns
    Min tRTP        7.50 ns
    Min tRRD        7.50 ns
    Command Rate        2T
XMP timings table       CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
    XMP #1          6.0-6-6-16-27-2T @ 533 MHz (1.500 Volts)
    XMP #2          9.0-9-9-24-41-2T @ 800 MHz (1.500 Volts)

DIMM #2
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Kingston (7F980000000000000000)
    Size            4096 MBytes
    Max bandwidth       PC3-10700 (667 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         yes
    XMP revision        1.2
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-17-23 @ 457 MHz
    JEDEC #2        7.0-7-7-20-27 @ 533 MHz
    JEDEC #3        8.0-8-8-22-30 @ 609 MHz
    JEDEC #4        9.0-9-9-24-33 @ 666 MHz
XMP profile         XMP-1600
    Specification       PC3-12800
    Voltage level       1.650 Volts
    Min Cycle time      1.250 ns (800 MHz)
    Max CL          9.0
    Min tRP         11.25 ns
    Min tRCD        11.25 ns
    Min tWR         15.00 ns
    Min tRAS        33.75 ns
    Min tRC         45.00 ns
    Min tRFC        160.00 ns
    Min tRTP        7.50 ns
    Min tRRD        6.00 ns
XMP timings table       CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
    XMP #1          6.0-6-6-18-24-n.a @ 533 MHz (1.650 Volts)
    XMP #2          7.0-7-7-21-28-n.a @ 622 MHz (1.650 Volts)
    XMP #3          8.0-8-8-24-32-n.a @ 711 MHz (1.650 Volts)
    XMP #4          9.0-9-9-27-36-n.a @ 800 MHz (1.650 Volts)

DIMM #4
    Memory type     DDR3
    Module format       UDIMM
    Manufacturer (ID)   Silicon Power (7F7F7F7F7F7FD3000000)
    Size            8192 MBytes
    Max bandwidth       PC3-12800 (800 MHz)
    Number of banks     8
    Nominal Voltage     1.50 Volts
    EPP         no
    XMP         no
    AMP         no
JEDEC timings table     CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        6.0-6-6-16-22 @ 457 MHz
    JEDEC #2        7.0-7-7-19-26 @ 533 MHz
    JEDEC #3        8.0-8-8-22-30 @ 609 MHz
    JEDEC #4        9.0-9-9-24-33 @ 685 MHz
    JEDEC #5        10.0-10-10-27-37 @ 761 MHz
    JEDEC #6        11.0-11-11-28-39 @ 800 MHz

So, my question is why am I experiencing ~100 time slow down at certain addresses if I replace 4GB DIMM #2 from the Current Configuration above with the 8GB DIMM - identical one as DIMM #4 from the Current Configuration above?

1

Motherboards can be very particular about which combinations and type of RAM combinations they are willing to accept.

The manual is not very helpful and does not specify anything about the accepted RAM.

However, I noticed that the new 8 GB sticks are not identical to the old ones. You bought Kingston sticks instead of Corsair, and I can see that their JEDEC timings table specifications are slightly different. These specifications tell the computer what settings to run the RAM at for certain speeds, and may pertain to the slow-down that you have observed.

Mixing sticks of different types may confuse the motherboard into reducing performance to what it considers is the lowest common denominator.

I suggest to return the new Kingston 8 GB sticks and buy Corsair 8 GB sticks that are identical to the ones you already have installed.

|improve this answer|||||
  • Thanks so much for the answer. However there are 2 points... 1) I got the new Silicon Power sticks, not the Kingston Sticks. 2 Corsairs (2*8GB) and 2 Kingstons (2*4GB) were working just fine together. The 2 Corsairs (2*8GB), 1 Kingston (4GB), and 1 Silicon Power (8GB), the current config - also work fine together. What does not work is: 2 Corsairs (2*8GB) + 2 Silicon Power (2*8GB). 2) It's not just "reducing performance to the lowest common denominator", it simply makes accessing certain memory space literally like a 100 times slower (MemTest runs fine, then enormous slowdown)! – Fit Nerd Nov 9 '18 at 12:18
  • I am pretty sure it can be fixed with custom timings and/or voltages, but I have no idea what to set those to. – Fit Nerd Nov 9 '18 at 12:19
  • I made edits to the question to make it clearer by explicitly listing the config I want but which does not work. – Fit Nerd Nov 9 '18 at 12:27
  • In your 32GB config the voltages are identical at 1.5V. But I noticed that XMP is on for the previous sticks but off for the new ones. XMP has to do with overclocking and CPU speed. You might try to turn XMP off totally on all sticks, maybe in the BIOS? – harrymc Nov 9 '18 at 12:47
  • Your observations are correct! For all 8GB sticks (old and new) the voltages are the same 1.5V and the new 8GB sticks do not seem to have XMP on them. However, in BIOS I see XMP-related options (ability to select XMP profile) only with old DIMMs (which all have XMP info listed in SPDs). If I replace any 1 or 2 old DIMMs with any 1 or 2 new 8GB DIMMs, then the XMP-related options is not visible in BIOS at all - there is nothing to uncheck/change... At that point I can just change interleaving aspects, individual timings (per channel), and the multiplier (13.33 or 16.0 for my meory sticks). – Fit Nerd Nov 9 '18 at 12:56

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