CPU L2 Cache Memory setting in Vista

How to Set Vista for the CPU L2 Cache Memory Size​

   Information

The SecondLevelDataCache records the size of the processor cache, also known as the secondary or L2 cache. If the value of this entry is 0, Vista will attempt to retrieve the L2 cache size from the Hardware Abstraction Layer (HAL) for the platform. If Vista fails for some reason to retrieve the L2 cache size from HAL, then it uses a default CPU L2 cache size of only 256 KB. If the default value of the SecondLevelDataCache value is not 0, Vista will use the value (amount of memory) you set instead of 0 (for 256 KB) as the L2 cache size of. This value is designed as a secondary source of cache size information for Vista when the HAL cannot detect the L2 cache from the CPU.

   Note

This sets the SecondLevelDataCache inside the registry.

From Microsoft KB183063:

This is not related to the hardware; it is only useful for computers with direct-mapped L2 caches. Pentium II and later processors do not have direct-mapped L2 caches. SecondLevelDataCache can increase performance by approximately 2 percent in certain cases for older computers with ample CPU L2 memory (more than 64 MB) by scattering physical pages better in the address space so there are not so many L2 cache collisions. Setting SecondLevelDataCache to 256 KB rather than 2 MB (when the CPU has a 2 MB L2 cache) would probably have about a 0.4 percent performance penalty.

   Warning

Only set the value to what your processor actually has for the L2 cache size. Do not use a larger size than it actually has.

STEP ONE

Find Out the L2 Cache Size Reported by HAL

NOTE: This will show you how to see what the L2 cache size is for your CPU as it is reported to Vista by HAL. This value will be used in STEP TWO below to set the SecondLevelDataCache value for this as a backup in case HAL rarely could not detect the L2 cache from the CPU.

1. Generate a System Health Report.​

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2. Click on the Hardware Configuration arrow on the far right to expand it. (See screenshot below step 3)​

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3. Click on the Devices arrow on the far right to expand it. (See screenshot below)​

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4. Under Devices, scroll down to Motherboard Classes. (See screenshot below step 5)​

A) Click on the + sign to expand​

root\cimv2:SELECT * FROM Win32_Processor.​

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B) Click on the + sign to expand​

Win32_Processor.DeviceID="CPU0".​

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5. In that list, you will see L2CacheSize and the value beside it for it's size to use it in step 6 in STEP TWO below.​

NOTE: For this example you will see 6144 to be used for my CPU's 2x6144 (12MB) L2 size. Now, here's a kicker. The newer Yorkfield Core 2 Quads CPUs use the entire cache for both cores unlike the older CPUs that do not share. So a 2x6144 (12mb) L2 cache would use 12288 (2x6144) instead despite what is reported in Vista for HAL.​

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STEP TWO

Set the L2 Cache Size

NOTE: This will set the SecondLevelDataCache value in the registry, from the value gotten in STEP ONE, as a backup in case HAL rarely could not detect the L2 cache from the CPU and prevent having only a default L2 cache size of 256 KB used as L2 cache size instead by Vista.

1. Open the Start Menu.​

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2. In the white line (Start Search) area, type regedit and press Enter.​

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3. Click on Continue in the UAC prompt.​

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4. In regedit, go to: (See screenshot below)​

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HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management

5. In the right pane, right click SecondLevelDataCache and click on Modify.​

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6. Dot Decimal, and type in the value in bold (see table below) for your CPU L2 size from STEP ONE above. (See screenshot below table)​

NOTE: I have a CPU with a 2x6144 (12MB) L2 cache size, so I would use 6144 (Dec) or 1800 (Hex) since it is 2x. See STEP ONE above for how to get the L2 size for your CPU. Now, here's a kicker. The newer Yorkfield Core 2 Quads CPUs use the entire cache for both cores unlike the older CPUs that do not share. So a 2x6144 (12mb) L2 cache would use 122488 (Decimal) or 3000 (hex) instead despite what is reported in Vista for HAL.​

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[TABLE=class:-grid,-width:-400][TR][TD]
Decimal Value
[/TD]
[TD]
Hexadecimal Value
[/TD][/TR]
[TR][TD]
256 KB
[/TD]
[TD]
100 (hex)
[/TD][/TR]
[TR][TD]
512 KB
[/TD]
[TD]
200 (hex)
[/TD][/TR]
[TR][TD]
1024 KB (1MB)
[/TD]
[TD]
400 (hex)
[/TD][/TR]
[TR][TD]
2048 KB (2MB)
[/TD]
[TD]
800 (hex)
[/TD][/TR]
[TR][TD]
3072 KB (3MB)
[/TD]
[TD]
c00 (hex)
[/TD][/TR]
[TR][TD]
4096 KB (4MB)
[/TD]
[TD]
1000 (hex)
[/TD][/TR]
[TR][TD]
6144 KB (6MB)
[/TD]
[TD]
1800 (hex)
[/TD][/TR]
[TR][TD]
8192 KB (8MB)
[/TD]
[TD]
2000 (hex)
[/TD][/TR]
[TR][TD]
12288 KB (12MB)
[/TD]
[TD]
3000 (hex)
[/TD][/TR]
[TR][TD]
16384 KB (16MB)
[/TD]
[TD]
4000 (hex)
[/TD][/TR][/TABLE]

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7. Click on OK to apply.​

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8. Your registry will look like this below for a 2x6144 (12MB) L2 cache memory size.​

NOTE: See STEP ONE above to find out your CPU L2 cache size.​

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9. Close regedit.​

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10. Restart the computer to apply the change.​

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That's it,
Shawn

Related Tutorials

---

• How to Make a Program or Process Run with a Higher or Lower CPU Priority in Vista
• How to Set the Processor Affinity for a Application in Vista
• How to Change the Number of Processors Used at Boot Up in Vista

 

[ltwally]

LOL, now that will be interesting.

Yeah. Again: this is off the top of my head... but I'm pretty sure my memory is accurate on this one.

The design is curious. The L2 cache latency is improved, but the L3 cache is nowhere near as fast as even the current generation's L2 cache... so it's not a clear win-win situation. In some scenarios, it will result in an application running faster. In others... maybe not so much.

Though, I expect with the on-die memory controller and other enhancements, no code will actually execute slower than on current processors.

One thing we'll all have to get ready for is buying new motherboards - as with the new design comes a new socket (which hasn't happened for Intel in, what, 3 years?)

 

[greeneggsandham]

I have an Intel Pentium D 925 2 x 2mb L2, so would that be 1000 hex for a 4 meg cache?
I ask because the cores in pentium d's are just stuck together and the memory has to use the fsb to exchange data unlike the dou's.

 

[ltwally]

You would use hex 800 for 2megs; each core has a seperate cache, on your processor.

 

[greeneggsandham]

Cheers Itwally I thought this might be the case but I was not quite 100%, I did set it 2 1000 hex with no problems but I have just put it down 2 800 hex.

 

[ltwally]

No problem. Glad I could be of service.

As previously mentioned: Microsoft's own information on this setting indicates that it is a legacy item that will have no effect any CPU made in the past several years. Still, the correct value would be 0x800.

-ltwally

 

[mysiar]

Hi guys
Intel Core 2 Duo specs are here
Intel® Core™ 2 Duo Specifications

Piotr

 

[RiversWild]

Hello,

This is my first time here and I was wondering why when I perform the system health report it reports that my L2 cache size as 0. I have a Q9650 cpu which has an L2 cache of 12mb. I did go into registry editor and changed the Secondleveldatacache to 12288 decimal. I am just wondering if there is a reason it is reporting it this way or if there could be a problem with my cpu or motherboard?

Any help would be appreciated as I have searched everywhere for an answer to this but have come up with nothing.

Thanks so much for your help,
Riverswild

 

[ltwally]

I have no idea why Windows reports zero. What does CPU-Z say?

In the end, it doesn't matter what Windows thinks your L2 cache is. L2 cache is managed by the CPU, itself - not by your OS.

The "secondleveldatacahce" registry setting is an old legacy value, and has zero impact on any modern processor that I'm aware of. (The last CPU, to my knowledge, that it would have impacted was the Pentium II.)

 

[Everlong]

Hello,

This is my first time here and I was wondering why when I perform the system health report it reports that my L2 cache size as 0. I have a Q9650 cpu which has an L2 cache of 12mb. I did go into registry editor and changed the Secondleveldatacache to 12288 decimal. I am just wondering if there is a reason it is reporting it this way or if there could be a problem with my cpu or motherboard?

Any help would be appreciated as I have searched everywhere for an answer to this but have come up with nothing.

Thanks so much for your help,
Riverswild

I've seen a few problems with the Yorkfield cores, like Windows reporting 3 of the 4 cores as Unknown Devices in Device Manager.

Have you tried upgrading your BIOS for the motherboard?

 

[RiversWild]

Hello,

Thank you for the quick reply. CPU-Z reports 6144 x2 for L2 cache. I was just worried that maybe there is something wrong with my hardware as the system health report is reporting 0. I noticed this when I was doing a 3dmark06 and in my system details for my cpu it is also reporting L2 cache as 0. But if L2 cache is managed by the CPU and not by windows then I guess I have nothing to worry about. I am very new to this and this is my first computer build. It is very nerve racking for me.

Thank you so much for your reply and help!!
Riverswild

 

[RiversWild]

Hello Everlong18,

Yes I did upgrade the BIOS for the motherboard. Is there a way to tell for sure what version Bios I am running. I have a evga 780i sli motherboard.

Thank you so much,
Riverswild

 

[ltwally]

Hello,

Thank you for the quick reply. CPU-Z reports 6144 x2 for L2 cache. I was just worried that maybe there is something wrong with my hardware as the system health report is reporting 0. I noticed this when I was doing a 3dmark06 and in my system details for my cpu it is also reporting L2 cache as 0. But if L2 cache is managed by the CPU and not by windows then I guess I have nothing to worry about. I am very new to this and this is my first computer build. It is very nerve racking for me.

Thank you so much for your reply and help!!
Riverswild

I wouldn't worry about what Windows think about your cache size, as long as it's seeing all your CPU's (cores), as noted above by Everlong18.

I do not know what kind of detect methods 3dmark06 uses for CPU / L2 cache. If it's just spitting back the data that Windows provides it... well...

You might try upgrading it. Downloads links: Futuremark - Benchmarks

Your BIOS probably has an option in it for detailed information on boot. If you enable that, it should print out the L2 cache size on bootup.

 

[ltwally]

It's worth pointing out that if you replaced your original CPU with a new one that is a different model Windows can become "confused."

Example: I "borrowed" the CPU from a new machine at work for my own workstation. My Pentium-D (dual core) was suddenly a Core2Quad. The BIOS saw the new CPU correctly. However, Vista's device manager thought I had a pair of Pentium-D cores and a pair of Core2Quad cores.

My solution was a fit of rage where I wiped the harddisk just to teach it a lesson. Things worked great after re-install!!

Probably better solutions out there.

 

[RiversWild]

Sorry it took so long to reply. I was looking in my bios for the option you had mentioned but I couldn't find it. My devise manager does see all my cpu cores. I also built this computer with all new hardware and then installed windows. So, everything should be fresh. I have no idea. Seem weird to me.

Thank you for your help!!
Riverswild

 

[Akuanauta]

Hello, one more again.

This is very difficult but I will try to do a good question.
My memory cache have 4096 KB, and by default my memory cache only uses 256 KB of storage, right? (Says in the tutorial)
For I use the full potential of my memory cache i need to follow the tutorial, isn't it?(if i need)

So when i go to the second step(regedit) what i have to do, is replace the value 0 for 4096 (decimal) or 1000 (hex), this is right?

Thank you, for your help.​

 

[Brink]

Hello Akuanauta,

Since your CPU has a 4 MB L2 cache, then yes that would be correct.

Shawn

 

[Akuanauta]

Fine, thank's

 

[Brink]

You're welcome Akuanauta.

 

[Taheed]

Good evening everyone. My processor is a Intel Pentium Dual core T3200 @ 2.0GHZ and I was skeptical the settings required to utilize the tip.

 

[chuckbam]

I fooled with this tweak on a Q6600. I don't think I am going to use it. But, it is very interesting.