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

 

[ZoK-StaR]

Nice.. giving this ago. Thanks :D

 

[Brink]

Your welcome ZoK-StaR.

 

[New64Pooter]

hi there... this is a great site btw... thank you so much for your tutorials for vista64!!!

Anyway. I am confused about quad core L2 cache info in this thread.

This is my cpu as shown in that app recommended at top of page

So.. is this like 4096 for each core (so 16384)
or.. see the 2x in the screen shot... is it (8192)
or.. is is just 4096

Any help would be appreciated.. and again.. thank for your work on this site.. very cool

 

[Brink]

Hi New64Pooter,

Welcome to Vista Forums.

It will be for your 2 x 4096 L2 cache. This will be 8192 KB (8MB) or 2000 (hex).

Shawn

 

[New64Pooter]

great. your a star!!!

 

[Terrorist]

Thank You

 

[Brink]

Your welcome Terrorist, and welcome to Vista Forums.

Shawn

 

[Terrorist]

Your Tutorials are pretty cool and useful, well done Shawn

 

[johngalt]

Just out of curiosity, where can you look to see what Vista / Vista x64 is actually reporting from the Hall.dll? I don't want to make the change if it is not needed, as in the future I may upgrade the processor and forget to change the value / forget that I *have* changed the value...

 

[soldatz]

Just out of curiosity, where can you look to see what Vista / Vista x64 is actually reporting from the Hall.dll? I don't want to make the change if it is not needed, as in the future I may upgrade the processor and forget to change the value / forget that I *have* changed the value...

Indeed.

How can we tell what the HAL is currently reporting, and under what circumstances would Vista fail to retrieve the correct values?

 

[Brink]

Hi Johngalt,

Welcome to Vista Forums.

I'm not sure where to look to see what HAL is reporting other than looking at what it says in the program CPU-Z, but this is not what you are changing in this tutorial. You will just be changing the default value of only 256 KB to be used for the L2 cache if the HAL cannot be detected from the CPU by Vista for some reason. That's all.

Hope this helps,
Shawn

 

[johngalt]

IOW, if Vista reads HAL correctly, this key is meaningless, but if it doe not read it correctly, then it forces this value (as opposed to the default which is 256 KB).

Good to know. Now, if only I could see what Vista is reading from HAL in the first place....

Perhaps performance and monitoring tools? I'll go look.

 

[Brink]

Johngalt,

You can use the free program CPU-Z to see what the L2 cache is. It reads from Vista what Vista has reported from HAL. If the L2 cache information is correct, then you know Vista detected the HAL correctly.

CPUID

Hope this helps,
Shawn

 

[johngalt]

I meant to look at what Vista is actually reporting - and I found out where to look.

If you go to Performance Information and Tools (from Control Panel Classic, or from typing performance in the Start Menu), then click on Advanced tools in the left hand menu, you'll get a whole new set of performance tools. Now, select the last option, Generate a system health report, and allow it to run (confirm the UAC prompt). After it has run, you'll get a report with all sorts of information - expand (by double clicking or clicking on the directional arrow in a circle on the far right) Hardware configuration (if it closes Hardware, then repeat to open). Now, do the same for Devices. Scroll down to Motherboard classes, and expand (by clicking on the plus sign to the left of it) the root\cimv2:SELECT * FROM Win32_Processor. In that list, you'll see L2CacheSize and the value beside it.

Unfortunately, mine is showing 496, whereas I actually have 4096 * 2 for a total of 8192....Interesting.

According to what you said, CPU-Z reads what the OS reports, as opposed to polling the hardware itself. Isn't that actually not a true assessment then?

Oh, and BTW - My sig is from my CPU-Z validation....:P

 

[Brink]

Johngalt,

It appears that the value reported in the System Health Report from Vista is a 2x value like in CPU-Z. My CPU has a 12 MB L2 cache and is reported as having 6144 in the System Health Report. In CPU-Z I show 2x6144.

I may be mistaken on whether CPU-Z reads from the OS or hardware. It is not real clear at their website on which one it reads from.

Yes, I have seen you sig.

Shawn

 

[johngalt]

Hopefully that is correct. If not....

 

[Brink]

It should be. For you, I would use 8192 KB (8MB)----2000 (hex) in step 6.

Shawn

 

[sale666]

quick question... mine says 2x1024... should i set as 1 mb or 2 mb?
thanks!

 

[johngalt]

Assuming you mean CPU-Z says 2 X 1024, set it for 2 MB.

 

[sale666]

yes cpu z says 2x1024!
i have Amd Athlon X2 6000+ processor