CPU L2 Cache Memory setting in Vista

ByLine
How to Set Vista for the CPU L2 Cache Memory Size
Synopsis
This will show you how to set the Vista for the actual CPU L2 cache memory size incase Vista fails to get it from the Hardware Abstraction Layer (HAL) and uses a default L2 cache size of only 256 KB instead of the actual size.
How to Set Vista for the CPU L2 Cache Memory Size

information   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   Note
This sets the SecondLevelDataCache inside the registry.

From Microsoft KB183063:

Microsoft KB183063 said:
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   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.​
2. Click on the Hardware Configuration arrow on the far right to expand it. (See screenshot below step 3)​
3. Click on the Devices arrow on the far right to expand it. (See screenshot below)​
Arrows.jpg

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.​

B) Click on the + sign to expand​
Win32_Processor.DeviceID="CPU0".​


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.​
System_Health_Report.jpg





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.​
2. In the white line (Start Search) area, type regedit and press Enter.​
3. Click on Continue in the UAC prompt.​
4. In regedit, go to: (See screenshot below)​
Code:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
5. In the right pane, right click SecondLevelDataCache and click on Modify.​
Before_Reg.jpg

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.

Decimal Value

Hexadecimal Value

256 KB

100 (hex)

512 KB

200 (hex)

1024 KB (1MB)

400 (hex)

2048 KB (2MB)

800 (hex)

3072 KB (3MB)

c00 (hex)

4096 KB (4MB)

1000 (hex)

6144 KB (6MB)

1800 (hex)

8192 KB (8MB)

2000 (hex)

12288 KB (12MB)

3000 (hex)

16384 KB (16MB)

4000 (hex)

Modify.jpg

7. Click on OK to apply.​
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.​
After_Reg.jpg

9. Close regedit.​
10. Restart the computer to apply the change.​
That's it,
Shawn





 
Last edited by a moderator:
Shawn Brink

Comments

Shawn I just thought id inform that for reson unknown to me the 4mb cache setting isnt 1600.

Its actually 1000. I am unsure as to why cause all the rest are correct.

Cheers
Anthony
 
Hi Maineearle,

You need to look up your CPU's specs to see that it says. Go to the manufacturer's website to do so.(EX: Intel or AMD) You can find the model number to look it up with by right clicking Computer (in Start menu) and click Properties. You can also find the model number in System Information.

Shawn
 
^i dunno if we can put 2000(since brink hasnt mentioned it) so better put 1000 to be safe.
 
q6600 has 2x 4096 L2, so i put in 1000?
it's set to 0 currently
Hi Violent Ken,

This means that you have 8 Mb shared cache between the 4 cores. You should use 2000 as the value. I updated the tutorial for this.

You can read more on your Intel Core 2 Quad Q6600 processor here:

http://www.intel.com/products/processor/core2quad/index.htm


Quad-Core Processor:
Provides four complete execution cores in a single processor with 8 MB of L2 cache and a 1066 MHz Front Side Bus. Four dedicated, physical threads help operating systems and applications deliver additional performance, so end users can experience better multi-tasking and multi-threaded performance across many types of applications and work loads.
Intel Advanced Smart Cache:
Shared Level 2 cache across each pair of cores that can be dynamically allocated to each processor core, within the pair can access data from fast L2 cache, significantly reducing latency to frequently used data and improving performance.
Shawn
 
My specs is Core 2 Duo T7300 @ 2 GHz, L2 Caches with 4096 KBytes(shown in CPU-Z 1.42). So I just set 1000(Hex)?
 
setting this parameter in Vista will do nothing, because according to microsoft, when there is 0 in SecondLevelDataCache , HAL on startup detects the appropriate setting...
 
Hi PietroR,

Welcome to Vista Forums. :party:

Yes, this is true. However, if Vista fails to retrieve the CPU L2 cache size from the Hardware Abstraction Layer (HAL) for some reason, it will use a default CPU L2 cache size of only 256 KB. This will most likely be less than what your CPU actually has. It can cause a slight performance drop if this happens. :(

Shawn
 
Dear friends,
As in preamble of this thread is mentioned:
it is only useful for computers with direct-mapped L2 caches. Pentium II and later do not have direct-mapped L2 caches.
If your computer has Core... processor, you can write any number from 0 to all Fs to this register, nothing happens.
 
anyhow, in my experience, most of the "tweaks" are eighter useles, or dangerous - like switching off the last access timestamping on ntfs, etc. those are all rather old tweaks from old times :)
 
Hi Brink, I was just wondering if this would be worth my while? When you have time let me know what you think. Thanks a lot.

I appreaciate your time.Bare Foot kid :shock:
 
Last edited:
Hi Bare Foot Kid,

Usually this will never make a difference. Only if for some reason Vista fails to read the HAL from the CPU. Even then, it would be a very low performance hit.

Shawn
 
Hi Brink. I thought that was what you were saying. That's why I asked first. I do thank you for your response. Later, Bare Foot Kid


:cool:
 
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