Correctly set your level 2 cache and improve performance !!

I read about this trick the other day over Internet. Open Registry by going

to START-RUN and typing REGEDIT. Navigate to

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

Management\SecondLevelDataCache. Based on the kind of CPU you have, this

value should change. Here are some of the defaults. Intel Celeron - 128 ,

AMD Duron - 64. PII and Athalon: 512. Cyrix and AMD K6-3 256. Pentium IV-

1024. Figure out what your CPU type is and what L2 cache it supports and

set it accordingly. It is important to know what critics have to say about

this tweak. Opinions vary and I have put following three articles that have

been brought to my attention which may help you understand why it may not

be effective in some situations:

Do not change the SecondLevelDataCache entry (from Microsoft technet

article

nol/windows2000serv/reskit/serverop/part2/sopch06.asp>)

Some third-party sources have erroneously reported that modifying the

SecondLevelDataCache registry entry in HKEY_LOCAL_MACHINE \System

\CurrentControlSet \Control \Session Manager\Memory Management can enhance

system performance. The second level (L2) cache is recognized by the

operating system and is fully utilized regardless of the setting of this

parameter.

(from Microsoft knowledge base item Q183063

)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

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 computer has a 2

MB L2 cache) would probably have about a 0.4 percent performance penalty.

(From an arstechnica article

1.html>) One of the most infamous NT tweaks since the introduction of NT4

has got to be the "L2 cache" tweak, a lone registry entry which stipulates

the amount of L2 cache (or secondary cache) that the OS will make use of.

Well, as with many things in life, the effects of this tweak are not so

black and white. If you're using a processor that implements a direct-

mapped L2 cache design (like Pentium I's), then this registry adjustment is

indeed for you. However, if you own any Intel processor post-PI, or any

modern AMD processor (K6-2 and newer), then your processor is using a set-

associative L2 cache design, and thus you need not specify your L2 cache

size. Let me explain.

If you choose not to futz with the registry key in question, the OS will

call on the HAL (Hardware Abstraction Layer) for retrieval of the L2 cache

size when you boot your computer. If this happens to fail, a default value

of 256KB is used for all logon sessions on that boot session. This is where

the myth that NT can only use 256KB of L2 cache comes from. But it's false.

See, the HAL is able to retrieve the processor (L2) cache from any

processor using the set-associative cache design, it's only the relatively

few processors out there with direct-mapped L2 caches that the HAL won't

chat it up with. Thus, this tweak only applies to a select number of people

anymore (like people with Pentium I procs between 166-233MHz, as lower

rated procs had only 256KB cache).