question about system cache

[mike085]

Hi, newbie here.

I was wondering what exactly the "system cache" is and does.

I've had a thinkpad (2378 dxu) for a few months, and I've noticed that in the task manager's performance tab, my system cache starts out around 200,000 K right after startup and keeps increasing. After leaving the system on for a while, the system cache as reported in the task manager continues to climb upwards of 700,000-800,000K. Is this normal behavior? Thanks in advance.

-mike

[lvlolvlo]

"he system cache is responsible for a great deal of the system performance improvement of today's PCs. The cache is a buffer of sorts between the very fast processor and the relatively slow memory that serves it. (The memory is not really slow, it's just that the processor is much faster.) The presence of the cache allows the processor to do its work while waiting for memory far less often than it otherwise would.

There are in fact several different "layers" of cache in a modern PC, each acting as a buffer for recently-used information to improve performance, but when "the cache" is mentioned without qualifiers, it normally refers to the "secondary" or "level 2" cache that is placed between the processor and system RAM. The various levels of cache are discussed here, in the discussion on the theory and operation behind cache (since many of the principles are the same). However, most of the focus of this section is on the level 2 system cache."

http://www.pcguide.com/ref/mbsys/cache/

Not to sound like an ^sshat but try using a search engine like google as this was the first link, and it's pretty easy to understand.

[mike085]

ok, i understand that. I know what L1 and L2 cache do. But is the disk cache supposed to be that bloated? to the order of 800,000KB?

[beeblebrox]

... It think, that "lvlolvlo" is getting a bit confused with the hardware cache that resides on the CPU and the system cache that you asked for.

PC systems have many layers of cache. Internal registers, level 1 (small), level 2 (larger), level 3 (even larger), which mostly reside as SRAM on the CPU die (e.g. Pentium III has 256k to 512k), the Banias up to 1Mbyte, Dothan (2 Mbyte), Itanium, Xeons even more.

What you mean is, the 700-800 Mbyte of system cache, that is taken from your main memory. That is Microsoft Windows, that allocates spare memory to its programs for better performance. Ever noticed, that if you start a large program,it takes a while to load, then after you closed the program and restarted it again, it just took a blink to re-start? That is the system cache of Windows.

You can disable it in the registry, but doesn't make much sense, since Windows only uses unused memory for caching and changes the sizes.
I have 1 Gbyte main memore, disabled page file, and the computer flies. Cache size is usually around 500-600 Mbyte, the rest is programs.

Hope, that helped you

[Rahula]

Beeblebrox:

Quote:
"I have 1 Gbyte main memore, disabled page file, and the computer flies. Cache size is usually around 500-600 Mbyte, the rest is programs. "

I hope you don't mind my digressing from the main topic, but as a newbie, I am curious as to what pagefile does and what ramifications if it is disabled. On my T23, I notice that the pagefile takes up 589,824 KB. I always wondered what would cause this amount to increase or decrease.

[lvlolvlo]

I hope you don't mind my digressing from the main topic, but as a newbie, I am curious as to what pagefile does and what ramifications if it is disabled. On my T23, I notice that the pagefile takes up 589,824 KB. I always wondered what would cause this amount to increase or decrease.

That which you are refering ot is a "page file" that windows uses. it's like fake ram that windows uses and needs on systems with lower amounts of ram. if you allow it dynamically change then you will result in a fragmented hd. personally i would just manually set it. at 3 times your RAM if needed and hd space allowing.

[Rahula]

Ahhh ..... now I know.

Since I have recently increased my RAM to 768 MB, which now exceeds the pagefille amount, do I need to increase or lower the pagefile amount? Also, how do I prevent the pagefile from changing dynamically in order to prevent a fragmented HDD, which lvlovlo cautioned against?

[SimonCC]

this is something that i also need to know, i have 512 mb ram so should i set initial and maximum page file at 1536mb??? This sounds excessive to me but this is a confusing topic as people seem to recommend differant levels.

[waterside]

The problem is that there is no hard-and-fast rule that suits all situations. There are many 'rules of thumb' used as first estimates.

Your own usage will dictate what values make most efficient use of your disk space. If you have lots of spare disk you can use larger values without concern - you'll be wasting space but if you're not using it otherwise it really isn't wated.

If you have 1GB memory then a 3G swap size might be overkill. On the other hand if you have 128MB memory 384MB swap probably isn't enough.

I have 512MB memory and have a 1GB swapfile. I never come close to using it but don't have a need to make it smaller and don't want to run out of memory in those rare instances when I do need it.

[lvlolvlo]

The problem is that there is no hard-and-fast rule that suits all situations. There are many 'rules of thumb' used as first estimates.

Your own usage will dictate what values make most efficient use of your disk space. If you have lots of spare disk you can use larger values without concern - you'll be wasting space but if you're not using it otherwise it really isn't wated.

If you have 1GB memory then a 3G swap size might be overkill. On the other hand if you have 128MB memory 384MB swap probably isn't enough.

I have 512MB memory and have a 1GB swapfile. I never come close to using it but don't have a need to make it smaller and don't want to run out of memory in those rare instances when I do need it.

yeah whatever he said. just use some logic/sense in the matter. if you have 1gb ram you won't need 3gb pagefile, i know some people that have 1gb ram and turned off page file, and they've never looked back. i know of one person (met them on a forum) that has a pagefile of 2gb. so just picture yourself like this...

Pagefile:
Light Computer User(Word processing and internet) = 1xRAM
Medium Computer User(Above plus moderate gaming) 1.5xRAM
Heavy Computer User(Above plus design stuff) 2xRAM

The reason why I said 3 x RAM in my earlier post is b/c i assumed that ppl generally had 256mb ram as that's the tp default.

Use your judgement, remember everything is an opinion and that which might be true for some is not true for all.