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Disk Cache
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Jul 18, 2001, 03:57 PM
Now I know since everyone is (rightly) bitching about Macworld this seems a little strange but here goes...

I upgraded to Mac OS 9.1 today and noticed that you could increase the disk cache as far as 32 MB...so I did this and didnt notice any great changes (although launching photoshop seemed slower)

Could someone explained this disk cache thing please...if anything else it'll give you a break from the slaughter going on in the rest of the threads....

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Jul 19, 2001, 11:52 AM
Come On guys....just a little help...please....

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Jul 19, 2001, 12:07 PM
If memmory serves me right and I'm thinking of the right thing, this is the first box in the memory control panel. It generally increases in size as you add more physical RAM to your machine. I believe it is a cache which keeps the most recently accessed files or data from recently accessed files. I don't think it will really improve speed alot.

Maybe one of the other members will confirm this or correct me.
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Jul 19, 2001, 12:14 PM
Yep, and it used to be limited to a max of 8160K and will default to that same figure if you had enough RAM and did not manually increase it beyond the default.

As the disk cache uses RAM, perhaps the slowdown that you noticed is due to less free RAM being available?
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Jul 19, 2001, 12:17 PM
As I understand it, it's caching directory information. For that reason Apple now (it didn't for a long time) suggests an optimal size based upon the size of disk volumes. The OS will look at where files are on the drive and cache it. If this is the case, 32MB cache probably won't help, in fact it will hurt because the RAM is not available elsewhere (if you don't have much RAM).
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Jul 19, 2001, 12:19 PM
My understanding is that it's best kept at the default value. Too high or too low can reduce performance.
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Jul 19, 2001, 07:10 PM
The prescribed optimal is based on how much RAM you have.

It caches recently used data (instructions etc) for fast access.

My default is 4096, and I run it on 8160 - thats all you need. Any more than 8160 is saying "my numbers bigger than yours" and nothing more.

Pretty much only servers would benefit from the larger cache, as they execute the same things over and over again.

If you must, 16 megs is ok - but more than 16 and you'll notice a slowdown (due to less RAM, if you don't have much, and the size of the cache becoming too bulky to handle with speed).
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Jul 21, 2001, 07:26 PM
Uh what he said . For a more tehcnical explanation, take a look at:


By default, the disk cache requirement is the number of megabytes of RAM you have multiplied by 32k. On my iMac, for example, with 64MB of RAM, the default disk cache is 2048k.
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