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Cache

Posted on 1998-02-15
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What is Cache and is it important?
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Question by:jcdew
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froderik earned 50 total points
ID: 1018284
It depends on what we are talking about. There are software cache and hardware cache which are the same thing logically but not physically. Cache is a place used as memory for recent actions made by the object using it.

A typical example of the use of software cache is WWW browsers that uses cache to remember recently visited pages so that they don't need to be downloaded over the nerwork again.

Hardware cache is used I think by the processor for buffering when reading and writing to disks. I am not totally sure about this. If you want to know more about it I can find out.

Cache is an important technique but it is not important for the avarage user to know about it. When it comes to WWW browsers it can be useful to understand it but it is not necessary. The default settings for it are probably just fine.
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by:jrhelgeson
ID: 1018285
Cache is a small amount of fast memory used to store data temporarily to allow quick access. Their are two levels of cache: Level 1 or L1, is cache that is resident with the CPU and Level 2 or L2, is cache on the motherboard to supplement the small L1 cache. L1 usually ranges from 8-32KB and L2 is usually 128-1024KB. The cache works similarly to the registers inside of the CPU.

Disk cache (like smartdrive) is memory space allocated to store information read from the hard drive as a temporary storage space before the cpu needs to process it.
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by:jrhelgeson
ID: 1018286
Yes it is important.
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by:froderik
ID: 1018287
jcdew

I think that if you were more interested in hardware cahce, feel free to reject my answer and let jrhelgeson answer instead. jrhelgeson seems to know a great deal about it.
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by:jrhelgeson
ID: 1018288
I must say that you gave a good answer yourself, being that he gave no specifics for the question.

There is another type of cache, spelled cash.  Represented by the $ symbol, but we all know what that means.
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by:jrhelgeson
ID: 1018289
and yes, $ cash is important.
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by:jrhelgeson
ID: 1018290
The purpose of having *any* type of cache is to speed up performance (including $cash). :o)

It is a -temporary storage facility- used to store information where it can be easily accessed.  Much like having a toolbelt, and a toolbox.  L1 cache is like the tool in your hand, it is right there ready for use.  L2 cache is tools in the tool belt, not currently in use, but will be at a moments notice.  Memory cache is like having the toolbox sitting just a few inches from reach, just takes a few seconds longer to grab what you need than if it were in your tool belt.  Then to carry this analogy one step further, The hard drive would be like a tool chest out in the truck, quite time consuming to run clear out there and grab every little tool you'd need.  Therefore-

1) Your toolbox (ram memory) needs to be large enough to carry all of the tools (programs) you need loaded on a regular basis.
--Too much memory *can* be just as bad as not having enough because then windows will need to manage and lug that thing around everywhere.

2) The tool belt (L2 Cache) needs to be large enough to effectively keep the cpu from having to run back and forth from the Ram memory and the hard drive, but again, you too large of a cache, and the effect is counter productive.

3) L1 cache is so small because just like us, we only have 2 hands, we can only do so much at once.  Trying to hold to many things at once is completely counter productive.

this is an analogy I came up with while i was typing it. and if i do not say so my self, I think it's pretty good.
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by:froderik
ID: 1018291
I agree. You explain a rather abstract concept, for someone unfamiliar with hardware, with a good analogy that really makes sense. Very nice. Maybe you should write a book that explains hardware to the average user? :)
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by:sico
ID: 1018292
Basically me old chin chilla. Lets put it this way - You go to work every morning. On the first day you use a map to get to work. For the rest of the time you dont need to waste time looking at a map cos you remember the route! You have used some brain cache!!!! same thing on a pc. i.e every file has a location the cache remembers the file name and its location (if accessed often) so it dosnt have to bother the File Allocation Table and waste time (Hard disk cache!).

Does this help?...
P.S Brain cache only works if you havent been out on the razzle the night before (otherwise you may get a GPF).
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by:jrhelgeson
ID: 1018293
sico,
Does that mean that homing pigeons have cache memory?

:o)
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by:sico
ID: 1018294
Pigeions have about 220meg cache and 10k physical... and what sounds like a device conflict on the sound card.
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