Laptops Laptops Laptops.. and cache?

[My Buttons are Magic!]

right... i need a laptop for university in september ( if i get in) -but probably get a laptop anyways!

and i saw two on the internet that i would love to get ( fits all the specifications)

 

just what is cache?

i did G.C.S.E ict and i have a faint recognition of learning about it... just cant remember what it is!

 

EDIT: and what about advent laptops? ive never heard of them before

[Guest Jordan]

Cache, is if i remember rightly is a small amount of RAM on the CPU that allows it to quickly store data before processed by other devices in the computer. This mean the CPU can have more work dumped on it before it can be used.

 

The more the better.

[=NukeBlaze=]

^ Expanding a bit further.

 

The basic reason why Cache exists is as follows:

 

Memory subsystems suck.

 

In a perfect world, where RAM and processor spoke to one another at the same speed with little latency in between, and the hard disk could transfer data just as quickly as the previous two, cache would not exist. Cache exist to act a small, but quick memory buffer to lessen the performance impact caused by the lack of bandwidth and the the lag between communication of two devices called "latency". If you are interested what type of memory cache is composed of, I recommend looking into DRAM, and SRAM, of with cache is typically SRAM, due to its speed attributes.

 

Now, you might ask why they just don't ratchet up the bandwidth between all the chips in the system to not have use Cache. Well, it starts to get expensive and complicated. You have to start adding more copper traces on the motherboard for data to travel between chips, greater complexity in making sure those signal stay free of interference as you crank out the frequency of transmission, the manufacturing gets more expensive, making sure there is good latency times between everything...etc..etc. It becomes a mess.

 

The hard drive is automatically crippled in speed because of the mechanical method it uses to read/write data. There is a spinning metal plate/s covered in a ferrous-magnetic surface that is read by a platter read/write head floating fractions of a millimeter above it as it spins at 7200 RPM(typical). I think it amazing that modern HDD can even transfer information at 30-50 MB/s using this method. But, here is a bottle neck. Compare the Hard disk transfer speed of 30-50 MB/s, to a modern RAM system that has a bandwidth of 6400 MB/s! This is yet another reason why most modern HDD comes with 8 MB of Cache , built into their own little circuit board.

 

 

Now, lets say you are buying a laptop, and they advertising cache on the processor. This means you are probably looks at intel's core 2 duo chips, which have either a 4 or 2 MB on chip cache. In performance tests, the difference between two chips with the same frequency, but one has 2 MB cache while the other has 4 MB, is roughly ~5% on average.

 

Intel's chips are a bit more affected by cache since they do not have an on processor memory controller like the AMD athlon64 line, but that is another tale for another day.

What does this mean? If you are looking at an intel chip in a laptop, how much cache its has should be lower in priority than say...how much RAM it has...or if it has better video/screen capability.