2MB Cache or 8MB

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Kris Riley
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Joined: Jul 29 2003

In a hard drive, does anyone know the difference btwn a 2MB Cache and an 8MB Cache? What does this mean?

cstv
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Joined: Jul 26 2002

Cache is intermediate memory that runs at a higher speed than the memory that feeds it.

The faster memory is, the more expensive it tends to be. it's also very difficult to make large amounts of memory work at speed, so computer manufacturers came up with a very clever idea of having memory in levels.

let's take the simplest system; you have your RAM and a CPU.

Compared to the CPU, RAM is pretty slow and if the CPU had to talk directly to it all the time your PC would be equally slow. so instead when your CPU requests something from RAM, the bits requested get sent to the cache, and along with those bits, all the bits close to the requested ones go too. this way, there are pretty good odds that the next thing the CPU requests will already be in the cache.

the same thing happens with your hard drive. Hard drives are really slow, so the cache is there to speed things up a bit.

obviously things are a little more complicated than that, but that's basically what's going on.

in theory you want the biggest cache you can lay your hands on, but if you end up paying through the nose for it then i wouldn't bother. the figures you're really interested in are read/write speed benchmarking tests done by independant testers such as magazines, websites, etc...

hth,
mark.

jove
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Joined: Aug 18 2000

As CSTV says, the cache sits between the high speed of the cpu and the slow physical speed of the disk arm and therefore can buffer operations while the arm takes an age to move from one track to the next. Its principal role is to hold recently read data so that if it is requested again no disk read is required - a response time in microsecs instead of millisecs - but note it is ONLY A BENEFIT ON A RE-READ. It also provides benefits by reading ahead, so if the application wants data from following physical clusters they might already be in the cache by the time it wants them, again saving disk wait time.

However, when you are reading in a 5GB file the read speed depends on the physical rate at which you can get bits of the disk and I think that the difference between 2MB and 8MB will not be noticeable.

Having said that I would agree with CSTV that big cache is better for the the times that it can help, but for video it's not worth much extra.

Cheers, JOVE

RayL
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Joined: Mar 31 1999

One area of editing where high-speed high-cache disks would be wonderful is multicamera timeline redraw. With 4 x 1hour clips + titles + music tracks, screen redraw is a significant drag on speed of timeline navigation.

Alas, timelines are redrawn in series, rather than in parallel.

Ray Liffen

PaulD
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Joined: Aug 31 2002

Hi
What's needed is an edit program that you can turn timeline picons off, but when you roll-over part of a clip, of select an area with a marquee, then the thumbnails would become visible (instantly)! ;)

[This message has been edited by PaulD (edited 01 August 2003).]

Kris Riley
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Joined: Jul 29 2003

Thanks for all the help! I seem to understand this a bit more now!!!!