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What exactly is HDD cache?

Last response: in Storage
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January 6, 2011 8:53:11 PM

1) What could go wrong if HDD cache didn't buffer between read & write and the disk?

2) Why exactly is 16MB cache better than 8MB?

3) Why is 8MB cache the standard?

More about : hdd cache

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a b G Storage
January 6, 2011 9:58:49 PM

Prologue: You need to understand the vast speed differences between system memory and disk. Data is moved between the two devices during disk reads and writes. The cache on a disk decouples the system from the horribly slow speed of the disk. The CPU can slam the data into the cache and go do something else.

The CPU (or some controller) has to write a full sector at a time and may not interrupt that process or the sector is lost. So without a cache/buffer writing would be a very haphazard process.

16M vs 8M - more is generally better. The CPU can send commands to the disk controller and go do something else. Note Windows is not very good at this but its getting better.

8M is not the standard. I remember 1M caches on disks and there are disks with 64M today. Disk manufacturers test extensively on the best size - or bang for the buck. You wouldnt see a benefit with a 32 M cache on a drive with 8M today. They tend to work off a ratio of cache size to storage size.

People spend their lives studying this stuff - its hugely interesting, but I think SSD's will make all of this go away when their price gets low enough
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a b G Storage
January 7, 2011 1:20:23 AM

Read speeds also improve. With a large enough cache, there's a very good chance that the next piece of data that you need will be found in the cache.

Large drives are now shipping with 64 MB of cache.
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a b G Storage
January 7, 2011 1:35:48 AM

vvhocare5 said:


People spend their lives studying this stuff - its hugely interesting, but I think SSD's will make all of this go away when their price gets low enough

Not at all. Modern SSDs have larger and even more complicated cache systems than HDDs do. Several SSDs have 128MB or more of cache.
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January 14, 2011 1:49:34 PM

Best answer selected by advice pro.
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