

Busting Modern Hardware Myths (2013) - nkurz
http://highscalability.com/blog/2013/6/13/busting-4-modern-hardware-myths-are-memory-hdds-and-ssds-rea.html?

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Fr0styMatt
An important overall point that the article seems to be highlighting is that,
in general (independent of these myths), developers are becoming less and less
familiar with what the underlying system is doing. Or perhaps the more correct
term is that developers are becoming more 'distant' \-- there are more layers
of abstraction in the whole system than there have been in the past. At the
top, programming languages themselves want to get more abstract to make the
process of writing software more efficient and in some ways more automated. At
the bottom, hardware needs to use clever design to hide performance
limitations that we come up against.

The problem is that sometimes, these abstractions leak. Knowing that what
you're seeing is one of those leaks is key to not go down the rabbit hole of,
for example, chasing a bug that ends up being caused by a hardware failure
(painful experience!). So you have to keep notice of those layers below those
you're directly working with; while you don't have to live there, you
shouldn't totally ignore their existence.

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yvdriess
Are any of these a surprise to anyone here?

I am not asking this rhetorically.

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p1esk
For me, the surprise was to learn that access time for L1 cache is 3 cycles. I
thought it should be 1 cycle.

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Tuna-Fish
Actually 4 cycles for modern cpus. The access time of a cache depends mostly
on it's size (wire delay and switching time for the access tree). This means
that cache sizes are always tradeoffs between hit rate and access time. As
cpus get better at hiding latency, the access latency is loosened.

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codehero
In Myth 4 SSDs, Thompson claims that:

"there's a limited number of times you can READ and ERASE a block" (emphasis
mine)

My understanding is that ERASE cycles are what's limited; reading and writing
are not destructive to the flash.

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nitrogen
Supposedly MLC NAND is susceptible to data deterioration due to reads.

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adwn
I have never heard of the myth that "HDDs provide random access". As far back
as I can remember, HDDs were always the archetypal example for _non_ -random
access storage media.

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Florin_Andrei
> _As far back as I can remember, HDDs were always the archetypal example for
> non-random access storage media._

I'm pretty sure that's tape, not HDD.

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adwn
> _I 'm pretty sure that's tape, not HDD._

Nope, I'm only 27.

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1amzave
It's less a matter of age than environment -- there are still plenty of places
using lots of tape. (It's not like we're talking about vacuum tubes or core
memory here...)

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adwn
Clarification: I didn't mean to imply that tape is dead, but that during the
15 years that I've been programming, tape drives have only been used in
enterprise-level backup systems, and are not used as "archetypal example" in
articles intended for a more general audience.

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nimish
Or: welcome to the memory mountain, enjoy your stay.

