speed measured (Was: Re: AGFA SD card)
Michael J. Mahon wrote:
[color=blue]
> This is very unlikely to happen in photographic applications, since
> a card is very seldom "recycled" in its entirety more than once a day,
> and 10,000 such cycles would correspond to continuous use for over 25
> years![/color]
I got this information from the primer on MLC/SLC,
[url]http://www.memorynet.co.uk/info/faq-single-layer-cell-versus-multi-level-cell.shtml[/url]
.. My understanding is that the cell in the SLC card can assume either
of its two states -- either there is a charge in the cell, or there
isn't. The MLC card has its cell in either of the 4 states -- the cell
can containeither of the four intermediate amounts of electrical charge
(the full charge, two thirds of a full charge, one third of a full
charge, and no charge). Such an "analogous" arrangement in MLC is less
reliable (it is more susceptible to an external electrical field which
can easier discharge the cell and switch it in another of the 4
states). Over time, the charge in a cell can dissipate either
naturally, or helped with external electrical field or when been put
through X-Ray machine in airport. The distinction between the 4 charged
levels in a MLC card is less than the difference between the
charged/not charged state in SLC card. It is easier for a cell in an
MLC card to switch sporadically into another state out of the four
possible states. So, it may still be beneficial to get an SLC card.
Less probability of arbitrary corruption of memory.
I got an external SD card reader (Sandisk's ImageMate 8-in-1) and
connected to my laptop via an USB2 port. I transferred a 111-MB movie
file from the card into PC and back, and timed the transfer time with a
stopwatch. Here are the results:
Sandisk SD card -- read/write speed = 9.2MBps / 5.3MBps
Transcend/Agfa SD card -- read/write speed = 8.5MBps / 6.5MBps
This is strange ! The Transcend card performed up to its specification
(7.7MBps/6.8MBps). But the Sandisk card perfomed even better on reading
speed (than Transcend), and only slightly worse on writing speed. It
should not be happening. The Sandisk technical support claims that the
Sandisk Standard 256MB card has a read/write speed of up to 2.8 MB/s,
but in some batches the speed can be as low as 1.5MB/s. I do not know
what to think of these results. I did the speed measurements again, and
I got the same results with the accuracy of few percent. I am
perplexed. And I do not know what card to keep :-(
Well, Michael, I know, you told me several times already that I should
stop obsessing over a card, and go and take the pictures. I did take
some pictures. But on overall scheme of things, I am an asocial nerd,
and I have nobody to show or email the pictures. Thus no motivation to
make 'em. The only thing left for me is to obsess over choosing a card,
trying to maximize the output (speed+quality) while minimizing the
input (price).
D.
Re: speed measured (Was: Re: AGFA SD card)
drocillo wrote:[color=blue]
> Michael J. Mahon wrote:
>
>[color=green]
>>This is very unlikely to happen in photographic applications, since
>>a card is very seldom "recycled" in its entirety more than once a day,
>>and 10,000 such cycles would correspond to continuous use for over 25
>>years![/color]
>
>
> I got this information from the primer on MLC/SLC,
> [url]http://www.memorynet.co.uk/info/faq-single-layer-cell-versus-multi-level-cell.shtml[/url]
> . My understanding is that the cell in the SLC card can assume either
> of its two states -- either there is a charge in the cell, or there
> isn't. The MLC card has its cell in either of the 4 states -- the cell
> can containeither of the four intermediate amounts of electrical charge
> (the full charge, two thirds of a full charge, one third of a full
> charge, and no charge). Such an "analogous" arrangement in MLC is less
> reliable (it is more susceptible to an external electrical field which
> can easier discharge the cell and switch it in another of the 4
> states). Over time, the charge in a cell can dissipate either
> naturally, or helped with external electrical field or when been put
> through X-Ray machine in airport. The distinction between the 4 charged
> levels in a MLC card is less than the difference between the
> charged/not charged state in SLC card. It is easier for a cell in an
> MLC card to switch sporadically into another state out of the four
> possible states. So, it may still be beneficial to get an SLC card.
> Less probability of arbitrary corruption of memory.[/color]
This is theoretically true, but has no bearing on the actual
reliability of products. Both schemes are quite robust in
practice, and the MLC chips have lower costs, and therefore are
driving flash memory prices.
This is a difference without a distinction, from the point of
view of the user. Neither card has any reliability problem.
[color=blue]
> I got an external SD card reader (Sandisk's ImageMate 8-in-1) and
> connected to my laptop via an USB2 port. I transferred a 111-MB movie
> file from the card into PC and back, and timed the transfer time with a
> stopwatch. Here are the results:
>
> Sandisk SD card -- read/write speed = 9.2MBps / 5.3MBps
> Transcend/Agfa SD card -- read/write speed = 8.5MBps / 6.5MBps
>
> This is strange ! The Transcend card performed up to its specification
> (7.7MBps/6.8MBps). But the Sandisk card perfomed even better on reading
> speed (than Transcend), and only slightly worse on writing speed. It
> should not be happening. The Sandisk technical support claims that the
> Sandisk Standard 256MB card has a read/write speed of up to 2.8 MB/s,
> but in some batches the speed can be as low as 1.5MB/s. I do not know
> what to think of these results. I did the speed measurements again, and
> I got the same results with the accuracy of few percent. I am
> perplexed. And I do not know what card to keep :-([/color]
The algorithms used to write are particularly "interesting", and
can lead to surprising results. Worse, different devices (like
cameras) usually use different write schemes.
[color=blue]
> Well, Michael, I know, you told me several times already that I should
> stop obsessing over a card, and go and take the pictures. I did take
> some pictures. But on overall scheme of things, I am an asocial nerd,
> and I have nobody to show or email the pictures. Thus no motivation to
> make 'em. The only thing left for me is to obsess over choosing a card,
> trying to maximize the output (speed+quality) while minimizing the
> input (price).[/color]
Ah! Your more interested in flash memory than in digital
photography! I'll bet you can find lots of others who share
your interest on a forum dedicated to flash memory. ;-)
-michael
Music synthesis for 8-bit Apple II's!
Home page: [url]http://members.aol.com/MJMahon/[/url]
"The wastebasket is our most important design
tool--and it is seriously underused."
Re: speed measured (Was: Re: AGFA SD card)
Michael J. Mahon wrote:
[color=blue]
> Ah! Your more interested in flash memory than in digital
> photography! I'll bet you can find lots of others who share
> your interest on a forum dedicated to flash memory.[/color]
Before posting my question about SD cards on the digital cameras forum
and crossposting it to the handheld computer forums, I made a search
for the forums dedicated to flash memory cards only. I did not find
them. I interpreted this fact by hypothesizing that nobody is
interested by talking about flash memory per se, but only in a
particular application. The users of digital cameras and of handheld
computers could well encounter the same problems which I had, so these
forums seemed to me to be the appropriate place to post.
Well, I found also the forums comp.arch.embedded and
sci.electronics.design which talked about bare flash memory, but this
was the flash memory used in too remote applications such as
reprogrammable controllers.
So far, I have the said thoughts boiling in my head with no opportunity
to spill it outside into some other enthusiasts' heads.
D.
Re: speed measured (Was: Re: AGFA SD card)
drocillo wrote:[color=blue]
> Michael J. Mahon wrote:
>
>[color=green]
>>Ah! Your more interested in flash memory than in digital
>>photography! I'll bet you can find lots of others who share
>>your interest on a forum dedicated to flash memory.[/color]
>
>
> Before posting my question about SD cards on the digital cameras forum
> and crossposting it to the handheld computer forums, I made a search
> for the forums dedicated to flash memory cards only. I did not find
> them. I interpreted this fact by hypothesizing that nobody is
> interested by talking about flash memory per se, but only in a
> particular application. The users of digital cameras and of handheld
> computers could well encounter the same problems which I had, so these
> forums seemed to me to be the appropriate place to post.
>
> Well, I found also the forums comp.arch.embedded and
> sci.electronics.design which talked about bare flash memory, but this
> was the flash memory used in too remote applications such as
> reprogrammable controllers.
>
> So far, I have the said thoughts boiling in my head with no opportunity
> to spill it outside into some other enthusiasts' heads.[/color]
I understand.
I think the problem is that flash memory is so trouble-free in operation
that no one has any cause to be concerned with any aspect of it except
capacity, speed, and price. I've never found any *bad* flash memory,
and I've never heard from anyone who wore some out!
-michael
Home page: [url]http://members.aol.com/MJMahon/[/url]
"The wastebasket is our most important design
tool--and it is seriously underused."
Re: speed measured (Was: Re: AGFA SD card)
Michael J. Mahon wrote:
[color=blue]
> I think the problem is that flash memory is so trouble-free in operation...
> I've never found any *bad* flash memory,
> and I've never heard from anyone who wore some out![/color]
Yes ! And the housing boom will last forever ! The prices will never
fall !
Re: speed measured (Was: Re: AGFA SD card)
drocillo wrote:[color=blue]
> Michael J. Mahon wrote:
>
>[color=green]
>>I think the problem is that flash memory is so trouble-free in operation...
>>I've never found any *bad* flash memory,
>>and I've never heard from anyone who wore some out![/color]
>
>
> Yes ! And the housing boom will last forever ! The prices will never
> fall ![/color]
In this case, more like, "The card will last longer than the camera!"
-michael
Music synthesis for 8-bit Apple II's!
Home page: [url]http://members.aol.com/MJMahon/[/url]
"The wastebasket is our most important design
tool--and it is seriously underused."
Re: speed measured (Was: Re: AGFA SD card)
Michael J. Mahon wrote:[color=blue]
> drocillo wrote:[color=green]
> > Michael J. Mahon wrote:
> >
> >[color=darkred]
> >>I think the problem is that flash memory is so trouble-free in operation...
> >>I've never found any *bad* flash memory,
> >>and I've never heard from anyone who wore some out![/color]
> >
> >
> > Yes ! And the housing boom will last forever ! The prices will never
> > fall ![/color]
>
> In this case, more like, "The card will last longer than the camera!"[/color]
No. It is more like: "In the past 5 years, my house grew significantly
in price. Houses of everyone whom I know grew up in prices. Therefore,
everyone's house in the US grew up in price. The growth will be
indefinite".
"My memory cards never failed. Cards of everyone around me whom I know
never failed. Therefore, nobody in the world had their memory cards
failed. In fact, the cards will never fail".