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Old Jun 17, 2003, 5:05 PM   #1
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Default USB 2 Card Readers vs. USB 1

:?

Hi,

Recently I tested my new 6 in 1 USB2 Card Reader from SanDisk and found one interesting thing I missed before the purchase.

My settings for the test:

SanDisk SmartMedia Card 128 MB.
Pentium II - 450MHz.
OLYMPUS USB-1 Card Reader.
SanDisk USB-2 Card Reader.

The information for the reference I received from SanDisk:

> > SmartMedia card speed:
> > Read: 3.5MB/sec
> > Write: 500KB-1MB/sec (variable)
> > USB 1.1 ports have a shared bandwidth of 1.5 MB/sec.
> > USB 2.2 ports have a shared bandwidth of 60 MB/sec.

My thoughts and the results:

USB 1.1 port is limited by 1.5MB/sec bandwidth, but Read operation for SmartMedia card can be performed at 3.5MB/sec. The bottleneck here is a USB 1.1 port. By using USB 2.0 card we are shifting our bottleneck to SmartMedia card itself, and can perform Read operation with the max SmartMedia card speed 3.5MB/sec. It is 3.5/1.5 = 2.33 times faster.

==============================================
> OLYMPUS Card Reader on original USB-1 port:
>
> Read = 2.30 / Write = 4.38;
> ==============================================
> SanDisk 6 in 1 Card Reader plugged into new PCI based USB-2 port:
>
> Read = 0.59 / Write = 4.23;
> ==============================================

The read operation from USB 1.1 to USB 2.0 improved by 2.30/0.59 = 2.3 times.

Look like 2.3x is the max improvement we can get for the SmartMedia card by changing USB 1.1 to USB 2.0 (for Read operation).

For the write operation the bottleneck is SmartMedia card itself for both USB 1.1 and USB 2.0.

Look like we should not expect any improvement for the Write operation by switching from USB 1.1 to USB 2.0.

My conclusion:

USB-2 interface is 40 times faster, than USB-1, but do not expect such improvement by switching from USB-1 based Card Reader to USB-2 based Card Reader. The limitation is Flash Card itself.

The fastest Flash Card on the market has up to 7MB/sec transfer rate. It is far from USB-2 60MB/sec!!!


Thank you,

Andrei.
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Old Jun 17, 2003, 5:13 PM   #2
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Thank you!! I was just going to ask if anyone knew anything about this. And now i do!! Thanks again.Tealblue
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Old Jun 17, 2003, 10:45 PM   #3
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You should also check out this link:

http://www.robgalbraith.com/bins/mul...id=7-6191-6217

It is a good techincal review of 8 readers some USB2 and some FireWire. The fastest reader + fastest card is more than 8 times faster than the USB1 reader they had tested (don't know if its a good one or not.) Of course, that is a firewire reader. But the fastest USB2 reader wasn't far behind.

Eric
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Old Jun 18, 2003, 12:16 PM   #4
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Hi,

I just wanted to point out, that the bottleneck for any USB-2 based Card Reader is a Flash Card itself (or MicroDrive itself).

The fastest card I know is 40x CF card, and it has the max transfer rate of 6-7MB/sec.

It is not the match for USB-2 speed: 60 MB/sec.

With most USB-2 Card Reader the transfer rate will be limited by Flash Card itself.

Watch for better Card to come on the market :P
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Old Jun 18, 2003, 1:45 PM   #5
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Of course the card limits it. There are very few devices which can supply data that the actual speed of USB2 (if any. digital video camera? I doubt it. No hard disks can.... Anyone? We're talking "single device"!).

But it's not the "40x" ness of the card which limits it. That is write speed, not read speed. There are other limiting factors that read speed. The card is read in chunks. If that matches the internal buffers of the CF, then you'll get higher throughput. If the reader isn't reading in a pattern which matches the design of the CF (and many CF brands are different from each other) then you won't get optimum throughput.

Eric
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Old Jun 18, 2003, 2:51 PM   #6
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Yes, I was also coming to similar conclusions after I saw the card/USB1/USB2 comparison tables. Also I was thinking, bottlenecks for the future will be getting much bigger image files off media on to hard drives.

When we had 1Mpix cams, JPEG only, we got by with 4Mb Smartmedia. Now we can shoot 18-36 Mb files per pic, taking more and adding movie. There's also those 12Mpix cams as well. Even 1Gb Microdrive is going to seem small. But how many of us consider how long it will take to pull all the pics off full media?
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Old Jun 18, 2003, 3:15 PM   #7
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Yes, the write speed is usually slower, because of FLASH Memory technology nature.

It requires longer duration to perform the write operation. Why?

1) Flash Memory requires erasing the existing data before new data is written into the card. It is taking some extra time. Not so much, but still noticeable. Erasing can be perform for entire card or in clusters depend on card configuration. This is different from the regular RAM.
2) The writing procedure itself for the FLASH Memory is more complex and requires second power supply for the core of the chip.
3) The writing procedure performed in short burst with the same data for the same address. The entire writing diagram became longer.
4) Verification for the written data is taking some time also. In many cases it is taking the same time as the reading procedure from the Flash Card.

Because of 4) the writing procedure will never became faster than reading procedure.

Many Flash Memory makers are optimizing Flash Memory write procedure and it is became some close to read procedure time.
:P
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Old Jun 18, 2003, 4:52 PM   #8
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:P

One more thing to add about Hard Drive throughput (burst mode):

Any modern HD with 7200 rpm and ATA-100 Controller (1.5GB and higher) has ~100MB/sec the transfer rate.

It is well above USB-2 transfer rate, which is 60MB/sec.

For today the HD isnít the bottleneck from the transfer rate point of view.

Any modern computer with USB-2 port is able to handle any Flash Card with 50-60MB/sec read or write speed, but Ö we have to wait for such Flash Card to became the reality.

For now we have to enjoy the max speed of 7MB/sec for certain types of CF cards.
:P
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Old Jun 18, 2003, 11:05 PM   #9
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No 7200 rpm ATA-100 hard disk can consistently transfer data as fast as USB2. Check out this web site:
www.storagereview.com

It has some of the best testing methodology of anywhere I've seen. I trust their tests and recommend them without reservation.

The fastest drive they have tested is the Western Digital 200G JB drive, it it gets 56.5MB per second at the start but only 36MB per sec and the other end. I assume those are not burst, but I don't know. It doesn't say, but they are usually good about saying it when its burst. I would rather have large average transfer rates.

Now, the monster SCSI drives they are making can sustain more than 60MB/sec. But you'll pay through the nose for it.

Having written low level drivers for flash memory some time ago, your description is a little different than when I did it. We didn't need a "second power supply for the core of the chip."

I would have argued that because of your #4 & #3 it will never be as fast as reading.

It's good to hear that flash has advanced far enough that it's close to read time. I'm surprised because I'd think they'd have to skip the verify (or parallelize the write of one address with the verify of another.) Skipping verify isn't that appealing and parallelizing is probably expensive.
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Old Jun 19, 2003, 9:51 AM   #10
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:P

I used this site for HD characteristics reference:
http://cscserver.cc.edu/jerryisaacs/...harddrive.html

Regarding HD I just wanted to point, that it is not a bottleneck.

Even if average speed is 36 MB/sec it is still much higher than 7MB/sec.

:P
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