What means Max 15 Mb/s showin in SDHC cards? at DVinfo.net

Francois Dormoy · January 9th, 2009, 08:06 PM

I bought a SanDisk Ultra II 16GB/15MB SDHC Card to use in my Sony XDCAM-EX1 camera and it works perfectly well with the highest bit rates (1080p30HQ at 35 Mb/s bit rate).
However, the card shows that the max bit rate is 15 Mb/s.
So can you explain what it means ? Why should a card showing a linit of 15 Mb/s works well to record clips at 35 Mb/s rate ?

Brooks Graham · January 9th, 2009, 08:31 PM

Look carefully at the capitalizations used:

Mb = megabit
MB = megabyte

Ignoring the overhead involved in various types of data transfer, there are eight bits per byte.

The codec rate is 35 Mb/sec (which somewhere between 4.5 and 5.5 megabytes per second)

As for speed ratings on flash cards, they are usually fibs told by over-zealous product marketing drones.

Craig Seeman · January 10th, 2009, 09:32 AM

BTW on the back of the package of the Sandisk Ultra 2 32GB cards it says 9MB write 15MB read.

I did a read/write test Crystal Disk Mark and I thought the results were 20MB write 17MB read or something like that.

January 9th, 2009, 08:06 PM	#1
Francois Dormoy Regular Crew Join Date: May 2008 Location: Montreal, Canada Posts: 81	What means Max 15 Mb/s showin in SDHC cards? I bought a SanDisk Ultra II 16GB/15MB SDHC Card to use in my Sony XDCAM-EX1 camera and it works perfectly well with the highest bit rates (1080p30HQ at 35 Mb/s bit rate). However, the card shows that the max bit rate is 15 Mb/s. So can you explain what it means ? Why should a card showing a linit of 15 Mb/s works well to record clips at 35 Mb/s rate ?

January 9th, 2009, 08:31 PM	#2
Brooks Graham Regular Crew Join Date: Nov 2008 Location: San Francisco, CA Posts: 121	Look carefully at the capitalizations used: Mb = megabit MB = megabyte Ignoring the overhead involved in various types of data transfer, there are eight bits per byte. The codec rate is 35 Mb/sec (which somewhere between 4.5 and 5.5 megabytes per second) As for speed ratings on flash cards, they are usually fibs told by over-zealous product marketing drones. Last edited by Brooks Graham; January 9th, 2009 at 08:46 PM. Reason: bad math

January 10th, 2009, 09:32 AM	#3
Craig Seeman Inner Circle Join Date: Feb 2004 Location: Brooklyn, NY, USA Posts: 3,841	BTW on the back of the package of the Sandisk Ultra 2 32GB cards it says 9MB write 15MB read. I did a read/write test Crystal Disk Mark and I thought the results were 20MB write 17MB read or something like that.