« on: September 17, 2014, 12:03:45 PM »
Got any links to support this, or is this all just seat-of-the-pants common sense reasoning?
I covered many things in your quote. All are factual.
As for the way SD cards work, you can look it up, there are plenty of links. That's why there are two modes of formatting for SD cards in your camera, a regular format and a low level format.
I thought most users knew that formatting a card with a regular format does not actually erase the photos, it merely marks the FAT table to indicate that the files can be overwritten.
The thing that many do not know is that when the flash card decides to over write a file, it must first erase a much larger memory block, and this takes time. The Flash controller may also fragment a file due to the wear leveling, so a file is spread to different places on the card. This operation for a SD card does not happen until you go to write a file. It can slow a SD card down so much that Video recording stops.
There are many different factors in play. Start with Wikipedia, the section on Real World Performance.
Also, be aware. Card speeds are rated by saving a huge file to a completely erased card, there is no erasing of used memory blocks, and no fragmentation. As you'd expect, real world performance is slower than card rated speeds.
CF Cards handle erasing differently with a process akin to that used for SSD's in your computer.I've had two cameras with bent CF pins. One was a used Minolta DSLR that I had bought (Just before Sony bought them). I was able to straighten the bent pin out, and it was fine.
The other was a used Canon P&S that I bought for a dollar. The charger, battery, and CF card were worth more than that.
Many SD card advocates are not aware that you must do a low level format on a previously filled SD card in order to get rated write speeds. If you just do a regular quick in camera format, the write speed slows to a crawl. If you do a low level format every time, then the card gets lots of write cycles, since a low level format writes a 0 to every memory cell.
With a AD card, its best to buy a big one, and do a low level format whenever you have saved enough files to reach the card capacity.
For example, you have a 64GB card.
You do 4 photo sessions using 16 GB and doing a regular format(does not erase the cells or data). The card software tries to equalize card usage, so it tends to not over write cells with data in them until it has to. Thus, by the 4th 16GB session, the entire card has been written to, and now data must be erased to save more. This is very slow, so your right speed drops. Time to do a low level format to get the speed you are paying for.