[Thinkpad] OT: 1 GB flash card
ferko at attglobal.net
Fri Sep 17 21:43:22 CDT 2004
Thanks, Vicky .. much to digest and sort through .. and we'll give it
a go. If I can see a before - after difference, will report back.
Vicky Lamburn wrote:
> generally speaking - yes it is limited by the camera's hardware.
> 1 x = 150KByte/sec (as per CD-ROM speed)
> so 40x = 6,000Kbyte/sec (or roughly 6MB/sec)
> It's much the same thing if you were to place a 52x CD-ROM on a PIO-1
> enabled IDE bus system it would work but not transfer the data without
> sufficient CPU horse power at 52x speed but at a slower speed. If the
> IDE bus was DMA enabled, it could potentially reach the maximum speed
> of 52x transfer rate. (Not wishing to get into issues of CAV etc. here)
> So if the camera can do a sutained 4 x write speed, that's
> 600Kbyte/sec max meaning that even if the card was 40x rated it would
> only write at 4x.
> If however your camera did 16x but you have a 4x card, the potential
> for data corruption arises, much as you might get with a 4x rated
> CD-R, burned at 16x speed.
> I'm not sure if there is any camera that writes a 6,000Kbyte/sec - but
> certainly a PCMCIA bus has the potential to transfer at this speed
> with a DMA based (read PC-Card) spec design. The 6,000Kbyte/sec
> transfer rate at 40x on a Compact Flash card would probably only be
> met if the card was to be on the IDE bus mimicking a hard disk, and
> the IDE bus was operating in a DMA/ATA-x mode.
> It's also like sticking an ATA-5 (100Mbyte/sec) DMA disk on a IDE bus
> on designed for polled transfers (PIO 0-4), it won't get 100Mbyte/sec
> but its downwardly compatible and will still work, just slower. That
> said even on a ATA-5/6 IDE bus - I'd be impressed to see close to
> 100Mbyte/sec being sustained.
> Essentially if the card is to be used to save stuff on a camera - a
> slow card will be fine if your not too worried about how long it takes
> to copy to the computer. (If directly plugged in, otherwise then you
> have the issue of the connection method which could limit the transfer
> speed). if the card is to be used as a storage medium for computer
> files of a large size of used in an IDE -> Compact Flash adapter, then
> the 40x cards make more sense to obtain.
> Think this pretty much covers it :)
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