Information

Dear forum members,
We are delighted to inform you that our forums are back online. Every single topic and post are now on their places and everything works just as before, only better. Welcome back!



Discussion

Discussion on Article:
SanDisk Extreme IV Compact Flash Card and New Card-Readers

Started by: Ajax9000 | Date 07/31/07 08:46:46 PM
Comments: 4 | Last Comment:  08/02/07 07:55:09 PM

Expand all threads | Collapse all threads

[1-1]

1. 
Nice that you looked at ReadyBoost. But what would have been far more interesting is if you'd looked at the performance when directly connected to a PATA bus.

Basically, A poor mans SSD can be made using a cheap CF2IDE adapter -- these sort of things http://www.sintech.cn/en/index.html & http://www.addonics.com/products/flash_memory_reader/default.asp#int.

As CF uses an IDE interface, I understand that the CF2IDE adapters are little more than physical connects, so they shouldn't impact on performance. In other words performance of a CF-based pseudo-SSD should relate to it's speed rating. Also, it may be that NAND latency is the limiting factor rather than SATA vs PATA.

In terms of a boot system a dual CF2IDE adapter would be even better -- you could use a slightly slower (say 133x) 12-16GB card for the OS and apps, and a faster (say 266x) 4-8GB card for the swap/page file. The thing I like about the double CF2IDE adaptor is the possibility of having swap on a smaller/cheaper card, so NAND wear out of the swap can be contained to a more affordably replaced item (even with the wear levelling features in the memory controllers of the newer CF cards, I'd imagine the swap file would still present a problem).

Addonics promote/sell this for laptops, but I've yet to see any performance figures.
0 0 [Posted by:  | Date: 07/31/07 08:46:46 PM]
Reply
- collapse thread

 
"As CF uses an IDE interface, I understand that the CF2IDE adapters are little more than physical connects, so they shouldn't impact on performance. In other words performance of a CF-based pseudo-SSD should relate to it's speed rating."

Actually there are two signalling modes used by CF cards: "removable device mode" and "TrueIDE" mode. The pin assignments are completely different in these cases depending on whether attached to a card reader that knows about how CF cards work or an IDE controller that thinks it's talking to a hard disk.

In the latter mode, instead of allowing more-or-less direct access, the card's built-in controller has to emulate an IDE device. Also, most cards that support DMA do not support it in TrueIDE mode. This means that cards may only achieve a tenth or less of their rated speed (the rating is given for removable device mode) in TrueIDE mode.

Another factor to watch out for is that many CF cards, even in TrueIDE mode, do not support booting in the normal way that a hard disk does because their controller doesn't emulate a partition table. The Extreme II emulates a partition table but the Extreme III does not and (I believe) nor does the Extreme IV.

If you need cards for this application I would recommend purchasing special industrial cards from Transcend, since SanDisk has stopped making industrial CF cards. This special type are more expensive but they support DMA in TrueIDE mode and emulate a partition table. These are absolutely necessary if you just want to swap your hard disk for a CF card with no further hassles.

Finally, I'd recommend not using a page file if you're using a system embedded onto a CF card.
0 0 [Posted by:  | Date: 08/02/07 03:22:55 PM]
Reply

[1-1]

Back to the Article

Add your Comment