What do you need to know about optimizing storage card speed?

[murduck]

I found this great article on What do you need to know about optimizing storage card speed? from Pocket PC Magazine.
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What do you need to know about optimizing storage card speed?

I've decided to collect all the information you need to know about storage card optimization because it's another unexplored/undescribed area, as far as Pocket PC-related articles are concerned.

First, what format should you use, if you have both a CF and an SD slot? Is it true that SD cards are much slower than CF cards? Not at all. Actually, it were only early Pocket PC models (most importantly, the Compaq iPAQ 38xx series) that had a very slow SD interface. Otherwise, there're only usability-related differences between the two card formats except for some (very rare) exceptions like the Dell Axim x50v (which has a considerably faster and better optimized SD interface than CF).

Second, what can I store on them? Almost anything except

- mail bodies that ActiveSync synchronizes to your Messaging (in pre-WM2003SE parlance, Pocket Inbox). Note that I've emphasized "bodies that ActiveSync synchronizes" because attachments (see this and this thread) and WebIS Mail-downloaded (via POP3, not AS-synchronized Outlook ones!) mail can be stored on cards
- system databases
- the system registry
- by default, the RAM contents of the \Windows directory: DLL's, help files, uninstallation-related files etc. You can, however, relocate most of them to an external storage card and/or the built-in File Store (if there is). This subject is too large to be discussed in this article; therefore, the reader is referred to the Windows Mobile Technology relocation tutorials/tips; in addition, I also recommend this thread.
- ActiveSync-synchronized files in \My Documents (you can, however, use MobSync to circumvent this limitation).

It should be stressed that it's not only the type of files/data that can be stored on storage cards that is different, but, fundamentally, the speed of the medium, which is the main reason why PDA's have power-hungry, meagre (32/64/128 Megabytes) and expensive dynamic RAM memory at all, and why they don't use hundreds of Megabytes of simple/much cheaper flash ROM-based memory. Storage cards are two or even three orders of magnitude slower than RAM in cases; this is why they can't be used at all as, for example, dynamic program/system memory. The latter, for example, stores the heap/stack/the program code - this memory is constantly accessed/changed. If you, for example, change a variable in your program, then, the memory cell(s) holding that variable (assuming it's not a registry variable) is also changed. You can have an idea of how slow this would become if the flash ROM controller needed, say, 1-2 milliseconds to store this new value in the ROM...

In real life, because you can only use your card as a storage medium (like your hard disk in your desktop PC), the speed problem won't be so apparent unless you start doing fancy things like
- install applications that store tons (hundreds) of files on it and expect tolerable speed upon installation. Applications like this are several IR remote controller apps (some of them store their device databases in separate files), Pocket Informant (if you decide to manually relocate it), the adventure Fade etc.
- relocate the Pocket Internet Explorer (PIE for short) cache to it (more on this relocation later), unless you optimize the card
- install NetFront on the storage card (NetFront has its cache directory in a subdirectory of its home directory by default unless you have version 3.2+ and relocate the cache to somewhere else)
- start applications that require a steady (not bursty!) transfer rate to the card. A particular example of the latter is NoteM, the well-known MP3 recorder app (please read this roundup and this summarization for more info on this program and its alternatives). If your card has problems with these kinds of apps (because it's slow by nature or uses a file system that slows it to a crawl), it will not be able to keep up even with the moderate transfer rate requirements (56 kilobits/sec) of NoteM, let alone its high-quality (128 kilobits/sec) recording mode.

File systems

Storage cards are pretty flexible. You can use different so-called file systems on a storage card as you can (to a certain degree) modify the (logical) characteristics of a, say, floppy disk. Remember the times of 800.com (com in this case, is not a dotcom commerce site but an old MS-DOS extension type), which made it possible to store even around 840 kbytes on a 360 kbyte DS/DD 5 1/4 diskette? It achieved this by raising the track-per-inch ratio from 48 to 96, raising the sector-per-track ratio from 9 to 10 and raising the number of tracks (by an additional two or three) to 82-83? Storage cards aren't that flexible (you can't increase their capacity because they aren't magneto-mechanical units but have a pre-defined number of memory cells, which can't be increased), but still, the basics of floppy (or, for that matter, hard disks, where 'clusters' came into picture) file systems are still a good analogy.

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Murduck

[BigZam]

great stuff man, thanks.

[murduck]

This is really a good Tips. I will try it at soon i get the time and backup first my data using SPB Backup 1.5

Murduck

[manperez]

Thanks, Murduck, for a great explanation about storage cards!

Manny