Storage FAQ
By Chris De Herrera, Copyright 2001
 Version 1.01  Revised 11/1/2001

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Introduction

So you've got a Pocket PC, Handheld PC or Palm-size PC and you want to know more about storing information on it.  This FAQ covers common issues and solutions for using internal and external storage. 

Where Can I Store Stuff?

When you first got your device, you probably noticed that you can store information on it right away.  Well this information is stored in internal ram.  You can add a CompactFlash or PC Card flash card to store data and programs as well. The CompactFlash or PC Cards appear as Storage Card in the device. In the Pocket PC 2002, some models allow for internal storage to the extra flash that is not used by the Flash ROM.

Internal Ram

The internal ram is used to store both programs and data.  It is compressed real time using 2 different methods to maximize the amount of information you can store.  One method is to compress the whole file as it is received. This is good for programs and some data that is in ASCII format. The other method of compression is to split every other byte of data into 2 separate streams.  Then the resulting streams of data are compressed.  The second method of compression is very good for Unicode (2 byte) representation of data.  Certain types of data like the registry and the internal databases must be stored in internal ram.  If you develop applications,. the internal ram for storage is called the Object Store by Microsoft.

Internal Ram - Limitations

There are some limitations to using internal ram for storage.  Prior to Windows CE 3.0, the internal ram for storage was limited to 16 MB. In Windows CE 3.0, this limit has been increase to 256 MB.  In Windows CE 1.0 and 2.0, the largest file was limited to 4 MB in size.  In Windows CE 2.1 and later, the largest file is limited to 16 Mb.  So if you need to use really large files, you should consider using external storage.

Flash ROM

In the Pocket PC 2002 some of the devices like the HP Jornada 560 series, Casio E-200 and the iPAQ 3700/3800 series allow for internal storage of files in the extra flash that is not used by the ROM.  The iPAQ and Jornada use an application from Intel called Persistent Storage. Persistent Storage is a new way to format and write to flash in sections. I've found that writing to flash is very slow - like about 1/2 hour to write a 3.3 MB file. So be patient if you choose to store things here. The good news is that if you run your batteries out, the information stored here will be retained.

External PC Card, CompactFlash Card or MultiMedia/Secure Digital Card

The PC Card, CompactFlash card or MultiMedia or Secure Digital Card is a separate area to store both programs and data.  The programs and data are not compressed before being stored.  You can store much larger files on the external storage.  There is 2 types of storage available, flash and hard disk. Flash storage is fairly fast from about 250k/second to over 1 MB/second and it is much lower power at about 50 mA to read and write to it. Most users do not notice a significant reduction in the battery life of their device when using a flash card. The hard disk storage is very large and economical.  You can get hard drives up to 2 GB in size for PC Cards and 1 GB for CompactFlash Cards. Hard disks require much more power than flash.  The lowest power hard disk from IBM requires approximately 250 ma so your battery life will be diminished greatly.  Both flash and hard disks use the FAT file format and are compatible with notebook PCs and card readers for the desktop so you can transfer files faster than using ActiveSync.  I have a list of compatible PC Cards and CompactFlash Cards that you may find helpful in deciding which type of card to purchase. The MultiMedia Card or Secure Digital Card are much slower than CompactFlash or PC Cards since the data is written in a serial fashion to the card.  The big advantage that they offer is the small size of the media.

Using External Storage

Please note that external storage does not expand the amount of ram you have available to run programs.  You can use external storage to install applications if you choose Storage Card when you install them using ActiveSync's Add/Remove Programs.  If you want to move programs from internal ram to external storage, you should uninstall them and then reinstall them while selecting Storage Card as the destination. For all external storage, you should create a directory called My Documents in the root of the disk.  This directory is merged with the My Documents in ram when you view the My Documents directory on the device. Some programs do not search directories other than My Documents so this may be crucial to your ability to maximize the external storage.  Also, there is no utility to format or check (scandisk) your external storage which is included with your device. You can purchase a program called Flash Format from CNetX or Format Flash Card from PDA Resources.

Where does the Program Execute?

The internal ram and external PC Card or CompactFlash card are used to store programs only. When you choose to run a program stored in either place, the program is copied into ram (the execution space, not the storage space) to execute.  This means that there is 2 copies of a program if it is being executed. 

Conclusion

Now you have a better idea of where you can store programs. There is a great difference between internal and external storage that you should consider when you decide what you need or want to do with your device.  You can learn more about how RAM is used in Windows CE through the RAM FAQ.

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