As people have acquired Windows Mobile 5.0 devices and upgrades, many of them have noticed that these devices are a bit slower than previous Pocket PCs.
Until now, most people have chalked this up to this operating system’s switch from using RAM for long-term storage to using Flash ROM for this task. Accessing Flash ROM is inherently slower than RAM.
But a recent posting on the Windows Mobile Team Blog by Mike Calligaro says it is a bit more complicated than this.
Many Sectors Make Light Work
In layman’s terms, Flash ROM has a shorter lifespan than RAM does. The number of times data can be written to each sector on the chip is limited. Therefore, Windows Mobile tries to spread out where it saves data as much as possible.
When something in Flash ROM needs to be changed, the data is copied into RAM and changed there, then saved in a different sector of Flash ROM.
The initial sector of Flash ROM is then marked as invalid, so it won’t be used again. However, the original data isn’t erased, because that takes valuable time. And not just time in computer terms; according to Calligaro, erasing a sector can take a couple of seconds.
Occasionally, when the handheld is idle, the operating system will go through and erase the contents of invalid sectors and re-validate them.
Here’s the Rub
While this might seem like an entirely workable system, there are some applications that require a great deal of data to be re-written, and the Pocket PC can run out of available sectors.
This means that invalid sectors need to be erased and revalidated, a process that greatly slows down the performance of the application.
Calligaro goes into much more detail in his explanation.
Why Not Dump It?
It is quite possible that, at this point, some people are wondering why Microsoft moved to using Flash ROM for long-term storage.
It did so because this solves one of the greatest problems ever to plague Pocket PC users.
In order for RAM to keep holding its contents, it must have a constant source of power. Even when the device is off, power must keep being supplied to its memory chips or everything in them is lost.
This means that, if a handheld wasn’t recharged fairly frequently, all the information stored on it would be erased. This resulted in many, many people losing irreplaceable information… and a few handhelds being tossed out windows.
The situation with the latest generation of Pocket PCs is completely different. Flash ROM doesn’t require power just for storage. Unless data is actually being written or erased, a Flash ROM chip requires no power at all.
Therefore, if a user forgets to charge their handheld for weeks or even months, none of the information on it is lost.
And it doesn’t end there. Last year, Calligaro put together a complete list of all the advantages of this new system of storage.