Some users of Windows Mobile 5 are reporting “erratic behavior” during which their devices spontaneously slow down and speed up, according to a lengthy thread on the Windows Mobile Team blog. Concerns appear greatest among users who have upgraded their devices from Windows Mobile 2003 to Windows Mobile 5. Writing on the Windows Mobile Team Blog, Microsoft’s Mike Calligaro explains that the problem comes about because Windows Mobile 5 stores “persistent storage” data in flash ROM, rather than in battery-backed RAM. The advantage of flash-based persistent storage is that data survives a complete power failure, he notes. The disadvantage, on the other hand, is that flash must be erased before it is written, and can only be erased a full block at a time; and, with NOR flash, erasing a block can take up to two seconds.