The limits on describing limits
BlackBerry PlayBook OS is a microkernel, so many things that might be a core limit in some operating systems, become dependent on the particular manager that implements that service under BlackBerry PlayBook OS, especially for filesystems, where there are multiple possible filesystems.
Many resources depend on how much memory is available. Other limits depend on your target system. For example, the virtual address space for a process can vary by processor from 32 MB on ARM to 3.5 GB on x86.
Some limits are a complex interaction between many things. To quote the simple/obvious limit is misleading; describing all of the interactions can be complicated. The key thing to remember while reading this chapter is that there can be many factors behind a limit.