case study:symbian OS,modern operating system,3rd edition

object-oriented
microkernel design(takes up much less memory upon boot and support new functionality to be loaded and plugged at any time)
client/server resource access

Memory Management:
it does not use the virtual memory/swap space model and not use demand-paging.
actually,pages are replaced, but the page being replaced is just discarded.this means only code pages can be replaced,since only they are backed on the flash memory.
有个概念就是在嵌入式系统，存储设备是flash memory,它既当内存用，又当永久存储用，所以有种技术叫做execute in-place.
security:gatekeeper:the system asks user for permission of installing every application.

communication in Symbian OS:

CSY:communication server
TSY:telephony server
PRT:protocol module
MTM:message type module