Storage space and memory: mobile phone architecture versus PC architecture
In this respect, there is no difference between regular PC and Android.

The terminologies, however, is slightly confusing.

System memory refers to the storage space that is used by system files, and Device memory refers to all storage space. Device memory does not refer to RAM. Your device's RAM can be seen in Settings -&gt; More -&gt; Application Manager.


  is there a single memory chip acting as both a storage medium for files when the device is turned off as well as random access memory for the running operating system executables and apps in execution?


Sort of. Most Android device uses a System-on-chip (SOC). What is included in a SOC varies depending on the particular chip and device, but a typical SOC may have CPU, RAM, GPU, wireless, and possibly storage manufactured in a single chip. In regular PC, these are usually separate components, SOC is used in mobile devices to save space wasted due to separate component packaging, but internally there is still a delineation between the components.


  Where can I see the amount of space available on my SIM card?


AFAIK, you can't. Android have very limited support for SIM card facility. It uses the SIM card only for Telephony functions and importing existing contacts there into the device's address book.