Managing memory and files

RAM is finite and shared. Memory management is the OS deciding which process gets which part of memory, for how long, and making sure no process strays outside its own area.

The tasks:

• Allocate memory to a process when it starts (and more as it asks for it).
• Deallocate memory when a process finishes, so the space can be reused.
• Protect memory so one process cannot read or overwrite another's area.
• Track free and used memory, so the next request can be satisfied.
• Move data between RAM and secondary storage when RAM is full (virtual memory — background, not required detail).

Without this, two programs would be handed the same address and both would crash.

File management is the OS organising everything stored on disk so that files can be found, opened, protected and deleted.

The tasks:

• Create, delete, rename and copy files and folders.
• Maintain a directory structure (folders inside folders), so files are grouped and easy to locate.
• Keep a record of where each file is stored — which blocks or clusters hold its data — plus its size, type and dates.
• Set and check access rights (read-only, read/write, which user may open it).
• Track free space on each storage device.
• Handle file extensions so the correct application opens the file.

Every file has a directory entry, like a library catalogue card:

The user sees a friendly name; the OS uses the rest.