Unit 3: Memory and device management

• Address binding: mapping program addresses to memory addresses at compile time (absolute code), load time (relocatable code) or execution time (dynamic, using an MMU).
• Relocation: adjusting addresses when a program is loaded at a different location — relocation register adds a base value.
• Loading: static loading (whole program before execution) vs dynamic loading (routines loaded when called).
• Linking: static linking (libraries copied into the executable) vs dynamic linking (shared libraries — .dll, .so — linked at run time).

A logical address is generated by the CPU; a physical address is the actual location in memory. The Memory Management Unit (MMU) maps logical to physical addresses at run time, for example by adding a relocation (base) register value. Swapping temporarily moves a process from memory to disk (backing store) and back, so that more processes can run than fit in memory at once.

• Protection: base and limit registers, page-table protection bits (read, write, execute), valid–invalid bits.
• Sharing: shared pages for common code (reentrant code), shared memory segments for IPC.

Paging divides logical memory into fixed-size pages and physical memory into frames of the same size. A page table maps each page to a frame, so a process need not be contiguous. Paging removes external fragmentation.

• Logical address = (page number p, offset d); physical address = frame number × page size + d.

Segmentation divides a program into variable-size logical segments (code, data, stack). A segment table stores each segment's base and limit.

Virtual memory lets a process run even if only part of it is in memory. Demand paging loads a page only when it is needed; accessing a page not in memory causes a page fault.

Frame allocation can be equal or proportional to process size. Thrashing happens when processes have too few frames and spend more time paging than executing; it is controlled with the working-set model or by reducing multiprogramming.

I/O devices connect through controllers; data moves by programmed I/O, interrupts or DMA. A disk has platters, tracks, sectors and cylinders; access time = seek time + rotational latency + transfer time. Disk scheduling reduces seek time.

• Device driver: OS module that hides device details and translates generic I/O requests into device-specific commands.
• Disk management: formatting (low-level and logical), partitioning, boot block, bad-block handling, RAID for reliability and performance.