Memory

Memory

1. Memory management

2. Logical Addressing

   • Base 0-F
   • Linked list
   • Limit register
   • Map logical addresses in program to physical addresses
     • Physical address = base register + logical address
   • Several translations for each instruction
   • Compiler generates list of all names in program
   • Linker converts each name into logical address
     • Offset from process origin
   • Program loaded
     • loader stores process origin in base register

3. Allocating/releasing memory

   • Paging
     • Divides RAM into small page frames
     • Page map table
     • Small chunks of process placed where they may fit
     • Logical Pages
       • Size of logical address space
         • 2^address size
       • Theoretical max num of pages
         • logical add space / page size
   • Partitioning
     • Variable
       • Process allocated memory from a gap large enough when it arrives
     • Fixed
       • Memory divided into n regions with fixed boundaries
         • Can be different sizes
     • Contiguous block for whole process
     • Inflexible
     • Fragmentation
     • Allocation algorithms
       • Best Fit
         • Smallest free partition
       • Worst Fit
         • Largest free partition
       • First Fit
         • First free partition