DESIGN PROCESS OF REAL-TIME OPERATING SYSTEMS (RTOS) - Software Design for Six-Sigma: A Roadmap for Excellence - page 61

TABLE 3.1 Memory Management Design Options: A Comparison

Purpose Advantages Disadvantages Efficiency Implementation

Run-Time Stack Points to the memory

locations of
programs waiting to
run

Supports reentrancy; each
task has their own stack

Only supports first-in,
last-out

Fast Easy

Dynamic Memory
Allocation

Service Provided by
the operating system
allowing tasks to
borrow memory
from the heap

Allows the program to
request memory

Does not allow for
deterministic
operating system

Very slow, takes too
much time to
allocate and
deallocate for
real-time systems

Difficult

Memory
Protection

Protect system
memory

Is necessary for memory
validity

For system calls, tasks
must give up control
to the operating
system

Relatively fast Mildly difficult

Virtual Memory Gives the illusion of

contiguous memory

Makes programming easier
and allows programs that
require more memory than
physically available to run

Nondeterministic
memory access
times

Can be slow if memory
is on disk instead of
RAM

Difficult and not
recommended
for real-time
operating
systems