3. Memory Management

3. Memory Management
	Chapter 1. Introduction

Memory
Important resource. Must be managed carefully.
- Which parts of memory are being used and which ones are free
- Allocate and deallocate memory for processes
- When main memory is not enough, allocate space on disc
Memory Management
Happens on two ways:
1. With SWAPPING & PAGING: Processes are transferred continuously between main memory and disc.
2. Without SWAPPING & PAGING
- Monoprogramming
  Simple Systems (IBM-PC)
  Memory is split between the operating system and the only user process.
  Figure 1.8. Memory Management
  One program at a time:
  - User types a command
  - OS takes the program from disc
  - OS puts a prompt when the program process terminates
- Multiprogramming with fix partitions (batch)
  MFT-Multiprogramming with a Fixed number of Tasks (used for IBM OS/360)
  - Multiple Queues: a big partition may have an empty queue, while small partitions have full queues.
  - Single queue: as soon as one partition is free, the job closer to queue head runs ( if it fits in the partition). A big partition may be allocated to a small job.
- Multiprogramming
  - More than one process in memory
  - On interactive systems: many user are allocated at same time
  - Time expended waiting I/O is not wasted
  GOAL: improve CPU utilization


2. Process		Chapter 2. Unix