COMP1214 Systems & Platforms: Operating Systems Concepts Dr. Yvonne Howard – Rikki Prince – 1

Lessons from last sessions The main concerns of an OS – Providing application developers with an interface to use system resources – Managing the system resources How can devices communicate with the OS? The separation of concerns among – I/O devices, I/O device controllers (hardware), Device drivers & OS 2

Plan Identifying OS concepts Discuss individual concepts – Establish relevance to OS concerns 3 OS concepts Files Processes Memory mgmt System calls Relating concepts

Discussion Are you familiar with the following OS concepts? What are they? – Files – Processes 4 OS concepts Files Processes Memory mgmt System calls Relating concepts

Files 5 OS concepts Files Processes Memory mgmt System calls Relating concepts

Files 6 OS concepts Files Processes Memory mgmt System calls Relating concepts path name root directory working directory special files pipes

Linking and mounting 7 OS concepts Files Processes Memory mgmt System calls Relating concepts

Discussion Have you seen the list of processes running on: - A windows environment? - A UNIX environment? What types of processes can you see? -Is it one process per application? What is the life-cycle of a process? 8 OS concepts Files Processes Memory mgmt System calls Relating concepts

Windows Task Manager 9

Linux ps command 10

Processor modes Processors can be running in – Kernel mode – User mode The processor enters kernel mode: – At start-up, interrupt, error.... The processor enters user mode: – By an instruction (which sets the respective register in the CPU) Certain instructions can only be executed in kernel mode (privileged instructions) – Accessing CPU registers – Memory used by the kernel – I/O 11 OS concepts Files Processes Memory mgmt System calls Relating concepts

Kernel mode-User mode in Win NT 12 OS concepts Files Processes Memory mgmt System calls Relating concepts SOURCE: support.novell.com

Processes Multiprogramming – More tasks than processors – Processors switching between tasks – Illusion of parallelism Scheduling – Which task is next? One application requires one or more such tasks (processes) 13 OS concepts Files Processes Memory mgmt System calls Relating concepts

Processes Each task/process can access system resources Illusion of exclusive use of – Memory (Address space) – Storage – … Can be notified of events by the OS or other processes (signals) 14 OS concepts Files Processes Memory mgmt System calls Relating concepts

Discussion What is the use of each type of memory in the hierarchy below? How is memory shared among processes? What if a program needs more memory than available in RAM? 15 OS concepts Files Processes Memory mgmt System calls Relating concepts

Memory layout & Processes 16 OS concepts Files Processes Memory mgmt System calls Relating concepts Memory available per process? ADDRESS SPACE Memory needed larger than RAM? VIRTUAL MEMORY Process Address Space Process Table …

Discussion Which concerns of an OS does each of the following concepts relate to? – Process – Files – Memory management How can the OS provide a clean interface to the resources it manages? 17 OS concepts Files Processes Memory mgmt System calls Relating concepts

Accessing system resources An OS provides applications with APIs/libraries to access system resources – System calls can be invoked by applications in user mode – And are executed in kernel mode It is important that these are stable or else applications have to be re-written each time they change 18 OS concepts Files Processes Memory mgmt System calls Relating concepts

System calls 19 OS concepts Files Processes Memory mgmt System calls Relating concepts

OS concept map 20 CPU File System p1 p2 pN p3 Virtual Memory Address Space Other File System Other System Other File System Other System OS concepts Files Processes Memory mgmt System calls Relating concepts

Other online resources CPU components and animation – Lessons/CPU/Lesson.html Lessons/CPU/Lesson.html Computer architeture resources (advanced) –

Lessons learned We are aware of the importance of OS We have introduced basic OS concepts We are familiar with the following concepts – Processes – Address space – Files – Processor modes: Kernel mode/User mode – System calls – The UNIX Shell Textbook: sections OS concepts Files Processes Memory mgmt System calls Relating concepts

next OS lectures: How can we deal with system resources competing for CPU and Memory? – Process scheduling – Memory management – File system – Virtual memory How can processors/computers be combined? How can a file system be reliable and secure? WHAT ABOUT SPECIFIC OPERATING SYSTEMS? 23