Chapter 1 (PART 2) Operating System Concepts Department of Computer Science Southern Illinois University Edwardsville Spring, 2016 Dr. Hiroshi Fujinoki CS 314 Operating Systems Chapter_One_2/001

Chapter_One/002 Operating System Concepts This PPT presentation covers Section 1.5 of the textbook. (1) Process (2) Deadlock avoidance in I/O resource management (3) Files and file descriptor (4) Special Files CS 314 Operating Systems

Chapter_One/003 Subjects covered about “process” What is “process”? How is it different from “program”? What we can do by “processes”? A: “Process” is a program in execution. HDD “program” is an executable file stored in a disk program Stored as a file Q: What is “process”? Solutions CS 314 Operating Systems

Chapter_One/004 Then how a “program” can become “process”? HDD program Stored as a file Memory CPU A program becomes a process when one is loaded into the memory for execution by CPU Load CS 314 Operating Systems

Chapter_One/005 Things needed for a program to be executed in memory Memory HDD  Program Code  Stack Memory  Heap Memory Address Space Program X Program Z CPU PCB-Z PCB-A PCB-X PCB = Process Control Block PCB is a data structure for the CPU to keep track of each process Process Program CS 314 Operating Systems

Chapter_One/006 Example of “program” and “process” Program Process Static object, usually exists as an executable file Program in execution This is a program This is a process (program in execution) CS 314 Operating Systems

Chapter_One/007 Intermediate summary of “process” It is a program in execution A process consists of the contents in process address space and PCB Process address space consists of:  Program Code  Stack Memory Space  Heap Memory Space Collection of assembly instructions CPU runs Stack data structure for sub-routine calls Other data structure (local/global variables) Questions  Where are PCBs located?  What information does PCB hold? CS 314 Operating Systems

Chapter_One/008 Things needed for a program to be executed in memory Memory Program XProgram Z CPU PCB-Z PCB-A PCB-X Program Y OS  Where are PCBs located? In the operating system CS 314 Operating Systems

Chapter_One/009 Operating System Structure  Monolithic Structure  VM (Virtual Machine)  Micro-Kernel Windows uses these concepts This PPT presentation covers Section 1.7 of the textbook. CS 314 Operating Systems

Chapter_One/010 Monolithic Structure OS Operating systems are essentially a collection of procedures. Monolithic Structure OS No structure in a collection of procedures (Any procedure or a user application can call any other procedure) OS Procedures Disk I/O Process Mgmt.Memory Mgmt.Printer Spooler IPC KB I/O user Program Big mess But fast (no overhead) CS 314 Operating Systems

Chapter_One/011 How is a Monolithic-Structured OS implemented? OS Procedures Disk I/O Process Mgmt. Memory Mgmt. Printer Spooler IPC KB I/O Disk I/O Memory Mgmt. Process Mgmt. IPC KB I/O Printer Spooler Source code modules Concatenate into one source code file Compile OS Operating system as an executable program CS 314 Operating Systems

“OS” in a broader definition Chapter_One/012 How is a Monolithic-Structured OS implemented? OS Operating system as an executable program awk grep sort Disk I/O Memory Mgmt. Process Mgmt. IPC KB I/O Printer Spooler Program System calls External Commands user execute exec (); “OS Kernel” CS 314 Operating Systems

Chapter_One/013 Virtual Machine (VM) Without VM HardwareOperating System App1App N    user OS 1 Virtual Machine SupportOS 2 OS 3    A virtual machine UNIX Windows 2000 Application programs Hardware With VM MS-DOS Extra layer on top of hardware CS 314 Operating Systems

Chapter_One/014 Hardware OS 1 Virtual Machine Support OS 2 OS 3    Hardware 1 OS 2 OS 3    OS 1    Hardware 2 Hardware 3 Concept of VM For each application program, it looks like they are being executed by the dedicated hardware CS 314 Operating Systems

Chapter_One/015 Without VM Memory Process X Process Y Process Z OS With VM Memory OS 1 OS 3 OS 2 Process X Process Y VMS VM 1 VM 2 VM 3 Process Manage Process Manage Process M Process N Process Manage Process A Process B Process Manage VM Manage Implementation of of VM CS 314 Operating Systems

Chapter_One/016 Summary of Virtual Machine (VM) VM A virtual computer where computer hardware is software-emulated by VMS (Virtual Machine Support) Provide virtual dedicated machine (= hardware) to each OS Multiple operating systems (and its applications) at once (Q: What’s the difference from “multiple boot”?) - For flexibility - For robustness One VM crashes, others still survive (EG: Windows-NT) CS 314 Operating Systems

“OS” in a broader definition Chapter_One/017 OS awk grep sort Disk I/O Memory Mgmt. Process Mgmt. IPC KB I/O Printer Spooler External Commands “OS Kernel” Micro-Kernel Architecture CS 314 Operating Systems

“OS” in a broader definition Chapter_One/018 awk grep sort Disk I/O IPC KB I/O Memory Mgmt. Process Mgmt. Printer Spooler External Commands OS “OS Kernel” Micro-Kernel Architecture (continued) Memory Mgmt. Process Mgmt. Printer Spooler CS 314 Operating Systems

Chapter_One/019 Micro-Kernel Architecture (continued) Computer Hardware Operating System User Program User-Mode Kernel-Mode In ordinary OS (not Micro-Kernel OS), OS has to provide all the user services in Kernel-mode services OS kernel tends to be huge System Call OS Procedure (in the OS kernel) CS 314 Operating Systems

Chapter_One/020 Micro-Kernel Architecture (continued) Computer HardwareOperating System User Program User-Mode Kernel-Mode Spooler Micro-Kernel Architecture is based on Client-Server Model ClientServer Micro-kernel Architecture Make the OS kernel as small as possible Operating System becomes a service broker CS 314 Operating Systems

Chapter_One/021 Micro-Kernel Architecture (continued) What is it good for? MS Windows uses micro-kernel architecture for this reason (1) Each OS function becomes a module A bug in OS can be fixed by replacing a module (what we should do if “monolithic structure kernel”?) (2) Better robustness OS functions may be executed in user-mode (a bug in a module will not crash the kernel) CS 314 Operating Systems

Deadlock Chapter_One/022 Deadlock avoidance in I/O resource management What is “deadlock”? More than one process wait for resource for each other for forever Example Resources Printer HDD Assume that there are two processes Each of the two processes requires printer and HDD at the same time Without the printer and HDD, neither can finish its tasks Process A Process B Assigned wait (Circular-wait) CS 314 Operating Systems

Chapter_One/023 Concept of files and file descriptor Logical data storages in computer systems What is a file? What is “file descriptor”? Logical identification for each file being used in a computer system. HDD file OS user  open  read  load  use  close CS 314 Operating Systems

Concept of files and file descriptor (continued) ABXY File Names “A.txt” User HDD OS Location on disk Sectors Track Platters Open “A.txt” Find/Access Load File Descriptor Read (FD) Write (FD) Append (FD) File NamesSector Locations File Allocation Table Chapter_One/024 A.txt 1E  23  CD  CS 314 Operating Systems

Chapter_One/025 Concept of Special Files Ordinary File user OS HDD file Can not be seen by human user user OS HDD Special Files Keyboard Users can I/O to many devices as if they were a file Modem Internet Request Request (1) Response (4) Internet Request Network Special Files CS 314 Operating Systems printer

user OS HDD Printer (LPT) Keyboard (KB) fd = open (my_text, READ_WRITE); write (fd, out_buffer); read (fd, in_buffer); close (fd); fd = open (LPT, WRITE); write (fd, out_buffer); close (fd); fd = open (KB, READ); read (fd, in_buffer); close (fd); Can not be seen by human user Chapter_One/026 Concept of Special Files CS 314 Operating Systems file

Chapter_One/027 Special Files A concept in OS where a user can handle many different I/O devices using the same interface (APIs) that is used for actual files. When you open (reserve) a resource, OS gives you “descriptor” Some special files are read-only and some others may be write-only Read-OnlyRead/Write Write-Only - Disks - Keyboard - Printer - Network - Mouse - CRT Monitor (with touch-pen support) - CD-ROM - CRT Monitor CS 314 Operating Systems