Introduction to Computer Systems and Operating Systems

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1 Introduction to Computer Systems and Operating Systems Minsoo Ryu Real-Time Computing and Communications Lab. Hanyang University

2 Topics Covered 1. Computer History 2. Computer System Architecture 3. Operating System Concepts 2 2

3 From B.C 4000 What is the First Computer? Input/Output Physical movements by hands and read by eyes No programming and no special I/O devices Very volatile memory and slow Abacus! The first hand-held computer? 3 3

4 The ENIAC (1946) The first computer that uses electricity Technology Vacuum tubes Floor space 1,000 square feet Weight 30 tons Input/Output Cards, lights, switches Human operators Speed Less than 5,000 operations per second 4 4

5 Mainframe Computers (1) From 1960s to 1970s Technology Transistors Input devices Panel switches, paper tape, punched cards Card readers, magnetic tape Output devices Display lights on the console Line printers 5 5

6 Mainframe Computers (2) Cost vs. performance Computers were very expensive $750,000 plus $185,000 for a high speed printer Humans were cheap Significant amount of setup time Human programmer/operator Program, setup, monitor, and debug Significant amount of setup time 6 6

Mainframe Computers (3) Simple Batch Systems To reduce setup time By batching similar jobs Automatic job sequencing Automatically transfers control

7 Mainframe Computers (3) Simple Batch Systems To reduce setup time By batching similar jobs Automatic job sequencing Automatically transfers control from one job to another. Resident monitor Instead of human operator When a job completes, it transfers the control back to the monitor Resident Monitor 7 7

Mainframe Computers (3) Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time CPU is multiplexed among them Eventually a job may have to wait for some

8 Mainframe Computers (3) Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time CPU is multiplexed among them Eventually a job may have to wait for some task such as I/O operation CPU is switched to another job Benefit Increase of CPU utilization Reduction of CPU idle time Job scheduling is required When multiple programs are ready 8 8

9 Mainframe Computers (4) Emergence of faster I/O devices Slow mechanical devices Card reader -> CPU -> line printer CPU works in the microsecond range Card reader could read 1200 cards per minute Fast magnetic devices Card reader -> tape drives -> CPU -> tape drives -> line printer Performance is limited only by the much faster magnetic units 9 9

10 Mainframe Computers (5) Performance improvement by Spooling Simultaneous Peripheral Operation On-Line Tapes: sequential-access devices Disk systems: random-access devices Spooling overlaps the I/O of one job with the computation of other jobs Card reader cannot write onto one end of the tape while the CPU read from the other The entire tape had to be written before it was rewound and read Disk can be used as a very large buffer Overlapped CPU and I/O operations 10 10

11 Since 1970s Modern Computers With the advent of microprocessor chips Workstations and personal computers 11 11

12 Advent of Operating System Concepts Eliminated the need for human operator Separation of programming from operating Modern OS features Multi-programming and multi-tasking Several programs are kept in main memory They run at the same time (time-sharing) Interactive and on-line system User enters a command and the system executes them The system seeks the next control statement from the user s keyboard or mouse Multi-user environment Different users can use the computer at the same time 12 12

13 Migration of Operating-System Concepts and Features 13 13

14 Several Names of Operating System Resource allocator Manages and allocates resources Control program Controls the execution of user programs and operations of I/O devices Kernel The one program running at all times All else being application programs 14 14

15 Topics Covered 1. Computer History 2. Computer System Architecture 3. Operating System Concepts 15 15

16 Computer System Architecture CPU controls everything in the computer system 16 16

17 How To Control the CPU? We can tell the CPU through machine language CPU can understand and execute only instructions An instruction is a command given to a processor Each instruction is a sequence of 0s and 1s Physical operations such as load, store, add, sub, mul, Programming means Constructing a sequence of instructions The result is called program 17 17

18 von Neumann Architecture von Neumann machine has A CPU including registers, RAM (random access memory), von Neumann machine works by Fetching instructions from memory Executing them on registers CPU Registers Arithmetic Logic Unit Control Unit Memory 0001 load 0002 store 0003 add mul 0998 sub 0999 load I/O devices screen disk 18 18

19 Machine Programming Programming using assembly language One-to-one with instructions Load R Load R Add R3 R1 R2 Store 1008 R3 Reg[R1] Mem[1000] Reg[R2] Mem[1004] Reg[R3] Reg[R1] + Reg[R2] Mem[1008] Reg[R3] Assembly programming is difficult and tedious Use higher level languages C, C++, Java Compilation High-level language Assembly code Machine instructions 19 19

20 I/O Device Controller Each I/O device has a controller (or interface) CPU communicates with the I/O controller Control register: write commands Status register: read the device s internal state Input register: fetch data Output register: write data Control Registers CPU I/O instructions in, out, ins, outs Status Registers Input Registers Output Registers Device s I/O Controller 20 20

21 CPU Execution and I/O The two main jobs of a computer CPU execution Input/Output Usually, the main job is I/O The CPU execution is incidental 21 21

22 Topics Covered 1. Computer History 2. Computer System Architecture 3. Operating System Concepts 22 22

23 What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware Operating system goals: Execute user programs and make solving user problems easier Make the computer system convenient to use Use the computer hardware in an efficient manner 23 23

24 Another Definition of Operating System An operating system is an virtual machine that is easier to program than the raw hardware 24 24

25 What Do Operating Systems Do? Hardware abstraction Provide clean, uniform, and standard abstraction Illusion Make hardware limitations go away Protection Make CPU, Memory, I/O, and user programs secure Coordination and Optimization Allow things to work together efficiently 25 25

26 Abstraction? Hardware Abstraction Picking out key features to reduce complexity Something should be lifted out and preserved Something should be left behind and erased Hardware abstraction Provide clean, uniform, and standard abstraction hiding hardware complexity from users Application Program Operating System Virtual Machine Interface Physical Machine Interface Hardware 26 26

27 Illusion Make hardware limitations go away As if there are infinite number of processors (time sharing) As if there is extremely large memory (virtual memory) Every process things it is the one As if it has been provided dedicated resources Proc 1 Proc 2 Proc 3... Proc n Operating System Hardware 27 27

28 I/O Protection Must ensure that users cannot issue I/O instructions They must do it through the operating system Must ensure that a user program could never gain control of the computer in kernel mode i.e.,) a user program that, as part of its execution, stores a new address in the interrupt vector 28 28

29 Memory protection Memory Protection kernel from user programs User programs from one another At least for the interrupt vector and the interrupt service routines Separation of each program s memory space Determine the range of legal addresses Base register holds the smallest legal memory address. Limit register contains the size of the range Memory outside the defined range is protected 29 29

30 Use of A Base and Limit Register 30 30

31 Hardware Address Protection 31 31

32 CPU Protection Must prevent a user program from getting stuck in an infinite loop and never returning the control to the operating system Timer interrupts computer after specified period to ensure operating system maintains control. Timer is decremented every clock tick When timer reaches the value 0, an interrupt occurs Timer commonly used to implement time sharing 32 32

33 Coordination and Optimization Make many things work together efficiently Concurrency Overlapped I/O and Processing I/O devices and the CPU can execute concurrently Multitasking and multi-user support Efficiency Multithreading Effective storage management Caching, paging, and swapping Fast interrupt handling 33 33

Fundamental Concepts and History

Fundamental Concepts and History Minsoo Ryu Real-Time Computing and Communications Lab. Hanyang University msryu@hanyang.ac.kr Topics Covered I. Fundamental Concepts II. Evolution of OS 2 Key Concepts