Administrivia Website. cis.poly.edu/jsterling/cs3224 Text: Modern - - PDF document

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CS3224 Operating Systems

Introduction

• Administrivia
• What’s the course about?
• History
• Hardware basics
• System Structure

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Administrivia

– Website. cis.poly.edu/jsterling/cs3224 – Text: Modern Operating Systems; Tanenbaum.

• Read the material before the lecture.

– Instructor: Sterling;

• jsterling@poly.edu;
• LC117
• Office hours: See my website: http://cis.poly.edu/jsterling

– Projects:

• Two projects.
• Work in pairs or alone. Your choice.
• Pick your partner soon. First project starts in a couple of

weeks.

• Each project is 15% of the grade.

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Administrivia

– Exams:

• One midterm (30%)
• Final Exam (40%)
• Closed book.
• Questions include multiple choice, short answer, essay and code.

– Optional Homework

• Hard copy turned in at the beginning of class.
• Can only help your grade.
• If you have questions, ask in class and we’ll go over them. After all,

as usual, if you’re confused, someone else is too.

– Coverage

• Core material: chaps 1-6.
• Unix and Windows details: chaps 10 & 11
• Additional material on virtualization (in chap 7) and security (chap 9)
• Some outside material, too. There will be handouts/links as

needed.

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What’s the course about?

• Will we write an OS in this course?

– No.

• Will we learn how to do super cool things

with Windows or Unix?

– No

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So, what will we learn?

• Lots of terminology. (Sorry.)
• First, what’s an OS?
• The ideas and some of the algorithms behind:

– Processes. – Deadlock. – Memory Management. – I/O management. – File Management.

• In particular, how Unix and Windows handle

these issues.

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History

• First Generation:

1945-1955

• Second Generation:

1955-1965

• Third Generation:

1965-1980

• Fourth Generation:

1980-

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History

• First generation

1945-1955

– Technology: vacuum tubes, access time 100

• ms. (that’s 1/10 of a

second) – Language: machine language. – OS? Ha! – Input: switches, patch cords and punch cards

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History

• Second Generation 1955-1965

– Technology: transistors, access time: 100 µs. – Storage: tape, then disks. – Languages: COBOL, Fortran, Algol, LISP and (of course) assembler. – OS:

• “batch” systems / “monitor”

– With SPOOLing

• Experimental: CTSS

supported

– dual mode – memory protection – time sharing

– Input: most often punch cards.

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What’s a monitor?

Monitor Read input tape Process commands Run jobs sequentially Refresh at end of job User Area (Rest of memory)

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Poly’s 7040

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Batch processing and spooling here at Poly

Decks of cards Small (cheap) computer (IBM 1401) 2400 ft reel Big (expensive) computer (IBM 7040)

Input tape (Card images) Output tape

(print images)

Print images

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Poly’s 1401 (corner of 7040)

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History

• Third Generation

1965-1980

– Technology: Integrated

• Circuits. 1 µs and up.

– Languages: PL/1, C, Basic… – OS:

• Started with Batch,
• Time sharing became wide
• spread. Why? Memory

protection!

– Significant systems:

• Hardware:

– Mini-computers (e.g PDP series) – IBM 360 family

• Major operating systems:

OS 360 (Frederick Brooks), Multics, Unix.

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Thanks for the Memory

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History

• Multics (1965-2000)

– Goal: create a computing

• utility. Focus on time-sharing.

– Follow-up to CTSS. – AT&T, MIT and General Electric. – Target machine was the GE 635 mainframe. – Early example of many ideas used in later hardware and

• perating systems.
• Combined segmentation and

paging

• Developed in high level

language

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History Multics begat…

• AT&T pulled out at the end of the

60’s.

• AT&T researchers were without a

cool operating system.

• Ken Thompson decided to write a

trimmed down version for personal use.

• Found an under-utilized PDP-7

“minicomputer” as the target.

• Used GE-635 for development.
• Assembly language.
• Later ported the OS to the hot new

PDP-11 minicomputer.

• Goal: rewrite OS in a high level

language.

– Thompson tried FORTRAN. Nah. – Then created B. Still no. – Dennis Ritchie improved on it…

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History Unix Open Source

• Originally universities and others got

licenses for the source because AT&T didn’t figure it was worth much…

• Berkeley added many features,

resulting in BSD Unix.

• TCP/IP was developed on BSD Unix.
• The two versions diverged.
• ’87 minimal version of Unix written by

Tanenbaum for educational purposes.

• MINIX. Source provided.
• Disgruntled MINIX users demanded

more features. Tanenbaum refused to let MINIX get too large. (He did add support for hard drives.)

• Meantime AT&T blocks Berkeley from

making their source code free.

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Linux

• A Finnish student decided to

write his own version. Posts version 0.98 on the web in ~1990.

• Thanks in part to Ma Bell, the

penguin got more market share than the little devil.

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4th Generation

1980-

• Largely focused on

microprocessors, networking, distributed systems

• Mid-70s: the Intel 8080 and CP/M

(Gary Kildall)

• ~80: 8086 and msdos. (similar to

cp/m).

• 1985: Windows 1.0. Graphical

user interface for MSDOS – not an

• perating system.
• 1990: Windows 3.0 for ‘386.
• Windows 95.

– virtual memory – multi-programming, etc – Later on, long file names. – fancy new GUI, closer to the Mac

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NT

• Late 80’s Microsoft knew they were going to need a “real” OS

– Hired VAX VMS designer, David Cutler for complete rewrite. – Targeting heavy business apps. Compete with OS/2 – Intended to be highly portable.

• NT 3.1 in ‘93

– “Layered” – Looked like Windows 3.1

• NT 4 in ’96

– Layering was reduced to improve efficiency. – GUI was made compatible with Windows 95.

• NT 5 in 2000 (actually named Windows 2000, but…)

– added many features that had already appeared in Win ’98, such as support for USB and plug-and-play.

• NT 5.1 – XP finally merged the “home” and “office” environment.

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Improvements in NT vs. 95/98

• Support for multi-processor
• File system security
• Fully 32-bit (as opposed to having some legacy

16-bit) code

• Fully reentrant
• Shared memory visible only to the processes

involved.

• Better protection for operating system

But less compatible with old MSDOS programs.

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Hardware

• Processor: instruction set architecture
• Protection: Dual mode, privileged

instructions, memory protection

• Computer view (with buses)
• Memory hierarchy
• I/O, Interrupts

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Instruction Set Architecture (ISA)

• Registers

– Special purpose:

• Program counter, Stack pointer, Processor Status Word
• Pentium: EIP, ESP and EFLAGS
• MIPS: ??

– General purpose:

• Pentium: EAX, EBX, ECX, EDX. Not really totally general.
• MIPS: S0, … T0, …
• Instructions:

– Arithmetic, Data transfer, Comparison, Branching – I/O – Halting …

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Assembly Language Examples

MIPS x86 Arithmetic

// S3 = S0 + S1 ADD S3, S0, S1 // BX = BX + AX ADD BX, AX

Transfer data

// S1 = S0 ADD S1, ZERO, S0 // BX = AX MOVE BX, AX

Compare

CMP AX, 1000

Conditional Branch

// if (AX == 100) … JZ Label

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Privileged Instructions

• HALT

– Who should be free to halt the computer? – Who should be free to write anything they want onto the hard drive or your screen? – Who should be free to changed the system time?

• Some machine instructions have to be blocked from the

“average” user program.

– Called privileged instructions – Only the kernel should be permitted to use them – How does the hardware know when the kernel is running? – How do we switch to the kernel in order to do these things.

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Pentium Privileged Instructions

• LGDT — Load GDT register.
• LLDT — Load LDT register.
• LTR — Load task register.
• LIDT — Load IDT register.
• MOV (control registers) — Load and store control registers.
• LMSW — Load machine status word.
• CLTS — Clear task-switched flag in register CR0.
• MOV (debug registers) — Load and store debug registers.
• INVD — Invalidate cache, without writeback.
• WBINVD — Invalidate cache, with writeback.
• INVLPG —Invalidate TLB entry.
• HLT— Halt processor.
• RDMSR — Read Model-Specific Registers.
• WRMSR —Write Model-Specific Registers.
• RDPMC — Read Performance-Monitoring Counter.
• RDTSC — Read Time-Stamp Counter.

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Dual Mode

• Dual Mode:

– user mode vs. system (or kernel or supervisor) mode. – Supported in hardware. A bit in a status register identifies the current mode. – There must be an instruction to safely switch from user mode to kernel mode.

• Generally called TRAP. (INT on x86.)
• Switches mode and transfers control to kernel code.

– Some processors have more than just two modes.

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Intel Status Register

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Options for Memory Protection

• None.
• Tag each block of physical memory with the id of

the process that owns it.

• Base Register / Limit Register
• Segmentation
• Paging

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Basic PC Layout

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I/O

• Bus:

– Wires: Data, Command, control – Protocol

• Port:

– Command, Status, Read and Write registers – Access. Memory-mapped or special instructions. – Memory-mapped I/O vs. “IN / OUT”

• Programming

– Programmed I/O – Interrupt – DMA

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Interrupts

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OS Components

• Provide

– system utilities for users. – system calls for programmers.

• Process Management

– Create, kill, schedule, synchronize and support communication

• Memory Management

– Allocate memory to processes, manage free memory, share memory.

• File Management

– Create, delete, move files and directories.

• I/O Management

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System Calls

• What?

– Programmer’s view of the OS. – Provides safe interface between user code and kernel services. – Provided through a hardware instruction (usually referred to as TRAP) to switch modes and simultaneously transfer control.

• Examples

– Process management:

• pid = fork()
• s = execve(name, argv, environp)
• pid = waitpid(pid, &statloc, options)
• exit(status)

– Directory management: mkdir, rmdir, link, unlink, mount, umount.

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System Calls

How does one work? E.g. read.

– Call the “read” library function.

• read(from_file_descriptor, into_buffer, size)
• This is user level code that is linked into your program.
• Arguments to the function are put on the stack.

– The read function sets a code (on the stack or in a register) – Execute “Trap” instruction. – Hardware

• picks up new address from the interrupt table for the trap handler
• automatically jumps to that routine.
• switches to kernel mode (!!)

– Set up the “appropriate” environment, including stack. Identify which system call was intended and jump to the appropriate routine. – Return from the trap. That switches mode back to user and goes back to the “read function”. – Return from the read function to the user’s program.

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System Call

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System call examples

A shell

while(TRUE) { // repeat forever typePrompt( ); // display prompt readCommand(command, parameters) // input from terminal if (fork() != 0) { // create child process // Parent Code waitpid( -1, &status, 0); // wait for child to exit } else { // Child process code execve (command, parameters, 0); // execute command } }

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Unix System Calls

vs.

Win32 API

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Tanenbaum’s OS Zoo

• Mainframe operating systems
• Server operating systems
• Multiprocessor operating systems
• Personal computer operating systems
• Real-time operating systems
• Embedded operating systems
• Smart card operating systems

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OS Architecture (or Structure)

• Monolithic
• Layered
• Virtual
• Client-server
• (Ignoring Exokernel)

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Monolithic

• One large program.
• May consist of a number of identifiable modules
• But all code is simply linked together.
• Nothing to prevent one (poorly coded) portion

from damaging the rest of the system.

• Examples:

– Unix is frequently cited – NT is called monolithic by Solomon&Russinovich

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Layered

• Identify a number of separate “layers” of the system.
• The lowest layer does not depend on any other layer

and can be completely tested separately.

• The next layer depends only on the layers below it.
• THE

– Classic system designed this way by Dijkstra – Six layers. – However no hardware protection.

• MULTICS

– Described as using “rings”, same idea. – Provided hardware support. Each layer had its own address space. – An outer layer had to “trap” to request a service from an inner layer.

• NT

– Also described as Monolithic and… – HAL: Hardware abstraction layer. Intended to make NT more easily portable across varying hardware architectures. – Kernel: Thread scheduling, context switches, … – Executive: Process management, memory management, i/o management, buffer management.

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THE Layers

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Windows NT Structure

• Structure of Windows 2000 (slightly simplified).
• Shaded area is Executive
• Boxes labelled “D” are device drivers

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Virtual Machine

• Background:

– IBM sold big expensive machines, e.g. IBM 360/370, for batch processing. OS/MFT and OS/MVT. – They also had a single user, interactive operating system (CMS). [Not sure why they wrote CMS.] – Users wanted time sharing. IBM finally agreed but was slow in delivering. – An IBM research group came up with a way of writing an OS (VM/370) that would “look like” a bare bones 360. Or even several of them. Each was called a virtual machine. Separated function of multiprogramming from that of providing an extended machine.

• VM/370 was called a virtual machine monitor (aka a hypervisor)

– You could then run another OS on top of the virtual machine. Since you could have multiple virtual machines, this meant that you could allow several people to simultaneously use CMS, for example, on a single computer. You could also run another OS, such as one of the batch operating systems

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How VM/370 works

• Assume CMS running on top of VM/370.
• Consider when a CMS user issues a system call.

– Traps to the “real” hardware and code in VM/370 – VM/370 knows which virtual machine this trap is for and passes control back to the appropriate spot in that machine. This transfers control back to the trap handler in CMS.

• What happens when CMS issues a privileged instruction

(generally I/O)?

– Since CMS That traps to the real hardware (running VM/370) as an error. VM/370 looks to see what mode the CMS thinks it’s in. – If it’s in kernel mode, then VM/370 executes the I/O on the behalf

• f CMS.

– If in user mode, then VM/370 transfers control to the error handler in CMS.

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Other virtual machines

• Java
• Apple’s emulator for the 68000 running on the PowerPC.
• Virtual 8086 mode in Pentium. Here the hardware itself

provides emulation of another (similar) architecture.

• Note the above examples have one machine emulating a

different machine, unlike what VM/370 was accomplishing.

• VMWare.

– One version runs on top of Linux, Windows or MacOS to provide a virtual Pentium. – A second version runs underneath in the same way VM/370 did,i.e as a hypervisor.

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Microkernel (Client-Server)

• Move code out of kernel mode and into user mode processes.
• Microkernel primarily has basic message passing services (IPC)
• May also need to contain device drivers.
• OS services all appear in user processes.
• Requests for services are sent as messages.
• Each service is forced to be self contained and not interfere with other services.
• Adaptable to distributed systems.
• Microkernel often includes device drivers since they must have access to privileged instructions

and hardware.

• Most frequently cited example is Mach (recent versions).

– Originally derived from BSD – evolved into a microkernel – has been used inside DEC’s Unix and Mac OS X.

• Another Example: Minix. “… memory manager, files system and each device driver being a

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MINIX A Microkernel

• MINIX microkernel

handles interrupts, basic process management, inter-process communication (~4K LOC)

• Device driver’s run as

user processes.

• Each one has its own

memory.

• They make calls to the

kernel to execute privileged instructions or access I/O ports.

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What/Where is the kernel

• Is the kernel another process?
• Where is it?
• In Unix and NT:

– The kernel is not a process. – The kernel is present in the top one (or two) GB of address space for every process. – User gets most of the lower address space. Lowest addresses may be reserved.