Mechanics and Introduction

Tom Kelliher, CS 318

Jan. 21, 1998

Announcements

Typo on the syllabus: MWF office hour is 10:30.

Assignment

Read Chapters 1-2.

Notes on the Syllabus

1. Objectives:
   1. Study operating system design.

   2. Understand threads and concurrency: Banking example.

   3. Appreciate connections to other areas of computer science.

2. C++ refresher project.

3. Internet resources.

4. Nachos project orientation. Project groups.

5. Late assignment policy.

6. Class preparation.

7. Topic outline and its relationship to Nachos. Possibilities for Other topics: deadlock, distributed systems, security and protection.

Introduction

OS As Interface

(Process = running program. Separate address spaces. Threads share an address space.)

1. Top-down view: virtual machine abstraction --- convenient ``user'' interface. Abstractions: files, applications. I/O devices integrated into filesystem.
2. Bottom-up view: management of real resources: CPU cycles, memory, disk space, device allocations.
3. Secondary concerns: efficiency, fairness.

Abstractions:

1. Multiprogramming, protection and security.
2. Virtual memory.
3. File systems.

Layering/Abstraction Within a Computer System

1. Hardware: CPU, memory, I/O.
2. Operating system: kernel, file system, device handlers.
3. Application programs: editors, compilers, workbench tools.
4. Users: people, other programs, computers.

The ``Hello world'' program:

1. Compiled into assembly code.
2. Assembled in machine code.
3. Written to a file.
4. Loaded into memory.
5. Linked against system libraries.
6. Executes.
7. Makes supervisor calls to access I/O devices through OS.

Historical Developments

1. Common device drivers:
   1. Reinventing the wheel.
   2. Abstract I/O device interface for software.
2. Resident monitors:
   1. Keep expensive hardware utilized.
   2. Automatic job sequencing --- compile, run user program.
   3. Monitor is always resident in memory.

      

      Protection?

3. System parallelism:
   1. Overlap processing of one job with I/O of another.
   2. Off-line processing (card to tape, vice versa).
   3. Spooling.
4. Multiprogramming (batch):
   1. Overlap processing yields multiple jobs in memory simultaneously --- job pool.

      

   2. CPU idle when job does I/O.
   3. Automatically switch (CPU scheduling) to ``next'' job.
   4. Job runs until completion or I/O.
   5. Protection?
5. Timesharing:
   1. Batch systems aren't productive for program development.
   2. Preemptive CPU scheduling.
   3. Brief quantum for each process.
   4. Response time important.
6. Realtime systems:
   1. Hard deadlines for process completion.
   2. Example: flight surface control on the Space Shuttle.
7. Workstations:
   1. Essentially, a single-user computer.
   2. Mainframe features trickle down.
   3. Why multiprogram a workstation?
      1. Increase productivity.
      2. Allows modular system design --- consider the windows in a GUI.
8. Parallel processing:
   1. Tightly coupled multiprocessors.
   2. Shared memory space.
   3. CPU scheduling issues.
   4. Working set locality.
   5. Finding parallelism opportunities within a problem.
9. Distributed systems:
   1. Loosely-coupled, independent systems.
   2. Private memory spaces.
   3. Client/server computing.
   4. Reliability, resource sharing, load balancing, communication, transparency.
   5. Granularity of parallelism.
   6. Network Latency.