Windows 7

Case study 1

Silberschatz, Galvin, Gagne. Operating System Concepts Essentials. 8th Edition. ISBN: 978-0-470-88920-6

A. Tanenbaum. Modern Operating Systems. 3rd Edition. ISBN: 0136006639 

Sources and extra reading

History of Windows 7 Windows 7 Design principles Threads and Scheduling. Process Manager Virtual Memory Manager Windows 7 file system. OS Security features Programmer Interface for Windows 7 (Win32 API). Windows Registry Exercises

Topics covered in this session

Windows 3.0 used the Win16 API which became increasingly popular.

XP brought support for 64-bit versions Vista released in 2006, not very popular. Windows 7 released in 2009 Windows 8 released in late 2012.

History of Windows 7

Key Goals: Security Reliability Extensibility Portability International Support Energy Efficiency Dynamic device support

Windows 7 Design Principles

Use of Access Control Lists (ACLs) for permissions to files, registry settings and kernel objects.

Address space layout randomization (ASLR). Bitlocker (encryption) allows encryption of removable

media. Code integrity module to ensure modules in the kernel

have valid signatures.

Security

An operating systems capacity to keep up with advances in computing technology.

Modular structure allows additional environmental subsystems to be added without affecting the executive

Portability —Windows 7 can be moved from one hardware platform to another with relatively few changes

Written in C and C++ Platform-dependent code is isolated in a dynamic link library

(DLL) called the “hardware abstraction layer” (HAL)

Extensibility

Applications that follow the IEEE 1003.1 (POSIX) standard can be complied to run on Windows without changing the source code. Applications created for previous versions of Windows run using various virtual machine techniques

Compatibility

Supports different locales via the national language support (NLS) API.

Supports UNICODE. Facilities for differences in date formats, currency etc.

International Support

Windows 7 Architecture

Foundation for the executive and the subsystems Never paged out of memory; execution is never preempted Four main responsibilities:

thread scheduling interrupt and exception handling low-level processor synchronization recovery after a power failure

Kernel is object-oriented, uses two sets of objects dispatcher objects control dispatching and synchronization (events,

mutexes, semaphores, threads and timers) control objects (asynchronous procedure calls, interrupts, power notify,

process and profile objects)

The Windows Kernel

Each process has one or more thread. Each thread has it’s own scheduling state:

Ready – Thread is waiting to run. Standby – highest priority thread which is waiting to run (next to

run). Running – currently executing on the processor (Until pre-

empted by a higher priority thread). Waiting – Waiting for dispatcher object to be signalled. Transition – While it waits for resources necessary for execution.

(e.g waiting for its kernel stack to be swapped from disk). Terminated – Thread has finished execution.

The Executive - Threads and Scheduling

Real-time threads are given preferential access to the CPU; but Windows 7 does not guarantee that a real-time thread will start to execute within any particular time limit.

This is known as soft real-time. The process manager provides services for creating,

deleting and using threads and processes.

Threads and scheduling continued

The Executive - Object Manager

Windows Objects == logical view of resources Windows 7 uses objects for all its services and entities;

the object manager supervises the use of all the objects Objects are manipulated by a standard set of methods,

namely create, open, close, delete, query-name, parse and security.

The Executive — Naming Objects

The Windows executive allows any object to be given a name.

Object names are structured like file path names in UNIX.

Windows implements a symbolic link object, which is similar to symbolic links in UNIX that allow multiple nicknames or aliases to refer to the same object.

Each object is protected by an access control list.

The executive name space is extensible to allow naming of files, registry keys, and other objects with their own special semantics.

The Executive — Virtual Memory Manager The design of the VM manager assumes that the

underlying hardware supports virtual to physical mapping, a paging mechanism, transparent cache coherence on multiprocessor systems, and virtual address aliasing.

The VM manager in Windows uses a page-based management scheme with a page size of 4 KB for both x86 and x64.

A physical page can be in one of six states: valid, zeroed, free, standby, modified and bad.

Virtual-Memory Layout (32-bit)

PageDirectory

…

4K page 4K page 4K page 4K page

pagetable

0

…

pagetable 511

…

page-directory entry 511

page-directory

entry 0

page-table entry

0

page-table entry 511

page-table entry

0

page-table entry 511

Top-level Page Directory Table

0 1 2 3

Virtual-to-Physical Address Translation

Translation for a 32-bit Virtual Address to a Physical Address 2 bit index into top-level page directory to get page directory 9 bit index into page directory to get page directory entry for page table 9 bit index into page table to get page table entry for physical page 12 bits for byte offset within physical page

So we have a 3 level hierarchy for Win32 For 64 bit, it is a 4 level hierarchy

TOP

PDE PTE page offset

31 0

The Executive — I/O Manager

The I/O manager is responsible for file systems cache management device and network drivers

Works with VM Manager to provide memory-mapped file I/O.

Interfaces with the Windows cache manager, which handles caching for the entire I/O system.

The cache manager memory-maps files into the kernel memory Also tries to predict the future reading models Flush cache contents for writes: write-back cache, accumulates writes for 4-5 seconds,

then writes them

Uses NTFS (New Technology File System). Max file size (16TB) – Bigger than most readily available

drives. 4kb clusters default for drives over 2GB. NTFS uses logical cluster numbers LCN as disk

addresses. NTFS makes use of access control lists (ACL). Also supports FAT for portability (e.g Flash Drives).

Windows 7 File System

File I/O

The Executive — Security Reference Monitor

The object-oriented nature of the Windows kernel enables the use of a uniform mechanism to perform runtime access validation and audit checks for every entity in the system.

Whenever a process opens a handle to an object, the security reference monitor checks the process’s security token and the object’s access control list to see whether the process has the necessary rights.

The Executive – PnP and Power Managers

PnP (Plug-and-Play) manager is used to recognize and adapt to changes in the hardware configuration.

The power manager controls energy use of by the CPU and devices.

Windows 7 Architecture (Revisited)

Programmer Interface (Win32)

Access to Kernel Objects Sharing of objects between processes Process management Interprocess communication Memory Management

Five main aspects of Win32 API

Programmer Interface (Win32) Continued- Job, Process & Thread Management

Second column gives nearest UNIX equivalent

Programmer Interface (Win32) Continued- File System API Calls

Programmer Interface (Win32) Continued- File System API Calls

Second column gives nearest UNIX equivalent

Kernel can make use of registry, as well as third party applications.

Registry has been used since Windows 3.1

Contains keys and values.

Stores information in hives.

Windows 7 Registry