Transcript Electronic Commerce

COMP1321
Digital Infrastructures
Richard Henson
November 2013
Week 6: Boot up, Files, Storage
and the Windows Registry

Objectives:
 Explain how data is stored for easy retrieval on a
hard disk
 Explain the Windows boot-up process
 Explain why user and system settings need to be
configured for multi-user use and across a network
 Explain the role of the registry in Windows desktop &
network configuration, user settings, security
Operating System Boot Up
1.
2.
3.
4.
5.
6.
ROM-BIOS
Bootstrap sector/file for hard disk
System files from hard disk
Registry
Configuration of drivers, etc.
Logon…
BIOS Developments

Earlier motherboards had a single chip
containing the BIOS on ROM and a writeable
CMOS area
 the command line interface invoked was 16-bit

More recent motherboards use EFI
(Extensible Firmware Interface)
 uses a 32-bit command line
 only really exploited with Windows 7, and 2008
Server…
More about ROM-BIOS

Not all ROM…
 basic operating system
programs in the ROM part
 Configurable CMOS
settings allow
configuration and tuning
of devices connected
directly to the
motherboard
 including secondary
storage boot sequence…
OS programs
CMOS settings
More about booting
to an Intel platform

BIOS program “points” to selected medium
that contains a “boot loader” program
» contains “master boot record” (MBR)
» points to the boot partition


containing the operating system
Different media prepared in different ways
» hard disk still the conventional boot medium

number of partition options so potential choice of bootable
media
» CDs & USBs only have one partition
Storage of Data as Files

Taken for granted, but actually a very
ordered process including a minimum
of:
filename
filename suffix (type of file)
filesize
address of start of file…
More about Hard Disks

Storage happens because of physical
change…
magnetically active coating on a metal
platter
particles move in response to magnetic
field

Partitioning and Formatting are about
ordering the magnetic arms that move
the particles
the particles themselves…
Structure of a Partitioned
Hard Disk
Area of disk (could be whole disk)
allocated for secondary storage
 Formatting organises the magnetic
particles on the platter so they can store
data, byte-by-byte
 All about orientation of particles so they
store “0” or “1”… very precise!

more: http://www.hardwaresecrets.com/article/482
Saving to Disk

Assumes disk partitioned and formatted
resulting file organisation depends on
» operating system
» file system chosen

Unit of storage on disk is the sector
Traditionally, 1 sector = 512 bytes
» 2011 on… 1 sector = 4096 bytes!
» hard disks still have very many sectors on which
to store data, but smallest storage now 4K…
Partitions, Hard Disks and
Multiple Operating Systems

MBR starts the disk-based boot-up
 must be on the first (C:) partition


Possible to have different operating systems
on the same hard disk…
 varieties of Windows
 varieties of Unix…
MBR systems are different on Unix and Windows
 BUT…still possible to have ONE Unix partition coexisting
with Windows…
Storage of User/System
Settings: Windows Registry

Early Windows extended DOS text files of
system & user settings:
 SYSTEM.INI enhanced CONFIG.SYS
 WIN.INI enhanced AUTOEXEC.BAT

Windows 95 created a two dimensional
structure… known as The Registry
 principles later extended in Windows NT v4 to
allow system and user settings to be downloaded
to local registry across the network
Viewing/Editing the Registry

REGEDT32 from command prompt…
look but don’t touch!
 contents should not be changed manually unless
you really know what you are doing!!!

Registry data that is loaded into
memory can also be overwritten by
data:
from local profiles
downloaded across the network…
System Settings
 For
configuration of hardware and
software
different types of system need different
settings
system settings for a given computer may
need to be changed for particular users
» e.g. refresh rate for an epileptic user can be
configured when the user logs on
User Settings

More a matter of convenience for the user
 mandatory profiles
» users all get the same desktop settings!
» anything added is lost during logoff!
 roaming profiles - desktop settings preserved
between user sessions
» saved across the network…
Structure of The Registry?

Five basic subtrees (or hives):
 HKEY_LOCAL_MACHINE : local computer info.
Does not change no matter which user is logged on
 HKEY_USERS : default user settings
 HKEY_CURRENT_USER : current user settings
 HKEY_CLASSES_ROOT : software config data
 HKEY_CURRENT_CONFIG : “active” hardware
profile

Each subtree contains one or more subkeys…
Location of the Windows Registry
 Stored
in MBR partition
usually C:
actual folder depends on Windows
version…
»in XP… C:\windows\system32\config folder
The Registry Files &
Setting the Desktop

Six files (no file extensions!):
 Software
 System – hardware settings
 Sam, Security
» not even viewable through regedt32
 Default – default user
 Sysdiff – HKEY USERS subkeys

Also part of boot process: ntuser.dat
» user settings that override default user
Emergency Recovery if
Registry lost or badly damaged

Backup registry files created during text-based
part of windows installation
 also stored in:
» c:\windows\system32\config
» have .sav suffix
 only updated if “R” option is chosen during a
windows recovery/reinstall

NEVER UPDATED backup is saved to
 C:\windows\repair folder
 no user and software settings
 reboots back to “Windows is now setting up”
Backing up the Registry

Much forgotten… an oversight that may later
be much regretted!!!
 can copy to tape, USB stick CD/DVD, or disk
 rarely more than 100 Mb

Two options;
 Use third-party backup tool
» e.g http://www.acronis.co.uk
 Use windows “backup”
» not recommended by experts!
» but already there & does work!
» to copy the registry if this tool is chosen, a “system state”
backup option should be selected
System Backup and Recovery

It won’t break down…
 famous last words!


Early versions of DOS/Windows did
encourage backup
From Windows NT v4 onwards, Microsoft
made a real effort…
 problem was, you had to either be an avid reader
or go on a course to find out where the backup
option are and where to use them!
 Contrast with Apple approach…
» assured that the system will handle it
» fine until the system itself crashes!