Technology Basics - Questy's study guide

Windows 95 Overview

Document centric - a user can concentrate on document content rather than the location of the program

- Windows 95 administers the applications originally used to create the document.

- Employs a 32 bit preemptive multitasking and multithreading model.

- Preemptive multitasking is a process scheduling technique where the operating system, rather than the application, always has control of the microprocessor.

- Multthreading describes a program's ability to divide its requests for CPU time into threads of a unit code execution.

The Windows 95 Registry The Registry is designed as a database used by OLE to store information on OLE servers. It is used by Windows 95 to store the information typically found in Windows 3.x .INI files and the reg.dat file. The Registry can be used for troubleshooting and enhancing perfomance in Windows 95. The registry is a heirarchical tree which contains information about many things in the computer. The following is a list of the Registry subtrees and what they contain:
Subtree	Information stored within
HKEY_CLASSES_ROOT	Contains information about OLE servers and file associations. It contains the same information that is typically stored in the reg.dat in Windows 3.x.
HKEY_CURRENT_USER	Contains the preferences of the user who is currently logged in. Receives stored information from the user's subtree located in HKEY_USERS.
HKEY_LOCAL_MACHINE	Contains hardware information and settings for any device ever installed in the computer.
HKEY_USERS	Contains preferences for every user that has ever logged into the computer.
HKEY_CURRENT_CONFIG	Contains settings for all hardware devices currently installed in the computer. Does not contain settings for devices included in HKEY_DYN_DATA.
HKEY_DYN_DATA	Contains dynamically stored data on performance monitoring.
Regedit.exe is used to modify the Registry. The Registry contains three properties: Name, Data Type, and Value. The Data Type can be a binary value (a collection of bits), a string value (a string of readable characters) and a DWORD value (a binary value limited to 4 bytes).

Intel Memory Protection Architecture

The 386 architecture has four priveledge levels designed to protect data from being damaged. Level 0 is the highest, and level 3 is the lowest. Windows 95 only uses levels 0 and 3. It uses level 0 for 95 core components and level 3 for user applications and non-critical components.

Virtual Machines: A virtual machine is an illusional environment created by the operating system in memory. Virtual machines run in ring 3 of the Intel architecture. These are designed to allocate resources to programs that might normally be halted by other programs in memory. Each MS-DOS application runs in its own virtual machine, as they are designed to have total and uninterupted access to all system resources. All other non-MS-DOS based programs run in the System virtual machine.

Windows 95 Core Components: Windows 95 has three core components: Kernel, User and GDI. All three are .DLL files which reside in the system as both 16-bit and 32-bit applications to maintain backwards compatibility.
Kernel- Responsible for basic O/S functionality, managing virtual memory, task scheduling, and File I/O services.
User- Manages the user interface, including input from devices and interaction with drivers.
GDI- Responsible for all graphics manipulation.

Plug and Play: Plug and Play- designed for hardware installation to require no intervention from the user.; A plug and play system needs to consist of the following to be complete:; - A plug and play operating system; - A plug and play BIOS; - Plug and play hardware; Legacy Cards- Hardware designed prior to Plug and Play which, when installed, will not automatically be setup by the OS and must be setup manually.; Bus Enumerator- Type of driver based on a specific bus architecture. Used to build the hardware tree in the registry.

Plug and Play Docking: Docking- The process which a computer uses to establish connection with a docking station.; There are three types of docking:; Hot- Computer can be at full power when it is docked or undocked; Warm- Computer can be in sleep mode when it is docked or undocked; Cold- Computer can must be turned off before being docked or undocked

Disk operations: IFS (Installable File System)- architecture which allows multiple file systems to coexist on the same computer.; VFAT- 32-bit virtualized File Allocation Table used in Win95.; VCache- 32-bit protected mode cache driver which replaces the real-mode SmartDrive.; Long File Names- Win95 supports extended file names which can contain up to 255 characters, unlike DOS which was limited to the 8.3 structure. In Win95, each long file name has a duplicate 8.3 for backwards compatibility.

Memory

Conventional Memory- First 640k of RAM, used for DOS applications and TSR's.

Upper Memory- 384k RAM located between 640k and 1mb. Used to load MS-DOS device drivers to help increase space available for DOS applications.

High Memory Area- Region between 1024k and 1088k.

Extended Memory- Region extending from 1088k to the end of the memory. Was created for DOS applications to be able to access RAM outside of the first 640k.

Expanded Memory- Uses bank-switching to page data in and out of memory quickly.

Virtual Address Spaces

Each process is alloacted a virtual address space for the process's threads to use. This virtual space appears to be 4g in size, with 2g to process for its storage, and 2g for operating system components.

0-4M MS-DOS Compatibility Arena

The lower 4m is reserved for real-mode device drivers, TSRs and 16-bit applications.

4M-2G 32-Bit Windows Applications (Private Arena)

This area is reserved for 32-bit Windows applications, which receive their own unique address space.

2G-3G DLLs and Shared Objects (Shared Arena)

This area is used to share core system components, shared DLLs, and 16-bit Windows applications.

3G-4G Reserved System Area

Ring 0 components are mapped into this area; this area is not accessible by Ring 3 components.

Threads and Processes: Thread- The basic entity to which the operating system allocates access to the CPU.; Process- The code, data and resources which makeup an application. Each process contains at least one thread that execute's the process code.; Thread Priorities- Used to determine which thread will be allowed to run next. Each thread can have a priority number between 0 and 31 with 31 being the highest priority. The ranges of 0-31 are for NT compatibility. The priority values are divided into two sections: 0-15 for variable priority threads, and 16-31 for fixed priority threads.; Thread Scheduling - there are three states a thread can be in:; Ready- Thread is ready to be executed by the scheduler.; Waiting- Thread is waiting for an event to occur to come into the ready state.; Running- Thread is running; only one thread can be running at one time.; Primary Scheduler- Responsible for making sure the highest priority thread is running.; Secondary Scheduler- Makes sure no thread hogs the CPU.

Multitasking: Preemptive multitasking- The O/S divides time into slices (20ms for Win95) and proportions the evenly between running applications.; Cooperative multitasking- Applications are required to give up control of the CPU and let other applications take their turn. Some applications tend to hog the CPU using this method.; Multithreading- Used by the preemptive multitasking in Win95 to allow an application to have multiple paths of execution (threads).

Video

VGA fallback- ensures an incompatible video driver will not prevent you from accessing the system. For this to work, there must be a line in the [boot] section of the system.ini reading -- DisplayFallback=0

The color depth is measured in bpp (bits per pixel). The following is a chart relative to the realtionship between bpp and color depth.

Color Depth	BPP
16 colors	4
256 colors	8
32k colors (16-bit)	15
64k colors (16-bit)	16
16.7 million colors	24

Printing: Image Color Matching- Allows applications to provide closer matches for color between graphics displayed on the screen and the same graphics when they are printed. Each devices properties are stored in a profile. These profiles were designed by InterColor 3.0 (a number of vendors which included Kodak, Microsoft, Apple, Silicon graphics, etc.).; Bidirectional printing- Allows two-way communications between the printer and computer. The printer is able to send status and diagnostic information to the computer and its operating system.; What is needed for bidirectional printing:; - A bidirectional printer; - An IEEE 1284 compliant printer cable; - A bidirectional printer port on the computer; Printer Drivers; Unidrv.dll- Printer driver which is used to print to all non-postscript printers.; Friendly Names- Allows printer to be named with a "normal" name which is up to 32 characters in length.; EMF Spooling- Increases performance in the way the computer spools print jobs to the temporary file and allows the application to return to a usable state quicker.; MS-DOS application printing support; Windows 3.x and DOS-based files have been known to have printing problems in Windows 95. The problem is that the program will say that it has spooled the print job to the printer, but the printer never receives the job. The problem is being caused by the programs inability to understand the Windows 95 printing system. Windows 95 has included an MS-DOS printing compatibility feature to allow older programs to print to a virtual LPT port. Windows 95 will map an LPT port to the desired print queue which the older program recognizes.; Printer Icons; Every printer has an icon which refers to how it is used to print:; Printer icon with a hand icon - local printer which is shared; Printer icon alone - local printer unshared; Printer icon with cable attached to bottom - network printer; Printer icon with diskette - printer which is set to print to a file; Point-and-print- the method of using drag and drop to print a document. For example, you can create a shortcut to a printer on your desktop. Then, you can take a MS Word document and drag it to the printer icon. This will then print the document without the need to start the application.; Windows 95 detection log files:

SETUPLOG.TXT - Used to log installation of Windows95. Will note last utility run prior to a system halt.

DETCRASH.LOG - Used to log hardware detection during setup. Readable only by setup to determine which module was running when the system halted.

DETLOG.TXT - Equivalent of DETCRASH.LOG written in a readable format.

NETLOG.TXT - Logs detected network component information.

The Windows 95 Registry is designed as a database used by OLE to store information on OLE servers. It is used by Windows 95 to store the information typically found in Windows 3.x .INI files and the REG.DAT file. The Registry can be used for troubleshooting and enhancing perfomance in Windows 95. The registry is a heirarchical tree which contains information about many things in the computer.

REGEDIT.EXE - Used to modify the Registry.

The Windows 95 Registry is composed of USER.DAT and SYSTEM.DAT, two hidden, read only system files.

The majority of the configuration settings of Windows 95 are in the registry.

A virtual machine is an illusional environment created by the operating system in memory. These are designed to allocate resources to programs that might normally be halted by other programs in memory. Each MS-DOS application runs in its own virtual machine, as they are designed to have total and uninterupted access to all system resources. All other non-MS-DOS based programs run in the System virtual machine.

Windows 95 has three core components:

Kernel - Responsible for basic O/S functionality, managing virtual memory, task scheduling, and File I/O services.

User - Manages the user interface, including input from devices and interaction with drivers.

GDI - Responsible for all graphics manipulation.

All three are .DLL files which reside in the system as both 16-bit and 32-bit applications to maintain backwards compatibility.

Plug and Play is designed for hardware installation to require no intervention from the user.

A plug and play system needs to consist of the following to be complete:

A plug and play operating system, A plug and play BIOS, Plug and play hardware

Legacy Cards - Hardware designed prior to Plug and Play which, when installed, will not automatically be setup by the OS and must be setup manually.

Disk operations:

IFS (Installable File System) - Architecture which allows multiple file systems to coexist on the same computer.

VFAT - 32-bit virtualized File Allocation Table used in Win95.

VCache - 32-bit protected mode cache driver which replaces the real-mode SmartDrive.

Hard Drive caching in Windows 95 is handeled with VCache.

Even if a computer has only one physical drive, it can have up to twenty four logical drives. FDISK is used to partition a drive.

Long File Names - Win95 supports extended file names which can contain up to 255 characters. In Win95, each long file name has a duplicate 8.3 file name for backwards compatibility.

Windows 95 can run either 32 or 16 bit applications.

When powering up Windows 95, pressing F8 when you see the "Starting Windows 95" message will cause the system to bring up the Windows 95 start up menu and allow you to chooose startup information.

Windows 95 supports PNP technology and can be used in a LAN, WAN or remote connection. It can also be used for peer to peer networking and supports long file names (LFN) up to 250 characters.

When an LFN is saved, the system creates a short 8.3 file name, then each 12 characters is stored in its own directory. The LFN entry is given the combined attributes of hidden, read-only, system and volume labels.

Windows 95 version B is an OEM product designed for installation on new hard drives. Version B uses a 32-bit FAT while version A uses a 16-bit FAT.

Windows 95 uses the fat32 file system.

DLL files are shared executable pieces of code that helps reduce the size of applications that use them.

The Add/Remove programs control panel can be used to create startup disks.

The F4 key allows you to boot into an old operating system in a system that has Windows 95 as the default OS

The portion of the Windows 95 system that allows Windows 95 to always run in protected memory mode so that no mode switching need occur is known as the protected Mode FAT file system or VFAT.

The recommended way to access the registry is through the control Panel and select the related icon.

All items in the Windows 95 environment are treated as objects and have properties. The object settings and properties are located on the properties sheet.

The Control Panel, the Windows 95 Registry and the System Policy editors are locations where Windows 95 can be viewed AND configured.

To change the program associated with a file type: Open Folder View or Explorer, Highlight the file, select View pull down, select Options, select File Types.