Lesson 1: A New Operating System

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In this lesson, we take a look at the Windows 95 operating system and examine what makes it so different from the Windows 3.x operating system.

After this lesson, you will be able to:

  • Identify the basic differences between Windows 95 and 98 and earlier versions of the Windows operating system.
Estimated lesson time: 15 minutes

As covered in Chapter 15, "Software: MS-DOS and Windows 3.x," Windows 3.x is an operating environment created on top of MS-DOS to provide a graphical user interface (GUI) and other features that make it easier to run programs and manage files. Windows 95 is a complete operating system that includes an improved GUI as well as other useful features. It has a unique desktop appearance and features multimedia and Internet access.

Windows 95 is dramatically different from Windows 3.x. Installing devices, managing memory, optimizing the system, and troubleshooting are handled in a completely different way than in Windows 3.x.

Although Windows 95 will run most MS-DOS and Windows 3.x software, and even bears some superficial resemblance to those operating systems, it is constructed very differently. Windows 95 is comprised of two products: a DPMI (DOS Protected Mode Interface—an improved MS-DOS) and the protected mode GUI. The MS-DOS part of Windows 95 looks and acts pretty much like the old MS-DOS; however, because it is DPMI-compliant, it can support use of extended memory even though it does not support multitasking.

When you first boot up Windows 95, you see the message "Starting Windows 95." At this point, Windows is starting the DPMI. After the DPMI is loaded, Windows 95 loads the GUI. Notice that it is not necessary to use the GUI to boot up to Windows 95; this is important because many computer repair functions, particularly for the hard disk drive, are handled at a MS-DOS prompt.


MS-DOS is available in Windows 95, although it resides in the background, and many novice users will never use it directly in command mode. MS-DOS external commands can be found in the Windows\Command directory of the bootable drive. Its unofficial name is MS-DOS 7. The IO.SYS and MSDOS.SYS from older versions of MS-DOS are still there, but their functions are completely different. All the functions of MSDOS.SYS and IO.SYS have been combined together into IO.SYS, and MSDOS.SYS has been turned into a hidden, read-only text file in the root directory of the boot drive. MSDOS.SYS is used as a startup option. Configuring and using MSDOS.SYS is covered in detail in Lesson 3 of this chapter.

COMMAND.COM remains and still performs basically the same functions as the old COMMAND.COM: to provide the command prompt. When the computer boots up and says "Starting Windows 95," press the F8 key and select "Command Prompt Only" to get to an MS-DOS 7 prompt. Type VER and you will see "Windows 95."

The Windows 95 GUI

The Windows 95 GUI is a protected-mode overlay of the MS-DOS 7 shell. It loads its own device drivers. It does not need to load device drivers from CONFIG.SYS unless Windows 95 does not have a built-in protected-mode driver for a particular device. Windows 95 also has support for FILES, BUFFERS, DOS=UMB, and just about every other setting found in CONFIG.SYS. Assuming that there are Windows 95 drivers available, there is no need for a CONFIG.SYS file. The GUI loads a protected-mode driver for most CD-ROMs, has VCACHE for disk caching, and protected-mode mouse support for Windows 95, Win 3.x, and MS-DOS applications. As with CONFIG.SYS, there is no requirement for AUTOEXEC.BAT.

The Virtual Memory Manager (VMM) supports memory usage both at the MS-DOS 7 level and the GUI. At the MS-DOS 7 level, VMM does little more than load a simple MS-DOS. When the GUI is loaded, VMM takes advantage of the power of 386 (and better) protected mode to create virtual machines (VMs)—one for Windows 95 and one for any MS-DOS program running in Windows 95. Along with the VMM is the Installable File System (IFS), which provides support for hard drives, CD-ROMs, and network drives. The IFS also provides the support for long filenames. The IFS runs both for MS-DOS 7 and the GUI.

While the GUI is running, the main functions of Windows 95 are handled by three core operating components:

  • The kernel: loads applications, handles all aspects of I/O, and allocates virtual memory.
  • The user component: handles all input from the user—mouse, keyboard and so forth.
  • The graphical device interface (GDI) modules: provide routines that draw the images on the display.

Windows 95 applications use the operating system as a pool of resources (memory, modem, video, and printer). Programs or dynamic-link libraries (DLLs) make "calls" to these three modules whenever they need to place something on the screen, check the status of the mouse, use memory, or gain access to anything else they might need. This operates similarly to Windows 3.x. However, there are also major improvements:

  • Most functions run in full 32-bit protected mode. Win 3.x functions run in 16-bit real mode.
  • Windows 95 runs as a preemptive multitasker, allocating time to each program. Win 3.x offered a cooperative multitasking feature that made it possible for programs to take turns using processor time.
  • In Windows 95, GDI and the user component use fixed memory areas called heaps to keep track of all resources. Heaps for Windows 3.x are 64 KB in size. Improvements with hardware and applications have proven that 64 KB is often too little and frequently causes problems. Windows 95 heaps are variable in size and no longer subject to this restriction.
  • The user interface is at the top of the Windows 95 architecture. Windows 95 can use either its default interface, the Windows 3.x interface, or another interface. Old Windows and MS-DOS applications run within the GUI.

The Windows 95 File Structure

Disk structures have not changed in Windows 95. Partitions are still exactly the same, so the MS-DOS 7 bootable files of Windows 95 must still be installed to the C drive. Windows 95 still uses 16-bit FAT (FAT16) formats for hard disk drives and floppy disk. The FDISK and FORMAT commands are still used to set up hard drives. A hard drive that was partitioned with FDISK and formatted with an older version of MS-DOS is exactly like a Windows 95 drive. Windows 95 OSR2 and Windows 98 support 32-bit FAT (FAT32). This file system improves storage efficiency by reducing cluster sizes on large partitions. The following table shows the Windows 95 versions and their appropriate file system.

Version Description
Version A The original Windows 95 release—intended for upgrading from Windows 3.1. Uses FAT16 file system.
Version B The OEM (original equipment manufacturer) version—intended for installation on new computers only. Uses FAT16.
OSR2 The final version of Windows 95 (sometimes referred to as Version C)— intended for installation on new computers only. Uses FAT32 file system. End users cannot buy this version as a retail product.

32-Bit VFAT

Disk access is provided through the 32-bit VFAT (virtual file allocation table). Unlike the 16-bit FAT used in previous versions, VFAT is a virtual device driver that operates in protected mode. This provides more reliability and works with a greater variety of hardware. Don't confuse 32-bit VFAT with 32-bit FAT, which has to do with how data is stored on a hard disk partition (the cluster size) while VFAT has to do with how files are accessed.

VFAT was formerly known as 32-bit file access in Windows 3.1.

Long Filenames

In MS-DOS and Windows 3.x, filenames were in what is called an 8.3 ("eight dot three") format. That is, the filename itself was restricted to a maximum of eight characters in length, and the extension to a maximum of three characters in length. Filename and extension are connected by a period, or "dot." Windows 95 supports long filenames (LFNs). The LFN removes the 8.3 filename limitation of older MS-DOS and Windows operation systems. In a regular MS-DOS 8.3 file specification directory, all file records are stored in 32-byte records. Ten of these 32 bytes are "reserved." The other 22 bytes are used to store information on starting clusters, creation date, and creation time, and 11 bytes are for the filename itself. LFNs exist on FAT partitions by chopping the filename into 12-byte chunks (stealing one of the "reserved" bytes) and allowing up to 13 chunks, creating a filename of up to 255 characters.

When an LFN is saved, the system creates a short name that conforms to the 8.3 standard. Then, each 12 characters is cut off and stored in its own directory section. The directory entries that make up the long filename are called LFN entries. These must be backwardly compatible with MS-DOS programs and with MS-DOS itself.

Windows takes the first six characters (no spaces) of the filename, adds a tilde (~), a number, and then the extension. If two or more files have the same first six characters, the number is incremented by one for each. For example, two files named "long file name one.txt" and "long file name two.txt" would become "longfi~1.txt" and "longfi~2.txt".

To make LFNs compatible with MS-DOS means to make sure that MS-DOS ignores the LFN entries in the directory structure. This is achieved by giving LFN entries the bizarre attribute-combination of hidden, read-only, system, and volume label. There is nothing in the MS-DOS code that tells it what to do if it runs into a file with this combination of attributes, so MS-DOS will not interfere with them.

Older disk utilities are incompatible with long filenames and will try to erase the LFN entries. It is critical that any disk utility that tries to diagnose the directory structure, including the SCANDISK that is included with MS-DOS 6 and earlier, should never be run on a computer with LFNs. The SCANDISK that comes with Win 95 is compatible with LFNs.

The Registry

The main difference between Windows 95 and Windows 3.x is the Registry. The Registry consists of two binary files called SYSTEM.DAT and USER.DAT that are located in the Windows directory. Because they are hidden read-only files, they are prevented from being accidentally removed or changed. The Registry holds information on all the hardware in the computer, network information, user preferences, and file types, as well as anything else that pertains to Windows 95. The idea of the Registry is to have one common database for everything that comprises the computer. The Registry is designed to replace CONFIG.SYS and AUTOEXEC.BAT, as well as every .INI file (especially WINDOWS.INI and SYSTEM.INI). Windows 95 still reads these files at boot up to provide backward compatibility with Win 3.x programs that use them.

Windows 95 Enhancements

Windows 95 is dramatically different from any of the Windows 3.x series—not only in its look, but because it provides many enhancements that make it even more versatile and user-friendly. For an A+ technician, proficiency in using the Windows 95 environment requires a great deal of study and hands-on experience.

Windows 95 represents an evolutionary step in operating the system. The following table compares the features of Windows 3.x, Windows 95, and Windows 98. (The A+ Certification does not include Windows 98 at this time; it is included for reference only.)

Windows 3.x Windows 95 Windows 98
A 16-bit program. A 32-bit program. A 32-bit program.
An MS-DOS-based application that supplements an operating system. An operating system. An operating system.
All hardware upgrades require a software driver to be installed in order for the new hardware to work with Windows. Supports Plug and Play hardware installation. Allows user to simply plug in new hardware and let Windows 95 configure it. Supports Plug and Play hardware installation. Allows user to simply plug in new hardware and let Windows 98 configure it. Expanded hardware support for USB (universal serial bus), IEEE1394 serial bus, ACPI (Advanced Configuration and Power Interface) and DVD (digital video disc), Windows Driver Model (WDM), Multiple Display Support, and more.
Supports filenames up to only 8.3 format, such as filename.doc or spreadsh.xls. Supports filenames up to 250 characters. Supports filenames up to 250 characters.
Supports only multitasking. Supports both multitasking and multithreading (running several processes in rapid sequence within a single program). Supports both multitasking and multithreading.
Cannot run the new 32-bit applications. Can run older Windows and MS-DOS applications, plus the new 32-bit applications written specifically for Windows 95 and Windows NT. Can run older Windows and MS-DOS applications, plus the new 32-bit applications written specifically for Windows 95 and Windows NT.
Program Manager and program group-centered interface. Document and work-centered interface. Document and work-centered interface. Optional Web-like interface.
Designed to be a stand-alone, single-user computer interface. Designed to be an interactive terminal on a local area network (LAN), wide area network (WAN), or remote or dial-up connection. Designed to be an interactive terminal on a local area network (LAN), wide area network (WAN), or remote or dial-up connection.
Uses Program Manager as the starting point. Designed around a Start button used to launch a program or open a document. Designed around a Start button used to launch a program or open a document.
Windows for Workgroups provided limited support communication and networking. Integrated support for for communication and networking. Provides TCP/IP (Transmission Control Protocol/Internet Protocol) and PPP (Point-to-Point Protocol) support. Improved support for communication and networking. Network-card friendly (supports Network Driver Interface Specification—NDIS). Supports PPTP (Point to Point Tunneling) and VPN (Virtual Private Network). Supports Windows Sockets 2.0, Web-based Enterprise management (WBEM), and much more.

Advantages of Windows 95

There are several changes, not readily visible to the user, that make Windows 95 superior to the older versions of Windows.

Windows 95 has a better system of managing computer resources: memory (RAM), video RAM, hard disk drives, and network communications.

Programs designed to run on Windows 95 carry out tasks effortlessly. They tend to be faster, more efficient, and less likely to crash than with earlier Windows programs.

Microsoft's goal was to build a backward-compatible 32-bit operating system that allowed people to continue using their favorite MS-DOS programs and existing hardware. Some additional advantages of Windows 95 are:

  • User-definable interface: The desktop is completely and easily customized by the user.
  • New accessories: The standard Windows accessory package has been improved and expanded.
  • Interconnectivity: It is designed to run as part of any network system.
  • Direct cabling: Any two computers with Windows 95 and a free COM or parallel port can be connected for data sharing. One computer acts as a host and shares its files with the other.

Lesson Summary

The following points summarize the main elements of this lesson:

  • Windows 95 is an operating system.
  • The new GUI is more user-friendly than the Windows 3.1 interface.
  • Early versions of Windows 95 are 16-bit operating systems and utilize 32-bit VFAT.
  • The final version of Windows 95 (OSR2) and Windows 98 can run either 16-bit or 32-bit FAT systems (32-bit is the default).
  • Windows 95 fully supports Plug and Play.
  • Windows 95 supports multitasking and multithreading.
  • One of the advantages of Windows 95 is its improved communication and networking capabilities.

Microsoft Corporation - A+ Certification Training Kit
Microsoft Corporation - A+ Certification Training Kit
Year: 2000
Pages: 127

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