Operating System Design/Case Studies/Windows 9x

Windows 9x references to the Windows family, Windows 95, 98 and Me operating systems. They were set apart from the earlier Windows versions: 1.0, 20, and 3.0 by their device drivers, virtual memory management and MSDOS.SYS and MS-DOS kernel. The reign of Windows 9x ended in 2001 when the Windows NT based Windows XP was released for both home and office use.

Architecture
The Windows 9x architecture was a step up in many ways from its predecessors. The GUI was redesigned, the kernel supported virtual memory and had a VFAT{virtual file allocation table} filesystem unlike its FAT16 and FAT12 filesystems before. Windows 95b was the 3rd version of 95 released and included support for FAT32. All versions of 9x supported FAT16 drive compression through Drivespace, a program originally from MS-DOS 6.22

The Kernel
The kernel was just a different version of the MS-DOS kernel, with added virtual memory and memory protection that was lacking in Windows 1.0+. It was of monolithic architecture, different from its successors NT 3.1+.

The Registry
The registry acted as a temporary and convenient holding place for program and system data. The directories are conventionally named as follows: HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS, HKEY_CURRENT_CONFIG, and HKEY_PERFORMANCE_DATA. Each one of these stored specific types of data like, hardware configuration data, application data, performance data, and user data. The system can access this anytime and the current user is allowed to access and edit it also.

File Names
File names in Windows 9x were allowed to have up to 255 characters, a special feature in the VFAT filesystem. Previous versions of Windows were limited to MS-DOS style 8.3 letter filenames.

Graphical User Interface
The GUI was one significantly changed in the Windows 9x series. With the start button, the toolbar and taskbar both by default on the bottom of the screen, allowing running program to be selected. There was also a new widget set (that is, a different standard look and feel to the applications) and many new fonts are available.