The Windows 95 architecture includes several improvements over earlier versions of Windows. These changes, which strongly impact most areas of system performance, include the following:

∑ Fully integrated 32-bit, protected-mode operating system, eliminating the need to run MS-DOS separately

∑ Complete 32-bit kernel, providing improved memory management and process scheduling, plus improved system-wide robustness and improved cleanup after an application closes or fails, delivering a more stable and reliable operating environment

∑ Preemptive multitasking and multithreading support, providing improved system responsiveness, smooth background processing, and improved system capacity, allowing multiple applications and system tasks to run well concurrently

∑ 32-bit installable file systems to support better performance and long filenames

∑ 32-bit device drivers for all system components, ensuring better performance and better resource management

Many Windows 95 features provide dynamic configuration, reducing or eliminating the need for users to adjust their system settings. The following self-tuning features in Windows 95 are designed to improve performance and reduce support costs.

Dynamic swap file and dynamic caching using VCACHE.

Windows 95 uses dynamic sizes for the virtual-memory swap file, the cache for file and network access, and the CD-ROM cache. Both the swap file and cache sizes can grow or shrink, depending on the computerís memory configuration and the demand for memory from applications. This relieves users or administrators from having to change the cache parameters as new memory or new applications are added. Windows 95 can take advantage of new memory automatically and expand or reduce the file and cache sizes automatically based on demands when applications are loaded or unloaded. Also, the networking, disk, CD-ROM, and paging caches are integrated and will scale as more memory is added to the computer. For more information, see "Optimizing the Swap File" and "Optimizing File System Performance" later in this chapter.

32-bit disk and file access for fast hard-disk access.

These mechanisms allow Windows 95 to access the hard disk or file system directly, bypassing the computerís BIOS. Using 32-bit file and disk access improves performance and allows Windows 95 to handle BIOS requests in protected mode, rather than in real mode. For more information, see Chapter 20, "Disks and File Systems."

Background print rendering.

For a computer that has sufficient memory to take advantage of it, background print rendering is available automatically to reduce the return-to-application time for printing. With this feature, Windows 95 first writes an enhanced metafile (EMF) format file, which is a device-independent rendering of the print job that is much faster to produce than a device-specific rendering. In the background, Windows 95 uses the EMF file to create the device-dependent rendering while the user continues to work in the application. For more information, see "Optimizing Printing" later in this chapter.

Automatic system adjustments during Windows 95 Setup.

During installation, Windows 95 Setup makes decisions about certain operating system features based on the hardware configuration. For example, in a computer with low memory, Windows 95 turns off background print rendering, because this feature increases the operating system working set that is loaded into memory and cannot be paged out to the swap file.

Built-in tools for monitoring and adjusting system performance.

The following tools in Windows 95 are available for managing performance-related settings:

∑ System option in Control Panel provides settings for tuning and troubleshooting. For information, see "Optimizing the Swap File," "Optimizing File System Performance," and "Setting Graphics Compatibility Options" later in this chapter.

∑ System Monitor can be used to track the performance of key system components, as described in "Tracking Performance with System Monitor" later in this chapter.

∑ DriveSpace includes a protected-mode driver that is installed by default, providing faster performance than the earlier real-mode compression driver and using only an additional 10 or 15 percent overhead. If you are using any real-mode disk-compression utilities other than DriveSpace or DoubleSpace, plan to switch to a protected-mode version. Contact the manufacturer to determine availability of protected-mode drivers that are compatible with Windows 95.

∑ Disk Defragmenter can improve file access time by defragmenting uncompressed FAT drives and compressed DriveSpace or DoubleSpace drives. Fragmentation occurs over time, as programs read from and write to the hard disk. Eventually, files must be stored in noncontiguous sectors on a disk. Fragmentation doesnít affect the validity of the information, but it takes much longer for the computer to read and write fragmented files.

For more information about DriveSpace and Disk Defragmenter, see Chapter 20, "Disks and File Systems."