OS/2 2.0 CONFIG.SYS Statements

Customizing the OS/2 2.0 CONFIG.SYS file improves performance and reduces memory requirements. This section describes some OS/2 2.0 CONFIG.SYS statements.

Some users might want to shorten the installation process by copying files from a network server or from a previously installed system. However, using the statements from an existing system configuration CONFIG.SYS file for another system might not enable optimum performance of the operating system, because many of the parameters for the CONFIG.SYS statements are dynamically determined based on the configuration of the system. For example, disk cache sizes and swap file sizes are determined by hard disk and memory sizes. Refer to the online help for detailed descriptions of CONFIG.SYS statements and DOS and WIN-OS/2 settings.

DISKCACHE=
Specifies the number of blocks of memory to allocate for use by the FAT disk cache, and specifies lazy write and disk-read threshold size.

DISKCACHE speeds up applications that read hard disks by keeping hard disk data frequently accessed in a cache. However, increasing the size of the disk cache decreases the size of available memory. See "File System Caches" for information about default disk cache sizes.

IFS=
This statement is required to install the High Performance File System. Parameters similar to those for the FAT DISKCACHE statement can be specified. The specified cache size and threshold value perform the same functions. See "File System Caches" for cache size defaults.

Lazy writing for HPFS defaults to On. A RUN=CACHE statement is required to change the state of lazy writing. CACHE also can be executed from a command prompt.

PRIORITY_DISK_IO=
Specifies disk input/output priority for applications running in the foreground. When PRIORITY_DISK_IO=YES is specified in the CONFIG.SYS file, an application running in the foreground receives disk I/O priority over applications running in the background. Thus, the application in the foreground has better response time than applications running in the background.

LIBPATH=, PATH=, OR DPATH=
Specifies the directories to search through to find DLLs, EXEs, and data. Specify the most frequently accessed directories first so the operating system can find them faster.

MAXWAIT=
Sets the amount of time a process waits before the system assigns it a higher priority. The amount of time to set depends on the number of concurrent applications and the activities the applications perform. The system default is 3 seconds.

PRINTMONBUFSIZE=
Sets the parallel port device driver buffer size, in bytes. This statement is used in conjunction with print monitor programs. This statement enables a user to increase the size of the parallel port device driver buffer and thereby improve performance of data transfer to devices connected to the parallel port. The parallel port device driver allocates and registers its monitor chain buffer based upon the specified value. Ensure that the monitor supports the changing of this buffer.

PROTECTONLY=
Selects one or two operating environments. The OS/2 operating system requires this statement in the CONFIG.SYS file.

RMSIZE=
Specifies the highest conventional memory address allowed for the DOS session.

If PROTECTONLY=NO is specified, a user can reduce the size of the DOS session further by specifying RMSIZE. This allows a user to decrease the size of the DOS session, thereby making more memory available for OS/2 2.0 sessions.

SWAPPATH=
Specifies the size and location of the swap file. The swap file (SWAPPER.DAT) temporarily stores pages that the system has removed from physical memory to satisfy a request for memory. The default location for the file is SWAPPATH= \OS2 \SYSTEM.

The operating system pre-allocates the initial swap file size based on the size in the SWAPPATH statement in the CONFIG.SYS file. However, if necessary, as a system runs, OS/2 2.0 increases the size of the swap file.

To change the pre-allocated size in the CONFIG.SYS file, modify the SWAPPATH= statement (sizes are specified in KB). To customize the swap file size for a particular environment, modify the default value to reflect the smallest default value, according to Table 1 (for example, 2MB); then restart the system. Start the desired application, view the OS2 \SYSTEM \SWAPPER.DAT file and record the size periodically. Take the largest size that you record and add 1-2MB. If this size is larger than the recommended size in Table 1, choose the larger value. For more information, see "Swap File."

Normal operation of OS/2 2.0 involves considerable disk activity as operating system functions are loaded and pages are moved in and out of the swap file. To improve performance, consider dedicating a separate partition for the swap file next to the operating system partition. This helps avoid fragmentation of the swap file, because other files will not be added and deleted from the dedicated partition. Disk access time will be minimized.

Ensure that the dedicated partition is large enough to contain the swap file as it increases in size.

SET DELDIR=
Allows a user to restore files that have been deleted. By default, this setting is commented out because backing up each deleted file slows system performance.