Understanding the System Parameters

The installation of OS/2 Version 2.0 provides the user with a chance to tailor the OS/2 and DOS system parameters from the OS/2 Setup and Installation panel. During normal operation of OS/2 V2.0 there is little need to directly edit system files such as CONFIG.SYS. The installation of OS/2 generates a CONFIG.SYS file in the root directory of the installation drive, similar to that shown in Figure "A Typical OS/2 Version 2.0 CONFIG.SYS". Note that in this example the user has installed OS/2 V2.0 on the "D:" logical drive.

The CONFIG.SYS files for OS/2 V2.0 are similar to those in previous versions of OS/2 with a few exceptions. Here is a brief explanation of the function performed by each line in the CONFIG.SYS used as an example above. A full description of each of the statements used can be found in the Online Command Reference.

01   IFS=D:\OS2\HPFS.IFS  /CACHE:384 /CRECL:4 /AUTOCHECK:CDEFG

This line installs the High Performance File System (HPFS) driver. Installable File System (IFS) drivers load code to manage disks and other storage media with file systems other than FAT (File Allocation Table).

The /CACHE parameter specifies the amount of memory (KB) that the HPFS file system driver will use for file system disk caching. The cache for the FAT file system is handled by the DISKCACHE= statement, line 22 in this example. The amount of cache specified in the CONFIG.SYS can have a significant impact on performance. The OS/2 V2.0 installation process will select an amount of cache for the system based on the amount of installed memory, the disk size and the file system being used. The optimum amount of cache to use will depend on the factors just mentioned, and the mix of operations performed by the system. For example, an I/O intensive system, such as a server, may perform better with a larger cache.

The /CRECL parameter specifies the maximum record size (in multiples of 2KB) for caching. This value is also important for performance as it represents the maximum size an I/O can be, and still be read into the HPFS cache.

For more information on the parameters associated with the HPFS driver, refer to the Online Command Reference.

02   PROTSHELL=D:\OS2\PMSHELL.EXE

This line loads PMSHELL.EXE as the user interface program and OS/2 command processor. PROTSHELL replaces the default OS/2 command processor (CMD.EXE) with another command processor.

03   SET USER_INI=D:\OS2\OS2.INI
04   SET SYSTEM_INI=D:\OS2\OS2SYS.INI
05   SET OS2_SHELL=D:\OS2\CMD.EXE
06   SET AUTOSTART=PROGRAMS,TASKLIST,FOLDERS
07   SET RUNWORKPLACE=D:\OS2\PMSHELL.EXE
08   SET COMSPEC=D:\OS2\CMD.EXE
10   SET PATH=D:\OS2;D:\OS2\SYSTEM;D:\OS2\MDOS\WINOS2;
       D:\OS2\INSTALL;D:\;D:\OS2\MDOS;D:\OS2\APPS;
11   SET DPATH=D:\OS2;D:\OS2\SYSTEM;D:\OS2\MDOS\WINOS2;
       D:\OS2\INSTALL;D:\;D:\OS2\BITMAP;D:\OS2\MDOS;D:\OS2\APPS;
12   SET PROMPT=$i[$p]
13   SET HELP=D:\OS2\HELP;D:\OS2\HELP\TUTORIAL;
14   SET GLOSSARY=D:\OS2\HELP\GLOSS;

These lines set OS/2 V2.0 system variables stored in the OS/2 V2.0 environment. The environment is a special place in storage used by the operating system and applications to store and look up values of variables. DOS sessions and OS/2 sessions operate independently; therefore each command processor that starts a session can have its own environment. For information on how command processors within a session inherit the environment, refer to the Online Command Reference.

The main change from OS/2 V1.3 is the inclusion of some variables used by the Workplace Shell, namely lines 3 though 7.

09   LIBPATH=.;D:\OS2\DLL;D:\OS2\MDOS;D:\;D:\OS2\APPS\DLL;

This sets the LIBPATH variable. It is used to identify a set of directories to be searched when OS/2 loads dynamic link libraries. LIBPATH is not a part of the environment and therefore cannot be viewed with the SET command. Also, unlike the PATH environment variable, the current directory is not searched first. The entry " .; " at the beginning of the LIBPATH statement is used to force OS/2 V2.0 to search the current directory.

15   PRIORITY_DISK_IO=YES

Specifies disk input/output priority for applications running in the foreground. When PRIORITY_DISK_IO=YES is specified, applications running in the foreground will receive disk I/O priority over applications running in the background.

16   FILES=20

Determines the maximum number of files available in DOS sessions. Regardless of the FILES= setting, all DOS programs are initialized to a maximum of 20 files. It is the responsibility of an application to increase the number of files up to the maximum set by the FILES= statement. Each DOS session can also be customized by changing the appropriate DOS setting. This statement has no effect in OS/2 sessions.

17   DEVICE=D:\OS2\TESTCFG.SYS
18   DEVICE=D:\OS2\DOS.SYS
19   DEVICE=D:\OS2\PMDD.SYS

Install device drivers using the DEVICE= statement. Both DOS and OS/2 device drivers can be loaded with this statement in the CONFIG.SYS. OS/2 V2.0 device drivers are initialized when you start OS/2 and can process requests from either DOS or OS/2 programs. DOS device drivers are also initialized when you start the OS/2 operating system but they can only process requests from DOS programs.

TESTCFG.SYS is a new device driver in OS/2 V2.0 which is used during the install process to test the system configuration. This DEVICE statement should not be removed from the CONFIG.SYS as it is also used by the selective install process and during device driver installation.

20   BUFFERS=30

Sets the number of disk buffers the system will keep in memory. Each buffer uses 512 bytes of available memory. If you run many programs in OS/2 sessions, you can increase the speed of your system by increasing the value specified for BUFFERS (for example, BUFFERS=70). However, remember that when you increase the number of disk buffers, you decrease the available memory by 512 bytes for each buffer specified. In memory-constrained systems (4MB) reduce the number of buffers to 20.

21   IOPL=YES

Allows I/O privilege to be granted to requesting processes in OS/2 sessions.

22   DISKCACHE=64,LW

Specifies the number of blocks of storage (KB) allocated to the FAT file system cache. This parameter can have a marked effect on performance. See the comments on line 01 of this example CONFIG.SYS and also the Online Command Reference for more information on the parameters associated with DISKCACHE.

23   MAXWAIT=3

Sets the length of time, in seconds, a process waits before the system assigns it a higher priority. The most appropriate length of time to set MAXWAIT to depends on the number of applications that must run concurrently and the kinds of activities the applications perform. The default is 3 seconds.

24   MEMMAN=SWAP,PROTECT

This line specifies the various memory management options for the OS/2 V2.0 environment. SWAP enables paging whereas NOSWAP disables paging. PROTECT enables the use of protected memory by DLLs. There is also the MOVE/NOMOVE parameter which has no effect under OS/2 V2.0 and is provided for compatibility with OS/2 V1.3 only.

25   SWAPPATH=D:\OS2\SYSTEM 2048 4096

The swap file (SWAPPER.DAT) is used to temporarily store pages that the system has removed from physical memory in order to free up space to satisfy page-in requests generated as a result of page faults. If paging is enabled, this command specifies the location and initial size of the swap file. The first parameter specifies the amount of disk space (in KB) at which the system will begin to warn you that there is less than this amount of space left on the partition containing your SWAPPER.DAT file. The second parameter specifies the size of the swapper file (in KB) initially allocated at the time OS/2 is started.

26   BREAK=OFF

The Ctrl-Break keys sequence will stop a command from completing its task. The BREAK parameter instructs the system to check if you pressed Ctrl-Break before the system carries out a program request. BREAK=ON could decrease overall performance, but means the operating system will probably intercept Ctrl-Break faster.

27   THREADS=256

This specifies the maximum number of threads available to OS/2 V2.0 and its applications. The maximum that can be specified here is 4095. Normally the system default of 256 is sufficient. In memory-constrained systems (4MB) reduce this to 128.

28   PRINTMONBUFSIZE=134,134,134

This sets the parallel-port device-driver buffer size. Each number corresponds to the buffer size for LPT1, LPT2, or LPT3 respectively. The minimum value that can be specified is 134 bytes and the maximum is 2048 bytes. The system will default to 134 bytes if PRINTMONBUFSIZE is not specified or is out of this range. Changing these values will allow you to increase the size of the parallel-port device-driver buffers and thereby increase performance of data transfer to devices connected to the parallel ports.

29   COUNTRY=001,D:\OS2\SYSTEM\COUNTRY.SYS

This specifies the country code and the file containing the country information used. This information is selected by the user at installation. Refer to the Online Command Reference for more details and information on code-page switching.

30   SET KEYS=ON

This permits commands issued at the OS/2 command prompt to be retrieved later and reissued and/or edited.

31   REM SET DELDIR=C:\DELETE,512;D:\DELETE,512;E:\DELETE,512;
       F:\DELETE,512;G:\DELETE,512;

The DELDIR environment variable is new with OS/2 V2.0 and is used by the UNDELETE command. DELDIR specifies a path used to store files that have been DELETED or ERASED. A separate directory and maximum directory size must be specified for each logical disk. Installation will add an appropriate DELDIR statement to the CONFIG.SYS but remarks it out. To enable UNDELETE, remove the 'REM' from the beginning of this line.

32   BASEDEV=PRINT02.SYS
33   BASEDEV=IBM2FLPY.ADD
34   BASEDEV=IBM2SCSI.ADD /LED
35   BASEDEV=OS2SCSI.DMD
36   BASEDEV=OS2DASD.DMD

These lines install base device drivers for the following:
PRINT02.SYS; Device support for locally attached printers on Micro Channel workstations.
IBM2FLPY.ADD; Device support for diskette drives on Micro Channel workstations.
IBM2SCSI.ADD; Device support for Micro Channel SCSI adapters. The /LED parameter is only applicable when running on a PS/2 Model 95 and if present, the device driver will use the system information display panel to simulate a disk activity light.
OS2SCSI.DMD; General-purpose device support for non-disk SCSI devices.
OS2DASD.DMD; General-purpose device support for disk drives.

In addition, OS/2 V2.0 includes the following base device drivers:
PRINT01.SYS; Device support for locally attached printers on non-Micro Channel workstations.
IBM1FLPY.ADD; Device support for diskette drives on non-Micro Channel workstations.
IBM1S506.ADD; Device support for non-SCSI disk drives on non-Micro Channel workstations.
IBM2ADSK.ADD; Device support for non-SCSI disk drives on Micro Channel workstations.
IBMINT13.I13; General-purpose device support for non-Micro Channel SCSI adapters.

A device driver is a file that contains the code that the OS/2 operating system needs to recognize a device and correctly process information received from or sent to that device. A base device driver is one that is needed when the OS/2 operating system is first started.

The BASEDEV statement is used to load base device drivers. Device support for disks, diskettes, printers connected to the workstation, and other devices, is loaded with the BASEDEV statement.

Unlike the DEVICE statement, the BASEDEV statement cannot contain either drive or path information because the OS/2 operating system cannot process such information at the stage of the startup sequence when the BASEDEV statements are processed. The root directory of the startup partition is first searched for the specified file name, then the \OS2 directory of the startup partition. If drive or path information is included in a BASEDEV statement, an error is generated.

In addition, BASEDEV statements are not necessarily processed in the order in which they appear in your CONFIG.SYS file. The extensions of the file names specified in the BASEDEV statements are examined; the statements are then processed in the following order of file name extensions: .SYS .BID .VSD .TSD .ADD .I13 .FLT then .DMD

37   REM IFS=D:\OS2\CDFS.IFS /Q
38   REM DEVICE=D:\OS2\CDROM.SYS /Q /I /N:4

These lines contain the CD-ROM file system IFS driver and the IBM CD-ROM device driver for OS/2 V2.0 If CD-ROM device support was selected at the OS/2 Setup and Installation screen during installation, then these lines will be present. Refer to the Online Command Reference for an explanation of the parameters used.

39   SET BOOKSHELF=D:\OS2\BOOK
40   SET EPATH=D:\OS2\APPS

Lines 39 and 40 are two more environment variables used by OS/2 V2.0 or applications. For example, the BOOKSHELF environment variable points to the path of the system .INF files. These files are used by the system VIEW.EXE.

41   DEVICE=D:\OS2\APPS\SASYNCDB.SYS

The SASYNCDx.SYS device driver loads the asynchronous communications device interface (ACDI) support for the PM terminal program. If the PM Terminal program was not installed, this line may be REMarked out. If this is the case, delete "REM" from the beginning of the line to enable ACDI support. Remember, after changes are made to the CONFIG.SYS the system needs to be rebooted for the changes to come into effect. Refer to the Online Command Reference entries for Device Drivers (COM.SYS) for an explanation of how device drivers such as SASYNCH.SYS and COM.SYS are used.

42   PROTECTONLY=NO

This line allows OS/2 to run both DOS and OS/2 processes. If only OS/2 applications are required, specify PROTECTONLY=YES.

43   SHELL=D:\OS2\MDOS\COMMAND.COM D:\OS2\MDOS /P

The SHELL= line specifies the DOS command processor (COMMAND.COM), or allows you to replace the DOS command processor with another command processor. In this example we are loading and starting the DOS COMMAND.COM processor. The parameters following it are specific to the command processor. In this case the parameters are the path for COMMAND.COM and /P, which is used to retain COMMAND.COM in storage. The SHELL= statement does not affect either the OS/2 SET command, or the SHELL command in BASIC.

44   FCBS=16,8
45   RMSIZE=640
46   DEVICE=D:\OS2\MDOS\VEMM.SYS
47   DEVICE=D:\OS2\MDOS\VMOUSE.SYS
48   DOS=LOW,NOUMB
49   DEVICE=D:\OS2\MDOS\VDPX.SYS
50   DEVICE=D:\OS2\MDOS\VXMS.SYS /UMB
51   DEVICE=D:\OS2\MDOS\VDPMI.SYS
52   DEVICE=D:\OS2\MDOS\VWIN.SYS
53   DEVICE=D:\OS2\MDOS\VCDROM.SYS

Lines 44 through 53 are needed to configure and load drivers for the DOS environment.

The first line sets the file control block (FCB) management information for DOS sessions. A FCB is a record that contains all of the information about a file (for example, its structure, length, and name). If a program tries to open more than the number of files specified in the FCBS statement, the system closes the least recently used file control block and opens the new file. This parameter should not need to be changed and has no effect on OS/2 sessions.

The RMSIZE= statement specifies the highest storage address allowed for the DOS operating environment. In certain circumstances this can be used to limit the size of the DOS environment.

In line 48, the DOS= parameter specifies whether the DOS kernel will reside in the high memory area (HMA) and whether the operating system or DOS applications will control upper memory blocks (UMBs). The HMA refers to space between 1MB and 1MB+64KB and UMBs reside between 640KB and 1MB.

If DOS=HIGH/LOW,UMB is specified in CONFIG.SYS, then the operating system controls the UMBs. This means that DOS applications can be loaded into upper memory but cannot allocate UMBs.

On the other hand, if DOS=HIGH/LOW,NOUMB is specified in CONFIG.SYS, then the operating system will not control any UMBs and DOS applications can allocate UMBs but cannot be loaded there.

Lines 46 and 47, and 49 through 53 contain the device drivers for the virtual DOS/Windows environment. More information on these specific drivers and a complete discussion of tailoring the DOS environment under OS/2 V2.0 may be found in OS/2 Version 2.0 - Volume 2: DOS and Windows Environment.

54   DEVINFO=SCR,VGA,D:\OS2\VIOTBL.DCP
55   SET VIDEO_DEVICES=VIO_VGA
56   SET VIO_VGA=DEVICE(BVHVGA)
57   DEVICE=D:\OS2\MDOS\VVGA.SYS
58   DEVICE=D:\OS2\MDOS\V8514A.SYS

These lines configure the display environment under OS/2 V2.0

The DEVINFO= statement in line 54 is used to prepare a device (such as a keyboard (KBD), display terminal (SCR), or printer (LPT#)) for codepage switching. Separate DEVINFO statements are required for each device to be used for codepage switching.

This line prepares the display screen for codepage switching. The display statement specifies your display name and a file named VIOTBL.DCP that contains a video font table for displaying characters in each of the codepages supported by the system.

Lines 55 and 56 set environment variables related to the display driver being used.

Lines 57 and 58 load virtual device drivers for the VGA and 8514/A devices, for use by the DOS/Windows environment. In this example, the user specified VGA resolution with an 8514/A adapter installed.

If OS/2 V2.0 were installed on a system with an XGA adapter, and high resolution was specified for the Windows environment (that is, Windows was to be run full-screen only), then the appropriate lines in the CONFIG.SYS would be:

        DEVINFO=SCR,VGA,D:\OS2\VIOTBL.DCP
        SET VIDEO_DEVICES=VIO_XGA
        SET VIO_XGA=DEVICE(BVHVGA,BVHXGA)
        DEVICE=D:\OS2\MDOS\VVGA.SYS
        DEVICE=D:\OS2\MDOS\VXGA.SYS

Adding or changing your display adapter support after installation can be performed automatically using the OS/2 V2.0 selective install process. A complete description of how this is done can be found in the Master Help Index under adding display adapter support.

59   DEVICE=D:\OS2\POINTDD.SYS
60   DEVICE=D:\OS2\MOUSE.SYS

POINTDD.SYS provides mouse-pointer draw support in all text modes for OS/2 sessions. To function, an appropriate mouse device driver must also be loaded. In this example, this is done in line 60 with the MOUSE.SYS driver. These two lines will provide support for a PS/2-style mouse.

If the pointing device used was a Microsoft mouse attached to the COM1 port, line 60 would change to:

60    DEVICE=D:\OS2\MOUSE.SYS SERIAL=COM1

Some pointing devices such as the Logitech** mouse need a device-dependent device driver as well as the MOUSE.SYS device-independent device driver.

Refer to Pointing Device Support and the Online Command Reference, if installing support for a pointing device not directly supported by the OS/2 installation procedure.

61   DEVICE=D:\OS2\COM.SYS
62   DEVICE=D:\OS2\MDOS\VCOM.SYS

The COM.SYS device driver supports ports COM1, COM2, COM3, and COM4. It does not provide support for specific devices that are attached to the COM port. Instead, it provides enabling support for the asynchronous communications interface itself. Application programs, subsystems, and system programs must provide the support needed to use devices attached to the COM port. VCOM.SYS is a virtual device driver that provides support in DOS sessions for up to four COM ports.

Note: The COM.SYS device driver is used for all IBM PS/2 models. There is no COMDMA.SYS device driver for the IBM PS/2 Models 90 and 95 as described in the Online Command Reference.

Some devices which attach to the COM ports provide their own device drivers. COM.SYS allows other drivers which support COM ports to be installed, provided they are listed in the CONFIG.SYS before COM.SYS. When COM.SYS is loaded, it will claim all COM ports not already allocated to other device drivers.

In the following example DEVCOM1.SYS uses COM1 and PRINTER4.SYS uses COM4. COM2 and COM3 are available for use by COM.SYS.

        DEVICE=C:\OS2\DEVCOM1.SYS
        DEVICE=C:\OS2\PRINTER4.SYS
        DEVICE=C:\OS2\COM.SYS

63   CODEPAGE=437,850
64   DEVINFO=KBD,US,D:\OS2\KEYBOARD.DCP

Line 63 sets the system codepages (defined character sets) to be prepared by the OS/2 operating system for codepage switching. Line 64 is DEVINFO specification for the keyboard. It specifies the keyboard layout and a file named KEYBOARD.DCP that contains a keyboard layout table for translating keystrokes into the characters of each codepage supported by the system. Codepage support in OS/2 V2.0 is similar to that provided under previous versions of OS/2. More information on DEVINFO and CODEPAGE can be found in the Online Command Reference.