


	CHAPTER 3:   HP 95LX DOS

===== Introduction =====

The HP 95LX contains the primary components of ROM-executable MS-DOS 3.22.

More specifically, the HP 95LX contains the DOS Kernel and the Command
Processor, but only a few external commands. 

Generally speaking, DOS works the same on the HP 95LX as it would on a
standard PC (except for the missing external commands). For this reason, these
notes discuss only the DIFFERENCES between the operation of
MS-DOS 3.22 on the HP 95LX and DOS operation on a standard PC.

DOS BOOT SEQUENCE
-----------------

On a standard PC, DOS boots off disk and runs from RAM. On the HP 95LX, DOS
boots out of ROM and runs from ROM. Thus on the HP 95LX DOS, RAM
requirements are greatly reduced since only DOS DATA is stored in RAM. 

There is no provision on the HP 95LX to boot from disk. However, a disk can
contain CONFIG.SYS and AUTOEXEC.BAT files - see below.

DOS INITIALIZATION
------------------

On a standard PC, DOS makes the boot disk drive the default drive and searches
the root directory of that drive for a CONFIG.SYS file.

On the HP 95LX, DOS initialization has been changed to first search for
CONFIG.SYS on drive A: and, if not found, to search on drive C:. If
CONFIG.SYS is found on drive A:, THAT CONFIG.SYS is processed and A:
becomes the default drive. In this case, any CONFIG.SYS that is on drive C:
will not be processed. If CONFIG.SYS is not found on drive A:, then C: becomes
the default drive and any CONFIG.SYS found there will be processed.

THE DOS EXEC FUNCTION
---------------------

In ROM-executable MS-DOS 3.22, the EXEC function has been extended to first
search a table of ROM-executable programs before searching disk in case the
program name has no drive path specified.

On the HP 95LX, the table contains the names COMMAND and $SYSMGR. The COMMAND
program is the DOS Command Processor; the $SYSMGR program is the System
Manager.

THE DEFAULT SHELL
-----------------

On standard DOS systems, the default shell is COMMAND.COM; on the HP 95LX,
COMMAND.COM is the System Manager.

The System Manager is the program that directs execution of the built-in
and special add-on applications. The HP 95LX System Manager does not
process any AUTOEXEC.BAT files.

THE DOS COMMAND PROCESSOR
-------------------------

The COMMAND.COM program is available in the HP 95LX, but it is not normally
run at initialization time since DOS goes directly to the System Manager
shell. There are two ways to access the command processor:

	* Invoke the command processor from within the System Manager program.

	* Change the shell to the command processor by including the line

		SHELL=COMMAND /P

	  in the CONFIG.SYS file and rebooting. 

	  This causes DOS to go directly to COMMAND.COM - the System Manager is
	  not invoked and the built-in application keys will not be active. The
	  commands that are available are the internal command-processor
	  commands, any external programs on disk, and the two ROMed program
	  commands listed above.

	  One use of this method is to get access to DOS in order to perform
	  some custom initialization and then run the System Manager using the
	  $SYSMGR command.


DISK-RESIDENT EXTERNAL COMMANDS

The HP 95LX contains two external commands, COMMAND.COM and CHKDSK.EXE, which
reside in the root directory of the ROM disk.

The COMMAND.COM program is only a stub that invokes the actual command
processor residing in ROM. This stub is provided in case some program accesses
the command processor by its full name (including extension). As mentioned
above, COMMAND (without path or extension) will be executed directly from ROM.

CHKDSK is the standard DOS check-disk command.

The HP 95LX also contains the DEBUG.EXE program in a hidden directory called
_SYS. This directory is off the root of the ROM disk. This is the standard DOS
DEBUG program.

INTERNATIONAL SUPPORT
---------------------

MS-DOS 3.22 supports the COUNTRY= configuration parameter and DOS calls that
allow tailoring DOS and applications to local language characteristics.
Some of this information depends on the the PC's character set. DOS 3.22
supports only code page 437 (switchable code pages start with DOS 3.3).
Since the HP 95LX uses code page 850, the country-specific
information in HP 95LX DOS has been updated to match code page 850.


 NOTE: The international support built into the HP 95LX System Manager
       does not use these DOS capabilities.
