* The Command Interpreter 
   
 The command interpreter, COMMAND.COM, is the part you interact with on the  
command line. It consists of these parts: 
     
Resident Portion: 
 
 The resident portion resides in memory immediately following IBMDOS.COM and its 
data area. This portion contains routines to process Int\22 (Terminate Addr),
Int\23 (Ctrl-Break Handler), and Int\24h (Critical Error Handler), as well
as a routine to reload the transient portion if needed. For DOS 3.x, this
portion also contains a routine to load and execute external commands, such as
files with exensions of COM or EXE.
 
 When a program terminates, a checksum is used to determine if the application  
program overlaid the transient portion of COMMAND.COM. If so, the resident  
portion will reload the transient portion from the area designated by COMSPEC=  
in the DOS environment. If COMMAND.COM cannot be found, the system will halt. 
 
NOTE: DOS 3.3+ checks for the presence of a hard disk, and will default to  
      COMSPEC=C:\\. Previous versions default to COMSPEC=A:\\. Under some DOS 
      versions, if COMMAND.COM is not immediately availible for reloading 
      (i.e., swapping to a floppy with COMMAND.COM on it) DOS may crash. 
 
 All standard DOS error handling is done within the resident portion of  
COMMAND.COM.  This includes displaying error messages and interpreting the  
replies to the "Abort, Retry, Ignore, Fail?" message.   
 
   
 IBM's original documentation spoke of installing alternate command  
interpreters (programs other than COMMAND.COM) with the SHELL= statement in  
CONFIG.SYS. Unfortunately, IBM chose not to document much of the interaction  
between IBMDOS.COM and IBMBIO.COM. By the time much of the interaction was  
widely understood, too many commercial software programs had been written to  
use peculiarities of COMMAND.COM itself. There is only one commercial  
replacement for COMMAND.COM (a program called Command Plus) and it is not  
widely known or used. 
 
 
 "Shell" programs exist which use DOS only for disk management while they more  
or less comprise a new operating system. These include: 
 
     DesQview			Windows			OmniView 
     GEM			TopView			TaskView 
 
 


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