DOS Plus
Encyclopedia
DOS Plus is an operating system
written by Digital Research
, first released in 1985. It can be seen as an intermediate step between CP/M-86
and DR-DOS
.
It is able to run programs written for either CP/M-86 or MS-DOS
2.11, and can read and write the floppy formats used by both these systems. Up to four CP/M-86 programs can be multitasked
, but only one DOS program can be run at a time.
as MS-DOS. Like MS-DOS, it has a command-line interpreter called
DDT86 ALARM UK8 PRN=LPT1 Num 10:17:30
The left-hand side of the status bar shows running processes
. The leftmost one will be visible on the screen; the others (if any) are running in the background. The right-hand side shows the keyboard layout in use (UK8 in the above example), the printer port assignment, the keyboard caps lock
and num lock
status, and the current time. If a DOS program is running, the status line is not shown. DOS programs cannot be run in the background.
The keyboard layout in use can be changed by pressing Ctrl
, Alt
and one of the function key
s F1-F5.
to support its multitasking features:
It also contains subsets of the standard DOS commands and CP/M commands - for example, it has both a built-in
The
CD N:=C:\DATA\ACCOUNTS
will cause the directory
This feature is also present in Concurrent DOS, Multiuser DOS
, System Manager 7, and REAL/32, however, these systems extent the concept to all unused drive letters from A: to Z:, except for drive letter L:. DR DOS 3.31 - 6.0 (initial 1991 release only) also support this (including drive letter L:). Under the later systems, the 4DOS
/NDOS command processor supports this features as well. Interestingly, floating drives are implemented in the BDOS kernel, not in the command line shell, thus this feature can also be used from within DOS applications when entering directory paths for as long as the application does not parse and split the dirspec for further processing.
Using a similar feature, Concurrent DOS, Multiuser DOS, System Manager and REAL/32 will dynamically assign a floating drive L: to the load path of a loaded application, thereby allowing applications to refer to files residing in their load directory under a standardized drive letter instead of under a fixed absolute path. This load drive feature makes it much easier to move software installations on and across disks without having to adapt paths to overlays, configuration files or user data stored in the load directory or subsequent directories. (For similar reasons, the appendage to the environment block associated with loaded applications under MS-DOS/PC DOS 3.0 (and higher) contains a reference to the load path of the executable, however, this consumes more resident memory, and to take advantage of it, support for it must be coded into the executable, whereas DRI's solutions transparently works with any kind of applications.)
Another interesting feature resulting from the BDOS' internal organization of current working directories as relative links to parent directories is the theoretically unlimited directory depth supported by all those above mentioned operating systems - in contrast to MS-DOS/PC DOS (and DR DOS since 1992), where an MS-DOS compatible internal data structure named Current Directory Structure (CDS) limits directory depths to a maximum of 66 characters.
These features can be contributed to the fact, that CP/M itself did not have a concept of subdirectories and DOS was only some kind of emulation under these operating systems, so directories had to be translated to internal CP/M structures in some intelligent way.
/ MSDOS.SYS
combination of MS-DOS). This file is in the CP/M-86 CMD
format, and is structured internally as a number of modules:
:YES. PC compatible versions were supplied with the Amstrad
PC-1512
and the TRAN Jasmin Turbo. The non-PC compatible BBC Master 512 and its successor, the Solidisk's PC Plus, also came with DOS Plus.
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
written by Digital Research
Digital Research
Digital Research, Inc. was the company created by Dr. Gary Kildall to market and develop his CP/M operating system and related products. It was the first large software company in the microcomputer world...
, first released in 1985. It can be seen as an intermediate step between CP/M-86
CP/M-86
CP/M-86 was a version of the CP/M operating system that Digital Research made for the Intel 8086 and Intel 8088. The commands are those of CP/M-80. Executable files used the relocatable .CMD file format...
and DR-DOS
DR-DOS
DR-DOS is an MS-DOS-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86...
.
It is able to run programs written for either CP/M-86 or MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
2.11, and can read and write the floppy formats used by both these systems. Up to four CP/M-86 programs can be multitasked
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
, but only one DOS program can be run at a time.
User interface
DOS Plus attempts to present the same command-line interfaceCommand-line interface
A command-line interface is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks...
as MS-DOS. Like MS-DOS, it has a command-line interpreter called
COMMAND.COMCOMMAND.COMCOMMAND.COM is the filename of the default operating system shell for DOS operating systems and the default command line interpreter on Windows 95, Windows 98 and Windows Me...
. There is an AUTOEXEC.BATAUTOEXEC.BATAUTOEXEC.BAT is a system file found originally on DOS-type operating systems. It is a plain-text batch file that is located in the root directory of the boot device...
file, but no CONFIG.SYSCONFIG.SYSCONFIG.SYS is the primary configuration file for the DOS, OS/2 as well as similar operating systems. It is a special file that contains setup or configuration instructions for the computer system.- Usage :...
. The major difference the user will notice is that the bottom line of the screen contains status information similar to:DDT86 ALARM UK8 PRN=LPT1 Num 10:17:30
The left-hand side of the status bar shows running processes
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
. The leftmost one will be visible on the screen; the others (if any) are running in the background. The right-hand side shows the keyboard layout in use (UK8 in the above example), the printer port assignment, the keyboard caps lock
Caps lock
Caps lock is a key on many computer keyboards. Pressing it sets an input mode in which typed letters are uppercase by default. The keyboard remains in caps lock mode until the key is pressed again...
and num lock
Num lock
Num Lock is a key on the numeric keypad of most computer keyboards. It is a toggle key, like Caps Lock and Scroll Lock. Its state is commonly represented by an LED light built into the keyboard....
status, and the current time. If a DOS program is running, the status line is not shown. DOS programs cannot be run in the background.
The keyboard layout in use can be changed by pressing Ctrl
CTRL
CTRL may refer to several things:*Channel Tunnel Rail Link, a high-speed railway line opened in the 2000s in Britain*Control key, an input button present on most computer keyboards*Ctrl, an American comedy web series from NBC...
, Alt
Alt key
The Alt key on a computer keyboard is used to change the function of other pressed keys. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key. For example, simply pressing "A" will type the letter a, but if you hold down either Alt key while pressing A, the computer...
and one of the function key
Function key
A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions...
s F1-F5.
Commands
DOS Plus contains a number of extra commandsCommand (computing)
In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell....
to support its multitasking features:
- ADDMEM: Sets the amount of extra memory to allocate to EXEEXEEXE is the common filename extension denoting an executable file in the DOS, OpenVMS, Microsoft Windows, Symbian, and OS/2 operating systems....
programs. - ALARM: A message alarm clock.
- BACKG: Allows background processes to be listed and stopped.
- COMSIZE: Sets the amount of memory to allocate to COMCOM fileIn many computer operating systems, a COM file is a type of executable file; the name is derived from the file name extension .COM. Originally, the term stood for "Command file", a text file containing commands to be issued to the operating system , on many of the Digital Equipment Corporation mini...
programs. - PRINT: Print spooler.
- SLICE: Sets the amount of processor time to give to the foreground program.
- USER: Sets the user number to use when accessing CP/M media.
It also contains subsets of the standard DOS commands and CP/M commands - for example, it has both a built-in
COPYCopy (command)In computing, copy is a command in RT-11, RSX-11, OpenVMS, DOS, OS/2 and Microsoft Windows operating systems. The command copies computer files from one directory to another. The destination defaults to the current working directory. If more than one source file is indicated, the destination must...
command, and a PIPPeripheral Interchange ProgramPeripheral Interchange Program was a utility to transfer files on and between devices on Digital Equipment Corporation's computers. It was first implemented on the PDP-6 architecture by Harrison "Dit" Morse early in the 1960s...
utility, both of which copy files.The
CD command can assign one of the three drives N:, O: or P: to a directory on a different drive, in a similar manner to the MS-DOS command SUBSTSubstsubst is a command on the DOS, IBM OS/2 and Microsoft Windows operating systems used for substituting paths on physical and logical drives as virtual drives...
. For example,CD N:=C:\DATA\ACCOUNTS
will cause the directory
C:\DATA\ACCOUNTS to appear as drive N:. This so called floating drive feature allows to work with old programs which don't support subdirectories and can be used to make file handling at the command prompt much easier.This feature is also present in Concurrent DOS, Multiuser DOS
Multiuser DOS
Multiuser DOS is a soft real-time multi-user multi-tasking operating system for IBM PC-compatible microcomputers.An evolution of the older Concurrent CP/M-86 and Concurrent DOS operating systems, it was originally developed by Digital Research and later further developed by Novell...
, System Manager 7, and REAL/32, however, these systems extent the concept to all unused drive letters from A: to Z:, except for drive letter L:. DR DOS 3.31 - 6.0 (initial 1991 release only) also support this (including drive letter L:). Under the later systems, the 4DOS
4DOS
4DOS is a command line interpreter by JP Software, designed to replace the default command interpreter COMMAND.COM in DOS and Windows 95/98/Me. The 4DOS family of programs are meant to replace the default command processor. 4OS2 and 4NT replace CMD.EXE in OS/2 and Windows NT respectively...
/NDOS command processor supports this features as well. Interestingly, floating drives are implemented in the BDOS kernel, not in the command line shell, thus this feature can also be used from within DOS applications when entering directory paths for as long as the application does not parse and split the dirspec for further processing.
Using a similar feature, Concurrent DOS, Multiuser DOS, System Manager and REAL/32 will dynamically assign a floating drive L: to the load path of a loaded application, thereby allowing applications to refer to files residing in their load directory under a standardized drive letter instead of under a fixed absolute path. This load drive feature makes it much easier to move software installations on and across disks without having to adapt paths to overlays, configuration files or user data stored in the load directory or subsequent directories. (For similar reasons, the appendage to the environment block associated with loaded applications under MS-DOS/PC DOS 3.0 (and higher) contains a reference to the load path of the executable, however, this consumes more resident memory, and to take advantage of it, support for it must be coded into the executable, whereas DRI's solutions transparently works with any kind of applications.)
Another interesting feature resulting from the BDOS' internal organization of current working directories as relative links to parent directories is the theoretically unlimited directory depth supported by all those above mentioned operating systems - in contrast to MS-DOS/PC DOS (and DR DOS since 1992), where an MS-DOS compatible internal data structure named Current Directory Structure (CDS) limits directory depths to a maximum of 66 characters.
These features can be contributed to the fact, that CP/M itself did not have a concept of subdirectories and DOS was only some kind of emulation under these operating systems, so directories had to be translated to internal CP/M structures in some intelligent way.
Internal structure
DOS Plus boots from a single file called DOSPLUS.SYS (rather than the IO.SYSIO.SYS
IO.SYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers and the DOS initialization program.- Boot sequence :...
/ MSDOS.SYS
MSDOS.SYS
MSDOS.SYS an important system file on MS-DOS and Windows 9x systems. It is run after IO.SYS. In MS-DOS, it contains the core operating system code, the kernel...
combination of MS-DOS). This file is in the CP/M-86 CMD
CMD file (CP/M)
In CP/M-86, CMD is the filename extension used by executable programs. It corresponds to COM in CP/M-80 and EXE in DOS. The same extension is used by Microsoft Windows for unrelated batch files.-Binary format:...
format, and is structured internally as a number of modules:
- The BDOS basic disk operating system kernel, which handles multitasking and implements the CP/M API.
- The XIOS extended input/output system, which is the machine-dependent component that performs low-level disc and character I/O.
- The DOS emulator, which converts each MS-DOS function call into one or more CP/M calls. In the case of a request to change the current directory, for example, this would translate to a series of 'open directory' calls, one for each directory in the path.
- A stub which loads COMMAND.COM when required. This stub contains the string "OS=CPCDOS", suggesting that it is based on the Concurrent PC DOS codebase.
Computers that used DOS Plus
DOS Plus was the main operating system in ROM for the PhilipsPhilips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
:YES. PC compatible versions were supplied with the Amstrad
Amstrad
Amstrad is a British electronics company, now wholly owned by BSkyB. As of 2006, Amstrad's main business is manufacturing Sky Digital interactive boxes....
PC-1512
PC-1512
The Amstrad PC1512 was Amstrad's mostly IBM PC-compatible computer system, first manufactured in 1986. It was later succeeded by the PC1640.It launched for £499 and sold very well, as it was one of the first cheap PCs in Europe...
and the TRAN Jasmin Turbo. The non-PC compatible BBC Master 512 and its successor, the Solidisk's PC Plus, also came with DOS Plus.