MSX-DOS
Encyclopedia
MSX-DOS is a Disk operating system
developed by Microsoft
for the 8-bit
home computer
standard MSX
, and is a cross between MS-DOS
rev 1.0 and CP/M
.
support were simultaneously developed by Microsoft for the developing home computer standard MSX to add disc capabilities to BASIC, and to give the system a cheaper software medium than Memory Cartridges, and a more powerful storage system than cassette tape
. The standard BIOS
of an unexpanded MSX did not have any floppy disk support, so the additional floppy disk expansion system came with its own BIOS extension ROM (built-in on the disk controller) called the BDOS, it not only added floppy disk support commands to MSX BASIC
but also a booting
system, with which it was possible to boot a real disk operating system. In that case BDOS bypassed the BASIC ROMs so that the whole 64K of address space of the Z80 microprocessor inside the MSX computer could be used for the DOS or for other boot-able disks, for example disk based games. At the same time the original BIOS ROM's could still be accessed through a "memory bank switch
" mechanism, so the DOS based software could still use BIOS calls to control the hardware and other software mechanisms the main ROM's supplied. Also, because of the BDOS rom basic file access capacity was available even without a command interpreter, by using the BASIC extended commands.
One major difference between MSX-DOS and MS-DOS was that MSX-DOS did not use the "boot sector" on the floppy to boot, but booted using the BDOS ROM routines, and used the media descriptor value from the first byte of FAT to determine file system
parameters instead of from the bootsector. Also, because there could be more than one floppy disk controller in two or more cartridge slots, MSX-DOS could boot from several different floppy disk drives. This meant that it was possible to have both a 5¼" floppy disk drive and a 3½" disk drive, and you could boot from either one of them depending on which drive had a boot-able floppy in it.
compatible microprocessors, which was the CP/M system, written by Digital Research
. It was also often used with Z80
systems, because the Z80 used an extended 8080 architecture. Microsoft's own disk operating system was also inspired by CP/M.
To be able to run (slightly modified) CP/M software Microsoft decided to implement functionality similar to major parts of the CP/M BIOS, routines that CP/M systems used to do specific disk operating tasks, such as opening files etc. Instead of basing the command processor on CP/M's CCP, which was known for some user unfriendliness, a command line interpreter (COMMAND.COM
) inspired on its MS-DOS counterpart was used. Microsoft also chose its own FAT12
file system over CP/M's filing methods. This ensured that MSX-DOS floppies could also be used on an MS-DOS machine, and that only one single formatting and filing system would be used. This was an important decision, because CP/M disk were often not interchangeable between machines, incompatible disc formatting schemes being a factor in this.
Microsoft also added a standard set of disk commands to MSX-DOS, that were compatible with MS-DOS but not with CP/M. Finally they converted their "Pipelineing
" system from MS-DOS to MSX-DOS. The resulting DOS was a system that was much user friendlier than CP/M, but was (in principle) compatible with major CP/M software packages such as WordStar
, Turbo Pascal
and the "M80" assembler and "L80" linker.
which MSX-DOS could use for time stamping files.
Disk operating system
Disk Operating System and disk operating system , most often abbreviated as DOS, refers to an operating system software used in most computers that provides the abstraction and management of secondary storage devices and the information on them...
developed by Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
for the 8-bit
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
home computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
standard MSX
MSX
MSX was the name of a standardized home computer architecture in the 1980s conceived by Kazuhiko Nishi, then Vice-president at Microsoft Japan and Director at ASCII Corporation...
, and is a cross between 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...
rev 1.0 and CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
.
MSX-DOS
MSX-DOS and the extended BASIC with 3½-inch floppy diskFloppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
support were simultaneously developed by Microsoft for the developing home computer standard MSX to add disc capabilities to BASIC, and to give the system a cheaper software medium than Memory Cartridges, and a more powerful storage system than cassette tape
Compact Cassette
The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a magnetic tape sound recording format. It was designed originally for dictation, but improvements in fidelity led the Compact Cassette to supplant the Stereo 8-track cartridge and reel-to-reel...
. The standard BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
of an unexpanded MSX did not have any floppy disk support, so the additional floppy disk expansion system came with its own BIOS extension ROM (built-in on the disk controller) called the BDOS, it not only added floppy disk support commands to MSX BASIC
MSX BASIC
MSX BASIC is a dialect of the BASIC programming language. It is an extended version of Microsoft Standard BASIC Version 4.5, and includes support for graphic, music, and various peripherals attached to MSX Personal Computers. Generally, MSX-BASIC is designed to follow GW-BASIC, which is one of the...
but also a booting
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
system, with which it was possible to boot a real disk operating system. In that case BDOS bypassed the BASIC ROMs so that the whole 64K of address space of the Z80 microprocessor inside the MSX computer could be used for the DOS or for other boot-able disks, for example disk based games. At the same time the original BIOS ROM's could still be accessed through a "memory bank switch
Bank switching
Bank switching is a technique to increase the amount of usable memory beyond the amount directly addressable by the processor. It can be used to configure a system differently at different times; for example, a ROM required to start a system from diskette could be switched out when no longer...
" mechanism, so the DOS based software could still use BIOS calls to control the hardware and other software mechanisms the main ROM's supplied. Also, because of the BDOS rom basic file access capacity was available even without a command interpreter, by using the BASIC extended commands.
One major difference between MSX-DOS and MS-DOS was that MSX-DOS did not use the "boot sector" on the floppy to boot, but booted using the BDOS ROM routines, and used the media descriptor value from the first byte of FAT to determine file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
parameters instead of from the bootsector. Also, because there could be more than one floppy disk controller in two or more cartridge slots, MSX-DOS could boot from several different floppy disk drives. This meant that it was possible to have both a 5¼" floppy disk drive and a 3½" disk drive, and you could boot from either one of them depending on which drive had a boot-able floppy in it.
Development history
At the time (1984) MSX-DOS was written, there was only one popular disk operating system for 8-bit Intel 8080Intel 8080
The Intel 8080 was the second 8-bit microprocessor designed and manufactured by Intel and was released in April 1974. It was an extended and enhanced variant of the earlier 8008 design, although without binary compatibility...
compatible microprocessors, which was the CP/M 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...
. It was also often used with Z80
Zilog Z80
The Zilog Z80 is an 8-bit microprocessor designed by Zilog and sold from July 1976 onwards. It was widely used both in desktop and embedded computer designs as well as for military purposes...
systems, because the Z80 used an extended 8080 architecture. Microsoft's own disk operating system was also inspired by CP/M.
To be able to run (slightly modified) CP/M software Microsoft decided to implement functionality similar to major parts of the CP/M BIOS, routines that CP/M systems used to do specific disk operating tasks, such as opening files etc. Instead of basing the command processor on CP/M's CCP, which was known for some user unfriendliness, a command line interpreter (COMMAND.COM
COMMAND.COM
COMMAND.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...
) inspired on its MS-DOS counterpart was used. Microsoft also chose its own FAT12
File Allocation Table
File Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...
file system over CP/M's filing methods. This ensured that MSX-DOS floppies could also be used on an MS-DOS machine, and that only one single formatting and filing system would be used. This was an important decision, because CP/M disk were often not interchangeable between machines, incompatible disc formatting schemes being a factor in this.
Microsoft also added a standard set of disk commands to MSX-DOS, that were compatible with MS-DOS but not with CP/M. Finally they converted their "Pipelineing
Pipeline (software)
In software engineering, a pipeline consists of a chain of processing elements , arranged so that the output of each element is the input of the next. Usually some amount of buffering is provided between consecutive elements...
" system from MS-DOS to MSX-DOS. The resulting DOS was a system that was much user friendlier than CP/M, but was (in principle) compatible with major CP/M software packages such as WordStar
WordStar
WordStar is a word processor application, published by MicroPro International, originally written for the CP/M operating system but later ported to DOS, that enjoyed a dominant market share during the early to mid-1980s. Although Seymour I...
, Turbo Pascal
Turbo Pascal
Turbo Pascal is a software development system that includes a compiler and an integrated development environment for the Pascal programming language running on CP/M, CP/M-86, and DOS, developed by Borland under Philippe Kahn's leadership...
and the "M80" assembler and "L80" linker.
Improved versions
The first version of MSX-DOS did not have subdirectories, but in 1988 it evolved to version 2, offering facilities such as subdirectories, memory management and environment strings. Later versions of MSX computers (MSX-2) added an internal real-time clockReal-time clock
A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.-Terminology:The term is used to avoid...
which MSX-DOS could use for time stamping files.