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76-516: Basic , in IBM terminology, indicates a lower-level access method that deals with data sets in terms of physical blocks and does not provide either read-ahead, called anticipatory buffering , or synchronization — that is, the user program has to explicitly wait for completion of each input/output event. With BDAM, "the programmer can directly store and retrieve a block by specifying either its actual device address , its relative position within

152-399: A Zip file or COM Structured Storage . A Partitioned Data Set can only be allocated on a single volume and have a maximum size of 65,535 tracks. Besides members, a PDS contains also a directory. Each member can be accessed indirectly via the directory structure. Once a member is located, the data stored in that member are handled in the same manner as a PS (sequential) data set. Whenever

228-538: A basic access method BDAM reads and writes member data in blocks and the I/O operation proceeds asynchronously and must be tested for completion using the CHECK macro. BDAM uses the standard system macros OPEN , CLOSE , READ , WRITE ,and CHECK . The READ or WRITE macro instructions must provide the block address or key of the desired record. The CHECK macro has to be used to wait for completion of

304-493: A "file") can reside in up to 255 extents across multiple volumes. If the application has a dependency on the space being on contiguous tracks, you can allocate space for the direct data set in contiguous tracks by coding SPACE=(,,CONTIG) on the DD statement. Direct data sets must be preformatted before use by opening them as output and writing all the blocks sequentially. This can load all "dummy" records or load initial data. As

380-495: A 64 KiB page frame in the reserved upper memory area. 80386 and later systems could use a virtual 8086 mode (V86) mode memory manager like EMM386 to create expanded memory from extended memory without the need of an add-on card. The second specification was the Extended Memory Specification (XMS) for 80286 and later systems. This provided a way to copy data to and from extended memory, access to

456-401: A batch file is interpreted as a program to run. Batch files can also make use of internal commands, such as GOTO and conditional statements . The operating system offers an application programming interface that allows development of character-based applications, but not for accessing most of the hardware , such as graphics cards , printers , or mice . This required programmers to access

532-498: A configuration file similar to CONFIG.SYS and AUTOEXEC.BAT. If the MSDOS.SYS BootGUI directive is set to 0 , the boot process will stop with the command processor (typically COMMAND.COM) loaded, instead of executing WIN.COM automatically. DOS uses a filesystem which supports 8.3 filenames : 8 characters for the filename and 3 characters for the extension. Starting with DOS 2 hierarchical directories are supported. Each directory name

608-425: A conversation with fellow United Way National Board Executive Committee member Mary Maxwell Gates , who referred Opel to her son Bill Gates for help with an 8088-compatible build of CP/M. IBM was then sent to Digital Research, and a meeting was set up. However, initial negotiations for the use of CP/M broke down: Digital Research wished to sell CP/M on a royalty basis, while IBM sought a single license, and to change

684-481: A data set (file). Data sets are not unstructured streams of bytes , but rather are organized in various logical record and block structures determined by the DSORG (data set organization), RECFM (record format), and other parameters. These parameters are specified at the time of the data set allocation (creation), for example with Job Control Language DD statements. Within a running program they are stored in

760-399: A data set (relative block number), or the relative track within a data set at which the system is to begin a search. BDAM provides no index or structure to the file except as programmed by the application. In many applications, a hashing or randomizing function may be used to assign the block address based on a key in the data. If physical keys are used, the key of the last record within

836-581: A false end-of-record condition. The data set is an abstraction of a collection of records, in contrast to files as unstructured streams of bytes. A partitioned data set ( PDS ) is a data set containing multiple members , each of which holds a separate sub-data set, similar to a directory in other types of file systems . This type of data set is often used to hold load modules (old format bound executable programs), source program libraries (especially Assembler macro definitions), ISPF screen definitions, and Job Control Language . A PDS may be compared to

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912-524: A few developers and computer engineers still use it because it is close to the hardware. DOS's structure of accessing hardware directly allows it to be used in embedded devices . The final versions of DR-DOS are still aimed at this market. ROM-DOS is used as operating system for the Canon PowerShot Pro 70. On Linux , it is possible to run DOSEMU , a Linux-native virtual machine for running DOS programs at near native speed. There are

988-483: A file name with a space, has sometimes been used by viruses or hacking programs to obscure files from users who do not know how to access these locations. DOS was designed for the Intel 8088 processor, which can only directly access a maximum of 1 MiB of RAM. Both IBM and Microsoft chose 640 kibibytes (KiB) as the maximum amount of memory available to programs and reserved the remaining 384 KiB for video memory,

1064-521: A manifesto proposing the development of an open-source replacement. Within a few weeks, other programmers including Pat Villani and Tim Norman joined the project. A kernel, the COMMAND.COM command line interpreter (shell), and core utilities were created by pooling code they had written or found available. There were several official pre-release distributions of FreeDOS before the FreeDOS 1.0 distribution

1140-523: A member is deleted, the space it occupied is unusable for storing other data. Likewise, if a member is re-written, it is stored in a new spot at the back of the PDS and leaves wasted “dead” space in the middle. The only way to recover “dead” space is to perform file compression. Compression, which is done using the IEBCOPY utility, moves all members to the front of the data space and leaves free usable space at

1216-666: A more user-friendly environment, numerous software manufacturers wrote file management programs that provided users with WIMP interfaces. Microsoft Windows is a notable example, eventually resulting in Microsoft Windows 9x becoming a self-contained program loader, and replacing DOS as the most-used PC-compatible program loader. Text user interface programs included Norton Commander , DOS Navigator , Volkov Commander , Quarterdesk DESQview , and Sidekick . Graphical user interface programs included Digital Research's GEM (originally written for CP/M) and GEOS . Eventually,

1292-513: A number of other emulators for running DOS on various versions of Unix and Microsoft Windows such as DOSBox . DOSBox is designed for legacy gaming (e.g. King's Quest , Doom ) on modern operating systems. DOSBox includes its own implementation of DOS which is strongly tied to the emulator and cannot run on real hardware, but can also boot MS-DOS, FreeDOS, or other DOS operating systems if needed. MS-DOS and IBM PC DOS related operating systems are commonly associated with machines using

1368-413: A program run from one floppy while accessing its data on another. Hard drives were originally assigned the letters "C" and "D". DOS could only support one active partition per drive. As support for more hard drives became available, this developed into first assigning a drive letter to each drive's active primary partition , then making a second pass over the drives to allocate letters to logical drives in

1444-501: A retail version of MS-DOS, starting with MS-DOS 5.0. In the mid-1980s, Microsoft developed a multitasking version of DOS . This version of DOS is generally referred to as "European MS-DOS 4" because it was developed for ICL and licensed to several European companies. This version of DOS supports preemptive multitasking, shared memory, device helper services and New Executable ("NE") format executables. None of these features were used in later versions of DOS, but they were used to form

1520-566: A series of disagreements over two successor operating systems to DOS, OS/2 and Windows. They split development of their DOS systems as a result. The last retail version of MS-DOS was MS-DOS 6.22; after this, MS-DOS became part of Windows 95, 98 and Me. The last retail version of PC DOS was PC DOS 2000 (also called PC DOS 7 revision 1), though IBM did later develop PC DOS 7.10 for OEMs and internal use. The FreeDOS project began on 26 June 1994, when Microsoft announced it would no longer sell or support MS-DOS. Jim Hall then posted

1596-421: A single physical block on tape or DASD. FB and VB are fixed-blocked , and variable-blocked , respectively. RECFM=U (undefined) is also variable length, but the length of the record is determined by the length of the block rather than by a control field. The BLKSIZE parameter specifies the maximum length of the block. RECFM=FBS could be also specified, meaning fixed-blocked standard , meaning all

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1672-421: A specific operation before the data can be accessed or the data buffer reused. It is possible to start multiple input/output operations to run concurrently. Records in a direct data set can contain user-specified recorded keys of up to 255 bytes—all keys in a file must be the same length. Reads and writes can specify a key in addition to a disk address, and BDAM will search starting at the requested block up to

1748-415: A time can use them, and DOS itself has no functionality to allow more than one program to execute at a time. The DOS kernel provides various functions for programs (an application program interface ), like character I/O, file management, memory management, program loading and termination. DOS provides the ability for shell scripting via batch files (with the filename extension .BAT ). Each line of

1824-523: A year Microsoft licensed MS-DOS to over 70 other companies, which supplied the operating system for their own hardware, sometimes under their own names. Microsoft later required the use of the MS-DOS name, with the exception of the IBM variant. IBM continued to develop their version, PC DOS , for the IBM PC. Digital Research became aware that an operating system similar to CP/M was being sold by IBM (under

1900-481: Is a Partitioned Data Set Extended (PDSE or PDS/E, sometimes just libraries ) introduced with DFSMSdfp for MVS/XA and MVS/ESA systems. A PDS/E library can store program objects or other types of members, but not both. BPAM cannot process a PDS/E containing program objects. PDS/E structure is similar to PDS and is used to store the same types of data. However, PDS/E files have a better directory structure which does not require pre-allocation of directory blocks when

1976-539: Is a real DOS, like MS-DOS 6.22 or PC DOS 5.00. One makes a bootable floppy disk of the DOS, adds a number of drivers from OS/2, and then creates a special image. The DOS booted this way has full access to the system, but provides its own drivers for hardware. One can use such a disk to access cdrom drives for which there is no OS/2 driver. In all 32-bit (IA-32) editions of the Windows NT family since 1993, DOS emulation

2052-714: Is also 8.3 format but the maximum directory path length is 64 characters due to the internal current directory structure (CDS) tables that DOS maintains. Including the drive name, the maximum length of a fully qualified filename that DOS supports is 80 characters using the format drive:\path\filename.ext followed by a null byte. DOS uses the File Allocation Table (FAT) filesystem. This was originally FAT12 which supported up to 4078 clusters per drive. DOS 3.0 added support for FAT16 which used 16-bit allocation entries and supported up to 65518 clusters per drive. Compaq MS-DOS 3.31 added support for FAT16B which removed

2128-431: Is an optional built-in driver for a fourth line printer supported in some versions of DR-DOS since 7.02. CONFIG$ constitutes the real mode PnP manager in MS-DOS 7.0–8.0. AUX typically defaults to COM1 , and PRN to LPT1 ( LST ), but these defaults can be changed in some versions of DOS to point to other serial or parallel devices. The PLT device (present only in some HP OEM versions of MS-DOS)

2204-531: Is available in COMMAND.COM. Programs like the Microsoft CD-ROM Extensions (MSCDEX) provide access to files on CD-ROM disks. Some TSRs can even perform a rudimentary form of task switching. For example, the shareware program Back and Forth (1990) has a hotkey to save the state of the currently-running program to disk, load another program, and switch to it, making it possible to switch "back and forth" between programs (albeit slowly, due to

2280-408: Is based upon DOS 5. Although there is a default configuration (config.sys and autoexec.bat), one can use alternate files on a session-by-session basis. It is possible to load drivers in these files to access the host system, although these are typically third-party. Under OS/2 2.x and later, the DOS emulation is provided by DOSKRNL. This is a file that represents the combined IBMBIO.COM and IBMDOS.COM,

2356-502: Is invalid." These names (except for NUL) have continued to be supported in all versions of MS-DOS, PC DOS and DR-DOS ever since. LST was also available in some OEM versions of MS-DOS 1.25, whereas other OEM versions of MS-DOS 1.25 already used LPT1 (first line printer ) and COM1 (first serial communication device ) instead, as introduced with PC DOS. In addition to LPT1 and LPT2 as well as COM1 to COM3 , Hewlett-Packard's OEM version of MS-DOS 2.11 for

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2432-413: Is likely to render the media unbootable. It is, however, possible to replace the shell at will, a method that can be used to start the execution of dedicated applications faster. This limitation does not apply to any version of DR DOS, where the system files can be located anywhere in the root directory and do not need to be contiguous. Therefore, system files can be simply copied to a disk provided that

2508-504: Is provided by way of a virtual DOS machine (NTVDM). 64-bit (IA-64 and x86-64) versions of Windows do not support NTVDM and cannot run 16-bit DOS applications directly; third-party emulators such as DOSbox can be used to run DOS programs on those machines. DOS systems use a command-line interface . A program is started by entering its filename at the command prompt. DOS systems include utility programs and provide internal commands that do not correspond to programs. In an attempt to provide

2584-663: Is usually cataloged. An individual member of the GDG collection is called a " Generation Data Set ." The latter may be identified by an absolute number, ACCTG.OURGDG(1234) , or a relative number: (-1) for the previous generation, (0) for the current one, and (+1) the next generation. Generation Data Groups are defined using either the BLDG statement of the IEHPROGM utility or the DEFINE GENERATIONGROUP statement of

2660-523: The Data Control Block (DCB) or Access Control Block (ACB), which are data structures used to access data sets using access methods . Records in a data set may be fixed, variable, or “undefined” length. For OS/360, the DCB's DSORG parameter specifies how the data set is organized. It may be among others. Data sets on tape may only be DSORG=PS . The choice of organization depends on how

2736-698: The HP Portable Plus also supported LST as alias for LPT2 and 82164A as alias for COM2 ; it also supported PLT for plotters . Otherwise, COM2 , LPT2 , LPT3 and the CLOCK$ (still named CLOCK in some issues of MS-DOS 2.11 ) clock device were introduced with DOS 2.0, and COM3 and COM4 were added with DOS 3.3. Only the multitasking MS-DOS 4 supported KEYBD$ and SCREEN$ . DR DOS 5.0 and higher and Multiuser DOS support an $ IDLE$ device for dynamic idle detection to saving power and improve multitasking. LPT4

2812-640: The Intel x86 or compatible CPUs , mainly IBM PC compatibles . Machine-dependent versions of MS-DOS were produced for many non-IBM-compatible x86 -based machines, with variations from relabelling of the Microsoft distribution under the manufacturer's name, to versions specifically designed to work with non-IBM-PC-compatible hardware. As long as application programs used DOS APIs instead of direct hardware access, they could run on both IBM-PC-compatible and incompatible machines. The original FreeDOS kernel, DOS-C ,

2888-611: The S/360 line, a data set (IBM preferred) or dataset is a computer file having a record organization . Use of this term began with, e.g., DOS/360 , OS/360 , and is still used by their successors, including the current z/OS . Documentation for these systems historically preferred this term rather than file . A data set is typically stored on a direct access storage device (DASD) or magnetic tape , however unit record devices, such as punch card readers, card punches, line printers and page printers can provide input/output (I/O) for

2964-490: The extended partition , then a third pass to give any other non-active primary partitions their names (where such additional partitions existed and contained a DOS-supported file system). Lastly, DOS allocates letters for optical disc drives , RAM disks , and other hardware. Letter assignments usually occur in the order the drivers are loaded, but the drivers can instruct DOS to assign a different letter; drivers for network drives, for example, typically assign letters nearer to

3040-521: The read-only memory of adapters on some video and network peripherals, and the system's BIOS. By 1985, some DOS applications were already hitting the memory limit, while much of reserved was unused, depending on the machine's specifications. Specifications were developed to allow access to additional memory. The first was the Expanded Memory Specification (EMS) was designed to allow memory on an add-on card to be accessed via

3116-494: The 32‑ MiB drive limit and could support up to 512 MiB. Finally MS-DOS 7.1 (the DOS component of Windows 9x) added support for FAT32 which used 32-bit allocation entries and could support hard drives up to 137 GiB and beyond. Starting with DOS 3.1, file redirector support was added to DOS. This was initially used to support networking but was later used to support CD-ROM drives with MSCDEX . IBM PC DOS 4.0 also had preliminary installable file system (IFS) support but this

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3192-584: The 65,520-byte high memory area directly above the first megabyte of memory and the upper memory block area. Generally XMS support was provided by HIMEM.SYS or a V86 mode memory manager like QEMM or 386MAX which also supported EMS. Starting with DOS 5, DOS could directly take advantage of the HMA by loading its kernel code and disk buffers there via the DOS=HIGH statement in CONFIG.SYS. DOS 5+ also allowed

3268-510: The DCB RECFM parameter. RECFM=F means that the records are of fixed length, specified via the LRECL parameter. RECFM=V specifies a variable-length record. V records when stored on media are prefixed by a Record Descriptor Word (RDW) containing the integer length of the record in bytes and flag bits. With RECFM=FB and RECFM=VB , multiple logical records are grouped together into

3344-605: The DOS virtual machine is provided by WINOLDAP. WinOldAp creates a virtual machine based on the program's PIF file, and the system state when Windows was loaded. The DOS graphics mode, both character and graphic, can be captured and run in the window. DOS applications can use the Windows clipboard by accessing extra published calls in WinOldAp, and one can paste text through the WinOldAp graphics. The emulated DOS in OS/2 and Windows NT

3420-494: The IBM PC compatible market between 1981 and 1995. Although the name has come to be identified specifically with this particular family of operating systems, DOS is a platform-independent acronym for disk operating system , whose use predates the IBM PC. Dozens of other operating systems also use the acronym, beginning with the mainframe DOS/360 from 1966. Others include Apple DOS , Apple ProDOS , Atari DOS , Commodore DOS , TRSDOS , and AmigaDOS . IBM PC DOS (and

3496-582: The PDS/E is defined (and therefore does not run out of directory blocks if not enough were specified). Also, PDS/E automatically stores members in such a way that compression operation is not needed to reclaim "dead" space. PDS/E files can only reside on DASD in order to use the directory structure to access individual members. A Generation Data Group ( GDG ) is a group of non-VSAM data sets that are successive generations of historically-related data stored on an IBM mainframe (running OS or DOS/VSE ). A GDG

3572-512: The back. (Note that in modern parlance, this kind of operation might be called defragmentation or garbage collection ; data compression nowadays refers to a different, more complicated concept.) PDS files can only reside on DASD , not on magnetic tape , in order to use the directory structure to access individual members. Partitioned data sets are most often used for storing multiple job control language files, utility control statements, and executable modules. An improvement of this scheme

3648-540: The basis of the OS/2 1.0 kernel. This version of DOS is distinct from the widely released PC DOS 4.0 which was developed by IBM and based upon DOS 3.3. Digital Research attempted to regain the market lost from CP/M-86, initially with Concurrent DOS , FlexOS and DOS Plus (both compatible with both MS-DOS and CP/M-86 software), later with Multiuser DOS (compatible with both MS-DOS and CP/M-86 software) and DR DOS (compatible with MS-DOS software). Digital Research

3724-663: The block must be written as the key for that block. The BDAM application program interface can be compared with the interface offered by open , read , write and close calls (using file handles) in other operating systems such as Unix and Windows . BDAM is still supported by IBM as of 2012. Because of its dependence on physical device geometry new IBM direct-access devices used with z/OS emulate IBM 3390 devices regardless of their real physical characteristics. The programmer specifies DSORG=DA in his Data Control Block (DCB) to indicate use of BDAM. Space can be in up to 16 extents on each volume . The data set (equivalent to

3800-580: The blocks except the last one were required to be in full BLKSIZE length. RECFM=VBS , or variable-blocked spanned , means a logical record could be spanned across two or more blocks, with flags in the RDW indicating whether a record segment is continued into the next block and/or was continued from the previous one. This mechanism eliminates the need for using any "delimiter" byte value to separate records. Thus data can be of any type, including binary integers, floating-point, or characters, without introducing

3876-411: The boot sector is DR DOS compatible already. In PC DOS and DR DOS 5.0 and above, the DOS system files are named IBMBIO.COM instead of IO.SYS and IBMDOS.COM instead of MSDOS.SYS . Older versions of DR DOS used DRBIOS.SYS and DRBDOS.SYS instead. Starting with MS-DOS 7.0 the binary system files IO.SYS and MSDOS.SYS were combined into a single file IO.SYS whilst MSDOS.SYS became

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3952-404: The corresponding load drive whenever an application starts. There are reserved device names in DOS that cannot be used as filenames regardless of extension as they are occupied by built-in character devices. These restrictions also affect several Windows versions, in some cases causing crashes and security vulnerabilities. The reserved names are: In Windows 95 and Windows 98 , typing in

4028-404: The data is to be accessed, and in particular, how it is to be updated. Programmers utilize various access methods (such as QSAM or VSAM ) in programs for reading and writing data sets. Access method depends on the given data set organization. Regardless of organization, the physical structure of each record is essentially the same, and is uniform throughout the data set. This is specified in

4104-434: The dataset unmovable . Relative track addresses are three byte fields in the form TTR . All subfields are binary numbers. Relative block numbers are four byte (fullword) binary numbers indicating the block number in the file. The first block is block 0. This form of addressing can only be used with fixed length blocks ( RECFM=F ). Data set (IBM mainframe) In the context of IBM mainframe computers in

4180-499: The default OS kernel , though the MS-DOS component remained for compatibility. With Windows 95 and 98, but not ME, the MS-DOS component could be run without starting Windows. With DOS no longer required to use Windows, the majority of users stopped using it directly. As of 2024 , available compatible systems are FreeDOS , ROM-DOS , PTS-DOS , RxDOS and REAL/32 . Some computer manufacturers, including Dell and HP , sell computers with FreeDOS as an OEM operating system. And

4256-464: The end of the alphabet. Because DOS applications use these drive letters directly (unlike the /dev directory in Unix-like systems), they can be disrupted by adding new hardware that needs a drive letter. An example is the addition of a new hard drive having a primary partition where a pre-existing hard drive contains logical drives in extended partitions; the new drive will be assigned a letter that

4332-427: The entire area of the file for a record with a matching key. This allows multiple keys hashing to the same track to be handled automatically by the I/O subsystem. BDAM accepts disk addresses as either actual device addresses, as relative track addresses, or as relative block numbers. Device addresses are eight byte fields in the form MBBCCHHR . All subfields are binary numbers. Specifying device addresses makes

4408-400: The hardware directly, usually resulting in each application having its own set of device drivers for each hardware peripheral. Hardware manufacturers would release specifications to ensure device drivers for popular applications were available. The DOS system files loaded by the boot sector must be contiguous and be the first two directory entries . As such, removing and adding this file

4484-580: The introduction of Xenix . The company planned to improve MS-DOS over time, so it would be almost indistinguishable from single-user Xenix, or XEDOS , which would also run on the Motorola 68000 , Zilog Z-8000 , and LSI-11 ; they would be upwardly compatible with Xenix, which BYTE in 1983 described as "the multi-user MS-DOS of the future". IBM, however, did not want to replace DOS. After AT&T began selling Unix, Microsoft and IBM began developing OS/2 as an alternative. The two companies later had

4560-458: The location of the reserved name (such as CON/CON, AUX/AUX, or PRN/PRN) crashes the operating system, of which Microsoft has provided a security fix for the issue. In Windows XP , the name of the file or folder using a reserved name silently reverts to its previous name, with no notification or error message. In Windows Vista and later, attempting to use a reserved name for a file or folder brings up an error message saying "The specified device name

4636-399: The manufacturers of major DOS systems began to include their own environment managers. MS-DOS/IBM DOS 4 included DOS Shell ; DR DOS 5.0, released the following year, included ViewMAX , based upon GEM. Although DOS is not a multitasking operating system, it does provide a terminate-and-stay-resident (TSR) function which allows programs to remain resident in memory. These programs can hook

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4712-672: The name to "PC DOS". Digital Research founder Gary Kildall refused, and IBM withdrew. IBM again approached Bill Gates. Gates in turn approached Seattle Computer Products . There, programmer Tim Paterson had developed a variant of CP/M-80 , intended as an internal product for testing SCP's new 16-bit Intel 8086 CPU card for the S-100 bus . The system was initially named QDOS (Quick and Dirty Operating System), before being made commercially available as 86-DOS . Microsoft purchased 86-DOS, allegedly for US$ 50,000. This became Microsoft Disk Operating System, MS-DOS, introduced in 1981. Within

4788-563: The newer IDCAMS utility, which allows setting various parameters. IDCAMS can also delete (and optionally uncatalog) a GDG. DOS DOS ( / d ɒ s / , / d ɔː s / ) is a family of disk-based operating systems for IBM PC compatible computers. The DOS family primarily consists of IBM PC DOS and a rebranded version, Microsoft 's MS-DOS , both of which were introduced in 1981. Later compatible systems from other manufacturers include DR-DOS (1988), ROM-DOS (1989), PTS-DOS (1993), and FreeDOS (1998). MS-DOS dominated

4864-501: The same name that IBM insisted upon for CP/M), and threatened legal action. IBM responded by offering an agreement: they would give PC consumers a choice of PC DOS or CP/M-86 , Kildall's 8086 version. Side-by-side, CP/M cost US$ 200 more than PC DOS, and sales were low. CP/M faded, with MS-DOS and PC DOS becoming the marketed operating system for PCs and PC compatibles. Microsoft originally sold MS-DOS only to original equipment manufacturers (OEMs). One major reason for this

4940-505: The separately sold MS-DOS ) and its predecessor, 86-DOS , ran on Intel 8086 16-bit processors. It was developed to be similar to Digital Research 's CP/M —the dominant disk operating system for 8-bit Intel 8080 and Zilog Z80 microcomputers—in order to simplify porting CP/M applications to MS-DOS. When IBM introduced the IBM PC , built with the Intel 8088 microprocessor, they needed an operating system. Chairman John Opel had

5016-506: The system calls are passed through to the OS/2 windowing services. DOS programs run in their own environment, the bulk of the DOS utilities are provided by bound DOS / OS2 applications in the \OS2 directory. OS/2 can run Windows 3.1 applications by using a modified copy of Windows (Win-OS/2). The modifications allow Windows 3.1 programs to run seamlessly on the OS/2 desktop, or one can start a WinOS/2 desktop, similar to starting Windows from DOS. OS/2 allows for 'DOS from Drive A:', (VMDISK). This

5092-606: The system timer or keyboard interrupts to allow themselves to run tasks in the background or to be invoked at any time, preempting the current running program and effectively implementing a simple form of multitasking on a program-specific basis. The DOS PRINT command does this to implement background print spooling. Borland Sidekick , a popup personal information manager (PIM), also uses this technique. Terminate-and-stay-resident programs are also used to provide additional features not available by default. Programs like CED and DOSKEY provide command-line editing facilities beyond what

5168-690: The use of available upper memory blocks via the DOS=UMB statement in CONFIG.SYS. The DOS emulation in OS/2 and Windows runs in much the same way as native applications do. They can access all of the drives and services, and can even use the host's clipboard services. Because the drivers for file systems and such forth reside in the host system, the DOS emulation needs only provide a DOS API translation layer which converts DOS calls to OS/2 or Windows system calls. The translation layer generally also converts BIOS calls and virtualizes common I/O port accesses which many DOS programs commonly use. In Windows 3.1 and 9x,

5244-417: The user changes them. Under DOS, this problem can be worked around by defining a SUBST drive and installing the DOS program into this logical drive. The assignment of this drive would then be changed in a batch job whenever the application starts. Under some versions of Concurrent DOS , as well as under Multiuser DOS , System Manager and REAL/32 , the reserved drive letter L: will automatically be assigned to

5320-416: Was bought by Novell , and DR DOS became PalmDOS and Novell DOS ; later, it was part of Caldera (under the names OpenDOS and DR-DOS 7.02 / 7.03 ), Lineo , and DeviceLogics . Gordon Letwin wrote in 1995 that "DOS was, when we first wrote it, a one-time throw-away product intended to keep IBM happy so that they'd buy our languages." Microsoft expected that it would be an interim solution before

5396-513: Was derived from DOS/NT for the Motorola 68000 series of CPUs in the early 1990s. While these systems loosely resembled the DOS architecture, applications were not binary compatible due to the incompatible instruction sets of these non-x86-CPUs. However, applications written in high-level languages could be ported easily. DOS is a single-user, single-tasking operating system with basic kernel functions that are non-reentrant : only one program at

5472-464: Was previously assigned to one of the extended partition logical drives. Moreover, even adding a new hard drive having only logical drives in an extended partition would still disrupt the letters of RAM disks and optical drives. This problem persisted through Microsoft's DOS-based 9x versions of Windows until they were replaced by versions based on the NT line, which preserves the letters of existing drives until

5548-467: Was reconfigurable as well. Filenames ended with a colon ( : ) such as NUL: conventionally indicate device names, but the colon is not actually a part of the name of the built-in device drivers. Colons are not necessary to be typed in some cases, for example: It is still possible to create files or directories using these reserved device names, such as through direct editing of directory data structures in disk sectors. Such naming, such as starting

5624-543: Was released on 3 September 2006. Made available under the GNU General Public License (GPL), FreeDOS does not require license fees or royalties. Early versions of Microsoft Windows ran on MS-DOS. By the early 1990s, the Windows graphical shell saw heavy use on new DOS systems. In 1995, Windows 95 was bundled as a standalone operating system that did not require a separate DOS license. Windows 95 (and Windows 98 and ME, that followed it) took over as

5700-415: Was that not all early PCs were 100% IBM PC compatible . DOS was structured such that there was a separation between the system specific device driver code ( IO.SYS ) and the DOS kernel ( MSDOS.SYS ). Microsoft provided an OEM Adaptation Kit (OAK) which allowed OEMs to customize the device driver code to their particular system. By the early 1990s, most PCs adhered to IBM PC standards so Microsoft began selling

5776-518: Was unused and removed in DOS 5.0. DOS also supported Block Devices ("Disk Drive" devices) loaded from CONFIG.SYS that could be used under the DOS file system to support network devices. In DOS, drives are referred to by identifying letters. Standard practice is to reserve "A" and "B" for floppy drives . On systems with only one floppy drive DOS assigns both letters to the drive, prompting the user to swap disks as programs alternate access between them. This facilitates copying from floppy to floppy or having

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