DOS

DOS和Microsoft Windows

主条目：History of Microsoft Windows

早期版本的Microsoft Windows是一个在单独版本的DOS上运行的应用程序。^[12] With Windows for Workgroups 3.11, DOS was essentially reduced to the role of a boot loader for the Windows kernel. With Windows 95, 98, and ME, MS-DOS is included as the boot loader rather than being sold separately. 在Windows 95和98中，除了Windows ME，MS-DOS 组件不启动Windows就可以运行。^[13]

真正的32位版本的完全独立于DOS运行的Windows从NT开始，包括了2003，XP，和Vista。大多数版本包含一个DOS 子系统，NT DOS虚拟机（NTVDM），它在虚拟机中运行一个修改过的版本的MS-DOS 5.0来运行DOS software and Windows command-line programs of similar appearance which are not compatible with true MS-DOS.

版本

See Comparison of x86 DOS operating systems for a timeline and comparison of versions.

操作

在DOS下访问硬件

该操作系统提供了硬件抽象层来支持基于字符的应用程序的开发，但未提供访问大多数硬件如显示卡、打印机和鼠标的支持。这就要求程序员直接访问硬件，导致每个应用程序拥有自己的的一套驱动程序来支持每种硬件外设。Hardware manufacturers would release specifications to ensure device drivers for popular applications were available.^[14]

硬件名称保留字

主条目：Device file system

There are reserved device names in DOS that cannot be used as filenames regardless of extension; these are used to send application output to hardware peripherals. These restrictions also affect several Windows versions, in some cases causing crashes and security vulnerabilities.^[15]

A partial list of these reserved names is: NUL:, COM1: or AUX:, COM2:, COM3:, COM4:, CON:, LPT1: or PRN:, LPT2:, LPT3:, and CLOCK$.^[16]

驱动器盘符命名

主条目：Drive letter assignment

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 permits the use of both letters for one drive, and DOS will ask to swap disks. This permits copying from floppy to floppy or having a program run from one floppy while having 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 assigning the active primary partition on each drive letters first, then making a second pass over the drives to allocate letters to logical drives in the extended partition, then making a third, which gives the other non-active primary partitions their names. (Always assumed, they exist and contain a DOS-readable file system.) Lastly, DOS allocate letters for optical disc drives, RAM disks, and other hardware. Letter assignments usually occur in the order of the drivers loaded, but the drivers can instruct DOS to assign a different letter. An example is network drives, for which the driver will assign letters nearer the end of the alphabets.^[17]

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 with a primary partition to an original hard drive that contains logical drives in extended partitions. As primary partitions have higher priority than the logical drives, it will change drive letters in the configuration. Moreover, attempts to add a new hard drive with only logical drives in an extended partition would still disrupt the letters of RAM disks and optical drives. This problem persisted through the 9x versions of Windows until NT, which preserves the letters of existing drives until the user changes it.^[17]

引导顺序

The boot sector for PC-compatible computers is located at track zero. In DOS, this code will read the DOS BIOS into memory and execute it. The BIOS is located in IBMBIO.COM on DR DOS and PC DOS, and IO.SYS on MS DOS. The BIOS will then load the DOS kernel, located in IBMDOS.COM (PC DOS or DR DOS) or MSDOS.SYS (MS DOS). In the Windows DOS versions (MS DOS 7 and 8), the BIOS and kernel are combined in IO.SYS, and MSDOS.SYS is a text configuration file. The kernel then executes the CONFIG.SYS file. In CONFIG.SYS, the SHELL command specifies the location of the shell (typically COMMAND.COM). The shell will then launch, and open a startup batch file (typically AUTOEXEC.BAT).^[18]

应用软件

Arachne web browser

See also:DOS software

While DOS was the primary PC-compatible platform, several notable programs were written for it. These included:

• Lotus 1-2-3; a spreadsheet program that saw heavy use in corporate markets, and has been credited with the success of the IBM PC^[19]
• WordPerfect; a word processor that is currently produced for the Windows platform
• dBase; one of the earliest database programs
• Telix; a modem communication program
• Arachne; a DOS web browser
• DJGPP, the DOS port of gcc
• 4DOS, a replacement shell
• Borland's integrated development environment, which included Turbo Pascal, Turbo BASIC, Turbo C, and Turbo Assembler
• BBS hosting software RemoteAccess, Spitfire, Maximus, McBBS, and TAG
• Numerous GUI shell programs, offering ease-of-use over DOS' native command-line interface. These included Quarterdeck Desqview, GEOS, and the original versions of Microsoft Windows
• BASIC-language utilities BASICA and GW-BASIC
• Numerous first-person shooter games: Wolfenstein 3D, a joint venture between ID Software and Apogee Software (later 3D Realms); ID Software's Doom and Quake; and 3D Realms' Duke Nukem 3D, Shadow Warrior, and Rise of the Triad. All three 3D Realms' titles were built with the DOS-based Build engine, written by Ken Silverman and used for Silverman's Ken's Labyrinth.

限制

Several limitations plagued the DOS architecture. The original 8088 microprocessor could only address 1 mebibyte of physical RAM. With additional hardware devices being mapped into this range, the highest amount of available memory was 640 kibibytes, known as conventional memory. Due to DOS' structure, this was assumed to be the maximum, and DOS could not address more than this. An early workaround was expanded memory; later, extended memory was developed with the 80286. While these provided usuable memory to applications, they still had to start in conventional memory, thereby using part of the existing 640 kb. With the 80386 microprocessor's redesigned protected mode, DOS extenders and the DOS Protected Mode Interface were able to provide additional memory to applications, as well as multitasking. ^[20][21]

DOS also has an upper limit to the size of hard disk partitions. This has two causes. First, many DOS-type systems never had support for any file system newer than FAT16, which, by design, does not allow partitions larger than 2.1 gibibytes.^[22] Additionally, DOS accesses the hard disk by calling Interrupt 13, which utilizes the cylinder-head-sector system of mapping the disk. Under this system, only 8 gibibytes are visible to the operating system.^[23] Newer operating systems accomplished disk access via software means, e.g. 32-bit disk access.

模拟器

Under Linux it is possible to run copies of DOS and many of its clones under DOSEMU, a Linux-native virtual machine for running 实模式的程序。There are a number of other emulators for running DOS under various versions of UNIX, even on non-x86 platforms, such as DOSBox.^[24][25]

DOS 模拟器在Windows XP和Vista用户之中很受欢迎，因为这些系统与纯DOS不兼容。它们可以用来运行为DOS设计的软件（常被称作'过时软件'(abandonware)）。DOSBox是为在新式操作系统上玩游戏而设计的，最知名的模拟器之一。^[24][12] Tao ExDOS模拟器用于一些商业应用程序。^[26] VDMSound在Windows下由于它的GUI和声效支持也很受欢迎。

It is possible to run DOS applications under Microsoft Virtual PC, allowing better compatibility than DOS emulators. A legitimate version of MS-DOS can be installed which should allow all but the most stubborn applications to run.^[27]