|
In computing, Abort, Retry, Fail? is a computer error message in the DOS operating system which indicates a critical error and prompts the end-user for the course of action to follow. This and other similar error messages are given by the default critical error handler. The message was sometimes used as an example of poor usability design in computer user interfaces. == Background == The DOS family of operating systems (such as MS-DOS, PC DOS and DR-DOS) date back to early microcomputers, which were primitive by modern computing standards. A primary design consideration was that software written for CP/M be portable to DOS without changes. In most CP/M systems attempting to read a disk drive with the door open hung waiting for an input event until the disk drive door was closed, on some hardware it would hang until an actual physical disk was in the drive. Many users of CP/M were accustomed to this as a method of managing multiple disks, by opening the disk drive to stop reading until the correct disk could be inserted. Even the first IBM-PC had more advanced hardware such that the CPU could tell that the disk drive door was open, but returning an error would break software that assumed it could not open a file until the user had closed the drive door. Still it was desirable to improve the experience if possible. In DOS, a ''critical error'' is one which might be fixable by operator intervention. The classic example is an attempt to read from the floppy drive without a diskette loaded. The computer has no way of determining whether it should wait for the user to load a disk, or abort the operation. The handling of different errors was somewhat illogical, for instance while ''no'' disk in the drive caused the error, the ''wrong'' disk in the drive caused an immediate return with an error, even though that was also fixable by the user. When DOS encounters a critical error, it generates software interrupt 24 (INT 24). The associated interrupt service routine (ISR) is called the ''critical error handler''. The default critical error handler was part of COMMAND.COM〔 and it printed the "Abort, Retry, ..." prompt and waited for user input. Internal DOS commands and most of the line-oriented external commands included with DOS take advantage of this and do not install their own handler. A program can install its own critical error handler while running, and many of the more sophisticated programs,〔 in particular full screen programs, do so in order to avoid the messages disturbing the normal output of the program. Some software faked the missing "FAIL" response by jumping back to the calling program, skipping the return stack in DOS, a risky hack. Starting with MS-DOS/PC DOS 3.3, the ability to return "FAIL" from the critical error handler was added, which removed the biggest problem with the prompt (which earlier was known as "Abort, Retry, Ignore?") in that there was now a useful value to return that did not crash the program or repeat the prompt. DOS 3.3 COMMAND.COM provides the startup option /F in order to force the default critical error handler to return "Fail" on errors. This option is intended for unattended use, for example in conjunction with BBS software, as network server, or in embedded systems. The option is also supported by COMMAND.COM of PTS-DOS 6.51 and S/DOS 1.0, as well as by DR-DOS 7.02 and higher. OpenDOS 7.01 COMMAND.COM provides a similar feature to not install a critical error handler when startup option /N is specified, a feature, which is still supported in newer versions. Starting with version 4.0 the alternative command line processors 4DOS and NDOS support option /F and the corresponding 4DOS.INI/NDOS.INI directive CritFail=Yes as well.抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Abort, Retry, Fail?」の詳細全文を読む スポンサード リンク
|