The
AARD code was a segment of
obfuscated machine codeObfuscated code is source or machine code that has been made difficult to understand. Programmers may deliberately obfuscate code to conceal its purpose , to deter reverse engineering, or as a puzzle or recreational challenge for readers...
in the installer for a beta release of Microsoft Windows 3.1. The code ran several functional tests on the underlying
DOSDOS, short for "Disk Operating System", is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions Windows 95, 98, and ME.Related systems...
that succeeded on
MS-DOSMS-DOS is an operating system developed by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the main operating system for personal computers during the 1980s. It was preceded by M-DOS , designed and copyrighted by Microsoft in 1979...
, but resulted in a technical support message on competing operating systems. The name was derived from the initials of Microsoft programmer Aaron Reynolds, who used "AARD" to sign his work. ("AARD" was found in the machine code of the installer.) Microsoft disabled the AARD code for the final release of Windows 3.1.
The rationale for the AARD code came to light when internal memos were released during the United States Microsoft antitrust case.
The
AARD code was a segment of
obfuscated machine codeObfuscated code is source or machine code that has been made difficult to understand. Programmers may deliberately obfuscate code to conceal its purpose , to deter reverse engineering, or as a puzzle or recreational challenge for readers...
in the installer for a beta release of Microsoft Windows 3.1. The code ran several functional tests on the underlying
DOSDOS, short for "Disk Operating System", is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions Windows 95, 98, and ME.Related systems...
that succeeded on
MS-DOSMS-DOS is an operating system developed by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the main operating system for personal computers during the 1980s. It was preceded by M-DOS , designed and copyrighted by Microsoft in 1979...
, but resulted in a technical support message on competing operating systems. The name was derived from the initials of Microsoft programmer Aaron Reynolds, who used "AARD" to sign his work. ("AARD" was found in the machine code of the installer.) Microsoft disabled the AARD code for the final release of Windows 3.1.
The rationale for the AARD code came to light when internal memos were released during the United States Microsoft antitrust case. Internal memos released by Microsoft revealed that the specific focus of these tests was
DR-DOSDR-DOS is a DOS-type operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from CP/M-86.-Origins in CP/M:...
. At one point, Microsoft CEO
Bill GatesWilliam Henry "Bill" Gates III is an American business magnate, philanthropist, and chairman of Microsoft, the software company he founded with Paul Allen.He is ranked consistently one of the world's wealthiest people...
sent a memo to a number of employees, reading "You never sent me a response on the question of what things an app would do that would make it run with MSDOS and not run with DR-DOS. Is there [
sic] feature they have that might get in our way?" Microsoft Senior Vice President
Brad SilverbergBrad Silverberg is most noted for his work at Microsoft in 1990–1999 as Senior VP and product manager for MS-DOS, Windows, Internet Explorer, and Office...
later sent another memo, stating: "What the [user] is supposed to do is feel uncomfortable, and when he has bugs, suspect that the problem is DR-DOS and then go out to buy MS-DOS."
Following the purchase of DR-DOS by
NovellNovell, Inc. is a global software corporation based in the United States specializing in enterprise operating systems such as SUSE Linux Enterprise and Novell NetWare; identity, security and systems management solutions; and collaboration solutions. Together with WordPerfect, Novell was...
and its renaming to "Novell DOS", Microsoft Co-President Jim Allchin stated in a memo, "If you're going to kill someone there isn't much reason to get all worked up about it and angry. Any discussions beforehand are a waste of time. We need to smile at Novell while we pull the trigger."
Digital ResearchDigital 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. Digital Research should not be confused with Digital Equipment Corporation; the two were not...
released a
patchA patch is a piece of software designed to fix problems with, or update a computer program or its supporting data. This includes fixing security vulnerabilities and other bugs, and improving the usability or performance...
to enable the AARD tests to pass on DR-DOS in 1992.
What had been DR-DOS changed hands again. The new owner, Caldera Systems, began a lawsuit against Microsoft over the AARD code,
Caldera v. Microsoft, which was later settled. It is believed that the settlement ran in the order of $150m.
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