Raymond Chen, a veteran of Microsoft, recently revisited a story from over two decades ago regarding the HLT instruction and its relationship with Windows 95. This particular instruction was designed to instruct the CPU to enter a low-power state, making it especially beneficial for laptops by significantly reducing power consumption.
Although Microsoft had successfully implemented the HLT instruction in Windows 95, the company faced a dilemma. Some devices, including those from a prominent manufacturer, were found to become irretrievably locked when the instruction was executed. To avoid potential backlash, Microsoft made the decision to remove it from the operating system.
Understanding the Decision
When questioned about why Microsoft didn’t simply create exceptions for the devices that would be adversely affected by the HLT instruction, Chen provided clarity. The primary concern was the uncertainty surrounding the number of vulnerable devices already in circulation. Rather than risk widespread issues, the company opted to exclude the instruction altogether.
Modern users of Windows are familiar with Microsoft’s approach of establishing compatibility barriers to prevent operating system updates from being installed on hardware or configurations deemed problematic. Chen noted that while Windows 95 could have integrated detection mechanisms for systems that would freeze upon encountering HLT instructions, the sheer number of potentially affected systems posed a significant risk. By the time Windows 95 was ready for release, it was likely that not all problematic systems had been identified.
“The fact that many systems were affected indicates this was not an isolated incident,” Chen remarked. “We were likely only seeing the tip of a very fragmented iceberg.” Given that the failure mode resulted in unusable systems, the implications of a false negative were too severe. Thus, the decision was made to eliminate the HLT instruction from the operating system.
This decision has sparked debate over its merits. It inadvertently led to the emergence of a niche market where software vendors developed applications to execute the HLT instruction for Windows 95 users, often accompanied by a hint of sarcasm directed at Microsoft for omitting such a seemingly beneficial feature.
Chen’s response to the criticism was pointed: “I guess these people never received bug reports from customers saying, ‘I installed your custom program, and now my laptop freezes up as soon as it boots. How do I uninstall it if my laptop freezes up at boot?'” He elaborated on the issue, explaining that the system would become a “brick” until a restart, but upon restarting, it would still lead to a bricked state. “The OS boots into a brick,” he stated.
In hindsight, there may have been alternative approaches, such as implementing checks for HLT issues based on unexpected restarts during installation. However, the landscape of 1995 was markedly different, and Microsoft was understandably cautious about its new operating system being blamed for a wave of bricked laptops.
