Windows 95 laptops were missing low-power ‘HLT’ modes for a reason — better to drain your battery than brick your entire PC

This past month signified thirty years since Microsoft released Windows 95 on August 24, 1995. Remarkably, the Federal Aviation Administration (FAA), responsible for managing civil aviation in the U.S., confessed in June that it continues to rely on Windows 95 and floppy disks in their day-to-day tasks. Nevertheless, they emphasized their intention to transition to a contemporary operating system.

Despite the fact that the software company stopped providing mainstream support for Windows 95 on December 31, 2000, this operating system continues to be a topic of interest today, significantly contributing to the worldwide success and acceptance of Windows.

Over the last few months, I’ve been exploring a series of heartwarming tales about the background and design aspects of Windows 95. These stories include explanations for certain understated features in its user interface, which were influenced by carryovers from Windows 3.1, even though Windows 95 had the potential to display more vibrant graphical elements.

More recently, longtime Microsoft engineer Raymond Chen, who’s played a significant role in the development of the Windows operating system for over three decades, revealed an interesting tale in his ongoing “Old New Thing” series. This tale sheds light on why Windows 95 didn’t initially come with a power-saving feature to conserve battery life during idle periods on laptops.

As an analyst, I’d rephrase that as follows: In contemporary Windows versions, the 80386 HLT (Halt) command was incorporated during shipment. This instruction functions by instructing the CPU to momentarily halt itself, waiting for a hardware interrupt such as a key press, which in turn triggers the processor to enter a low-power mode when the operating system is running without active tasks.

In simpler terms, during the time when Windows 95 was being developed, the technology for modern operating systems that allows devices to enter low-power modes safely using instructions like MWAIT (Monitor Wait) wasn’t available yet.

HLT would brick too many devices

Raymond Chen explains that Microsoft purposefully did not incorporate the ‘HLT’ instruction in any of the Windows 95 code due to a deliberate decision. According to him, several laptops from a prominent manufacturer suffered from unresponsiveness upon booting (essentially becoming “bricked” to some extent) when the CPU attempted to activate this command.

As a tech enthusiast, I’ve always been intrigued by the world of aftermarket components and their capabilities. Back in the day with Windows 95, some ingenious minds managed to create components designed to execute HLT (Halt) instructions, which were all about conserving power. But here’s the kicker – they seemed rather disgruntled, muttering something along the lines of “What was Microsoft thinking? Why on earth didn’t they include this feature in Windows?

In simpler terms, because the system became inoperable when it failed (a ‘false negative’ scenario), the cost associated with this failure was excessive. Therefore, we decided to eliminate the Halt function to avoid such high costs.

Raymond Chen, Veteran Microsoft Engineer

Chen highlighted a significant issue within these elements, mentioning that they are filled with glitches which frequently lead to device malfunctions resulting in the freeze-up state. Furthermore, Chen emphasized by saying, “In essence, it boils down to these components turning into a brick.

As a researcher looking back, I acknowledge that it might have been feasible for Microsoft to implement a detection mechanism for the compromised systems that malfunctioned due to the HLT instruction activation, prior to the launch of Windows 95. However, given the vast and complex nature of the system landscape at that time, identifying all potentially affected systems before the release was practically impossible.

Given that a malfunctioning HLT instruction could render Windows 95 unworkable and the cost of a misdiagnosis being too significant, we opted to omit it from Windows 95.

2025-09-10 14:10

HLT would brick too many devices

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