Stories with Tag Boot Process

• An AlphaStation's SROM

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  Posted: 2025-03-31 06:15:52

  Verbose tl;dr

  The blog post details the author's journey in reverse-engineering the System ROM (SROM) of their AlphaStation 255/300. Driven by curiosity and the desire to understand the boot process, they meticulously documented the SROM's contents, including memory maps, initialization routines, and interactions with various hardware components. This involved using a logic analyzer to capture bus activity and painstakingly decoding the assembly code. Ultimately, they were able to create a disassembled listing of the SROM and gain a deep understanding of its functionality, including the system's initial boot sequence and setup of key hardware like the interrupt controller and memory controller. This effort allows for greater understanding and potential modification of the early boot process on this vintage Alpha system.

  This blog post details the author's deep dive into understanding the Serial ROM (SROM) of their AlphaStation 255/300. The SROM, a crucial component for booting these vintage Alpha systems, contains firmware responsible for initializing the hardware and bootstrapping the operating system. The author's investigation stemmed from a desire to gain a more comprehensive understanding of the inner workings of their AlphaStation and potentially explore modifications. Their initial approach involved reading the SROM contents using the SRM console, a firmware-based command-line interface. This yielded a raw binary dump, which, while accessible, lacked structure and human readability.

  The author then embarked on a journey to decode this binary data, suspecting the presence of meaningful information beyond just executable code. Their efforts focused on identifying specific data structures and constants within the SROM, aided by the Alpha Architecture Handbook and existing knowledge of firmware design. They meticulously documented their progress, highlighting discovered elements such as the system's base MAC address, various configuration settings, and checksums for data integrity verification. The process involved careful analysis of byte patterns and offsets, piecing together the puzzle of the SROM's internal organization. This painstaking work revealed insights into the boot process, including the execution of initial bootstrap code and the loading of subsequent stages of firmware. The author also discovered string data embedded within the SROM, providing clues about the system’s configuration and intended operation. Ultimately, the exploration provided a significantly enhanced understanding of the SROM’s role and composition within the AlphaStation’s architecture. While the author acknowledges the investigation is ongoing, the documented findings represent a significant step towards fully deciphering the SROM and its function.

  • AlphaStation
  • SROM
  • DEC
  • Digital Equipment Corporation
  • Vintage Computers
  • Retrocomputing
  • Firmware
  • ROM
  • system ROM
  • Hardware
  • Computer Architecture
  • Boot Process

  Summary of Comments ( 1 )
  https://news.ycombinator.com/item?id=43531695

  Verbose tl;dr

  Hacker News users discuss the blog post about an AlphaStation's SROM, focusing primarily on the intricacies and nostalgia of older hardware. Several commenters reminisce about working with AlphaStations and DEC hardware, sharing personal anecdotes about their experiences with these systems. Some delve into the technical details of the SROM, including its functionality and the challenges involved in working with it. Others appreciate the author's dedication to preserving and documenting these older machines. A few commenters express interest in similar exploration of other vintage hardware. The general sentiment is one of appreciation for the blog post and its contribution to preserving computer history.

  The Hacker News post titled "An AlphaStation's SROM" with the URL https://news.ycombinator.com/item?id=43531695 has a moderate number of comments discussing various aspects related to the linked blog post about an AlphaStation.

  Several commenters express fascination with the intricacies of older hardware and the process of reverse-engineering its firmware. One commenter details their own experience with DEC Alphas and the challenges of debugging them, highlighting the scarcity of documentation and the reliance on disassemblers and logic analyzers. This resonates with another user who mentions the complexity of SRM consoles and the difficulty in interpreting their output.

  There's a discussion thread related to the SROM (System ROM) and its role in the boot process. Commenters delve into the technical specifics, discussing checksum calculations, memory addressing, and the interaction between the SROM and other components. One commenter questions the author's interpretation of a specific byte sequence in the SROM, proposing an alternative explanation based on their experience with similar systems. This leads to a brief exchange about the nuances of endianness and its potential impact on the interpretation of the data.

  Another thread focuses on the practicality of emulating older hardware. One user suggests using an emulator like SimH to explore the AlphaStation's functionality without needing the physical hardware. Others discuss the benefits of emulating vintage systems for preservation and accessibility.

  A few comments touch upon the broader context of digital archaeology and the importance of preserving older computer systems. They appreciate the author's effort in documenting the inner workings of the AlphaStation, recognizing the value in understanding the history of computing.

  Finally, there are some shorter comments that simply express admiration for the author's work or share anecdotal experiences with AlphaStations and other vintage hardware. While not contributing significantly to the technical discussion, these comments add to the overall sense of community and shared interest in the topic.

• An invalid 68030 instruction accidentally allowed the Mac Classic II to boot

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  Posted: 2025-01-25 20:29:41

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  A quirk in the Motorola 68030 processor inadvertently enabled the Mac Classic II to boot despite its ROM lacking proper 32-bit addressing support. The Classic II's ROM mistakenly used a "MOVEA" instruction with a 32-bit address, which should have caused a failure on the 24-bit address bus. However, the 68030, when configured for a 24-bit bus, ignores the upper byte of the 32-bit address in this specific instruction. This unintentional compatibility allowed the flawed ROM to function, making the Classic II's boot process seemingly normal despite the underlying programming error.

  Doug Brown's blog post, "An invalid 68030 instruction accidentally allowed the Mac Classic II to successfully boot up," details a fascinating discovery related to the boot process of the Mac Classic II. This compact Macintosh model, released in 1991, utilized the Motorola 68030 processor. Brown, an enthusiast of retro computing, was investigating a peculiar behavior he observed while experimenting with the machine.

  The Classic II, as shipped, is equipped with a specific ROM chip. Brown had replaced this original ROM with a modified one. This modified ROM contained code designed to patch certain aspects of the system software. During the boot sequence with this modified ROM, an unexpected and seemingly erroneous instruction was being executed on the 68030 processor. This instruction, specifically a "MOVE from SR," attempted to move the contents of the status register (SR), a critical processor register holding flags and other control bits, into a data register. According to official Motorola documentation, this particular form of the instruction, involving a direct move from the status register, is undefined and should not function correctly on a 68030. One would typically expect such an illegal instruction to trigger an exception, halting the boot process.

  Remarkably, instead of crashing, the Mac Classic II continued to boot successfully. Brown's meticulous investigation revealed that, due to a specific quirk in the 68030's microcode implementation on the Classic II, this normally invalid instruction was actually being interpreted and executed as a legal, albeit different, instruction: "MOVE from CCR." The CCR, or Condition Code Register, is a subset of the larger SR, holding only the condition code flags. This unintentional substitution allowed the boot process to proceed unimpeded, despite the presence of the erroneous instruction.

  Furthermore, Brown discovered that the errant "MOVE from SR" instruction was a remnant of code designed for older Macintosh models that used the Motorola 68000 processor. On the 68000, this instruction was valid. When the ROM code was adapted for the 68030-based Classic II, this particular instruction was inadvertently left unchanged.

  The serendipitous outcome, where an invalid instruction was misinterpreted as a valid one with similar functionality, highlights the subtle complexities and occasional unintended behaviors that can arise within computer systems. It underscores how seemingly minor differences in processor microcode can have significant, and sometimes unexpected, consequences. The incident provided a unique learning experience for Brown, shedding light on the intricacies of the Mac Classic II's hardware and the legacy code it ran.

  • Mac Classic II
  • 68030
  • Boot Process
  • Hardware
  • Software
  • Retrocomputing
  • Macintosh
  • Operating System
  • Low-Level Programming
  • Assembly Language
  • CPU
  • instruction set
  • bug
  • unintentional behavior
  • computer history

  Summary of Comments ( 1 )
  https://news.ycombinator.com/item?id=42824562

  Verbose tl;dr

  Hacker News commenters on the Mac Classic II boot anomaly generally express fascination with the technical details and the serendipitous nature of the discovery. Several commenters delve into the specifics of 680x0 instruction sets and how an invalid instruction could inadvertently lead to a successful boot, speculating about memory initialization and undocumented behavior. Some share anecdotes about similar unexpected behaviors encountered during their own retrocomputing explorations. A few commenters also highlight the importance of such stories in preserving computer history and understanding the quirks of older hardware. The overall sentiment reflects appreciation for the ingenuity and occasional happy accidents that shaped early computing.

  The Hacker News post discussing the article "The invalid 68030 instruction that accidentally allowed the Mac Classic II to boot" has generated several interesting comments.

  Several users discuss the nature of the undocumented movc instruction and its behavior on different Motorola 680x0 processors. One user highlights the difference between the 68020 and 68030 behavior regarding the CCR and SR registers, pointing out that setting specific bits in the SR unintentionally enables MMU functionality on the 68030, which wasn't intended for the Classic II. This accidental side effect is what allowed the machine to boot. The discussion expands to cover how these subtleties often lead to unexpected discoveries in computing.

  Another commenter reminisces about working with early Macintosh ROMs and the challenges of debugging without source code or comprehensive documentation. They mention the use of disassemblers and the process of painstakingly figuring out the purpose of various memory locations and instructions.

  A separate thread delves into the specific MMU configuration enabled by the errant instruction. Commenters analyze the resulting address mapping and speculate on how this setup might impact performance and memory access. They also discuss the implications of running code designed for a simpler memory model on a system with an active MMU.

  One user shares an anecdote about a similar "happy accident" in embedded systems development, where an undocumented behavior of a peripheral chip led to a performance boost. They draw a parallel with the Mac Classic II situation, emphasizing how unintended consequences can sometimes have positive outcomes.

  The conversation also touches upon the broader history of Macintosh development and the constraints faced by engineers at the time. One comment mentions the limited resources and tight deadlines that often led to unconventional solutions and "hacks."

  Finally, several comments simply express appreciation for the article and the insights it provides into the inner workings of early Macintosh hardware. They praise the author's ability to explain complex technical details in a clear and engaging manner.

• Why did Windows 95 setup use three operating systems?

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  Posted: 2024-11-17 19:54:24

  Verbose tl;dr

  Windows 95's setup process involved three distinct operating systems to ensure a smooth transition and maximize compatibility. It began booting from a DOS-based environment to provide basic hardware access and initiate the installation. Then, a minimal Windows 3.1-like environment took over, offering a familiar GUI for interacting with the setup program and allowing access to existing drivers. Finally, the actual Windows 95 operating system was installed and booted, completing the setup process and providing the user with the full Windows 95 experience. This multi-stage approach allowed the setup program to manage the complex transition from older systems while providing a user-friendly interface and maintaining compatibility with existing hardware and software.

  Raymond Chen's blog post, "Why did Windows 95 setup use three operating systems?", delves into the intricate, multi-stage booting process employed by the Windows 95 installation procedure. Rather than a straightforward transition, installing Windows 95 involved a complex choreography of three distinct operating systems, each with a specific role in preparing the system for the final Windows 95 environment.

  The initial stage utilized the existing operating system, be it DOS or Windows 3.1. This familiar environment provided a stable launching point for the installation process, allowing users to initiate the setup program from a known and functional system. Crucially, this initial OS handled the preliminary steps, such as checking system requirements, gathering user input regarding installation options, and initiating the transfer of files to the target hard drive. This ensured that the subsequent stages had the necessary foundation upon which to build.

  The second operating system introduced in the Windows 95 installation was a minimalist DOS-based environment specifically designed for setup. This stripped-down DOS lacked the complexities and potential conflicts of a full-fledged DOS installation, providing a predictable and controlled environment for the core installation tasks. This specialized DOS environment executed directly from the installation media, circumventing potential issues arising from the existing operating system and allowing for low-level access to the hardware necessary for partitioning and formatting the hard drive, as well as copying the essential Windows 95 system files. It operated independently of the pre-existing operating system, ensuring a clean and controlled installation environment.

  Finally, the third operating system involved was the actual Windows 95 operating system itself. Once the setup-specific DOS environment completed the file transfer and preliminary configuration, the system rebooted, this time loading the newly installed Windows 95. This first boot of Windows 95 was not merely a functional test, but an integral part of the installation process. During this initial boot, Windows 95 performed crucial configuration tasks, including detecting and installing hardware drivers, finalizing registry settings, and completing any remaining setup procedures. This final stage transitioned the system from the installation environment to a fully operational Windows 95 system ready for user interaction.

  In essence, the Windows 95 installation process leveraged a tiered approach, employing the existing OS for initial setup, a specialized DOS environment for core file transfer and low-level configuration, and finally the Windows 95 OS itself for final configuration and driver installation. This multi-stage process ensured a robust and reliable installation, mitigating potential conflicts and providing a clean transition to the new operating system. This complexity, while perhaps not immediately apparent to the end user, was a key factor in the successful deployment of Windows 95.

  • Windows 95
  • Setup
  • Operating Systems
  • MS-DOS
  • Windows 3.1
  • Bootstrapping
  • Installation Process
  • Legacy Systems
  • Microsoft
  • Windows History
  • Real Mode
  • Protected Mode
  • Boot Process
  • Legacy OS
  • Installation
  • x86
  • 16-bit
  • 32-bit
  • x86 Architecture

  Summary of Comments ( 192 )
  https://news.ycombinator.com/item?id=42166606

  Verbose tl;dr

  Hacker News commenters discuss the complexities of Windows 95's setup process and the reasons behind its use of MS-DOS, a minimal DOS-based environment, and a pre-installation environment. Several commenters highlight the challenges of booting and managing hardware in the early 90s, necessitating the layered approach. Some discuss the memory limitations of the era, explaining the need to unload the DOS environment to free up resources for the graphical installer. Others point out the backward compatibility requirements with existing MS-DOS systems and applications as another driving factor. The fragility of the process is also mentioned, with one commenter recalling the frequency of setup failures. The discussion touches upon the evolution of operating system installation, contrasting the Windows 95 method with more modern approaches. A few commenters share personal anecdotes of their experiences with Windows 95 setup, recalling the excitement and challenges of the time.

  The Hacker News post "Why did Windows 95 setup use three operating systems?" generated several comments discussing the complexities of the Windows 95 installation process and the technical reasons behind using MS-DOS, a 16-bit preinstallation environment, and the 32-bit Windows 95 itself.

  Several commenters focused on the bootstrapping problem inherent in installing a new operating system. They pointed out that a simpler OS is required to launch the installation of a more complex one. MS-DOS served this purpose in the Windows 95 setup, providing a familiar and readily available platform to begin the process. The discussion included how the initial boot from floppy disk would load a basic DOS environment, which would then launch the next stage of the installation.

  The role of the 16-bit preinstallation environment was also discussed. Commenters explained that this environment, distinct from both MS-DOS and the final Windows 95 system, was crucial for tasks that couldn't be handled by the limited DOS environment, such as accessing CD-ROM drives and managing more complex hardware configurations. This intermediary step allowed the setup to gather information about the system, prepare the hard drive, and begin copying the necessary Windows 95 files.

  Some commenters delved into the technical limitations of MS-DOS, highlighting its 16-bit architecture and inability to directly handle the 32-bit components of Windows 95. The preinstallation environment bridged this gap, providing the necessary functionality to transition to the 32-bit world. This discussion touched upon the complexities of real-mode and protected-mode memory addressing, which were relevant to the transition between these different environments.

  The specific use of three separate systems was a point of interest. Some commenters speculated about alternative approaches, but acknowledged the practical constraints of the time. The existing familiarity with MS-DOS made it a logical starting point. The distinct preinstallation environment provided a dedicated space for setup-specific tasks without interfering with the final Windows 95 installation.

  A few comments also touched on the nostalgia associated with the Windows 95 installation process and the challenges of managing hardware configurations in that era. The need to manually configure drivers and settings was highlighted, contrasting sharply with the more automated installation processes of modern operating systems.