The Windows 3.1 Virtual Machine Control Block Part 1 (1994) | Hacker News Reader

The Windows 3.1 Virtual Machine Control Block Part 1 (1994)

archive.retro.co.za

61 pointsuserbinator11 comments

Unlike its ultimate successor in Windows NT, I feel like the story of the design and evolution of the Win32 kernel & the resulting triumph of Windows 95 as an honest-to-goodness protected memory, preemptive multitasking OS hasn’t really been told.

Moreover, the fact that it's actually more like a bare-metal hypervisor that runs DOS VMs seems to be little-known. The protection is the bare minimum necessary to keep them isolated - all hardware, unless specifically virtualised by VxDs, is effectively "passed through".

Yeah I'd like a Showstopper book for Windows 95.

Possibly I'm misunderstanding your post. In what sense did Windows 95 have protected memory? Even DOS programs could overwrite important Windows addresses, to say nothing of the convenient win32 APIs MS provided to scribble all over other applications memory space.

Windows 95 absolutely had protected memory: Every 32-bit process had its own address space without direct access to any other process’ memory.

DOS programs were run in V86 mode.

Yeah it was "less unprotected" at best. It was also trivial to deadlock the entire machine with user-mode code (the DirectX system-wide mutex being the most obvious example)

Some books I own that cover the software, and its progression through Windows/386 -> 3.0 -> 3.11 -> 95. They don't go behind the scenes (ie they're not Showstopper!) -

   Pietrek - Windows Internals (1993)
   Schulman, Maxie, Pietrek - Undocumented Windows (1992)
   Pietrek - Windows 95 System Programming Secrets (1995)
   Schulman - Unauthorized Windows 95 (1994)
   Oney - Systems Programming for Windows 95 (Microsoft Press, 1996)
   Williams - DOS and Windows Protected Mode (1994)

I picked them up from eBay and swapmeets for $notmuch. Some are in the Internet Archive's library (where you need a free account, and check books out by the hour)

There were so many fantastic, deep dives into the inner workings of operating systems and below in Dr. Dobbs Undocumented Corner.

I also highly recommend Robert R. Collins articles for Dr. Dobbs (they are easy to find), which shed light on, at the time, many undocumented features of the Intel CPUs of the day.

Thanks! I wasn't aware of these, despite being a subscriber for a couple of years.

This seems to be an online collection of these articles:

http://www.rcollins.org/ddj/ddj.html

Windows 95's System Monitor can actually be configured to show the current number of virtual machines running. (Add item -> Kernel -> Virtual Machines)

You can see in real time that the number of VMs will equal 1 plus the number of DOS windows currently open, as the article explains.

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