Reddit mentions of Unauthorized Windows 95: A Developer's Guide to Exploring the Foundations of Windows "Chicago"

Well.. this is a bit more complex than that. Turns out that Windows 95 depends on DOS in almost the same way that Windows 3.11 did. Windows 3.11 didn't depended on DOS as much as everybody thinks. There is a great book that explains this called Unauthorized Windows 95.

And, by the way, DOS was inaccessible in Windows 2000 because it was a Windows NT, Like Windows NT 4 before. In fact the first Windows who didn't have DOS on it was the fist version of Windows NT, Windows NT 3.1. Windows 8 isn't an evolution of Windows/DOS but an evolution of Windows NT.

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> Windows 95 was fantastic. I loved it so much (except that it wasn't DOS)

You might be interested to know that Windows 95 had about as much DOS in it as did the latest versions of the Windows 3.x series. Microsoft tried to sell it as a 'complete 32-bit rewrite', but in reality Windows 95 is mainly just a significant development of ideas that originated in Windows/386 2.11. Here's the rundown:

• Windows 1.x and 2.x - All ran exclusively in real mode, on top of DOS. DOS acted as a loader for Windows, and provided a number of core OS-level services (including the filesystem itself.) This was the beginning of the Win16 API, which provided graphics, window management, and a nice memory manager based on relocatable blocks with a maximum size of 64K. (Keep the memory manager in mind as you read on....)
  
  
• Windows/286 - 286 class machines had an address bus that was larger than 20 bits wide. This let them address an extra 64K at the top of the real mode address space, if they disabled something called the A20 gate. Widnows/286 was fundamentally the same real mode Windows as before, but it shipped with a driver (HIMEM.SYS) that let it control the A20 gate and open up a bit more memory. (Windows/286 was mostly a dead-end, and despite the name, could run on 8086 class machines.)
  
  
• Windows/386 - This is still real mode-windows, and Windows programs are still limited to a 20-bit address space (1MB). However, the difference is that Microsoft scratch built a small 386-specific operating system that let them run multiple real mode programs at the same time, using a special 80386 specific feature called 'Virtual 8086' mode. For the sake of discussion, let's call this OS VMM, for Virtual Machine Manager. Windows/386 booted from DOS into VMM, and then ran real mode Windows under VMM. The reason they did this is that VMM let Windows/386 run other real mode programs at the same time as Windows itself, so it could do a good job running multiple DOS programs alongside Windows programs. If you've ever wondered what a VxD is, it's a device driver for this lower level 32-bit OS. (Keep VMM in mind as you read on....)
  
  
• Windows 3.0 - The main innovation of Windows 3.0, is that Microsoft figured out a way to port the Win16 API itself from real-mode over to protected mode. What this means is that, finally, a single program can access more than 1MB of RAM without having to screw with paging strategies like EMS 3.2/4.0. Windows 3.0 brought this feature, the single biggest feature of OS/2, to mainstream PC's by being cheap to purchase and running alongside DOS. The only reason that Microsoft was able to make this change is that way back in Windows 1.0, they set some strict rules for how programs have to access memory. (The block based memory manager, etc.) This made it possible for Microsoft to make it easy to take existing real-mode programs and run them seamlessly on protected mode. (Many programs could run unchanged, if you toggled a bit in the .EXE file that said it was safe for protected mode.) Windows 3.0 also took the older versions of Windows and bundled them all together in one box. Note that at this point, the file system is still running Windows 1.0 style, down in DOS.... The VMM layer lets multiple programs use the same underlying real-mode DOS file system. It works, but it's slow... lots of processor mode switching and data marshalling.
  
  
• Windows for Workgroups 3.11 - This version of Windows (and it had to be 3.11, not 3.1) introduced 32-bit file access (32BFA). In previous versions of Windows, VMM had a small module that took DOS style file system calls and redirected them to the underlying DOS. 32BFA was a re-implementation of the DOS file system that ran directly in VMM as 32-bit code. This eliminated the need for all file system calls to switch into real-mode to use DOS to get to the disk. (Note that this was still possible, if you had an old-school device that only had a real-mode device driver.)
  
  
• Win32s - This was a layer on top of Windows 3.1 that provided many of the major Win32 API calls by translating them directly to Win16 calls. It also hooked into the Windows EXE loader and gave it the ability to run a different 32-bit EXE format. The major benefit of this is that it let you take a single program and run it on both Windows NT and Windows 3.1...with a 32-bit address space. Aside from a very low-level technique that worked on Windows 3.0, this is the first time that this line of Windows development has been able to run user-mode programs that could access a single block of memory that's greater than 64K in size.
  
  At this point, much of the architectural groundwork for Windows95 has been laid. There's a 32-bit kernel, the ability to load and run 32-bit Windows programs, and a 32-bit file system implementation. Viewed in this light, Windows 95 made the following improvements:
  
  
• The 32-bit file system was extended with long file name support.
  
• A number of the API calls (not all) in Win32s were extended with full 32-bit implementations. (The old Win32s entry points provided a place to put the call interface, and VMM provided 32-bit OS services.)
  
• The Windows 3.x shell (Program Manager and File Manager) was replaced with the Windows Explorer Shell.
  
• Microsoft altered DOS to boot directly into the Windows startup process. (To do this in earlier versions of Windows required that you explicitly start windows from your DOS startup script AUTOEXEC.BAT.)
  
  If you're interested in knowing more (and I can't imagine why), this book goes into gory detail:
  
  http://www.amazon.com/Unauthorized-Windows-Developers-Exploring-Foundations/dp/1568841698
  
  IIRC, Schulman demonstrates how to get Windows95 running in DOS only mode, in addition to a mode where DOS is directly running on top of VMM, without the Windows GUI. Microsoft never liked to admit to it, but DOS was a huge part of Windows 95. They only got rid of it in OS/2, Windows CE, and Windows NT. (And Xenix, if you go back far enough.)