smiling face Windows 95 InternalsPentium chip

As compared to windows 3.1, windows 95 comes with more built-in capability.  They include improved networking, a better kernel, superior multitasking, access to more memory  as well as better GUI (graphical user interface).

Anatomy of the Operating System
One of the main job of an operating system is to run applications and make sure that they function properly.  The architeture of Wndows 95 is given below.

API's under Windows 95
When windows 3.0 was first introduced, it was adapted to the 286 processor architecture.  As the 286 is a 16-bit processor, the possible set of commands that a program could enter was called Win16 API.  With the introduction of 32-bit processors, Windows 95 contains a newer API known as Win 32 API.  Since there are already thousands of older windows programs in the market that are perfectly functional, Windows 95 must support these older programs if not nobody will purchase it.  Hence, Windows 95 comes with both Win 16 and Win 32 API as well as a DOS-compatible API.

Kernel Modules

Kernel 16 and 32
Kernel16 was provided to maintain backward compatibility so as to support older 16-bit programs.  For the 32-bit programs, kernel32 was used instead of kernel 16 to fully harness the power of 32-bit computing.

GDI (Graphical user interface)
The GDI primarily acts as one of the kernel's helper program to take care of the graphical things in Windows 95.  Like the kernel, it exists in two forms GDI16 and GDI32.  whenever you put a bitmap on the screen, your request is channelled through GDI.  Areas under its control include bitmaps, colour, curcurs, icons,fontsand graphical objects.

User 16 and 32
The user interaction with the window boxs such as clicking a button, choosing from list boxs, and so on are handled by the User module.  As before it contains both a 16-bit and a 32-bit module.

Virtual Machine Manager (VMM32)
The VMM32 manages memory and provides support to the management of virtual memory.  It multitask DOS programs by creating multiple virtual PCs(vrtual machines) and they exploit a feature know as page mapping.  As an example, suppose a computer system has 32MB of memory.  The VMM32 can allocate memory from 10MB to 11MB to a DOS program.  Therefore the DOS program only sees 1MB of memory.  Whenever the DOS program tried to access memory let say memory location 600, the VMM32 will automatically map the memory adress by adding 10MB to the memory location.

Virtual Device Drivers (VxD's)
A progra, communicates with a piece of hardware such as a modem or graphics card by means of input/output addresses ( I/O addresses).  They are similar to memory addresses except that I/O addresses access I/O devices instead of memory.  A virtual device driver is a program that the operating system assigns to a particular I/O address.  For example,  a application program tries to access I/O address 100 which is assigned to the mouse driver.  Upon accessing the address, the mouse driver will cme into action, behaving like the original piece of hardware.

Memory Management under Windows 95
Security rings are used to protect memory space of a program so that they will not be altered by other unauthorised programs.  Ring 0 programs can protect memory in that they can allocate spaces of memory to particular programs and detect when an illegal program tries to access that particular block of memory, this invasion is known as a general protection fault, or a GP fault.  Ring 1 programs can also allocate memory but as long as they do not override a command of ring 0 program.  The same theory applies to the next ring level and so on.

Windows 95 only uses 2 rings, ring 0 and ring 3.  Only the  VMM and VxD's are in ring 0 and all the rest are in ring 3.
 

 
 
A Windows 95 pet trick, try this: 

1.  Right-click the Desktop, and choose New Folder. 
2.  Name it with the following "title": and now, the moment you've all been waiting for 
3.  Right-click on the folder, choose Rename, and rename it to: we proudly present for your viewing pleasure 
4.  Then rename it once more to The Microsoft windows 95 Product Team! 
5.  Then open the folder, and you'll see an animated creditrs screen, and it comes complete with music.

 
 
Crashing your machine 

1.  Open a DOS prompt. (Click on the start button, then programs and then the MS-DOS prompt) 
2.  At the prompt, type debug and press Enter. 
3.  You will see a dash in the MS-DOS window and this is debug's prompt.  At the prompt, type F 0:0 L ffff 0 and press Enter. 
4.  The system will hang.

 


  Back to last page
 
Reference:  The Expert Guide to Windows 95 by Mark Minasi