No standard to go by
When Microsoft introduced Windows 95, it had an intention to bring everyone over to a single 32-bit platform. Unfortunately, many people were still deeply rooted in 16-bit Windows 3.1 and DOS applications. The solution was to make Windows 95 both a 16-bit native and a 32-bit surface operating system. While it appeared to be fully 32-bit on the outside, its core was a direct descendant of DOS-16. In fact, if you booted into DOS and typed "ver", you would've received a message informing you that the OS was DOS version 7.
Windows 98 came and went. Windows 98SE came too, but managed to stay much longer. Finally, Windows Millennium stepped into the spotlight but didn't offer much and in some cases, even decreased performance. Deep within its soul however, Windows Millennium was still based on much of the same technology that was used to create Windows 95 - only Windows Me did a better job of hiding its ugly guts.
On the workstation front, everything was 32-bit and IT managers were satisfied with Windows NT 4's simplicity and stability. However, is support for standard peripherals was lacking. Also, if you were a gamer, Windows NT was out of the question. Everything that had anything remotely related to multimedia performance like games, and audio, ran poorly on Windows NT - but for good reasons. To keep its stability going, Microsoft designed what's known as the HAL, or the hardware abstraction layer.
HAL to the king
The HAL exists in all Windows OSes based on the NT kernel. Simply put, the HAL is your barrier from bad device drivers. When a device driver on a Windows NT machine tries to access a hardware device, it sends calls to the OS, and then the OS passes it through the HAL which checks and validates the call. If all is safe and sound, penetration is permitted. For those aspiring to become elite programmers, the HAL controls pointers in program code. If a device driver uses a pointer to reference a memory address or a hardware address, the HAL will do the grunt work for the driver instead. It's like saying "point to where you want me to touch, but I'll do the touching." An interesting feature is that the HAL also corrects certain errors in memory made by drivers or programs. It's like having ECC (error correction and checking) right in the core. All your hardware devices are shielded by the HAL from malicious access and in the IT world where down-time costs millions, up-time is king.
Back and bluer than ever
Windows 9x doesn't come with a HAL because of the need for maximum performance. For gamers and enthusiasts, everything needs to happen as fast as possible so Windows 9x gives device drivers direct access to hardware at the lowest level. While leaving the hardware devices wide open for access is great for performance, it leaves them extremely vulnerable. It's up to the developers to program responsibly and take it upon themselves to make sure they hack out clean code that doesn't prone the system to failure. As we all know very well though, Windows crashes so often that even experienced users are afraid of doing anything remotely critical on a 9x machine.