Introduction

The good old days

A computer system is more than just hardware and software, it is a philosophy or a vision about how users can interact with the computer and do tasks with it. In computer terms this philosophy or vision is known as a standard. So technically speaking when we talk about types of personal computers, we are also talking about standards. By the early 80s there were over 40 types of personal computers. 

Incompatibility was a major issue in those days. Each of these PCs were proprietary or closed systems meaning two things:

1. only authorized personnel by the parent company could build, service and repair the system
2. hardware and software designed for one system were incompatible for others.

Backward compatibility was not a high-priority; meaning that in most occasions newer systems were incompatible with older ones even from the same company! For users this meant their investment would be obsolete and the only thing they can do about it was buy a new system and adapt to its new philosophy, oops I meant to say standard ;)

The IBM-PC standard

All of this changed when the IBM-PC arrived. Unlike the competition, the IBM-PC had the following characteristics

1. Open-architecture: meaning other companies could develop hardware and software to enhance its capabilities.
2. Non-proprietary components: key components like the motherboard, CPU and operating system were supplied by other companies.
3. Backwards compatibility: software/hardware built for older PCs would work in newer systems

Since the IBM-PC used many non-proprietary components, in theory other companies could use them to build a compatible system or a clone that could run programs developed for the IBM-PC. Their was a catch, IBM had patented the piece of hardware/software needed to configure the system. This component was the BIOS (Basic Input Output System) and without it nobody could legally build an IBM-PC compatible system.

To make a long story short, a company known as Compaq was able to build a compatible BIOS that did not infringe IBM's patents. The PC compatible era arrived and with it the PC standard. The rest is history!

To PC or not to PC

As the PC standard grew in popularity, competing companies had to modify their personal computer strategies. In the modern world, one thing is certain: open standards are preferred over closed-systems. In order to survive, companies had to open their proprietary systems (at least to a certain level) and adapted one of the following strategies:

1. Evolve and modernize the proprietary system
   With this strategy, other companies can develop hardware to enhance the computer's capabilities. Open standards for hardware connectivity (example PCI and PS/2) are adapted for the purpose of facilitating development and reducing costs. It is not permitted to clone the system.
   
   
2. Semi-open the proprietary system.
   The company permits selected developers to clone the system under explicit contracts which usually indicates: a) the parent company can terminate the contract and b) royalties must be paid.  
   
   
3. Open the proprietary system.
   Company permits cloning their system.
   
   
4. Adapt to an existing open-platform.
   The company phases out the hardware and adapts the operating environment (OE) to the PC standard or some other open-system architecture.
   
   
5. Phase-out the entire system.
   Company adapts to another standard. Example: PC clone running Microsoft Windows.
   
   
6. Retire from the market

The Alternatives

The table below list personal computers and operating environments that have survived or arrived during the PC clone era.

1. The systems
   1. Introduction
   2. PC or not PC
   3. The alternatives
      1. Table of systems