The CPU Evolved from a 'Brain' to a 'Heart' - Memories of the PC Dawn

Do you remember that excitement?

The 1980s. PCs back then were much larger than today's smartphones, slower, and above all, expensive.

Even so, boys and businessmen of that time were thrilled by the future unfolding beyond the CRT screen.
It felt as if props from a sci-fi movie had finally come within reach.

When talking about the evolution of the PC, the existence of the 'CPU' cannot be avoided.

Back then, we often described the CPU as the 'brain of the PC.'
However, looking back, I feel that the expression 'brain' alone does not capture the full extent of its dramatic evolution.

That is because, in that era, the CPU transformed from a mere calculator into a heart that drives a new civilization.

1. The Dawn: The Huge Role Played by a Tiny Chip

1.1 It All Started with a Small Stone

When people saw the first microprocessors that appeared in the early 1970s, such as the Intel 4004, everyone was astonished by the fact that a tiny silicon chip that could fit in the palm of one's hand performed the same work as the massive computers of the past.

The role of the CPU (Central Processing Unit) at the time was surprisingly simple.

Read instructions from memory, interpret them, execute calculations, and issue commands to other devices (keyboards and displays).
Repeating these four basic operations as fast as possible.
This was the entirety of the 'brain's' job.

However, because it became possible to execute these simple tasks at a speed humans could not imitate, 'software' such as spreadsheet programs and simple games began to function as practical tools.

It can be said that the CPU as hardware opened the door to the new concept of software.

1.2 From 8-bit to the 16-bit Shock

The evolution during the dawn of the PC was like a marathon condensed into a short period.

(1) The 8-bit Era (Representative examples: Z80, Intel 8080)

These supported early hobby PCs and business machines.
Memory in this era was limited to a maximum of 64KB, but even so, it felt like infinite possibilities to the users of that time.

The story of Federico Faggin and Masatoshi Shima, who developed the high-performance Z80, leaving Intel, symbolizes the independent spirit and enthusiasm of the engineers of that time.
Perhaps their competitive spirit accelerated the speed of evolution.

(2) The 16-bit Era (Representative examples: Intel 8086, 80286)

This was the decisive blow for the 'PC Revolution'.
The amount of information that could be processed at once doubled, and above all, the memory that could be handled expanded to the megabyte level all at once.

This evolution made the ideas of a Graphical User Interface (GUI) and full-scale multitasking operating systems a reality.
Inside a small box, it became possible to perform multiple tasks simultaneously.

2. Evolution into a Multifunctional 'Heart'

How did the CPUs of the dawn era become the prototypes for modern high-performance processors?
If we organize their roles and evolution, their transformation becomes clear.

2.1 Expansion and Specialization of Computing Power

Early CPUs were mainly for simple integer calculations.
However, as the development of more complex applications, especially scientific and technical calculations and 3D games, progressed, the need for floating-point arithmetic increased.

Initially, this specialized calculation was left to a separate chip called a numeric coprocessor (e.g., Intel 8087).

It was like a partner sitting right next to the CPU, taking over the tedious calculations.

Eventually, this became integrated inside the CPU.
This reduced the time taken for data exchange and achieved a dramatic increase in speed.

It became a reliable entity that took on not only main calculations but also complex specialized fields.

2.2 Cooperation with the Outside and Efficiency of Information Flow

Even if CPU performance increases, it is meaningless if data reaches the CPU from memory slowly.

Therefore, the introduction of cache memory began in earnest from the dawn era.
This is a technique where data that the CPU is likely to use next is kept close at hand (very fast memory near the CPU) in advance.

The 'secondary cache,' which was initially outside the CPU, was later incorporated into the CPU chip as 'primary cache'.
This is also an evolution in the design philosophy of information flow, regarding how the CPU pays attention to the outside world and how efficiently it gathers information 'at hand' to avoid interrupting work.

2.3 Multitasking and Ensuring Security

A major evolution seen in the Intel 80286 and later 16-bit CPUs was the introduction of protected mode.

This may be a surprising fact, but CPUs before that always carried the risk that if one program went out of control, it would drag down all other programs and the OS itself, causing the entire system to crash.

It was as if everyone in a single room could freely enter anyone else's room at any time.

Protected mode is a feature that gives each program its own 'protected area,' preventing others from entering or damaging it without permission.

It is precisely because of this evolution that we have been able to obtain the stable multitasking environment we have on today's PCs, where we can listen to music and create documents while keeping a browser open.

3. The Afterglow of Evolution

The evolution of CPUs in the early days was not merely a 'pursuit of speed.'

It was an evolution of the design philosophy of the comprehensive computing environment itself, including 'integration of specialized functions,' 'optimization of information distribution,' and 'stability of operations.'

The CPUs of those days were small stones holding the potential of the future.
And now, chips that have inherited those genes support everything in our business, lives, and communication.

It might be good to occasionally remember that the enthusiasm of those days and the dreams of the engineers who bet on those small chips are still moving the world today.

Book Introduction

・Our PC 30-Year History: Nippon PC Chronicle Kindle Edition
　Edited by SE Editorial Department
　Shoeisha (2012/12/20)
　A Japanese PC history textbook that looks back with photos. It explains the major changes in PCs over more than 30 years in two parts, using many photos and touching on social conditions to make the flow of time easy to understand. Part 1 is dedicated to explaining topics by era, incorporating 'testimonies (turning points)' from developers and people involved at the time to reveal behind-the-scenes development stories. Part 2 summarizes PC architecture and other topics by theme.
(* Book descriptions, etc., are generally based on the descriptions on the linked site (Amazon). Please refer to the link for detailed content.)

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