Analog and Digital Computers

Key Concepts

Analog is infinite Measurements such as voltage or temperature effectively have and infinite set of possible values. Digital, by contrast, is fixed at two (2) distinct possibilities Digital signals are best suited for modern computers Creating circuits to use digital signals and store binary values is a core component of modern computer architecture

Introduction

Humans developed devices to complete tasks (everyday and labor-intensive) 1) faster, and 2) reliably. As new materials and technologies become available (and cost-effective), these devices are upgraded or replaced.

Technological Advancements

It was left to people with rocks and sticks to turn and prepare soil for planting crops

As animals were domesticated, a work animal pulling wooden tools could prepare soil for planting quicker and more consistency that a group humans with shovels

As humans refined metals, the tools were replaced with steel plows

The creation of engines saw the mass replacement of work animals with tractors

Each stage of this brief (and overly-simplified) history of human agriculture improves speed, reliability, or both

Computers evolved in a similar way, starting as people with special skills and training to tally or calculate numeric values. Likely driven by trade and the development of money, sellers and buyers wanted to know the value and quality of products, along with the changing value of currency they were using

Fast-forward to today's high-speed stock market trading computers, considering thousands of variables to decide to buy or sell in the market

Analog Computing Devices

Analog

Analog, in the computer context, means signals or data represented by values that have a continuous and infinite number of variations

i.e.: The number of unique values between 0 and 1

Quick Question: Choose One Which of the following is made up of analog values?
A. A light switch	B. The tension of a spring
C. The number of students in our class this semester	D. State of a traffic light

Until relatively recently, computers were not digital devices. They were mechanical and electrical analog systems. These systems use mechanical or electrical motion to represent information

Mechanical Analog Systems

Gears and springs could be constructed to retain states and move to different states in a pre-determined sequence.

These Mechanical Computers could be built to perform a wide varies of tasks. The complexity of these systems were driven by the difficulty of the tasks they performed

Mechanical computers were typically single-calculate (Specific-Purpose) computers. Changing the "program" meant swapping out gears, springs, and levers for a different set

More complex systems required special training to operate, maintain, and repair

Predicting the Tides with Torque

Nordsieck's Machine

UCLA's 1948 Mechanical Computer from Gizmodo.

Things to note

As seen in this video, electricity is used to turn shafts to move gears as needed

Also, the "program" is changed by swapping gears and shafts

Electrical Analog Systems

In the 1930s and 1940s, humans were able to make and control electricity to a highly precise level. With improved electrical switches, resistors, and capacitors; mechanical systems in analog computers were replaced with electrical current to represent states and changes in states

While electricity was used in Mechanical Computers, the power was used to turn shafts and move gears. True Electrical Analog computer systems use electricity in place of the gears, to represent states and changes in the calculations Analog Goes Electronic

Electric circuits replaced springs and gears with a faster and more reliable means of computing. Failure rates and normal wear-and-tear issues were minimized by removing mechanical systems

Electrical computing systems also made it easier to modify "programs"

Analog Computer Timeline

CHM Analog Computers

Digital Computing Devices

Further advances in electronic technology drove the next major advance in computers...Vacuum Tubes. While eventually replaced with transistors, vacuum tubes allowed computers to control electricity with electricity. Coupled with control circuits, digital computers could now be programmed and run using electricity to perform logical operations and maintain data between steps

Digital

Digital, in the computer context, means signals or data represented by values that have a finite set of possible values. The possible values for a digital system are finite, and do not have "fractional parts"

Digital computers are based on the binary (base 2) number system, where the only single-digit values are 0 and 1

i.e. the number a values between 0 and 1 in the whole number system

First Electrical Digital Computer

ENIAC (Electronic Numerical Integrator And Computer), built between 1943 and 1945—the first large-scale computer to run at electronic speed without being slowed by any mechanical parts. ENIAC

Vacuum tubes were replaced with Transistors in the late 1950s. Based on the semi-conducting nature of silicon, transistors are able to reliably represent digital values (0 or 1) using electricity (as we recall, an analog medium). They were a simple replacement for vacuum tubes as they perform the same type of function

Transistors were, however, cheaper, more energy-efficient, and far more reliable than vacuum tubes

Quick Question: Choose One Which of the following is made up of digital values?
A. The tension of a spring	B. Your current interest level in this reading
C. Pressure you can apply to a car's break pedal	D. Number of students on this class's Wait List

Conclusion

Analog signals have an infinite number of possible values. Each may be a tiny bit different that the next, but they are measurably different.

Digital signals have a fixed number of values, two (2). Digital signals are well suited for electronic circuits and can easily represent binary values.