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
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
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
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
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.