JK FILP-FLOP

The JK flip-flop augments the behavior of the SR flip-flop (J=Set, K=Reset) by interpreting the S = R = 1 condition as a "flip" or toggle command. Specifically, the combination J = 1, K = 0 is a command to set the flip-flop; the combination J = 0, K = 1 is a command to reset the flip-flop; and the combination J = K = 1 is a command to toggle the flip-flop, i.e., change its output to the logical complement of its current value. Setting J = K = 0 does NOT result in a D flip-flop, but rather, will hold the current state. To synthesize a D flip-flop, simply set K equal to the complement of J. The JK flip-flop is therefore a universal flip-flop, because it can be configured to work as an SR flip-flop, a D flip-flop, or a T flip-flop. NOTE: The flip flop is positive edge triggered (Clock Pulse)

A circuit symbol for a JK flip-flop, where > is the clock input, J and K are data inputs, Q is the stored data output, and Q' is the inverse of Q.

SR FILP-FLOP

The fundamental latch is the simple SR flip-flop , where S and R stand for set and reset respectively. It can be constructed from a pair of cross-coupled NOR logic gates. The stored bit is present on the output marked Q.
Normally, in storage mode, the S and R inputs are both low, and feedback maintains the Q and Q outputs in a constant state, with Q the complement of Q. If S (Set) is pulsed high while R is held low, then the Q output is forced high, and stays high even after S returns low; similarly, if R (Reset) is pulsed high while S is held low, then the Q output is forced low, and stays low even after R returns low.

The symbol for an SR latch.

D FLIP-FLOP

The Q output always takes on the state of the D input at the moment of a rising clock edge. (or falling edge if the clock input is active low)[6] It is called the D flip-flop for this reason, since the output takes the value of the D input or Data input, and Delays it by one clock count. The D flip-flop can be interpreted as a primitive memory cell, zero-order hold, or delay line.

These flip flops are very useful, as they form the basis for shift registers, which are an essential part of many electronic devices. The advantage of the D flip-flop over the D-type latch is that it "captures" the signal at the moment the clock goes high, and subsequent changes of the data line do not influence Q until the next rising clock edge. An exception is that some flip-flops have a 'reset' signal input, which will reset Q (to zero), and may be either asynchronous or synchronous with the clock.

D flip-flop symbol

Fourth Generation Computers (1971 - Present)

The 4th generation computers are marked by the usage of integrated circuits and microprocessors.
As the years passed, computers became smaller and smaller, and their prices became lower and lower. Millions of components could be placed onto a single silicon chip. Computers became more efficient and more reliable, and they could perform more and more operations.
They began to catch the eye of the general public, and soon more sophisticated software and equipment were designed.
Networks became commonplace, and the whole world was connected by the Internet and by the World Wide Web.

1971: Intel 4004

The Intel 4004 is a 4-bit microprocessor. Microprocessors are integrated circuits that contain thousands and millions of transistors. The Intel 4004 is the essence of a general-purpose computer. It performed many input and output operations and was also able to read and respond to instructions stored in its memory. The microprocessor was able to group all the components of a computer, including the CPU, or central processing unit, the memory, and the input and output controls on a single chip. The Intel 4004 was first used on March 2, 1972 in the Pioneer 10 space probe.

1972: Intel 8008

In November of 1972, Intel came out with a new 8-bit processor, known as the Intel 8008.

1974: Intel 8080

The Intel 8080 is a re-engineered version of the Intel 8008. It had a larger and more versatile instruction set.

1975: Altair 8800

The Altair 8800 is often called the first personal computer. It was developed by Micro Instrumentation Telemetry Systems (MITS), a small company centered in Albuquerque, New Mexico. The Altair 8800 was sold as an electronic hobbyist kit for only $397. The Altair computers were of blue box-shaped machines with dimensions of 17 inches by 18 inches by 7 inches. They were very simple, and so in complex that they did not even have a keyboard or display. These computers did not even have enough memory to perform any useful tasks. The Altair 8800 used an Intel 8080 microprocessor and had switches on the front panel for input and rows of neon light bulbs for the output. These lights were known as light-emitting diodes, or LEDs. It is hard to believe, but it is the in-complexity of the Altair 8800 that helped to establish the personal computer industry. Because of its limitations, the Altair allowed for other companies to refine the computer and do develop more software.One such example of software developed for the Altair 8800 is the development of a version of the programming language, BASIC, for this computer. BASIC was a popular programming language used by many minicomputers and other machines. It was simple and easy to develop. The BASIC programming language designed for the Altair was developed by Bill Gates and Paul Allen, the cofounders of the software giant, Microsoft. Microsoft was not the only company to develop programs and software for the Altair. In fact, more and more companies began entering the software business by developing software and peripherals for the Altair 8800. The personal computer soon became a business machine.

1976: CP/M

Developed in 1976 by Gary Kildall of the company Digital Research, CP/M was a popular operating system that made it possible for one version of a program to run on a variety of computers.



1976: Apple II

Apple Computer was started by Stephen G. Wozniak and Steven P. Jobs. In 1976, the company introduced the Apple II to the personal computer market. The Apple II was appealing to consumers, because of its abundance of appealing software and with its well-written manuals. The computer also was able to be plugged into a standard household outlet.

1979: VisiCalc

VisiCalc, standing for Visible Calculator, is the first personal computer financial analysis tool. This software was developed by Harvard business graduate Dan Bricklin and programmer Bob Frankston. VisiCalc was able to give immediate responses to "what if" questions. It turned personal computers like the Apple II into business machines and was an overnight success.

1981: Osborne I

Invented by Adam Osborne, the Osborne I was the world's first portable computer. By today's standards, it wouldn't exactly be portable because of the fact that it weighed a whopping 24 pounds. The computer had a 5-inch display, 64 kilobytes of memory, a modem, and two 5-¼ floppy disk drives. It sold for $1,795.

1981: DN100

The DN100 was the first workstation. It was developed by Apollo Computers, and it had much more power than some of the minicomputers around at the time. It was also available for a comparatively low price.

1983: Lisa

The Lisa, invented by Apple Computer, was the first PC to use graphical user interface. It had one MB of RAM and had a 12 inch black and white monitor. The Lisa had two 5-¼ floppy disk drives, 5 MB of profile hard drive, and it used a Motorola 680000 microprocessor. Unfortunately, Lisa was never successful because of its high price and slowness.


1983: Microsoft Word

The powerful word processor used in nearly every household today, Microsoft Word, makes its debut as "Multi-Tool Word" in 1983. Microsoft Word can be used for all sorts of word-processing tasks and for creating all sorts of text documents. It is now widely used and widely distributed. Two years after introducing Word to the general public, the company, Microsoft, then introduces its now-famous Microsoft Windows.

1983: Compaq Computer Corporation

In 1983, Compaq Computer Corporation built a portable computer, a clone of the IBM PC. Looking like a sewing machine, Compaq's computer weighed 38 pounds (13 kg). Amazingly, this was considered lightweight at the time! The Compaq personal computer was compatible with the IBM personal computer, and could use software designed for IBM computers. It was an immediate success, bringing in $110 million in its first year of sales.

1984: Apple Macintosh

The Apple Macintosh was designed by Apple Computer and had many of the same features as the Lisa computer, also designed by Apple. The main goal of the Macintosh was to create a computer that would accommodate as many as Lisa's features as possible at a much lower price. It slimmed down on Lisa's high-level languages, and it also used the minimum number of chips and circuit boards needed to operate efficiently. It had graphical user interface and a user-friendly design. The computer contained software in which users could point and click with a mouse. For example, there was MacPaint and MacWrite. The Apple Macintosh used a 32-bit Motorola 68000 central processing unit and had a 9 inch black and white screen. It was first sold for $2,500.

1985: Microsoft Windows Operating System

Microsoft makes its debut with its first windows operating system. The new Apple Macintosh had shadowed the personal computers, and now the Microsoft Windows Operating System gives PC compatibles the same capacities as the Macintosh. In future years, Microsoft continued to improve its operating system, and the company soon became the dominating software company for PC compatibles.

1985: C++ Programming Language

C++ is a general-purpose programming language that was derived from the C programming language. It had many of the C's capabilities, such as the ability to efficiently deal with objects such as bits, bytes, and words and the ability to efficiently implement user-defined type.

1989: SimCity

In 1989, the popular computer game, SimCity, was developed by Will Wright and Jeff Braun. SimCity was a video game that used simulators. The player starts with a plot of land, and he or she must build houses, buildings, roads, and other objects to ensure the survival of the city. The player must provide health care, education, and public services for the inhabitants of his or her city, and periodically, challenges presented themselves in the forms of natural disasters or monster attacks. The player was forced to make decisions that would best benefit their city.

1990: Windows 3.0

In 1990, the software giant Microsoft released a new version of Windows. Windows 3.0 was the first successful version of the software. It was user-friendly and it sported a new interface with new designs that allowed personal computers to support many images and other graphical applications. Windows 3.0 included programs such as Microsoft Word and Microsoft Excel, and it also allowed for many of these programs to be run simultaneously. It ran on an Intel 80386 microprocessor.

1996: Deep Blue

In 1996, IBM invents a supercomputer named "Deep Blue." Able to compute more than 100 million chess positions per second, Deep Blue challenged the reigning world chess champion Garry Kasparov to a chess match. Kasparov wins the match, with 3 wins, 2 ties, and 1 loss. This was the first time ever that a computer has beaten a reigning world chess champion. It brings up the question: will computers soon surpass humans in chess playing and in other aspects of intelligence?

Third Generation Computers (1964 - 1971)

The 3rd Generation Computers were generally much smaller in size than the 2nd and 1st generation computers.
This is because these newer computers made us of integrated circuits and semiconductors (a type of material that had the properties of an insulator and a conductor). 3rd generation computers also contained operating systems, which acted as overseers to the performance of a computer and which allowed computers to run different programs at once.
Another function of operating systems is to make sure everything is flowing smoothly inside the computer. The 3rd generation computers made the transition from transistors to integrated circuits and from punch cards to electronic computer systems.

1964-1965: IBM 360

The IBM 360 was introduced by IBM (duh!) in April of 1964, and was finally delivered in 1965. It was not actually a single computer, but was rather a family of six computers and their peripherals. These computers were all mutually compatible and all worked together. The first models of the IBM 360 used transistors, but later these computers made a transition from transistors to integrated circuits.

1965: PDP-8

The PDP-8 was a successor to the PDP-1. Because it was the first computer to successfully make use of integrated circuits, it was much smaller and cheaper compared to other computers available at the same time. When it first entered the minicomputer market, it sold for about $20,000. Five years later, this price was reduced to only $3,000. The PDP-8 was relatively simple in design-physically, logically, and electronically. It only had 4,096 words of memory, and its word length was only 12 bits. This machine became the first commercially successful minicomputer because of its reasonable cost, speed, and small size. Minicomputers are medium-sized computers that were much cheaper than the larger and bulkier mainframe computers.

1966: HP-2115

With the invention of the HP-2115, the company Hewlett Packard enters the computer business.

1969: UNIX

At the AT & T Bell Laboratories, programmers Kenneth Thompson and Dennis Ritchie developed a new type of operating system known as UNIX. UNIX is a multi-user operating system able to perform multiple tasks. In addition, UNIX is written in the C language, which allows it to be less machine-specific than other available operating systems. C was specifically designed for UNIX. Because UNIX used C, it was able to be used in any computer system. This was a big achievement at the time!

1970s: GUI

GUI (graphical user interface, pronounced gooey) was designed by the Xerox Corporation. GUI allowed users to be able to "point and click." In other words, the computer screen was designed to resemble a desktop. It had click-able folders, calculators, etc. which were represented by images known as icons. Users could click on these icons to move and manipulate the folders and other tools. GUI made using computers much easier and is currently found in modern-day computers.

Second Generation Computers (1956 - 1963)

The computers built in the 1950s and 1960s are considered the 2nd generation computers.
These computers make use of the transistors invented by Bell Telephone laboratories and they had many of the same components as the modern-day computer.
For instance, 2nd generation computers typically had a printer, some sort of tape or disk storage, operating systems, stored programs, as well as some sort of memory. These computers were also generally more reliable and were solid in design.

1957: FORTRAN

FORTRAN, an acronym for Formula Translator was the first successful programming language. This language used words and sentences instead of the binary machine codes that had been commonplace in computers prior to the 1950s. FORTRAN could be read by ordinary people with no previous programming experience or knowledge, and it made it easier for computers to be programmed. FORTRAN was extremely useful in that given a single statement, many instructions would be produced. FORTAN created programs that were just as good as those produced by human programmers. Not only was it one of the most successful programming languages ever, but it also dominated many other languages for years.

1959: COBOL

COBOL, the Common Business Oriented Language, was invented in 1959. This is a business programming language that allowed for computer programs to be easily read.

1960: PDP-1

DEC, or the Digital Equipment Corporation was founded by Kenneth Olsen and Harland Anderson in 1957. In 1960, DEC introduced the Programmed Data Processor, or PDP-1. The PDP-1 was a mainframe computer famous for its low costs. Compared to other computers that generally cost more than $1 million dollars, at "only" about $120,000 the PDP-1 was considered really cheap! The PDP-1 could be sold at such a low price because it did not contain many advanced peripherals and software. In other computers, these advanced systems amounted to nearly 80% of the computers' cost.

1961: IBM 1400 Series

The IBM 1400 Series were a major breakthrough for IBM. The first computer in this series is the IBM 1401. The 1401 was a computer system that used transistors instead of the vacuum tubes found in previous IBM computers. The system contained many peripherals, which included, among others, a new high-speed printer. This printer could print 600 lines per minute! The total cost of an IBM 1401 was $150,000. 12,000 of these computers were produced.

1962: SpaceWar!

Space War is the first interactive computer game. It was developed by MIT students Slug Russell, Shag Graetz, and Alan Kotok for the PDP-1 computer. In this game, players must battle against enemy spaceships and face obstacles like the gravity of the sun. The players used primitive joysticks to maneuver their ships. SpaceWar has helped to inspired future video games.

Late 1960s: Integrated Circuit

Introduced in the 1960s simultaneously by Texas Instruments and by Fairchild Semi-Conductor, the integrated circuit combines many tiny transistors and other electrical components onto a small silicon chip. It replaced the need for individual transistors. Later, these integrated circuits were refined so that one small chip could contain thousands of transistors, as well as other similar components. As more and more components were squeezed into a small silicon chip, the size of computers gradually decreased.

First Generation Computers (1940 - 1956)

Generally, the computers built during the World War II era are known as the first generation computers.

These are considered the first computers, and were extremely different from the computers we see today. Because the first generation computers were extremely difficult to program, they were designed for a specific task, and they never made it to the general market.

These primitive computers relied on vacuum tubes and magnetic drums. Vacuum tubes process data by allowing the passage of electrons while magnetic drums use magnetic material to store data. The 1st generation computers were also extremely slow. However, despite their great number of downfalls, these computers have gradually evolved into computers, as we know them today.

1939-1942: Atanasoff-Barry Computer

The Atanasoff-Barry Computer (ABC) was the first electronic computer. It was developed by physics and mathematics professor John Atanasoff and his graduate student, Clifford Barry. This computer used the binary system found in modern computers and its method for storing data is quite similar to that of the modern computer. However, in 1942, Atanasoff was recruited to the Naval Ordnance Laboratory to help with war research, and the ABC was never properly put into working order.

1941: Konrad Zuse-Z3A

German named Konrad Zuse invented the Z3, a computer used to design airplanes and missiles. It was the first program-controlled processor.

1943: Colossus

Built in December of 1943 in Bletchly Park (a research center a few miles north of London), Colossus is a computer specifically designed for code breaking. It was used by the British during World War II to break German coded messages.

1944: Harvard Mark I

Howard Aiken proposes the idea of a fully automatic computer in 1937. With the help of IBM, Aiken was able to develop the Mark I by 1944. The Mark I was about 50 feet wide and 8 feet tall, and it was able to handle 23 digit numbers. In addition to the four basic operations, addition, subtraction, multiplication, and division, the Mark I was also able to perform trigonometric and probability functions. To input data and instructions, the computer used paper tapes, which were merely toilet-paper-like rolls of punch cards. For output, the Mark I printed the results using two electric typewriters. The Mark I could perform simple addition problems in less than a second and simple multiplication problems in a second or so. However, for more complicated problems, the computer would require as long as a whole minute. The Mark I was known for being the first automatic computer. It used electromagnetic signals to move mechanical parts. Later, predecessors of the Mark I were introduced to the world, such as the Mark II and the Mark III.

1943-1946: ENIAC

In April of 1943, the building of the Electronic Numerical Integrator Analyzer and Computer (ENIAC) commenced. Developed by colleagues John Mauchley and J. Presper Eckert Junior and built at the University of Pennsylvania's Moore School of Electrical Engineering, ENIAC was the first general-purpose, all-electronic, programmable digital computer. It cost $400,000 to build and it occupied 50 feet by 30 feet of floor space. This humongous computer consisted of 18,000 vacuum tubes (used to process data), 70,000 resistors (used to resist the flow of electric current), 10,000 capacitors (the part of an electrical circuit used to store charge), 6,000 switches, and 1,500 relays (used to activate switches when changes in voltages occur). In addition, it weighed 30 tons and used up 160 kilowatts of electrical power. That's nearly enough to dim every single light in a city as big as Philadelphia! The initial purpose of the ENIAC was to compute the values for artillery range tables, but its first actual task was to make certain calculations for the construction of a hydrogen bomb. The giant computer made use of plug boards, through which its instructions were entered, and it also made use of conditional branching. Conditional branching gave the ENIAC flexibility, allowing it to execute instructions in different orders, based on the value of the data. The ENIAC also contained accumulators, special registers used to store data, and in addition the computer used a digital number system rather than the binary system used in modern computers today. Furthermore, the computer operated at extremely fast speeds and had the capability to perform 5,000 operations per second.
Although the ENIAC was a major breakthrough in the computing world, it also had its problems. For one thing, once a certain task was completed, it would take days to reprogram the computer so that another task could be performed. Every time the computer was completed an operation, it had to be re-wired and its program had to be changed. Because of the great complexities of the ENIAC, this could take many hours, and even days. Another liability of the ENIAC was that because there were so many tubes and components, there were many potential sources of breakdowns. It had to be continuously serviced, and it usually spent one-third of its time down for maintenance. The ENIAC was used from February 1946 until October 1955.

1945: EDVAC

John von Neumann (1903-1957), a mathematician and physicist at the Institute for Advanced Study in Princeton, played a key role in the development of the Electronic Discrete Variable Automatic Computer (EDVAC). The EDVAC was a successor to the ENIAC, and it had been designed to hopefully correct the weaknesses and problems of its predecessor. The EDVAC had a memory, which held the stored information and data. It was this stored memory that allowed for the EDVAC to be stopped and resumed at various times. The EDVAC also had a central processing unit (CPU), which can be found in many modern computers. The CPU of a computer is analogous to the brain of a person. Some of its duties include executing instructions and performing operations.

1944-1945: Plankalkul

Plankalkul ("Plan Calculus"), developed by Konrad Zuse, was the first real programming language. Plankalkul made use of structured data, in which the records in the database was, a mixture of alphabetic and numeric data. It also used conditional statements, which modified the execution of a program. However, Plankalkul was not generally known outside of Germany.

1947: Transistors

Transistors were first developed in 1947 by Bell Telephone laboratories. They replaced vacuum tubes, which were big, bulky, costly, and unreliable. Transistors are most often used to regulate the flow of an electrical current and to switch electricity on and off.

1948: SSEC

The Selective Sequence Electronic Calculator (SSEC) was developed by IBM. It occupied space 25 feet by 40 feet and used punch cards, punched tape, vacuum tubes, and relays. It could do 50 multiplications per second, but it was not successful because of its high cost. However, it was of some use. In 1969, it produced tables that were used to plot the course of the spaceship Apollo's flight to the moon.

1949: EDSAC

Maurice Wilkes was a mathematician and a physicist at Cambridge University in 1959 when, inspired by the creation of EDVAC, he designed the Electronic Delay Storage Automatic Calculator (EDSAC). The EDSAC was the first practical stored-program computer (a computer using its memory for the storage of data), although by today's standards, it would certainly be anything but practical. The EDSAC was humongous (it was smaller than the ENIAC though) and it contained 3000 tubes and used up 30 kilowatts of electric power.

1945-1951: Whirlwind

The Whirlwind computer is the result of a project conducted by Jay Forrester and Robert Everrett at MIT. Started in 1945, it took six years before the Whirlwind would be completed in 1951. Whirlwind was used as an aircraft trainer and flight simulator. Using a concept known as real-time control, Whirlwind was able to simulate flight conditions and to respond accurately to changes such as airspeed, altitude, as well as various other conditions.

1951: UNIVAC

The UNIVAC, or the Universal Automatic Computer, was developed in 1951 by John Mauchley and J. Presper Eckert Junior, the creators of the ENIAC. It was a commercial data-processing computer and was generally sold to governments or other commercial businesses, such as the United States Census Bureau and General Electric. In all, 48 of the machines were sold. Although not as big as the ENIAC, the UNIVAC was still humongous compared to today's computers. It weighed approximately 8 tons and occupied a space 14.5 feet by 7.5 feet by 9 feet. The machine was a stored-program computer and could store up to 12000 digits in its mercury delay line tubes. The UNIVAC had an operator keyboard and a console typewriter for input, and could print its results by a tape printer. One of the computer's first major achievements was its prediction of the outcome of the 1952 United States presidential election. The UNIVAC was right in predicting that Dwight D. Eisenhower would become the United State's next president.

1953: IBM 701

The IBM 701 was the first electrical computer. In three years, 19 of these machines were sold.

1954: IBM 650

The IBM 650 was the first mass-produced computer. Despite the fact that only 450 of these were sold in one year, a small number compared to today's statistics, far more of these were sold than any other machine before it. The 650 made use of magnetic drums, which allowed for fast access to stored material.

Definition of ASCII

ASCII stands for American Standard Code for Information Interchange.

Computers can only understand numbers, so an ASCII code is the numerical representation of a character such as 'a' or '@' or an action of some sort.

ASCII was developed a long time ago and now the non-printing characters are rarely used for their original purpose.
Below is the ASCII character table and this includes descriptions of the first 32 non-printing characters. ASCII was actually designed for use with teletypes and so the descriptions are somewhat obscure.

Extended ASCII

As people gradually required computers to understand additional characters and non-printing characters the ASCII set became restrictive. As with most technology, it took a while to get a single standard for these extra characters and hence there are few varying 'extended' sets.

The most popular is presented below: