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IBm PC/AT - Mark Dean


Abstract: A summary of the key points or contents of a document or invention.

Assignee: The person or entity to whom a patent is assigned or granted.

Atari: A brand of early personal computers and video game consoles.

Backward compatible: (adjective) designed to be compatible with older versions or systems.

Bus: In computing, a communication system that transfers data between components inside a computer or between computers.

Commodore PET: A personal computer produced by Commodore International in the late 1970s.

Computer Science:  the study of computers and computing, including the theoretical foundations of computation and practical techniques for their implementation and application.

CPU: (abbreviation) Central Processing Unit, the primary component of a computer that performs most of the processing inside the computer.

Deactivated: Rendered inactive or disabled.

Direct memory access (DMA) controller: a hardware device that allows certain hardware subsystems within a computer to access system memory independently of the central processing unit.

Distinguished: Highly respected or acclaimed.

Dominated: To be the most influential or powerful force in a particular industry or field.

Electrical Engineering: (noun) the branch of engineering that deals with the technology of electricity, specifically the design and application of electrical systems and devices.

Expansion bus: an electronic pathway that connects external devices, such as printers or peripherals, to a computer.

Gigahertz: (noun) a unit of frequency equal to one billion cycles per second, often used to measure the speed of a computer processor.

Handshaking sequence: (noun phrase) a series of signals exchanged between devices in a computer network to establish communication and synchronize the transfer of data.

Industry Standard Architecture (ISA): The 16-bit internal bus of IBM PC/AT and similar computers.

Megahertz: (noun) a unit of frequency equal to one million cycles per second, often used to measure the speed of a computer processor.

Memory expansion: (noun phrase) the process of increasing the storage capacity of a computer's memory.

Microcomputer: (noun) a small computer with a microprocessor as its central processing unit.

Microcomputer: A small-scale computer designed for personal or individual use.

Modern systems: (noun phrase) more recent or up-to-date computer systems or technologies.

Non-proprietary: (adjective) not restricted or controlled by a particular company or individual.

Patent request: (noun phrase) a formal application made to a patent office for the grant of a patent for an invention.

Patents: Legal protections granted to inventors for their new inventions or discoveries.

Peripherals: External devices that connect to a computer, such as printers, mice, and keyboards.

Progenitor: The originator or ancestor of something.

Tandy Corporation's TRS-80: a line of home computers produced by Tandy Corporation, introduced in 1977.

Terahertz: (noun) a unit of frequency equal to one trillion cycles per second, often used to measure the speed of a computer processor.

Universal Serial Bus (USB): (noun phrase) a standard connection interface used to connect devices to a computer, commonly used for peripherals like mice and keyboards.

Wide system bus: (noun phrase) a communication pathway within a computer that allows for the transfer of data between components.

Mark Dean

Mark Dean was born in Jefferson City, Tennessee on March 2, 1957. A bright and energetic child, he often endured questions from grade school classmates, asking if he was really Black because Black people were not supposed to be that smart. Mark was an outstanding high school athlete as well as a straight A student. His success continued in college as he graduated at the top of his class with a Bachelor of Science in Electrical Engineering from the University of Tennessee in 1979.

The John Fisher Distinguished Professor in the Department of Electrical Engineering and Computer Science at the University of Tennessee

The Birth of the IBM- PC

At the dawn of the 1980s the then new personal computer industry, was dominated by the Commodore PET, Atari, Apple II, and Tandy Corporation's TRS-80. With $150 million in sales by 1979 and projected annual growth of more than 40% in the early 1980s, the microcomputer market was large enough for IBM's attention. Whether IBM had waited too long to enter an industry in which Apple and others were already successful was unclear.

Then IBM President John Opel (1974-85) was not among those skeptical of personal computers (PCs). He put executive William Lowe was in charge of developing a PC for IBM. Lowe proposed that the new computer have an open architecture, use non-proprietary components and software, and be sold through retail stores, all contrary to standard IBM practice.

Lowe got promoted.

Don Estridge became head of PC project. His key team members included Bill Sydnes, Lewis Eggebrecht, David Bradley, Mark Dean, and David O'Connor.

Mark Dean would be granted  three of the original nine patents that all PCs are based upon.

The IBM Personal Computer, commonly known as the IBM-PC, is the original version and progenitor of PC compatible machines. It was introduced on August 12, 1981.


IBM Personal Computer / AT

The IBM Personal Computer / AT (Type 5170) was presented to the public on August 14, 1984.

The AT used as a CPU (central processing unit) what was then the latest Intel processor (80286,) at initially 6 MHz and later 8 MHz…


The hertz (symbol Hz) is the unit of frequency. It is defined as one cycle per second.. It is used to describe the speeds at which computers and other electronics are driven. Hertz are commonly expressed in multiples kilohertz (103 Hz, symbol kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), and terahertz (1012 Hz, THz). Kilo equals one thousand, mega equals one million, giga equals one billion and tera equals one trillion.


…which made possible through the new protected mode of the CPU, a memory expansion to a 20MB hard drive.


A new feature was the 16-bit wide system bus in place of the previous 8-bit bus. The AT extended the slot by just a few contacts, and the new bus remained compatible with the previous 8-bit cards to be operated as well. This bus was developed by a team led by Mark Dean.


Get on the Bus


In a computer, a bus is a communication system that transfers data between components inside a computer, or between computers. Computer systems generally consist of three main parts: a CPU that processes data, memory that holds the programs and data, and I/O (input/output) devices such as the computer’s screen, a mouse and keyboard. Buses move data between all of these devices.

This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocols. An attribute generally used to characterize a bus is that power is provided by the bus for the connected hardware.


In most traditional computer architectures, the CPU and main memory tend to be tightly coupled. In most cases, the CPU and memory share signaling characteristics and operate in conjunction. The bus connecting the CPU and memory is often referred to simply as the system bus. An external bus, or expansion bus, is made up of the electronic pathways that connect the different external devices, such as printer etc., to the computer.

Early microcomputer bus systems were such that each pin of each connector is linked to the same relative pin of all the other connectors). It was possible to allow peripherals to communicate with memory by attaching adaptors in the form of expansion cards directly to the system bus. As the number of potential peripherals grew, using an expansion card for every peripheral became increasingly untenable. This has led to the introduction of bus systems designed specifically to support multiple peripherals. However, these high-performance systems are generally too expensive to implement in low-end devices, like a mouse. This has led to the parallel development of a number of low-performance bus systems for these solutions, the most common example being the standardized Universal Serial Bus (USB).

Industry Standard Architecture:

Industry Standard Architecture (ISA) became the term for the 16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286. This bus design was (largely) backward compatible with the older IBM PCs as well as IBM PC compatibles.

In 1984, Dean and team member Dennis Moeller filed U.S. Patent request No. 4,528,626.

In 1985 they were granted the patent.


Dennis L. Moeller & Mark E. Dean

Microcomputer system with Bus Control means for Peripheral Processing devices


Patent number: 4528626


Abstract: A microcomputer system includes a main processor, a memory and a direct memory access controller (DMA) effective to control direct data transfer between the memory and input/output devices on channels. Bus control for data transfer is switchable between the DMA and processor[s] by a hold request/acknowledge handshaking [the action of exchanging standardized signals between devices in a computer network to regulate the transfer of data] sequence between the DMA and processor. A control line from the channels is activated by a peripheral processing device on a channel when it wishes to gain control of the busses for data transfer. Logic means co-act with the handshaking sequence to determine which device gains control of the busses. This logic is responsive to the DMA address enable output (AEN), the hold acknowledge output of the main processor (HLDA) and the channel control line output (-MASTER). When all these are deactivated, control passes to the main processor, when AEN and HLDA only are activated, control passes to the DMA controller and, when all three are activated, control passes to the peripheral processing device.


Type: Grant                                             Filed: March 19, 1984


Date of Patent: July 9, 1985                   Assignee: International Business Machines Corporation


The ISA lasted until 1993 when it was replaced by more modern systems.

STEM Topic 23: Ohm's Law - Problem Set

Physics has its own vocabulary which at its root is not logical. Different aspects of classical physics which describes the day-to-day world which we live are named after the person who first wrote about them.

Ohm - Georg Ohm gave his name to the measure of electrical resistance. In the field of electricity, the resister is the machine that you to function. A very common resister is an electric light. You want to turn on the light. It is called a resister because it’s not going to shine unless you supply it is supplied with enough electrical energy to get it to shine.

Volts - Alessandro Volta gave his name to the measurement of the amount of electrical force that produces a flow of electrons in an electrical circuit. 

Ampere - Andre Ampere gave his name to the measure of the size of the flow of electrical charge.

Ohm’s Law

The current (amperage) in a circuit is equal to the potential difference (voltage) divided by the resistance of the circuit.   I=V/R   where I (amperes) is the current through the conductor, V is the voltage measured across the conductor and R is the resistance of the conductor.

Example: What is the resistance of a circuit if the voltage across it is 12 volts and the current passing through it is 3 amperes?


Answer: Using Ohm's Law (V = I* R), we can rearrange the formula to solve for resistance: R = V / I. Plugging in the values, we get R = 12 V / 3 A = 4 ohms.

  1. If a resistor has a resistance of 100 ohms and a current of 0.5 amperes passes through it, what is the voltage across the resistor?

  2. If a circuit has a resistance of 20 ohms and a voltage of 100 volts is applied across it, what is the current flowing through the circuit?

  3. The voltage across a circuit is 24 volts, and the resistance is 6 ohms. What is the current flowing through the circuit?

  4. A resistor has a resistance of 50 ohms, and the current passing through it is 2 amperes. What is the voltage across the resistor?

  5. A circuit has a voltage of 36 volts, and the current passing through it is 6 amperes. What is the resistance of the circuit?

  6. The current passing through a circuit is 0.8 amperes, and the resistance is 10 ohms. What is the voltage across the circuit?

  7. A resistor has a resistance of 120 ohms, and the voltage across it is 60 volts. What is the current passing through the resistor?

  8. A circuit has a resistance of 5 ohms, and the voltage across it is 15 volts. What is the current flowing through the circuit?


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