Personal computers

Computer security as a discipline was first studied in the early 1970s, although the issues had influenced the development of many earlier systems such as the Atlas system and Multics. Unfortunately, many of the early seminal papers are often overlooked as developers (and sometimes researchers) rediscover problems and solutions, leading to wasted time and development effort.

We are identifying seminal papers in the field of computer security, synopsizing them, and putting them on a series of CD-ROMs. Each CD-ROM will also contain synopses of each paper on it and a key word index to aid the reader in locating papers quickly. The papers will be in their original text processing form (if available) and Postscript and PDF.

This information has several types of value. First, it provides a historical record of how computer security developed, and why. It provides a resource for computer security education. Instructors will be able to assign sets of papers for students to analyze without having to assemble the resource materials. Lastly, it provides a resource for practitioners, to which they can turn to see what has been suggested (and tried) before, under what conditions, and with what results.

We are beginning with seminal papers, technical reports, and other documents up to the early 1980's. Our first effort will include only those documents without copyright restrictions, because we wish to put out the first CD quickly (as proof that the idea of the project has merit). We plan to include between 10 and 30 papers. Later CDs will contain the contents of the first, plus substantially more papers.
These web pages contain information about the project. Please explore them!

SOMETHING ABOUT COMPUTERS

Generally, a computer is any electronic data-processing device that performs tasks, such as mathematical calculations or electronic communication, under the control of a set of instructions called a program. Programs usually reside within the computer's main memory and are retrieved and processed by the computer's electronics, and the program results are stored or routed to output devices, such as video display monitors or printers. It communicates with other electronic devices to receive data, store and manipulate them (using mathematical and logical calculations specified in a sequence of instructions called a program), and transmit the results; e.g. accept a sequence of numbers typed in at a keyboard, and plot a graph of them on a visual display unit, or monitor.

Computers are now familiar at work, home, and school, as desktop personal computers (PCs). They also exist as very small devices called microprocessors, to control electronic equipment and machinery, e.g. car engines; and as much larger devices such as supercomputers, used to model and predict weather, earthquakes, nuclear explosions, etc.
The heart of today's computers are integrated circuits (ICs), sometimes called microchips, or simply chips. These tiny silicon wafers can contain millions of microscopic electronic components and are designed for many specific operations: some control an entire computer (CPU, or central processing unit, chips); some perform millions of mathematical operations per second (math coprocessors); others can store more than 16 million characters of information at one time (memory chips).
Computer Types
General-purpose computers, such as personal computers and business computers, are very versatile because they can accept new sets of instructions. Each new set of instructions, or program, enables the same computer to perform a different type of operation. For example, one program lets the computer act like a word processor, another lets it manage inventories, and yet another transforms it into a video game.

Embedded
Special-purpose, or dedicated, computers are designed to perform specific tasks. Their operations are limited to the programs built into their microchips. An embedded system is dedicated to one specific task. They are special purpose systems. These microprocessors are the basic components of electronic calculators and can be found in many other electronic products, including cameras, digital watches, and automobiles. These computers are the basis for electronic calculators and can be found in thousands of other electronic products, including digital watches (controlling timing, alarms, and displays), cameras (monitoring shutter speeds and aperture settings), and automobiles (controlling fuel injection, heating, and air conditioning and monitoring hundreds of electronic sensors). Embedded systems typically have their programs stored in ROM as opposed to auxiliary storage and RAM. These programs are referred to as firmware - a combination of software and hardware.

Microcomputers
This a computer which uses a microprocessor as its CPU.

Notebook
Although some general-purpose computers are as small as pocket radios, the smallest class of fully functional, self-contained computers is the class called notebook computers. These usually consist of a CPU, data-storage devices called disk drives, a liquid-crystal display (LCD), and a full-size keyboard--all housed in a single unit small enough to fit into a briefcase.

Desktop PCs
Today's desktop personal computers, or PCs, are many times more powerful than the huge, million-dollar business computers of the 1960s and 1970s. Most PCs can perform from 16 to 66 million operations per second, and some can even perform more than 100 million. These computers are used not only for household management and personal entertainment, but also for most of the automated tasks required by small businesses, including word processing, generating mailing lists, tracking inventory, and calculating accounting information.

Minicomputers
These are systems designed for multi-user access from several terminals. Varies from processing power from a very powerful micro to a small mainframe. Minicomputers are fast computers that have greater data manipulating capabilities than personal computers and can be used simultaneously by many people. These machines are primarily used by larger businesses to handle extensive accounting, billing, and inventory records.

Mainframes
Supports hundreds of of terminals for multi-user access. Large amount of primary and auxiliray storage. Mainframes are large, extremely fast, multi-user computers that often contain complex arrays of processors, each designed to perform a specific function. Because they can handle huge databases, can simultaneously accommodate scores of users, and can perform complex mathematical operations, they are the mainstay of industry, research, and university computing centers.

Supercomputers
These are the fastest and most expensive systems. Although they are not multi-user machines, they are used when a vast amount of processing is to be done. The speed and power of supercomputers, the fastest class of computer, are almost beyond human comprehension, and their capabilities are continually being improved. The most sophisticated of these machines can perform nearly 32 billion calculations per second, can store a billion characters in memory at one time, and can do in one hour what a desktop computer would take 40 years to do. Supercomputers attain these speeds through the use of several advanced engineering techniques. For example, critical circuitry is supercooled to nearly absolute zero so that electrons can move at nearly the speed of light, and many processors are linked in such a way that they can all work on a single problem simultaneously. Because these computers can cost millions of dollars, they are used primarily by government agencies and large research centers.
Processing
A computer is a general-purpose machine that processes data according to a specific set of instructions. The instructions the computer uses are either stored permanently (in read-only memory, or 'ROM') or temporarily (in random-access memory, or 'RAM'). The computer and the equipment attached to it ('peripherals') are called hardware. The instructions the computer receives are called software. A set of instructions grouped together to perform a certain task is called a program.

Input and Output
The computer receives input through the keyboard or another input device. This input is transferred into memory (RAM), and then processed by calculating, comparing, or copying it. The computer outputs the results of the processing, usually on the screen, onto a disk, or over a communications channel.

Computer Architecture
Abstractly, the essential elements of a computer comprise:-
• a central processing unit (CPU);
• memory;
• input and output devices.
Almost all personal computers, workstations, minicomputers, and mainframes are based on the von Neumann design principle:
1. a single central processor;
2. a single path between the central processor and memory;
3. program is stored in memory; and
4. central processor fetches, decodes, and executes the stored instructions of the program sequentially.

A program is input into memory, and the CPU executes the instructions in the program, inputting data as needed, and outputting the results.
The CPU is the key part of a computer because its operational speed predominantly determines the speed of the computer as a whole. The CPU and fast memories are implemented with transistor circuits.
The memory stores programs and the initial, intermediate, and final computational data.
Programs are often activated and operated in a graphical user interface using the mouse to click on buttons or pull down menus.

Data Representation and Memory
Digital computers operate on data represented as binary numbers, such as 0, 1, 10, 11, 100, 101, 110, 111, ... (0, 1, 2, 3, 4, 5, 6, 7, ...). All data, whether in the form of magnitudes, text, pictures, sound, symbols, or calculus (such as integration and differentiation), are represented as binary numbers in a digital computer. Any type of data can be processed by addition, multiplication, comparison, or other simple operations by the ALU.
A "1" in binary is evaluated as an ON switch in the electronics. A "0" in binary is evaluated as OFF switch in the electronics. This value can also represent another meaning: a "1" in binary is TRUE and "0" is FALSE. Through these values you get binary logic, which allows a computer to actually "compute".
In a binary number with p positions, each position is occupied by either 1 or 0. 1 in the rightmost position represents 1 (i.e., 20), 1 in the second position from the right represents 2 (i.e., 21), 1 in the third position represents 4 (i.e., 22), and so on, and 1 in the pth position means 2p - 1. Thus, the binary number 101 is 1 x 22 + 0 x 21 + 1 x 20 --that is, decimal number 5.

Data are stored in a computer as binary digits, or bits. If a binary number consists of n positions, it is said to be an n-bit number. Eight consecutive bits is called a byte. Therefore, a binary number of 16 bits has 2 bytes, a binary number of 32 bits has 4 bytes, and so on.
One byte is enough information to store one alphanumeric character (e.g. letter or decimal digit). A kilobyte is 1024 bytes, a megabyte is 1024 kilobytes (1,048,576 bytes), and a gigabyte is 1024 megabytes (1,073,741,824 bytes).

Each location in a memory is assigned a unique numeric address, by which the location is accessed. Data stored in each memory location consists of a fixed number of bits. This number is usually a power of 2 -- i.e., 4, 8, 16, 32, or 64 bits); such a binary sequence is called a memory word, or simply word.
The physical memory of a computer is either random access memory (RAM), which can be read or changed by the user or computer, or read-only memory ( ROM), which can be read but not altered. Computer chips hold memory, as do floppy disks, hard disks, and CD-ROMs (compact discs).
Operating Systems
There is one special program called the operating system (OS) which manages the computer's operations, controlling devices and overseeing other programs, called applications. It stores and manages data and controls the sequence of the software and hardware actions. When the user requests that a program run, the operating system loads the program into the computer's memory and runs it. Popular OSs include Windows by Microsoft, UNIX, and the Macintosh OS.

Networks
Computers can communicate with other computers through a network to exchange data and share software and hardware resources.
Local area network (LAN)
consists of several PCs or workstations connected to a special computer called the server. The server stores and manages programs and data. Mainframe computers and supercomputers are usually connected to PCs, workstations, or "dumb" terminals used only to enter data into, or receive output from, the central computer.
Wide area networks (WANs)
Computers can connect to these networks to use facilities in another city or country. The largest WAN is the Internet.
Computers are more often also being equipped with a modem for connecting to the Internet and 'surfing' the WWW. The WWW is a system of information accessed through the Internet.

Alan Turing was a British mathematician who conceived of a machine that could compute by reading and writing an infinite tape according to some simple instructions and state transitions. From this he was able to show the existence of uncomputable functions. He played a significant rôle in cracking German codes during World War 2, and proposed a test for machine intelligence.

Database
A database is an information set organized for flexible searching and utilization. There are a wide array of databases, from simple examples such as simple tabular collections to much more complex models such as the relational model. The types of database are distinguished by many characteristics. One commonly used characteristic is the programming model associated with the database. Several models have been in wide use for some time.

Graphics
The first computer graphics were the output of text and numbers on electronic displays, though computer graphics today typically refers to creating images and not text. This field can be divided into two general areas: real-time rendering, and non real-time rendering. Development in computer graphics was first fueled by academic interests and government sponsorship. However, as real-world applications of computer graphics(CG) in broadcast television and movies proved a viable alternative to more traditional special effects and animation techniques, commercial parties have increasingly funded advances in the field.

Home Computers
This article discusses the early commercial computers that tended to be used in the home rather than for commercial purposes - during the 1980s. This breed of computer largely died out at the end of the decade due to the rise of the IBM PC compatible personal computer.

Internet
The Internet is a vast international public communications network that interconnects thousands of small and large networks so that they work as a single network to permit communication between any two connected end points. A world-wide collection of computer networks, connecting government, military, educational and commercial institutions, as well as private citizens to a wide range of computer services, resources, data and information. The WWW is built on the Internet.

Microsoft
Microsoft Corporation is the largest private-sector computer software producer in the world, headquartered in Redmond, Washington (a suburb of Seattle). The company was founded in 1975 by Bill Gates and Paul Allen to develop and sell BASIC interpreters.

Personal
A personal computer (PC) is an inexpensive microcomputer originally designed to be used by only one person at a time. The earliest known use of the term was in New Scientist magazine in 1964, in a series of articles called "The World in 1984". In "The Banishment of Paper Work," Arthur L. Samuel of IBM's Watson Research Center writes, "While it will be entirely feasible to obtain an education at home, via one's own personal computer, human nature will not have changed."

Programming and Software
Software is the various kinds of programs used to operate computers and related devices. A program is a sequence of instructions that tells a computer what operations to perform. Programs can be built into the hardware itself, or they may exist independently in a form known as software. Hardware describes the physical components of computers and related devices.

Computer Science
Computer science is the study of computers and their applications, in all aspects, as well as the mathematical structures that relate to computers and computation. Only in the last third of the 20th century has computer science been recognized as a separate discipline and developed its own methods and terminology. It has roots in electrical engineering, mathematics and linguistics, and is a blend of science, engineering and art. Computer science emphasizes the eternal truths of software and computers while Software engineering emphasize practical applications of software. In some ways they are the flip sides of the same coin. In other ways they are totally different.

Alan Turing
Alan Mathison Turing, b. June 23, 1912, d. June 7, 1954, was a British mathematician who conceived of a machine that could compute by reading and writing an infinite tape according to some simple instructions and state transitions. From this he was able to show the existence of uncomputable functions. For example, no program can determine if any arbitrary program will terminate. He played a significant rôle in cracking German codes during World War 2, and proposed a test for machine intelligence.