Biomedical subjects
Publications and source records attributed to L L Wear.
We have looked at general descriptions and illustrations of several software development tools, such as tools for prototyping, developing DFDs, testing, and maintenance. Many others are available, and new ones are being developed. However, you have at least seen some examples of powerful CASE tools for systems development.
There have been significant advances in the way we develop software in the last two decades. Many companies are using the new process oriented approach to software development. Companies that use the new techniques and tools have reported improvements in both productivity and quality, but there are still companies developing software the way we did 30 years ago. If you saw the movie Jurassic Park, you saw the perfect way not to develop software. The programmer in the movie was the only person who knew the details of the system. No processes were followed, and there was no documentation. This was an absolutely perfect prescription for failure. Some of you are probably familiar with the term hacker which describes a person who spends hours sitting at a terminal hacking out code. Hackers have created some outstanding software products, but with today's complex systems, most companies are trying to get away from their dependence on hackers. They are instead turning to the process-oriented approach. When selecting software vendors, don't just look at the functionality of a product. Try to determine how the vendor develops software, and determine if you are dealing with hackers or a process-driven company. In the long run, you should get better, more reliable products from the latter.
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The services and resources available on the Internet are immense and growing daily. In this and last month's article I have only scratched the surface of what is available. I have given two references that I have found very useful while learning about the Internet. I highly recommend both. However, if you would rather look for other books or articles, they are plentiful. In a recent newspaper, I saw seven books that had "Internet" in the title advertised by one book store. There were books for PC users, Mac users, and UNIX users. Lack of information is definitely not an excuse for not checking out the Internet!
To summarize this discussion, let us look at a prototype, a capsule scenario in an OS. You make a process creation request on your local timeshare system. The long-term scheduler queues up this request, and eventually creates the corresponding process. Your process takes its turns executing, scheduled by the short-term scheduler. You request a tape drive to retrieve some archived data you need, and thus invoke the resource manager. You use the file manager to access the archived data. You use the I/O system to interact with the application program and to print the reports. The memory manager is swapping pages of your data and program between main memory and secondary memory. The dispatcher in the kernel is loading your process context into the CPU when your process is next on the execute list. The interrupt handler in the kernel is servicing interrupt requests, such as those made when you do I/O to the tape. The concurrency control in the kernel is coordinating your updating and spooled printing activities. So, your process is invoking activities throughout the various layers of the OS. Most of the time, you are unaware of these many varied activities.
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We have seen document preparation systems evolve from basic line editors through powerful, sophisticated desktop publishing programs. This component of the application layer is probably one of the most used, and most readily identifiable. Ask grade school children nowadays, and many will tell you that they have written a paper on a computer. Next month will be a "fun" tour through a number of other application programs we find useful. They will range from a simple notebook reminder to a sophisticated photograph processor. Application layer: Software targeted for the end user, focusing on a specific application area, and typically residing in the computer system as distinct components on top of the OS. Desktop publishing: A document preparation program that begins with the text features of a word processor, then adds the ability for a user to incorporate outputs from a variety of graphic programs, spreadsheets, and other applications. Line editor: A document preparation program that manipulates text in a file on the basis of numbered lines. Word processor: A document preparation program that can, among other things, reformat sections of documents, move and replace blocks of text, use multiple character fonts, automatically create a table of contents and index, create complex tables, and combine text and graphics.
Productivity tools can greatly simplify our day-to-day work around the office. Many of these tools are inexpensive and can be "test driven" before they are purchased. However, a word of warning is in order. One of the most common ways computer viruses are spread is via shared software. If you are going to sample the myriad of programs available on computer bulletin boards and that friends have given you, practice safe computing. Before installing any new software, use a virus checker to make sure the new software is not contaminated. It should be noted that there have even been a few cases where reputable software vendors have shipped software that was contaminated with a virus. Finally, as networks of computers proliferate, you can expect to see growth in the quantity and quality of groupware. As we become more dependent on the computer to store all kinds of information, we will need better tools to carefully manage the distribution of, and access to, that information. Sharing documents presents another problem that will be discussed in next month's article: security. Computer security has been a concern of computer scientists for many years. Now with the advent of computer-based medical records, it has a direct impact on the health information management field.
In the early years of computing, manufacturers usually sold general purpose computer systems to their customers. These systems had only a minimal set of software components. End users normally would have to work with analysts, programmers, and operators to get applications developed and executed. Personal computers, workstations, or terminals connected to larger timeshared systems, are readily available to many computer users. Multitudes of new software packages allow these employees themselves to utilize computer resources. Such packages typically are grouped together as an application layer on top of the OS. In this article, we looked at one important component of that layer--information management systems. We will look at more applications in the next two articles.
Many factors are contributing to any increased awareness of and interest in computer security. This article has described two aspects of computer security, identification of users and cryptography as a tool for data security. We looked at a number of ways to verify the identity of a user, including things a person knows, has, or is. Combinations of techniques were considered as a means of increasing security. Next, we looked at some simple examples of cryptosystems, including the rail fence cipher (a transposition technique), and the Caesar cipher (a substitution technique). Two computer systems were described, DES (a product cipher), and RSA (a cipher based on exponentiation and the mod operation).
In this article, we looked at some decisions that apply to the design of reliable computer systems. We began with a discussion of several terms such as testability, then described some systems that call for highly reliable hardware and software. The article concluded with a discussion of methods that can be used to achieve higher reliability in computer systems. Reliability and fault tolerance in computers probably will continue to grow in importance. As more and more systems are computerized, people will want assurances about the reliability of these systems, and their ability to work properly even when sub-systems fail.
Cost of ownership includes (among others) initial cost, cost of operation, cost of maintenance, and cost of training. Two important components of initial cost are the cost of design and the cost of manufacturing. In this article, we have looked at how factors other than initial cost affect the total cost of ownership of a product. We also discussed how trade-offs can affect performance and cost. Before making any decision on purchasing a complicated new system, the user needs to evaluate the total cost of ownership to determine which product to buy. Unfortunately, it is not always easy to find all the information needed to make these decisions.
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We have looked at several aspects of networks in this article. As you read about networks, and use them, we hope our discussions will help you understand some of the associated concepts and terms. For instance, suppose someone describes an Ethernet installation as a bus topology LAN using the 1-persistent CSMA/CD protocol with horizontal cables on each floor connected by repeaters to a vertical cable backbone running from the basement to the roof. You now have seen what that description implies. To close this article, we ask you to refer back to Figure 1. Our sample network transfer from Marie to Lars was described as being accomplished through a number of layers or steps, most of which were transparent to the users. Building upon the material presented in this article, we can now give you a more detailed illustration of those layers. Figure 13 shows the seven layers in network model defined by the International Standards Organization, ISO: application, presentation, session, transport, network, data link, and physical. We do not have space here to discuss each layer in detail, but Figure 13 does give a typical operation that is done in each layer.
The two goals of this article are to give you a very brief overview of the evolution of computing and an introduction to the elements of a computer. The birth of the modern computer can be traced to John von Neumann. The model he proposed consisted of four major parts: the control unit, the arithmetic unit, the memory, and the input/output unit. His concept for a "stored program" computer provided the foundation for five decades of computer designs.
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