Linking Micros to Mainframes

In today's research world, with scientists automating the workbench, improving laboratory data collection, logging experiment reports, and retrieving tests from databases for application in product development, the use of workstations and personal computers is increasing at a rapid rate. Often these useful machines would be even more useful if they could commandeer main-frame resources too. That is one reason why micro-mainframe links, which allow personal computers to be connected to host compu

By | October 20, 1986

In today's research world, with scientists automating the workbench, improving laboratory data collection, logging experiment reports, and retrieving tests from databases for application in product development, the use of workstations and personal computers is increasing at a rapid rate. Often these useful machines would be even more useful if they could commandeer main-frame resources too.

That is one reason why micro-mainframe links, which allow personal computers to be connected to host computers, are a hot topic these days. Computer magazines are full of advertisements for the latest and greatest micro-mainframe links with the newest features. Because so many options are available, it is tempting to make plans and selections impulsively. But selecting links requires a major commitment. These products become part of your communications network, and you may want to expand upon them in the future. Picking one without thinking carefully about how it will be used could prove costly.

In planning a system, you must consider how to design configurations to provide redundant backup, continuous processing, transparent database access and security against intruders. Links are part of this process.

For the long term, users must go beyond designing configurations and selecting links to planning a framework that will take into ac count information flow, system compatibilities, network expansion, multiple networks, the addition of personal computers-and technological obsolescence of the system's components.

Link selection is a process of elimination and definition. You will find it helpful to develop categories that sort through the vast number of similar products, focusing on those products pertinent to your needs.

The type of solution is more important than the product itself. Once you have defined categories, it becomes easier to describe the problems to be solved, and it becomes second nature to rank features of various products. You can then take the top three or six products, compare their features and decide which best meets your needs.

Any product that allows you to connect personal computers, CAD/CAM graphics workstations, word processing systems, or intelligent terminals to a host mainframe computer for accessing information can be a micro-mainframe link. The link products can be hardware, software or a combination of the two. Although the examples below are oriented toward the IBM market, many similar links are available for DEC VAX products, which are widely used in scientific environments.


Connection of a personal computer to a host computer can be direct or remote. A computer that is within 2,000 feet of the controller is usually connected directly to it via coaxial cable. A personal computer remote from the host communicates via modem over telephone lines. The advantage of direct connection is that it generally provides faster transfer of data. The advantage of remote connection is that the PC can communicate with different hosts at different times.

The host computer is accustomed to seeing particular terminal protocols that tell it it is talking to a standard terminal that it recognizes. By emulating the terminal communication protocols of standard brands of terminals, non-standard devices can be attached to a host.

Emulator links are simple and straightforward. They are most appropriate when you want just basic read-only access to the host, not interaction. The lowest-level emulator makes a PC appear to be a dumb terminal recognizable in every way to a host. IRMA from Digital Communications Associates is the standard for local IBM 327X emulation. Other such products include 3270-PLUS from CXI, SNA/ Exchange from Intelligent Technologies, and 3270 SDLC Adapter from INS for remote connection. Depending on the transmission type and features, prices range from $200 to $1,600 per personal computer.

File Transfer Software

File transfer software permits file movement to and from the personal computer. Without it, data transfer is read-only.

File transfer software goes hand-in-hand with terminal emulation products. Often it is part of the terminal emulator; if not, it must be loaded in a separate step. You will need file transfer software when you want to download large quantities of data for local personal computer processing.

Simple file transfer capability can be purchased for under $300 per PC. Other systems generally range from $800 to $2,300, al though such sophisticated systems as RELAY from VM Personal Computing can cost $25,000.

Software Links

Application integrated interface links, or "integrated software links," are part of the application software that resides on the host. When you buy the software you buy the link that is part of the package. When you request data, you do not know how the transfer is implemented, only that the data are presented to you in a form that the application can use. McCormack & Dodge's PCLink and MSA's PeachLink are examples of such links.

These links embed terminal emulation as part of the system, incorporate file transfer and data re formatting capabilities to move data to and from the application, and simplify the user interface by which data requests are made. This greatly simplifies retrieving data from a database management system.

For example, assume that the host-based system is a statistical analysis package such as RS/1. The PC user wants to download data from the host into a spreadsheet, but the data reside in the database associated with the statistical package. A vendor of an integrated software link provides a user interface that allows users to define and recall the data they want without knowing the internal database structure and the spreadsheet format to which data are loaded. Users query for the data on their PCs, and the host system retrieves and consolidates the data from the database and transfers and reformats it into the proper rows and columns for the users' spreadsheets.

These application links are much more expensive than emulation or file transfer because of the value added by the accompanying application. Prices can average $25,000 to $50,000 depending on how many PC links are configured into the system.

Database Interfaces

Database interface products are designed to meet the needs of users who are developing their own local databases and would like to supplement them by retrieving data selectively from the host. The products allow data to be transferred between databases and PCs or among host databases. They permit a database subset to be downloaded to a PC for manipulation, update and review without concerning users with the particular system's database manager dictionary. Cullinet's InfoGate, Software AG's Natural/Link, and Sterling Software's Answer/DB are examples of such products.

Unfortunately, such links are ex pensive. A database can easily exceed $100,000 with a fixed number of links, and the cost of each additional link connection can approach $2,000.

File Servers

File servers collect and consolidate groups of personal computers, providing the connection to the host rather than linking individual PCs into the host as other links do.

File servers are useful in creating nodes of users whose processing and data uploading and downloading requirements can be managed and predicted to a reasonable extent.

For example, a file server would be suitable for a group of chemists, remote from the host, who use the same routines to analyze laboratory data on a variety of products. Each day the group can predetermine appropriate tests to be used and a predefined set of data can be downloaded to the file server for access by all the chemists. They can run the tests and, if necessary, request additional data from the host. The chemists can do all their data storing and processing at the server, and, at the end of the day,  upload the server data to the host database.

File servers are expensive- $10,000 to $50,000-but they can be so useful in some situations that their cost is justifiable.

Local Area Networks

Local area networks connect workstations so that they can communicate with each other. They can be baseband, broadband, wide-area or limited-area networks.

A baseband local area network connects workstations with standard "twisted pairs" of wire not unlike telephone wire and carries information in digital formats at the same frequency. It does not require special equipment at either end to convert from one frequency to another.

A baseband network is generally less expensive and easier to install than the other configurations. Baseband networks perform at speeds approaching 10 Mb per second, which makes them useful when high-speed transmission is desirable. On the other hand, their data transmission range is limited unless special pieces of equipment are used, and they are more susceptible to noise-created errors because the cable and wire are not shielded.

A broadband local area network connects workstations using coaxial cable in much the same way that television sets are linked by cable. Data (in digital format) are converted at the point of transmission to an analog signal and sent across the cable at some frequency. Many different types of data can be transmitted over the same cable, each with a different frequency.

Broadband networks perform at speeds in the 2 Mb per second range, and they are less susceptible to noise than baseband systems.

Broadband is a good choice for developing a "backbone" with smaller baseband and broadband networks connected into it. However, such systems are more expensive than baseband networks because they require special equipment to condition the signals and decode the frequencies at the receiving end.

Wideband networks use message-switching technology to network stations to each other over distances of several hundred miles.

Limited-area networks use twisted-pair wiring just like baseband networks, but they connect by means of the old faithful RS 232C interface ports that are standard on every workstation and PC. They are inexpensive (under $100 per PC connection) but slow; data transmission takes place at less than 9600 baud.

Local area networks are appropriate for groups of individuals in a single area doing the same kind of work. For example, a network can be beneficial to a department of chemists at a pharmaceutical company. Chemists can share tests and product results and store supplemental tests so that other chemists in the network can use them. A network is also appropriate for users who need to exchange similar data and could be used for electronic mail too.

If you define your needs, compartmentalize solution possibilities, and view products within categories and combinations of categories, you can build a micro-to-mainframe connection frame-work that can be expanded as your time and needs-and funding picture-dictate.

Ronald F Kopeck is the author of Micro to Mainframe Links, published this year by Osborne/McGraw-Hill.

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