We have mentioned before, in the history of the computer series, that digital computers have been developed as general purpose machines. You buy one of our systems, and you can use it to run a bank, operate the lottery, build a car, or control freight shipments for an airline. Of course there are differences in hardware, mainly in peripherals, depending on the application, but generally a modern computer is still a multi-purpose beast. The main difference is in the software. One of the most critical applications, using the latest developments in a combination of hardware and software, is the Real-time system. It produces state of the art performances, and has to be reliable. What is a Real-time System? The name says it all - everything this system does with the data you give it, it does right now, in real time. NON REAL TIME SYSTEMS It may be easier to understand the concept if we look at what is NOT a Real-time system. A typical use of a computer is to work out statistical information. Say you want to do a comparison of the number of smokers in the community today, compared with 10 years ago. (Fortunately you have figures obtained 10 years ago!) You hire a consumer research organisation to interview a cross-section of the community, asking the same questions used in the original survey. This company sends out researchers to stop people in the street and ask them the questions. In order to get a similar cross-section to the previous survey, they interview perhaps 25% more than the final number required. The survey sheets are sent back to head office, where they are keyed in to a computer database by the head office staff. An analyst works out a program which will select the appropriate survey data, and compare to the original survey. It produces tables and charts of all sorts of things, to justify the cost and time involved. This process has taken perhaps 3 months, and employed quite a few people. Total computer processing time? Maybe one minute. This is not Real-time as far as the computer is concerned. These other uses for computers are no less important, their applications are many and varied. A computer at a university may be used for research, or administering examinations, and scheduling tutorials. One at an electricity supplier might be used for customer accounts and billing. There could be more to the uses applied than billing. A link may exist to a government agency for cross-referencing names and addresses - most people use electricity! REAL TIME SYSTEMS Now consider the following. An airline has a maintenance base for its fleet of aircraft. These aircraft are required to be serviced at regular intervals, based on the mileage flown. They also require repairs based on faults reported by the flight crews or maintenance engineers, on a per flight basis. The maintenance base carries a large supply of parts ranging from nuts and bolts to complete engines, and including such things as radar equipment, and various navigational instruments. The warehouse is too large to be convenient for the technicians working on the aircraft, they have a smaller stock of frequently used parts on hand. The inventory for this equipment is kept on a computer database, stored on disks. As with everything else these days, there is a lot of pressure on the maintenance base to keep costs down. One of the biggest costs is all that expensive equipment sitting in the warehouse, not earning a cent. In part 2 we will look at how we can use a real-time computer system to reduce these costs. |
