Levels of computer control - Essay Example

Introduction There are various levels at which a computer system can exercise control, each of which will be discussed herein and compared to the specifics in the case at hand. The purpose of this paper is to either agree or disagree that the level of computer control implemented in the Therac-25 system was appropriate to the maximum efficient operation of the device. Levels of Computer Control Leveson shares nine levels of computer control. They are as follows: 1. The operator does everything; 2.

The computer tells the operator the options available; 3. The computer tells the operator the options available and suggests one; 4. The computer suggests an action and implements it if asked; 5. The computer suggests an action, informs the operator, and implements the action if not stopped in time; 6. The computer selects and implements an action if not stopped in time and then informs the operator; 7. The computer selects and implements an action and tells the operator if asked; 8. The computer selects and implements an action and tells the operator if the designer decides the operator should be notified; or 9.

The computer selects and implements an action without any human involvement (Leveson, 1995). The Therac-25 System The Therac-25 system was set at a certain level in order to allow the operator to maintain control over the machine at all times. It is given in the assignment that Although the computer is under operator control, yet clearly has sensors and information available to it to allow it to give error messages back to the operator, thus establishing it as in some sense a sort of independent actor exercising its own control.

Our concern here is the level in this control hierarchy at which those error messages are developed and resolved. (ComputingCases, 2008) Extensive computer control was boasted as one of the main innovations of the machine, especially since it allowed AECL to check for hazardous conditions using the software the complemented the machine. "The control console and printer etc. are all located outside the heavily shielded treatment room. Thus, when pressing the key to begin the treatment, the operator does not have any direct access to the machine or the patient.

All the occurrences in the treatment room must be observed through the TV monitor and the intercom" (ComputingCases, 2008). The intercom is two-way, while the monitor is only one-way (the operator can see the patient, but not the other way around). (ComputingCases, 2008) The first step of the process is for the operator to set up the patient and target the beam. This requires treatment parameters to be entered into the machine in the treatment room. After the operator leaves the room, the computer console is used to confirm each treatment parameter.

Then, the computer adjusts to the parameters that have been entered. Any mistakes in the parameters can be edited at this point without the operator having to start over (ComputingCases, 2008). "When the computer indicates that the setup has been done correctly, the operator presses the actuation switch. The computer turns the beam on and the treatment begins. There are three possible outcomes at this point, and they all depend on sensors on the machine. If the sensors indicate no trouble, the treatment concludes successfully.

If the sensors indicate a minor problem, like the beam being slightly out of tune, the computer turns the beam off immediately. The operator can then press a "proceed" key to retry the treatment up to 5 times. If the sensors indicate a more serious malfunction, like the beam being significantly stronger or weaker, the computer turns the beam off immediately and requires the machine to be completely setup from the beginning" (ComputingCases, 2008). Conclusion Reaching a conclusion at this point in the case is rather difficult.

That is, of course, because of knowing the ultimate outcome of the Therac-25 system. However, one must say that, at this particular point in the study, it appears that the level of computer control implemented in the Therac-25 system was appropriate to the maximum efficient operation of the device (ComputingCases, 2008). As discussed in this paper, there are various levels at which a computer system can exercise control. The Therac-25 system operated at a level of control that fell around Level 6 in Leveson's list of the various levels of control at which a computer can operate.

It is suspected, however, that this viewpoint will change when the next section of material is read. It was not, however, read before this paper at the request of the instructor (ComputingCases, 2008). References Guide to the supporting documents. (2008). ComputingCases.org. Retrieved March 12, 2008, from http://computingcases.org/case_materials/therac/supporting_docs/Guide_to_Supporting_Docs.html Leveson, N.G. (1995). Safeware: System safety and computers. Addison-Wesley. Therac . (2008).

ComputingCases.org. Retrieved March 12, 2008, from http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/therac_toc.html Why a socio-technical system (2008). ComputingCases.org. Retrieved March 12, 2008, from http://computingcases.org/general_tools/sia/socio_tech_system.html