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Looking inside a PC

Geoff I Swan
Physics Program
Edith Cowan University

David Veal and Stanislaw Paul Maj
School of Computer and Information Science
Edith Cowan University


Introduction

Computer Installation and Maintenance (CIM) is a one semester first year computing unit that teaches first line maintenance of PCs. By "first line maintenance" we mean on-site, in-situ problem identification and correction - the faulty module is identified and replaced. It was conceived and written in response to employer demand for these types of skills that were previously not being adequately provided by computing science degrees [Maj, Robbins, Shaw & Duley, 1997]. There are no pre-requisites for this unit, which is regularly oversubscribed and attracts students enrolled in a variety of degree programs including computing and business.

CIM consists of one two hour lecture plus one two hour workshop per week. A more detailed description of CIM content can be found in [Veal, Maj, Fetherston & Kohli, 1999]. In the workshops, students obtain hands-on practical experience in maintaining PCs (eg testing and then replacing a faulty CD-ROM drive). An understanding of some secondary school physics is necessary to understand CIM principles as well as health and safety issues. However, in a questionnaire on simple electric circuits (which is normally covered in lower secondary school science) we found that most CIM students performed poorly [Veal, Maj & Swan, 2000]. In general only a few CIM students have sufficient physics to properly support their learning. In this paper, we will describe some workshop activities trialed in semester 1, 2000 to address basic physics and maths in a CIM context.

The cathode ray oscilloscope (CRO)

A cathode ray oscilloscope (CRO) is an instrument that is mainly used for measuring voltages and periods (as well as seeing the shape) of periodic signals. It can also be used as a voltmeter for DC signals. It is an instrument well suited to looking inside a PC. This paper will describe activities using a CRO we have introduced into the CIM workshops to address students' physics and maths performance in a CIM context. They have also been designed to provide a practical reinforcement of CIM lecture content.

We had two major constraints that needed to be overcome for this to be successful. Firstly, the CRO is a technical instrument of some complexity that normally requires a good physics knowledge and time to master. Few CIM students have ever used a CRO, and many have not even seen a CRO as it is rarely used in secondary schools except for upper secondary school physics, and even then, usually for demonstration purposes by the teacher. Secondly, the CIM workshop schedule was tight and did not allow the time needed to master the instrument. However, we believed that in a supervised workshop environment it was possible to teach CIM students enough about the CRO to make meaningful measurements inside a computer in a short space of time.

CRO activities

Six activities using the CRO were trialed in the first half of two successive CIM workshops in semester 1, 2000. In the first workshop, students were given a worksheet that contained the first two activities (or tasks) to help familiarise themselves with the basic workings of a CRO.

In activity 1 (Household Battery), students familiarised themselves with the timebase and voltage settings of the CRO. They measured the voltage of a 1.5 volt household battery.

In activity 2 (Signal Generator), students used a signal generator to produce a 500 Hz sinusoidal signal, measured its period (and peak to peak voltage) with the CRO, and then calculated the frequency from their measurement. They also generated a 50s signal and observed square/rectangular and triangular pulses. Many students initially had insufficient math skills to calculate frequency from period with the presence of prefixes making the calculation even more difficult. Students gained valuable experience here.

In the second workshop, students were given the final four activities that required them to take the cover off and make measurements inside a PC. At no stage in CIM are students permitted to open the power supply unit or monitor or come into contact with mains or higher voltage levels.

In activity 3 (Power Plug Sockets), students measured the DC low voltages for the power plug sockets. For example, the socket connected to the red wire has a voltage of 5 Volts.

The next three activities refer to measurements on several pins of the 8-bit portion of a 16-bit ISA Bus. In activity 4 (ISA Bus Power Pins), students measure some DC low voltages from the ISA Bus. For example, pin B07 has a voltage of -12 Volts [REFS].

In activity 5 (ISA Bus Clock Signal), students measure the period of the ISA Bus clock signal (on pin B20) and then calculate the frequency. Most students were able to measure a period close to the expected value of 1.2 microseconds (which gives the expected frequency of 8.33 MHz) although many students were surprised that the signal looked rather more sinusoidal than the perfect square/rectangular wave they had expected from theory (ie from textbooks).

In activity 6 (ISA Bus Bandwidth), students use the bus frequency to calculate the bus bandwidth using the formula:

Bandwidth (MBytes/s) = Frequency (MHz) x 2 (Bytes) x 0.25 (efficiency)
At the conclusion of these activities, most students (40) completed a one page questionnaire in which they were asked to agree (or strongly agree) or disagree (or strongly disagree) with a number of statements and comment on perceived benefits and difficulties.

Student evaluation

Students were very positive about their experiences with the CRO. Almost all students (90%) agreed or strongly agreed that they were able to use a CRO to measure voltages and periods inside a computer. Most of these students believed that the familiarisation activities of the previous week were helpful. This was a pleasing result for us as we were not certain that we would be able to raise the confidence of students to use a CRO in such a short space of time.

Students believed that their understanding of period and frequency had improved. Certainly many students initially needed help from other students or the demonstrator in measuring periods, using prefixes, and performing calculations of frequencies. They found that seeing signals from inside a computer on the CRO was beneficial to them and they were able to link the activities with material covered in lectures. Students believed that time spent using the CRO was worthwhile and should be incorporated into future CIM workshops.

Some students also made comments of the most beneficial and difficult aspects of these activities. The most beneficial aspects were mainly the taking of "real" measurements (voltages and periods) on different pins, calculating frequencies and seeing actual waveforms. Difficulties included setting and reading the CRO, the maths, and even keeping "steady hands" when making measurements.

Conclusions

Students have successfully used a CRO to look inside a PC, see different types of waveforms, measure voltages and periods, and then calculate frequencies and bandwidths. They have gained practical skills and knowledge that complement and reinforce material covered in CIM lectures. Students believe that the activities are sufficiently worthwhile to include in future CIM workshops.

These activities were repeated for CIM students in semester 2, 2000, with the addition of a new activity on monitors that was well received. The feedback again was very positive and from semester 1, 2001, one workshop will be dedicated to CRO activities to allow all CIM students to look inside a PC.

References

Maj, S. P., Robbins, G., Shaw, D. and Duley, K. W. (1997). Computer and network installation, maintenance, and management - A proposed new curriculum for undergraduates and postgraduates. Australian Computer Journal, 30(3). ACS Australia.

Veal, D, Maj, S. P, Fetherston, T. and Kohli, G. (1999). Competency based assessment techniques for use in a computer installation and maintenance unit. Paper presented at The 3rd Baltic Region Seminar on Engineering Education, Goteborg, Sweden.

Veal, D., Maj, S. P. and Swan, G. I. (2000). Physics for hands on units in Computing Science. In A. Herrmann and M. M. Kulski (Eds), Flexible Futures in Tertiary Teaching. Proceedings of the 9th Annual Teaching Learning Forum, 2-4 February 2000. Perth: Curtin University of Technology. http://cleo.murdoch.edu.au/confs/tlf/tlf2000/veal.html

Please cite as: Swan, G., Veal, D. and Maj, S. P. (2001). Looking inside a PC. In A. Herrmann and M. M. Kulski (Eds), Expanding Horizons in Teaching and Learning. Proceedings of the 10th Annual Teaching Learning Forum, 7-9 February 2001. Perth: Curtin University of Technology. http://lsn.curtin.edu.au/tlf/tlf2001/swan.html


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