Looking inside a PC

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

Computer Installation and Maintenance (CIM) is a first year computing unit at ECU in which students acquire the sort of knowledge and skills needed for computer support positions. CIM includes one two hour fully supervised practical workshop each week, where students can gain hands-on experience in first line maintenance. As these units have no prerequisites, they are accessible to students from a wide range of backgrounds and situations.

It has been shown that these students typically lack sufficient physics and maths to properly support their learning in CIM. In 2000, we began trialing practical workshop activities designed to improve their physics and maths in a CIM context. They were tailored to illustrate and reinforce key computing concepts without compromising the standard lectures and workshops.

Central to these activities is a cathode ray oscilloscope (CRO). The CRO is used to look inside a PC, see different types of waveforms, measure voltages and periods, and then calculate frequencies and bandwidths. Students have reported a wide variety of benefits and believe that time spent on these activities is worthwhile.

Introduction

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)

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

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)

Student evaluation

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

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

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