Identify two benefits of using a digital camera as an input device in this control system.

Outline the use of a microprocessor in this control system.

Outline the function of an output transducer.

Compare a centrally controlled system with the system described above.

Identify two functions of the operating system.

Polling and interrupt are two operating system management techniques.

Suggest with reasons which of these two techniques is the most appropriate for this centrally controlled system.

Award up to [2 max].
([1] for each of the two benefits).

Digital cameras are relatively cheap;
Robust;
No need for AD conversion;
Generally very high quality pictures (useful to prevent malpractice);
Generally quick;

Example answer 1
No need for conversion because image is in digital format;
Thousands/millions of photos of eyes could be taken before needing replacement;

Example answer 2
It is directly connected to a microprocessor for image comparison;
It could be fitted (purchased), with a macro lens so that a close up scan of the Iris is possible;

Award up to [2 max].
Processor compares the inputted image/pattern with the images stored in memory;

If a match is found, it sends a signal to unlock doors /
(if match is not found, it sends error message/the doors remain locked);

Output transducer is a device (an actuator) which converts;
an electrical signal into physical quantity (a physical action);

Output transducer is a device which converts energy from one physical form to another;
e.g. electrical energy (signal) into electro-mechanical or kinetic energy / to produce action (lock/unlock door);

Note: Award one mark only for an answer that just says that the output transducer can be used to lock/unlock doors.

Award [1] for the meaning of centrally controlled system;
[1] for the meaning of a distributed system, and;
[up to 2 max] for an expansion/comparison addressing both kind of systems [up to 4 max];

Example answer
A centrally controlled system involves a central computer which controls all labs/doors;
A distributed system can have only a dedicated microprocessor with memory to control one of the labs/doors;

A centrally controlled system is more versatile;
Could be used in solving other business tasks (accept specific examples);
Can unlock all doors easily during an emergency;
Access rights can be updated easily;
Data is stored centrally and therefore easier to update;
A failure in a central system would affect all doors;

A distributed system can be programmed with ad hoc OS depending on the technologies used;
It may be practical choice when dealing with legacy systems/ specific devices/ old infrastructure/while updating the facilities;
It contributes a higher sense of partition of the physical space (territory) to groups / individuals;
Data are stored locally, so there is local consistency (and smaller size mean easier to manage);
Changes to data may be done locally, and if some data are common in two or more different systems, global inconsistencies across different systems may be introduced;

Award [2 max].
Memory management;
Resource allocation / Resource and Hardware management (printer, disk drives, etc.);
Booting / bootstrapping;
Loading and execute / provide service for applications software;
Disk/File system management;
Data security;
Provides a user interface to other levels of the machine;
etc.

Award [1] for choosing “interrupt”, [1] for explaining “interrupts” and [1] for justifying the choice in this context, up to [3 max].

Example answer:
Interrupt;
A signal sent from an input device to a computer causes the processor, and the main program that operates the computer (the operating system), to stop and figure out what to do next;
Interrupt is better in this situation because it does not waste central computer’s time (other tasks could be performed);
(example of emergency – it must give quick response);

Note: Award [1 max] for an answer of “polling”, but only if reasonably justified.

Polling – the continuous checking of all input devices by processor to see what state they are in/to see whether they are still connected/want to communicate;
So a faulty device that is polled will not reply;