Rationale: The first important aspect you will need to discuss with the interviewer is what kind of role you are assigned when testing a CD-ROM drive. This is a big task and this aspect needs to be clearly defined before you can start thinking about the steps that you need to carry out. When talking about your role in assessing the quality of such a device, make sure you ask the interviewer under which of the following categories you fall:
|Consumer||Obviously, as a consumer you wouldn’t have any technical background so you are most likely to assess the general functionality. A sensible approach would be making sure the CD-ROM reads and writes the type of media permitted at the right speed and in accordance to the capacity of the optical media.
|Member of the design team||Since every company has its own trademark and logo, a design team will be asked to come up with an original sketch of the product. They would have to distinguish between a design for laptops and PCs and make it as original and visually appealing as possible.
|Quality Engineer||If you are working in the quality assurance department, you ensure the product is suitable for the large audiences. Your task would be to determine whether the device is easily accessible and intuitive enough to be operated. For example, people with disabilities such as blindness should be able to clearly access the eject tray button. Also, a good point of discussion is health and safety; the case has to be sturdy enough and avoid sharp edges.
|Member of manufacturing team||As a member of the manufacturing team, your main role would be to check that all the components used are in a good state and conform to the general standards an ideal product should adhere to. At the same time you will also be responsible for handling the automated mechanics meant to put together the CD-ROM drive.
|Tester||As a tester, you will most likely be asked to verify the functional requirements of the device once this is manufactured. This implies rigorous testing under various parameters. The model answer below will tackle this category in more detail.|
There are various aspects that make some CD/DVD drives better than others. In the following lines we will discuss some of these, along with some proper ways of testing them.
First, we must separate the concepts of reading and writing when it comes to CD-ROM/DVD-ROM drives. If the device also has writing capabilities then we must test these two concepts separately. Let’s start with some notions on data reading from an optical storage disk (CD, DVD, Blu-Ray media, etc):
- The reading speed of a drive, as you may have noticed, is expressed as an integer value, followed by X (e.g. 52X). But what does this X actually mean?
- An X is equal to 0.1536 MB/s, so a CD-ROM that is capable of reading data at 52X would actually transfer it at a rate of 7.98 MB/s. This is quite slow compared to most hard disks nowadays, especially SSDs or the external drives with support for USB 3.0.
- Older drives used to support speeds of 2X or 4X, but nowadays 56X has been achieved.
- In addition to the reading speed of the device, the data transfer rate is also influenced by the system cache. The cache is a very fast memory section used by the operating system to temporarily store data. For example, if a 2-3MB file is copied from a CD/DVD drive, it is likely for the operating system to store it in the cache, in the event that it may be needed again soon.
- If the same file is requested shortly after, then the OS will fetch it from the cache rather than from the optical media disk. This aspect should also be taken into account when testing an optical drive. Not reading the same file twice in a short time interval will lead to more accurate estimations of the drive’s speed.
The writing speed is not influenced by the cache, so all the points above except for the last one apply to writing to an optical disk. Usually, the writing speed is slower than the reading speed because this operating is more ‘expensive’ and consumes more resources.
Some further aspects that we may wish to consider when testing a CD-ROM drives are as follows:
- The load time – the time it takes for the device to actually load the disk (time between the insertion of the disk and the moment when its contents actually show up in the file manager).
- The seek time – the user often needs to access files stored at random locations on the disk (non-contiguous blocks of memory). If this is the case, then the time it takes for the head of the CD-ROM to move from one location to another is called the seek time.
- Spinup and spindown times – the spinup time is similar to the load time and it is the interval between the moment when the disk was placed in the proper position for reading and the moment data is actually accessible to the user (in simpler terms, this is how much rotation time the disk needs before data can be accessed). The spindown time is the opposite of spinup and is the time it takes for the drive to ‘stop’ a rotating disk.
There are already many pieces of software that can test all these performance criteria of an optical drive. An example is Nero DiscSpeed.
To sum up, you need to keep in mind that whenever you are confronted with these types of open-ended questions you have to think outside the box and not limit yourself to one specific answer. The interviewer will most likely look for your ability to cover all the aspects involved and make the right links in any situation. Asking more questions in order to clarify the problem is a typical process called requirements gathering which takes place at the beginning of every complex project in order to establish exactly what the customer has in mind.