Ask the Teacher - 14th October 2013

Q: Why is it better to simplify everything to NAND gates?

A: (Please note: This question is more about detailed electronics rather than general computer science and well beyond what you need to know for GCSE or A level computing.)
Any other gate can be created by using a combination of NAND gates which makes it a very useful gate. There are several reasons why it is better to use a NAND gate instead of a NOT/AND gate, such as space taken on a circuit board is less (takes less transistors to make the NAND gate) and increases the speed of the circuit. To say it is better to simplify “everything” to NAND gates may not be correct. NAND gates are cheap and small so circuits are often constructed out of just NAND gates as using a combination of other gates may require less gates but more transistors taking more space, thus costing more. Also as far as when writing a diagram it is neater to draw a NAND gate rather than a NOT and then an AND gate.

Q: If RAM loses its data when power is removed, what is NVRAM? If you can't change the data on ROM, what is EEPROM?

A: NVRAM stands for Non Volatile RAM meaning it does not lose its data when it loses power. EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory. At GCSE level you are expected to know the main differences/characteristics of RAM and ROM.


Q: How does an exploding laptop battery demonstrate the consequence of computer failure? Such a failure is a demonstration of computer dependency upon its power supply, not the dependency of the power supply upon the correct output from the computer. To prove me wrong, show me a program running on a laptop which is able to explode the battery.

A: A computer failure can be any event which results in the computer not being able to perform its function, there are many different types of computer failure. In the event of a battery exploding I would call this a hardware failure. Computers are dependent on lots of pieces of hardware and software to be able to perform their functions, if any single piece of software of hardware stopped working it could result in a computer failure.