Which of the following buses is unidirectional?

The correct answer is A, 8 bit. A microprocessor is named after the width of its data bus, that is, the number of bits it can carry in and out in a single operation. Here there are eight data lines, so eight bits move at a time and the chip is an 8-bit microprocessor; the Intel 8085 is the classic example, with eight data lines and sixteen address lines. B is wrong because the sixteen address lines decide only how much memory the processor can reach, which is two raised to the power sixteen, or 65,536 locations, and not the name of the processor. C is wrong because 20 address lines belong to the Intel 8086 family, which could address one megabyte, and address lines again do not fix the bit size. D is wrong because a 32-bit processor would need thirty-two data lines. The rule to remember is simple: data lines give the bit size, address lines give the memory capacity.

The correct answer is B, Nibble. A byte is made up of eight bits, so half a byte is four bits, and four bits together are called a nibble. The term matters in hexadecimal arithmetic, because one hexadecimal digit represents exactly one nibble, which is why four binary digits convert neatly into a single hexadecimal character. A is wrong because a byte is the full group of eight bits, not half of itself, and it is the unit in which file sizes and memory are measured. C is wrong because a bit, short for binary digit, is the smallest unit of data and holds only a 0 or a 1, so it is one-eighth of a byte rather than one-half. D is wrong because word size is the number of bits a particular processor handles in one operation, which may be 8, 16, 32 or 64 bits depending on the machine, and is not a fixed fraction of a byte.

The correct answer is C, ROM. Read Only Memory is the permanent or non-volatile memory of a computer: its contents are written once and survive when the power is switched off, which is why the BIOS firmware that starts the machine and runs the power-on self-test is stored in it. A is wrong because RAM, or Random Access Memory, is volatile temporary memory; everything in it is lost the moment power is removed, which is why unsaved work disappears in a power cut. B is wrong because a CD-ROM is an optical secondary storage medium that you insert and remove, not the permanent internal memory built into the machine; the question asks for the computer's own memory. D is wrong because the CPU is the processing unit and not a memory at all, although the registers inside it do store a few values while a calculation is running.

The correct answer is A, Cache Memory. Cache is a small quantity of very fast static RAM placed between the processor and main memory to hold the instructions and data most likely to be needed next, and of the options given it has the shortest access time; only the registers inside the processor itself are faster. Cache is graded as L1, L2 and L3, with L1 nearest the core and quickest. D is wrong because random access memory is the main memory and is slower than cache, which is the whole reason cache exists. B is wrong because magnetic bubble memory is an old non-volatile technology that stored data as tiny magnetised regions in a thin film and was far slower than semiconductor memory. C is wrong because magnetic core memory, built from tiny ferrite rings, was the main memory of second generation computers and had access times measured in microseconds rather than nanoseconds.

The correct answer is B, Arithmetic Logic Unit. The ALU is the part of the processor that actually does the work on data: addition, subtraction, multiplication and division on the arithmetic side, and comparison along with the logical operations AND, OR and NOT on the logic side. Results produced by the ALU are placed in the accumulator register. A is wrong because the control unit performs no calculation; it decodes each instruction and issues the timing and control signals that direct the other units, which is why it is called the nervous system of the computer. C is wrong because the memory unit only stores instructions and data and hands them over when asked. D is wrong because the input unit merely accepts data from devices such as the keyboard, mouse and scanner and converts it into a form the machine can use.