Central Processing Unit (CPU) Interview Questions & Answers

Download PDF

It is a temporary memory storage area which helps to speed up data transfer within a computer. A Microprocessor looks for the data in the Cache memory as the data transferred Cache is much faster. If the data is not found in the cache, the CPU looks for it in the memory.

The following are two types of Cache:
Internal or Level 1: In this, the Cache is built into the Microprocessor.
External or Level 2: In this, the Cache is built on a separate chip.

Some of the memory components are:

★ Semiconductor Memory:
It is used by most by most modern computers. It is reliable, inexpensive and compact. However, it requires continuous power supply and data is lost if current is interrupted.

★ RAM and ROM:
They stand for Random Access Memory and Read Only Memory respectively.

★ Flash Memory:
This memory is electrically erasable and re programmable.

RISC stands for Reduced Instruction Set Computing.
★ It uses a small subset of instructions to carry out processes.
★ As the number of instructions are lesser, the speed of processing is much improved and faster.
★ However, when complex operations are dealt with, they have to be broken down into a series of smaller instructions.

It is a type of processing in which the CPU divides the problem into two parts. It works as:
★ Each part is sent to separate processors.
★ Each processor has its own memory. They individually solve the given problems and return the result.
★ The CPU assembles the results and hence, the problem is solved.
Some computers operate in terms of teraflops or trillions of floating-point instructions per second.

The speed of the bus is measured in megahertz (MHz), refers to how much data can move across the bus simultaneously. Personal computers have a bus speeds of 400 MHz or 533 MHz.

System Bus are parallel electrical paths that transport data between the CPU and Memory. - Bus Width: The number of electrical paths that to carry the data. It is measured in Bits. With larger Bus Widths, a CPU can transfer more data at a time.

It cannot retain its contents if not continuously refreshed by the CPU. Its types are:
i. Synchronous DRAM:
It is the faster type of DRAM, used in modern and more advanced systems.
ii. Rambus DRAM:
It is faster than Synchronous DRAM and is expected to become more commonly used.

It retains its contents with the help of CPU. It is faster and more expensive than Dynamic RAM. It is generally used for Level 2 cache.

Transistors are electronic switches that may or may not allow the flow of current in a current path.
★ When it allows current to flow, the switch is ON. This represents 1 bit.
★ When it does not allow current to flow, the switch is OFF. This represents 0 bit.
★ Transistors are placed into chips also known as IC. They measure in mm`s and are known contain millions of transistors.
★ Microprocessors these days are created using microns as their measuring size.

They comprise of the following key components:

Central Processing Unit:
It carries out the instructions of a computer system
Registers:
They store bits of information in a way that all the bits can be written to or read out simultaneously.
System clock:
simple count of the number of ticks that have transpired since some arbitrary starting date, called the Epoch.

It is an enclosure that contains most of the components of a computer system such as the Motherboard and other Storage devices.
Motherboard:
It is a Flat circuit board that holds the computer circuitry.
Storage devices:
These devices are used for long term storage of memory. Some of them are- hard drive, diskette, DVD_ROM, etc.

A Microprocessor is a miniature CPU unit that is etched on a silicon chip. A CPU (Central Processing Unit) hardware which carries out the instructions of a computer system. The Microprocessor unit consists of millions of tiny transistors. It has multi purposes and is programmable. They operate on numbers and symbols represented in Binary Numeral Language.

★ The instruction time is also known as the I-time.
★ It is the time taken by the Control Unit to get an instruction from memory and to load it to the register.
★ The time also includes the taken by the CU for instruction decoding and to find out the location of the required data.

It is designed to accommodate alphabets (- 256). It uses 16 bits to represent one character and requires twice as much space to store data. It can have a maximum of 65,536 possible values.

It stands for Extended Binary Coded Decimal Interchange Code. Its is primarily used in IBM and IBM-compatible mainframes.

It stands for the American Standard Code for Information Interchange. It is used on almost all computers, hence considered as a standard coding scheme.

Coding schemes are a common way of representing a character of data. It is required in computers for exchanging data. The following are a few common coding schemes-
★ ASCII
★ EBCDIC
★ Unicode

Some of the characteristics of the system clock are as follows:
★ The system clock is used to produce a specific pulse at a fixed rate of time.
★ The machine cycle of a system can be completed in a single or multiple clock pulses.
★ A single program instruction could be multiple instructions for the cpu.
★ Any central processing unit has a predefined set of instructions also known as the instruction set. These are the instructions that it can process and understand.
★ The clock speeds are nowadays measures in Ghz. 1ghz = 1000 mhz.

It is the time required by the control unit to move data from the memory to the registers in the ALU, the ALU is responsible for the execution of instructions on this data.

The following steps are involved in the execution of a program:
Fetch:
The control unit is given an instruction.
Decode:
The control unit then decodes the newly received instruction.
Execute:
During the execution the Control unit first commands the correct part of hardware to take action. Once that is found out the control is handed over to the hardware. Now the task is performed.
Store:
Once the task is saved successfully the end result is stored.
- After the cycle is complete the Control unit is again handled the conrol.

The number of bits that a cpu possess indicates the power of the computer. It also indicates how many number of bytes are present. In today`s date most computers can handle 32 or 64 bit length.

A byte is a collection or group of 8 bits. A byte can store a single character which can either be an alphabet, a number or a special character. The byte is generally used to measure the storage capacities.

This is also the short name for binary digits. By being binary it means that BIT can only have two values zero and one. A characteristic of BIT is that it can never be empty. Zero implies a power off state whereas one means on state.

There are three ways in which data can be represented namely Bit, Byte and Word:
★ Bit
★ Byte
★ Word

★ Registers can be considered to be special purpose memory which reside within the CPU.
★ The registers are high speed temporary memory used to help the CPU get access to data and instructions quickly and effectively. There are various type of registers such as Instruction register, Status register and data register.
★ The instructions register is responsible for the storage of the of the instructions that are being currently executed.
★ The status register is used to keep a tab of the status operations of the arithmetic logical unit.
★ The data register is used to store information or data that is to be processed, it is also used to store information or results that have been derived from a process.