(i) MHz (Mega Hertz)
(ii) GHz (Giga Hertz)

(i) Address Bus
(ii) Data Bus
(iii) Control Bus

Ultra-violet-rays is used to erase the content of a EPROM.

The Program Counter (PC) is a special register in the CPU which always keeps the  address of the next instruction to be executed.

A command which is given to a computer to perform an operation on data is called an instruction

(i) The address bus is used to point a memory location.
(ii) A decoder, a digital circuit is used to point to the specific memory location where the word can be located.
(iii) The address register is connected with the address bus, which provides the address of the instruction.
(iv) A data bus is used to transfer data between the memory and the CPU.
(v) The data bus is bidirectional and the address bus is unidirectional.
(vi) The control bus controls both read and write operations.
(vii) The system bus is a bunch of wires which is the collection of address bus, data bus and control bus that serves as communication channels between the microprocessor and other devices.

Every microprocessor has an internal clock that regulates the speed at which it executes instructions. The speed at which the microprocessor executes instructions is called clock speed. Clock speed is measured in MHz (Mega Hertz) or in GHz (Giga Hertz).

The two types of microprocessors which are based on their instruction sets.
(i) Reduced Instruction Set Computers (RISC)
(ii) Complex Instruction Set Computers (CISC)

Hard disk:
(i) Hard disk is a magnetic disk on which you can store data. The hard disk has the stacked arrangement of disks accessed by a pair of heads for each of the disks.
(ii) The hard disks come with a single or double-sided disk.
Compact Disk (CD):

(i) A CD or CD-ROM is made from 1.2 millimetres thick, polycarbonate plastic material. A thin layer of aluminium or gold is applied to the surface.
(ii) CD data is represented as tiny indentations known as "pits", encoded in a spiral track moulded into the top of the polycarbonate layer. The areas between pits are known as "lands".
(iii) A motor within the CD player rotates the disk. The capacity of an ordinary CD- ROM is 700MB.
Digital Versatile Disc (DVD):

(i) A DVD (Digital Versatile Disc or Digital Video Disc) is an optical disc capable of storing up to 4.7 GB of data, more than six times what a CD can hold.
(ii) DVDs are often used to store movies at a better quality. Like CDs, DVDs are read with a laser. The disc can have one or two sides, and one or two layers of data per side; the number of sides and layers determines how much it can hold.
(iii) A 12 em diameter disc with single sided, single layer has 4.7 GB capacity, whereas the single sided, double layer has 8.5 GB capacity.
(iv) The 8 em DVD has 1.5 GB capacity. The capacity of a DVD-ROM can be visually determined by noting the number of data sides of the disc. Double-layered sides- are usually gold-coloured, while single-layered sides are usually silver-coloured, like a CD.

(a) Bus: A bus is a collection of wires used for communication between the internal components of a computer.
(b) Data bus:
(i) Data busis a collection of wires to carry data in bits.
(ii) A data bus is used to transfer data between the memory and the CPU.
(iii) The data bus is bidirectional.
(c) Address bus:
(i) Address bus is a collection of wires to carry data in bits.
(ii) The address bus is used to point a memory location.
(iii) The address bus is unidirectional.
(d) Control bus:
(i) Control bus is a control line/collection of wires to control the operation/functions.
(ii) The control bus controls both read and write operations.

(i) CD/DVD/Blu-Ray
(ii) Hard Disk
(iii) Main Memory
(iv) Cache Memory

(i) The Central Processing Unit(CPU) has a Memory Data Register (MDR) and a Memory Address Register (MAR).
(ii) The Memory Data Register (MDR) keeps the data which is transferred between the Memory and the CPU. The Program Counter (PC) is a special register in the CPU which always keeps the address of the next instruction to be executed.
(iii) The Arithmetic and Logic unit of CPU places the address of the memory to be fetched, into the Memory Address Register.
(iv) A bus is a collection of wires used for communication between the internal components of a computer.
(v) The address bus is used to point a memory location. A decoder, a digital circuit is used to point to the specific memory location where the word can be located.
(VI) The address register is connected with the address bus, which provides the address of the instruction. A data bus is used to transfer data between the memory and the CPU.
(vii) The data bus is bidirectional and the address bus is unidirectional. The control bus controls the operations of both read or write operations.
(viii) The read operation fetches data from memory and transfers to MDR. control line performs two operations like read write using 1 or O.
(ix ) Also, the write operation transfers data from the MDR to memory. This organization is as shown in figure.

(i) The word in the RAM has the same size (no.of bits) as the Memory Data Register (MDR). If the processor is an 8-bit RAM processor like Intel 8085, its MDR and the word in the both have 8 bits.
(ii) If the size of the MDR is eight bits, which can be connected with a word in the memory which is also eight bits size. The data bus has eight parallel wires to transfer data either from MDR to word or word to MDR based on the control(Read or write).

(iii) This control line is labeled as which becomes 1 means READ operation and 0 means WRITE operation. shows content of M'DR and the Word before the READ operation. Also shows the content of MDR and the Word after the READ operation.

(iv) The read operation transfers the data (bits) from memory word to data register. The write operation transfers the data (bits) from memory data register to word.