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 Microprocessor's performance depends on the following characteristics:
(a) Clock speed
(b) Instruction set
(c) Word size

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

Computer architecture deals with the engineering considerations involved in designing a computer. Computer Organization deals with the hardware components that are transparent to the programmer.

Read-only memory (ROM):
(i) Read only memory refers to special memory in a computer with pre-recorded data at manufacturing time which cannot be modified. The stored programs that start the computer and perform diagnostics are available in ROMs. ROM stores critical programs such as the program that boots the computer. Once the data has been written onto a ROM chip, it cannot be modified or removed and can only be read. ROM retains its contents even when the computer is. turned off. So, ROM is called as a non-volatile memory.
(ii) Once the data has been written onto a ROM chip, it cannot be modified or removed and can only be read. ROM retains its contents even when the computer is turned off. So, ROM is called as a non-volatile memory.
Programmable Read-Only Memory (PROM) :
(i) Programmable read-only memory is also a nonvolatile memory on which data can be written only once. Once a program has been written onto a PROM, it remains there forever.
(ii) Unlike the main memory, PROMs retain their contents even when the computer is turned off.
(iii) The PROM differs from ROM. PROM is manufactured as a blank memory, whereas a ROM is programmed during the manufacturing process itself. PROM programmer or a PROM burner is used to write data to a PROM chip. The process of programming a PROM is called burning the PROM.
Erasable Programmable Read-Only Memory (EPROM):
(i) Erasable Programmable Read-Only Memory is a special type of memory which serves as a PROM, but the content can be erased using ultraviolet rays.
(ii) EPROM retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory.
(iii) An EPROM differs from a PROM. PROM can be written only once and cannot be erased.
(vi) EPROMs are used widely in personal computers because they enable the manufacturer to change the contents of the PROM to replace with updated versions or erase the contents before the computer is delivered. Electrically
Electrically Erasable Programmable Read-Only Memory (EEPROM):
(i) Electrically Erasable Programmable Read-Only Memory is a special type of PROM that can be erased by exposing it to an electrical charge.
(ii) Like other types of PROM, EEPROM retains its contents even when the power is turned off. Comparing with all other types of ROM,. EEPROM is slower in performance.

A Microprocessor's performance depends on the following characteristics:
(a) Clock speed
(b) Instruction set
(c) Word size
(a) Clock Speed
(i) Every microprocessor has an internal clock that regulates the speed at which it executes instructions.
(ii) 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).
(b) Instruction set
(i) A command which is given to a computer to perform an operation on data is called an instruction.
(ii) Basic set of machine level instructions that a microprocessor is designed to execute is called as an instruction set. This instruction set carries out the following types of operations:
1. Data transfer
2. Arithmetic operations
3. Logical operations
4. Control flow
5. Input/output
(c) Word Size
(i) The number of bits that can be processed by a processor in a single instruction is called its word size.
(ii) Word size determines the amount of RAM that can be accessed by a microprocessor at one time and the total number of pins on the microprocessor.
(iii) Total number of input and output pins in turn determines the architecture of the microprocessor.