Structure and Role of the Processor

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Program Control Unit: fetches program
instructions from memory, decodes them and
Multi-Core microprocessors: The strategy now is executed them one at a time.
to use the increase in transistor density to put
more than one processor onto the Arithmetic and logic unit: the ALU performs
microprocessor chip. These processors are called arithmetic and logical operations on data ssh as
cores and operate at lower frequencies than addition and subtraction; fixed-point and
single-core processors to overcome the heating floating point arithmetic; boolean logic and a
problem caused by clock frequency. Multiple range of other shift operations.
tasks can be run at the same time or a single Registers: Fast memory locations inside the
task can be split across several processors. processor or an I/O controller that may be
Increasing Clock Speed: All other things being The processor consists of the following: dedicated or general purpose.
Effect Of clock speed,
equal, a processor with clock speed or frequency word length and bus Internal Clock: derived directly or indirectly from
Limits on Clock Speed: A limit has to be set on of 2GHz should execute the same machine code the system clock.
width on performance
clock frequency, because the heat generated in program twice as fast as a processor with clock
the chip by higher chip frequencies cannot be Internal buses: Several internal buses link the
speed 1Ghz. As the 2GHz processor's clock cycle control unit, the ALU and the registers
removed quickly enough. The problem is made is half the duration of the 1 GHz processor's
worse when more transistors are packed into the clock cycle, it will take half the time to execute Logic gates: used for flow control
same space. an instruction.
Registers are fast memory locations inside the Stack Pointer: points to a stack holding return
Increasing word length: The word length of its registers affects the processor. General purpose registers are addresses procedure or function parameters, and
processors speed performance. The registers that can do available for the programmer to use in programs local variables; it is accessed when a procedure
arithmetic operations such as the general purpose register and the to store data temporarily. They have not been or function is called or an interrupt is serviced.
accumulator - usually have a similar word length. Typical word assigned a specific role by the processor
Program Counter: Points to the next instruction
lengths are 32 and 64 bits in modern processors. The bigger the designer. Dedicated registers are registers that
to be fetched and executed.
word length, the bigger the operands and results they can have been assigned a specific role. Programmers
accommodate. When operands and results exceed the word length may read or manipulate some but not all of these Status register: Holds condition codes to indicate
of the registers, extra processing must be done to split operands General Purpose and dedicated registers registers. Here are some dedicated registers: the outcome of operations. Also status
and results across several registers. This reduces speed information, such as whether interrupts are
performance. Every computer has its own system clock, a enabled or disabled, is indicated within the
quartz-controlled oscillator that supplies timing status register.
Increasing bus width: The worst performance penalty occurs in the system bus
between the processor and the main memory. If the current instruction signal. These timing signals regulate the rate at Accumulator: Holds the result of the current set
register's word length is not big enough to hold a complete instruction, the which instructions are executed and to of calculations, e.g , 'ADD #36' means add the
Computing: Structure and Role of the
system bus must be used again to transfer one or more operand words into synchronise the operation of various computer number 36 to the current contents of the
other registers, which slows down the performance of the processor. The components. Clock frequencies are measured in accumulator register and store the result in he
system bus is the bottleneck. The larger the data word or instruction word that megahertz of gigahertz. accumulator.
can pass along its length in one go, the fewer the number of times it has to be Processors are designed to execute instructions
System clock and clock speed Current Instruction Register: Holds the current
used. In a von neumann computer, a data or instruction word passes over the at a given frequency. This is known as clock instruction to be executed while it is decoded
data bus. A wider data bus should improve a computers speed performance. speed. Some instructions require more clock and executed.
Address words pass along the address bus. A wider address bus allows longer ticks than others. The system clocks frequency is
address fords, so more memory can be addressed. raised to the rate that the processor requires by Memory Address register: Holds the address of
frequency-multiplying circuits. This is done the memory location currently being accessed by
Bus Width: refers to the number of signal wires inside the processor, so it's called an internal the processor.
or lines allocated to a bus. The signal on an clock.
Memory buffer register: holds the data item
individual line represents one binary digit.
being transferred to or from the memory location
Therefore more wires means more binary digits Word Length: The language of the computer is currently being accessed by the processor.
binary. The computer works with binary words
which are codes for instructions, memory
addresses, characters, integer numbers, colours
of pixels and digitised sound samples. Each
binary word consists of binary digits.


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