Transcript Document

Compiled by :
S. Agarwal, Lecturer & Systems Incharge
St. Xavier’s Computer Centre,
St. Xavier’s College
Kolkata.
March-2003
CPU
Abbreviation of central processing unit, and pronounced
as separate letters. The CPU is the brains of the computer.
Sometimes referred to simply as the processor or central
processor, the CPU is where most calculations take place.
In terms of computing power, the CPU is the most
important element of a computer system.
On large machines, CPUs require one or more printed
circuit boards. On personal computers and small
workstations, the CPU is housed in a single chip called a
microprocessor.
Basic CPU Components
The CPU consists of
•The control unit which controls all operations of the
computer system.
•The arithmetic and logic unit which performs arithmetic
and logical operations. Arithmetic operations involve the
general mathematical calculations like addition, subtraction,
multiplication and division. Logical operations involve
comparisions like > < = etc.
• Registers which hold temporary data for a specific purpose
or function.
•Interface which communicate with external memory, I/O
units, and possibly other CPUs.
CPU CLOCK SPEED
The rate of speed that the processor executes commands is
measured by clock speed, or often called MHz (megahertz).
The processor requires a fixed number of clock cycles to
perform each instruction. The faster the clock speed, the more
instructions it can execute. Thus resulting in a faster running
computer system.
Listed below are some of the more common processors and clock speed on the market today.
Name of CPU
CPU Speed
Intel Celeron
500 MHz - 800 MHz
Intel Pentium II
233 MHz - 450 MHz
Intel Pentium III
450 MHz - 1 GHz
Intel Pentium III Xeon
600 MHz - 1 GHz
Intel Pentium 4
1.4 GHz - 2 GHz
AMD K6-II
550 MHz
AMD K6-III
450 MHz
AMD Duron
750 MHz -850 MHz
AMD Athlon K-7
1 GHz - 1.33 GHz
AMD Athlon XP
1.4 GHz - 1.8 GHz
Macintosh G3
466 MHz - 733 MHz
Macintosh G4
733 MHz
Obsolete CPUs
1. Intel Celeron 266 - 533 MHz.
2. Intel Pentium II 233 - 450 MHz
3. AMD K6-2 266 - 550 MHz
4. VIA Cyrix III 553 - 667 MHz
5. AMD K6-3 400 and 450 MHz
6. Cyrix MII
7. Pentium
8. AMD K6
9. Cyrix 686
ARITHMETIC-LOGIC UNIT
The arithmetic-logic unit (ALU) performs all
arithmetic operations (addition, subtraction,
multiplication, and division) and logic operations.
Logic operations test various conditions encountered during
processing and allow for different actions to be taken based on the
results.
The data required to perform the arithmetic and logical functions are
inputs from the designated CPU registers and operands.
The ALU relies on basic items to perform its
operations. These include number systems, data routing
circuits (adders/subtracters), timing, instructions,
operands, and registers.
•Typically, the ALU has direct input and output access to the
processor controller, main memory (random access memory or
RAM in a personal computer), and input/output devices.
•Inputs and outputs flow along an electronic path that is called a
bus.
•The input consists of an instruction word (sometimes called a
machine instruction word) that contains an operation code
(sometimes called an "op code"), one or more operands, and
sometimes a format code.
The operation code tells the ALU what operation to perform and the
operands are used in the operation. (For example, two operands might be
added together or compared logically.) The format may be combined with the
op code and tells, for example, whether this is a fixed-point or a floating-point
instruction. The output consists of a result that is placed in a storage register
and settings that indicate whether the operation was performed successfully.
(If it isn't, some sort of status will be stored in a permanent place that is
sometimes called the machine status word.)
Control Unit
The control unit maintains order within the
computer system and directs the flow of traffic
(operations) and data.
The control unit directs the entire computer system to carry out
stored program instructions.
The control unit must communicate with both the arithmetic logic
unit and main memory.
The control unit uses the instruction contained in the Instruction
Register to decide which circuits need to be activated.
The control unit co-ordinates the activities of the other two units as
well as all peripheral and auxiliary storage devices linked to the
computer.
The control unit instructs the arithmetic logic unit which arithmetic
operations or logical operation is to be performed.
The control unit is literally in control.
How the CPU works
The CPU is centrally located on the motherboard.
Since the CPU carries out a large share of the work
in the computer, data pass continually through it.
The data come from the RAM and the units
(keyboard, drives, etc.). After processing, the data is
sent back to the RAM and the units.
The CPU continually receives instructions to be
executed. Each instruction is a data processing
order. The work itself consists mostly of calculations
and data transport.
The Instruction-Execution Cycle
Many types of personal computers can execute instructions in
less than one-millionth of a second; supercomputers can execute
instructions in less than one-billionth of a second.
The CPU performs four steps in executing an instruction:
1. The control unit gets the instruction from memory.
2. The control unit decides what the instruction means and directs
the necessary data to be moved from the memory to the
arithmetic logic unit.
3. The arithmetic logic unit performs the actual operation on the
data.
4. The result of the operation is stored in memory or a register.
The first two instructions make up what is called the instruction
time. The last two instructions make up what is called the
execution time. The combination of these two is called a machine
cycle.
Each central processing unit has an internal clock (or system clock),
which produces pulses at a fixed rate to synchronise all computer
operations. A single machine cycle instruction is made up of a
number of subinstructions, each of which must take at least one clock
cycle.
Each type of CPU is designed to understand a specific group of
instruction called the instruction set.
How the CPU finds Instructions and Data
The location in memory for each instruction and each piece of data is
identified by an address, or a number that stands for a location in the
computer memory.
An address may be compared to a mailbox in everyday life, except
that the address can hold only one item - a fixed amount of data, a
number or a word - at any one time.
The following is an example of a simple case of adding
two numbers together and placing the result in a location
X. The command executed is - Let X = N1 + N2.
Interrupts (IRQs)
An interrupt is basically what it sounds like, a message from
one part of the computer to another (normally to the system
processor) that tells it that it needs to stop what it is doing,
and do something else instead.
An IRQ is an interrupt request, and is the name for the
actual signal that is used when a peripheral requests an
interrupt of the processor.
Interrupts play a key role in how the processor performs
input/output processing, and interfaces with every peripheral
in the computer, from the keyboard and mouse to the hard
disk and modem.
The PC Bus
The bus is actually a set of circuits that run
throughout the board and connect all the expansion
slots, memory, and CPU, etc. together. The various
components and devices must be linked together to
perform a function.
The 'bus' (or should we say 'BUSES'?) provides a
highway for passing information between the
devices on the system.
The bus ties these devices together, so that
•A signal from the keyboard is displayed on the
screen (CRT)
•A record from a file on a hard disk drive is read into
memory and processed at the direction of the CPU
•A file is sent to a printer for printing, etc.
SO we can say, electrical signals representating
information flows along the bus from one device to
another.
The computer may contain several types of buses (all located on
the motherboard). Some of the more common buses found are:
•CPU bus or 'system' bus.
•An address bus
•Memory bus
•I/O or Expansion Bus
•ISA Bus
•PCI Bus
•Micro Channel Bus
•EISA Bus
•External Buses (Can have external cables connecting devices)
•SCSI Bus
•PC Card Bus
•USB Bus
VARIOUS BUSES :
•The Processor Bus: This is the highest-level bus that
the chipset uses to send information to and from the
processor.
•The Cache Bus: Higher-level architectures, such as
those used by the Pentium Pro and Pentium II, employ a
dedicated bus for accessing the system cache. This is
sometimes called a backside bus. Conventional
processors using fifth-generation motherboards and
chipsets have the cache connected to the standard
memory bus.
•The Memory Bus: This is a second-level system bus
that connects the memory subsystem to the chipset and
the processor. In some systems the processor and
memory buses are basically the same thing.
•The Local I/O Bus: This is a high-speed input/output
bus used for connecting performance-critical peripherals
to the memory, chipset, and processor. For example,
video cards, disk storage devices, high-speed networks
interfaces generally use a bus of this sort. The two most
common local I/O buses are the VESA Local Bus (VLB)
and the Peripheral Component Interconnect Bus (PCI).
•The Standard I/O Bus: Connecting to the above three
buses is the "good old" standard I/O bus, used for slower
peripherals (mice, modems, regular sound cards, lowspeed networking) and also for compatibility with older
devices. On almost all modern PCs this is the Industry
Standard Architecture (ISA) bus.
All buses are located on the motherboard with the
exception of the External buses. External buses
connect to standard ISA or PCI expansion slots via
a controller/adapter card. This card acts as an
interface between the ISA/PCI bus architecture. The
cables connected to the adapter/controller card are
actually considered as the bus. Thus the 50 pin
cable connecting SCSI devices to the controller is
the actual bus.
There is a new bus called the "Universal Serial
Bus" that fits into this category. The difference is
that this bus connects directly to the system bus on
the motherboard.
A motherboard is the physical arrangement in a computer that
contains the computer's basic circuitry and components. On the
typical motherboard, the circuitry is imprinted or affixed to the
surface of a firm planar surface and usually manufactured in a
single step.
The computer components included in the motherboard are:
•The microprocessor
•(Optionally) coprocessors
•Memory
•BIOS
•Expansion slots
•Interconnecting circuitry
Additional components can be added to a motherboard through its
expansion slots. The electronic interface between the motherboard
and the smaller boards or cards in the expansion slots is called the
bus.
Microprocessor
A microprocessor is a computer processor on a microchip. It's sometimes called a logic
chip.
It is the "engine" that goes into motion when you turn the computer on. A microprocessor is
designed to perform arithmetic and logic operations that make use of small numberholding areas called registers. Typical microprocessor operations include adding,
subtracting, comparing two numbers, and fetching numbers from one area to another.
These operations are the result of a set of instructions that are part of the microprocessor
design.
When the computer is turned on, the microprocessor is designed to get the first instruction
from the basic input/output system (BIOS) that comes with the computer as part of its
memory. After that, either the BIOS, or the operating system that BIOS loads into computer
memory, or an application program is "driving" the microprocessor, giving it instructions to
perform.
Microchip
A microchip (sometimes just called a "chip") is a unit of packaged
computer circuitry (usually called an integrated circuit) that is
manufactured from a material such as silicon at a very small
scale. Microchips are made for program logic (logic or
microprocessor chips) and for computer memory (memory or
RAM chips).
CO-PROCESSOR
A special-purpose processing unit that assists the CPU in
performing certain types of operations.
For example, a math coprocessor performs mathematical
computations, particularly floating-point operations. Math
coprocessors are also called numeric and floating-point
coprocessors.
Most computers come with a floating-point coprocessors built in.
Note, however, that the program itself must be written to take
advantage of the coprocessor. If the program contains no
coprocessor instructions, the coprocessor will never be utilized.
In addition to math coprocessors, there are also graphics
coprocessors for manipulating graphic images. These are often
called accelerator boards.
MEMORY
A computer requires a memory to store and retrieve
instructions and data. There are a variety of storage
devices including semiconductor memories and
magnetic memories. Generally, the term memory refers
to only the small integrated circuits called chips, which
are used as a computer's internal memory.
BIOS
BIOS is a layer between the hardware and the software. If the
software wants to access the hard drive, it has to go through
the BIOS to make sure that the hard drive is working. The
BIOS translates between the two because hardware speaks
a machine language and software speaks a programming
language.
The BIOS is considered neither a hardware nor a software
but a firmware. BIOS is like software because it contains
instructions, but it is a hardware as it is an intricate part of the
motherboard’s circuitry.
BIOS is an integral part of the computer and comes with it when you bring it home. (In
contrast, the operating system can either be preinstalled by the manufacturer or vendor
or installed by the user.) BIOS is a program that is made accessible to the
microprocessor on an eraseable programmable read-only memory (EPROM) chip.
When you turn on the computer, the microprocessor passes control to the BIOS
program, which is always located at the same place on EPROM.
When BIOS boots up (starts up) the computer, it first determines whether all of the
attachments are in place and operational and then it loads the operating system (or key
parts of it) into the computer's random access memory RAM from the hard disk or
diskette drive.
With BIOS, the operating system and its applications are freed from having to
understand exact details (such as hardware addresses) about the attached input/output
devices. When device details change, only the BIOS program needs to be changed.
Sometimes this change can be made during the system setup. In any case, neither the
operating system or any applications you use need to be changed.
EXPANSION SLOTS
An opening in a computer where a circuit board can be
inserted to add new capabilities to the computer. Nearly all
personal computers (except portables) contain expansion
slots for adding more memory, graphics capabilities, and
support for special devices. The boards inserted into the
expansion slots are called expansion boards, expansion
cards , cards , add-ins , and add-ons.
If you open the PC
and examine the
system motherboard
you will notice that it
has a number of
different
expansion
slots with expansion
cards inserted into
them.
By using a collection of wires and protocols, each slot allows you to add
functionality to the PC by inserting printed circuit boards (expansion boards),
such as soundcards, graphics cards, TV cards etc. These boards
communicate with the other hardware devices in the system by means of the
data bus which facilitates communication with the microprocessor.
There are three types of expansion slots:
1. ISA (Industry Standard Architecture)
This bus architecture was developed by IBM for their PC/XT and PC/AT
machines and became a de facto industry standard. Generally these are the
long black slots you see on the motherboard.
2. PCI (Peripheral Component Interconnect)
Starting in the early 90s, ISA began to be replaced by the PCI local bus architecture.
These are the smaller, white slots on the motherboard. PCI is a 64-bit bus,
though it is usually implemented as a 32-bit bus.It can run at clock speeds of 33
or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps.
Although it was developed by Intel, PCI is not tied to any particular family of
microprocessors.
3. AGP ( Accelerated Graphics Port)
This is a interface specification developed by Intel Corporation. These are the
smallest, brown slots on the motherboard.. AGP is based on PCI, but is
designed especially for the throughput demands of 3-D graphics. Rather than
using the PCI bus for graphics data, AGP introduces a dedicated point-to-point
channel, so that the graphics controller can directly access main memory. The
AGP channel is 32 bits wide and runs at 66 MHz. This gives a total bandwidth of
266 MBps, as opposed to the PCI bandwidth of 133 MBps. AGP allows 3-D
textures to be stored in main memory rather than video memory.