1 chapter 2 central processing unit. 2 cpu the "brain" of the computer system is called...
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Chapter 2
Central Processing Unit
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CPU
• The "brain" of the computer system is called the central processing unit.
• Everything that a computer does is overseen by the CPU.
• CPUs have for years increased their performance.
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CPU History
• closely tied to the IBM and Intel. The CPUs have their roots to Intel's chip 4004 from 1971.
• seven or eight CPU generations up till today.
• The first microprocessor to make into a home computer was the Intel 8080.
• PC market moved from the 8088 to 80286 to 80386 to 80486 to Pentium, Pentium II, Pentium III and Pentium 4.
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Functions of CPU
• executes a collection of machine instructions that tell the processor what to do.
• Based on the instructions, a microprocessor does three basic things.
– perform mathematical operations. – process and transfer data – make decisions
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The CPU – speed measurement
• clock speed and data width.
• Norton System Information (SI).
– a relative number – 8086=1– Computing Index (CI) – CPU Speed– Disk Index (DI) – Disk Speed– Performance Index (PI) – Combined CI & DI
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CPU Frequencies
• The internal clock frequency is the speed inside the CPU.
• The external clock frequency (Front Side Bus or System Bus) is the speed between the CPU and RAM.
Internal clock frequency is higher than External clock frequency
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Bus & Bus Speed• connects one part of the motherboard to another.
• speed measured in megahertz (MHz)
– front side bus (FSB) – CPU to Northbridge.
– back side bus - CPU to level 2 (L2) cache.
– memory bus - Northbridge to the memory.
– AGP bus - the video card to the memory and the CPU.
– IDE or ATA bus - Southbridge to the disk drives.
– PCI bus - PCI slots to the Southbridge.
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Bus Connections
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How does a CPU work?
• centrally located on the motherboard.
• data come from the RAM and other units.
• receives and sends its data from and to buses. They can be divided into:
– system bus, which connects the CPU with RAM – I/O buses, which connect the CPU with other components.
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System Bus
• Any computer will have three major system buses
– Address Bus– Data Bus and – Control Bus.
CPUSystem Bus RAML2
CACHE
I/O BusesI/O UNITS
(Drives, keyboard,
port, adapter, etc)
Bridges(Chipset)
• System bus is the central bus of the PC that connect CPU with RAM.
• A bridge connects the I/O buses with the system bus and on to RAM. The bridge is part of the PC chipset.
• Chip sets are a bunch of intelligent controller chips, which are on a motherboard.
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Address Bus
• Unidirectional – one direction only
• carries addresses by CPU to memory and I/O elements.
• The size of the address is determined by the number of lines in the bus.
• The lines determine the number of memory locations and I/O, the CPU can address to.
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Address Bus - Example
If the address bus is composed of 16 lines, the CPU will be able to generate 216, or 65,536 distinct address codes. (1k = 1024). If the address bus size is increased to a 20-bit word size, what will be the possible addresses?
Possible addresses = 220 = 1,048,576 addresses
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Data Bus
• Bi-directional – both directions.
• Write operation – data from the CPU to memory.
• Read operation – data moves from memory to the CPU.
• size of the data bus usually corresponds to the word size of the computer.
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Control Bus
• Bi-directional.
• carries the timing and control signals.
• Some are output signals or input signals to/from the CPU to/from I/O elements.
• Each microprocessor has its own unique set of control signals.
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Types of data
• Instructions:
– called program code.
– include the commands send to your PC using your keyboard and mouse.
– e.g. Commands to print, save, open, etc.
• Data:– user data. – e.g. actual contents (the text or the letters).
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I/O Bus
• move data.
• connect all I/O devices with the CPU and RAM.
• buses speed is lower than the system bus.
• On modern PCs, you will usually find four buses:
– The ISA bus, an old low speed bus.
– The PCI bus, which is a new high speed bus.
– The USB bus (Universal Serial Bus), which is a new bus.
– The AGP bus (Accelerated Graphics Port) which is used for the graphics card.
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Physical aspects of the I/O buses
• consists of tracks on the printed circuit board.
• These tracks are used as:
– Data– Address – Control
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ISA bus (Industry Standard Architecture)
• Since about 1984, it is the standard bus for PC I/O functions.
• ISA was an improvement over the original IBM XT bus, which was only 8 bit wide. IBM's trademark name is AT bus.
• can run as 16 bit wide but it requires 2-3 clock ticks to move 16 bits of data.
• ISA bus works synchronous with the CPU.
• ISA bus has a theoretical transmission capacity of about 8 MB/s. (Actual speed does not exceed 1-2 MB/s.)
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Disadvantages of ISA Bus
• narrow or limited bandwidth – only 8 bits wide
• It is slow. It requires 2-3 clock ticks to move a16 bits of data.
• not “intelligent”, since the CPU has to control the data transfer across the bus.
• When PC communicates with the floppy drive, the rest of the PC is waiting for it to complete.
• It is not in used in the new Pentium 4 computer.
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PCI bus (Peripheral Component Interconnect)
• high speed bus of the 1990s made by Intel – 32 bit wide
• is processor independent. Therefore, it can be used with all 32 or 64 bit processors.
• is backward compatible with the ISA bus.
• is buffered in relation to the CPU and the peripheral components.
• handles the transmission in its own tempo.
• operate asynchronous.
• is intelligent – All PCI adapter cards configure themselves. Plug and Play. (PnP).
• is the central I/O bus, in all PCs.
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Plug and Play
• is part of the PCI specification. It means that all PCI adapter cards are self-configuring.
• During startup, communication takes place between the PC’s startup programs, the PCI controller and each PCI device (adapter).
• The adapter must be able to inform the I/O bus which I/O addresses and IRQ’s it can operate with and be able to configure itself to use the resources allocated to it by the I/O bus.
• When the exercise is successful, the adapter is configured automatically, and is ready to be used by the operating system.
• All the components involved (adapter, motherboard and Windows) have to be Plug and Play compatible for the system to work.
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Schematic overview of Plug and Play
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Extended System Configuration Data (ESCD)
• is a small data area which is stored in the motherboard’s CMOS storage.
• ESCD store is used to save adapter configuration information; e.g. PC’s configuration.
• ESCD also allows the user to manually allocate an IRQ etc. This can be done using the motherboard’s setup program.
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What is a chip set?
• The chip sets are a bunch of intelligent controller chips; it controls the system and its capabilities.
• All components communicate with the processor through the chipset transfer and organize the steady flow of data.
• makes a bridge between the CPU and other components. It permitted concurrent activity in all three locations, (multitasking). All data transfer to and from I/O units cross this intersection..
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Typical Chipset
PCI BusSystem Bus North Bridge
South Bridge
CPU
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MCH and ICH• a new architecture was introduced by Intel in 1999.
• Memory Controller Hub (MCH) replacing the north bridge.
• I/O Controller Hub (ICH) replacing the south bridge.
• The MCH is a controller located between the CPU, RAM and AGP. It regulates the flow of data to and from RAM. This new architecture has two important consequences:
– The connection between the two hubs is managed by a special bus (link channel), which can have a very high bandwidth.
– The PCI bus comes off the ICH, and doesn’t have to share its bandwidth with other devices.
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Two Bridges
• a north and a south bridge.
• Both bridges are essentially routers.
• north bridge takes all the heavy traffic
• south bridge routes in to a lot of different narrow routes
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Typical Chipset