Chapter 2 Central Processing Unit
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.
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.
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
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
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
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.
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.
CPU RAM L2 CACHE System Bus I/O Buses I/O UNITS (Drives, keyboard, port, adapter, etc) Bridges (Chipset) System Bus • System busis the central bus of the PC that connect CPU with RAM. • A bridgeconnects 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. • Any computer will have three major system buses • Address Bus • Data Busand • Control Bus.
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.
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
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.
Control Bus • Bi-directional. • carries the timing and control signals. • Some are output signals orinput signals to/from the CPU to/from I/O elements. • Each microprocessor has its own unique set of control signals.
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).
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.
Physical aspects of the I/O buses • consists of tracks on the printed circuit board. • These tracks are used as: • Data • Address • Control
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 ATbus. • 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.)
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.
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. • isbuffered 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.
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.
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 configurationinformation; 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.
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 CPUand othercomponents. It permitted concurrent activity in all three locations, (multitasking). All data transfer to and from I/O units cross this intersection..
CPU North Bridge South Bridge System Bus PCI Bus Typical Chipset
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 shareits bandwidth with other devices.
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