Semester One 2001/2002 Sheffield Hallam University1 The Motherboard Major circuit board in PC Holds CPU where calculations and instructions on data are executed Noughts and ones crunched at lightning pace!

Semester One 2001/2002 Sheffield Hallam University2 Motherboard Components Memory CPU –Central Processing Unit –Processor –The Chip Bus Expansion slots

Semester One 2001/2002 Sheffield Hallam University3 Memory Arrays of cells Each has a unique hexadecimal address Upon launching a program, instructions are pulled from disk into a contiguous block of memory Data is also stored in memory, but in a different place.

Semester One 2001/2002 Sheffield Hallam University4 Types of Memory RAM (Random Access Memory) allows reading and writing ROM (Read Only Memory) Both come in the form of semiconductors (chips) on the motherboard ROM is used to store basic instructions that must never be deleted. RAM is a main variable to consider when buying a computer

Semester One 2001/2002 Sheffield Hallam University5 RAM is Volatile The most important thing to know about RAM is that it is volatile –Contents are lost when power is removed –Powercuts can cause big problems Always save your work frequently Shortcut for most Windows applications is

Semester One 2001/2002 Sheffield Hallam University6 CPU Processor calculates and makes decisions using stored instructions and data Basis is fetch-execute cycle –instruction residing in a memory address is fetched via the bus, decoded and executed –next cycle fetches instruction from the next contiguous address –unless a different address is specified by a program

Semester One 2001/2002 Sheffield Hallam University7 Processor Speed Measured in megahertz (MHz) –where 1 MHz = a million fetch-execute cycles per second –often referred to as clock speed Currently (Sept 2001) clock speeds are around 3 GHz

Semester One 2001/2002 Sheffield Hallam University8 Processor Types and Manufacturers Main manufacturer is Intel Started with 8088, 80286, 80386, 80486, Pentium, Pentium II, Pentium III When arrived, other manufacturers got in –AMD, Cyrix Motorola make RISC (Reduced Instruction Set Computation) processors, used in the Archimedes and Macintosh computers

Semester One 2001/2002 Sheffield Hallam University9 More on Speed CPU type and CPU speed are not the sole determinants of a computer’s performance Other factors are: –amount of memory –type of memory –bus speed

Semester One 2001/2002 Sheffield Hallam University10 Amount of RAM No matter how fast the CPU, things slow down if it is kept waiting for data or the next instruction Retrieval from RAM is very fast but when it is full the PC must use Virtual Memory (HDD) Memory-hungry uses like multimedia, huge spreadsheets or too many applications open at once slow things down –or make it crash The more RAM the better! –(October 2001) 128MB for a machine running MS Office

Semester One 2001/2002 Sheffield Hallam University11 Virtual Memory Even with a lot of RAM it is possible to run out When this happens part of the HDD ‘pretends’ to be RAM –Virtual memory

Semester One 2001/2002 Sheffield Hallam University12 Main Memory As well as amount of RAM, type is important Most budget PCs come with EDO (Enhanced Data Out) RAM A faster, more expensive type of RAM is SDRAM (Synchronous Dynamic RAM)

Semester One 2001/2002 Sheffield Hallam University13 Cache Memory Even faster than main RAM is cache memory –small amount of super fast RAM living very close to the CPU –most recently used data stored here Two types of cache memory –Primary (internal) - located on the processor itself –Secondary (external) - not on the processor but close

Semester One 2001/2002 Sheffield Hallam University14 Speed of Retrieval From fastest to slowest: –primary/internal cache –secondary/external cache –SDRAM –EDO RAM –Older forms of RAM (DRAM) –virtual memory –ordinary HDD

Semester One 2001/2002 Sheffield Hallam University15 Upgrading You can sometimes replace the CPU with a faster one Tiny handle on motherboard holds chip in place (Zero Insertion Force socket) Remember other constraints on speed –memory –bus Often more cost effective to get a new computer

Semester One 2001/2002 Sheffield Hallam University16 RAM Most PCs have EDO RAM –72 pin SIMM (Single Inline Memory Module) chips If spare slots are available, can plug in extra SIMMs for more memory DIMMs (Dual Inline Memory Module) now more commonplace for Pentiums

Semester One 2001/2002 Sheffield Hallam University17 Bus Electronic path carrying data around system –Width - wider the bus (in bits) the more data can flow at the same time –Speed in MHz Most computers house more than one type of bus....

Semester One 2001/2002 Sheffield Hallam University18 Bus Types Local –Ferrying data within the motherboard between processor and memory –32 bit and 64 bit –On a fast motherboard, 133 MHz Off-board –slower, operating between motherboard and peripheral devices

Semester One 2001/2002 Sheffield Hallam University19 Bus - Most Critical Thing No point in a fast processor and lots of fast RAM without bus width and speed to match –overall performance determined by the slowest component RAM and CPU can be upgraded as they plug into motherboard –Bus is integral to board –Can only be changed by changing motherboard Get the bus right first time!

Semester One 2001/2002 Sheffield Hallam University20 Expansion Slots Motherboard has slots into which smaller boards can be inserted –daughter boards, cards, adaptors Video card controls monitor display LAN or Network Interface Card allows communication with a network The number of expansion slots is something else to think about when choosing a computer - leave plenty of room for future expansion