semester one 2001/2002 sheffield hallam university1 the motherboard major circuit board in pc holds...

Semester One 2001/2002

Sheffield Hallam University 1

The Motherboard

• Major circuit board in PC• Holds CPU where calculations and

instructions on data are executed• Noughts and ones crunched at

lightning pace!



Motherboard Components

• Memory• CPU

– Central Processing Unit– Processor– The Chip

• Bus• Expansion slots



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.



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



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 <CTRL + S>



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



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



Processor Types and Manufacturers

• Main manufacturer is Intel• Started with 8088, 80286, 80386, 80486,

Pentium, Pentium II, Pentium III• When 80386 arrived, other

manufacturers got in– AMD, Cyrix

• Motorola make RISC (Reduced Instruction Set Computation) processors, used in the Archimedes and Macintosh computers



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



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



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



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)



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



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



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



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



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....



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



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!



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

semester one 2001/2002 sheffield hallam university1 the motherboard major circuit board in pc holds...

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