The Motherboard

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! Sheffield Hallam University

2. Motherboard Components • Memory • CPU • Central Processing Unit • Processor • The Chip • Bus • Expansion slots Sheffield Hallam University

3. 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. Sheffield Hallam University

4. 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 Sheffield Hallam University

5. 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> Sheffield Hallam University

6. 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 Sheffield Hallam University

7. 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 Sheffield Hallam University

8. 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 Sheffield Hallam University

9. 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 Sheffield Hallam University

10. 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 Sheffield Hallam University

11. 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 Sheffield Hallam University

12. 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) Sheffield Hallam University

13. 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 Sheffield Hallam University

14. 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 Sheffield Hallam University

15. 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 Sheffield Hallam University

16. 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 Sheffield Hallam University

17. 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.... Sheffield Hallam University

18. 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 Sheffield Hallam University

19. 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! Sheffield Hallam University

20. 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 Sheffield Hallam University