1. COMP 1321 Digital Infrastructure
Richard Henson
University of Worcester
October 2017

2. Week 4: CPUs & Motherboards
Learning Objectives:
Explain main purpose of the motherboard
Explain how a CPU can handle input & output from slow & fast devices
Explain how motherboard architecture has changed in response to miniaturisation, energy-saving, and consumerisation demands

3. Why a Motherboard? CPU far too fragile to exist independently
i.e. needs a “mother”
motherboard delivers power and control to CPU via
control bus
timing chips
ROM and RAM
harnesses power of CPU effectively so it can interact effectively with i/o devices

4. Typical PC Motherboard

5. Motherboards, CPUs and Assembly Language
As mentioned last week, each CPU family has its own “instruction set”
That instruction set allows the CPU to:
perform calculations
move data about between memory locations
Get data from or send data to peripheral devices

6. Motherboards, Peripherals, and i/o
Input-output is part of the vocabulary of computer science
shortened to i/o
Using this same convention:
CPU, memory, and rest of motherboard are collectively “the computer”
anything that happens outside this environment is via “a peripheral”

7. Interrupts
This is a mechanism for a peripheral device to interrupt a CPU in the middle (well almost…) of a program
Not possible in early computers; only became possible with microprocessors and their associated instruction sets
Very useful feature of “solid state” CPUs…

8. Operating System i/o calls
When a computer program (any language…) needs i/o (either i or o!), it invokes an “i/o call” to the CPU, via the operating system
The actual “call” invokes an assembly language instruction for i/o:
with Intel 8086, this is INT 21
further instruction selects motherboard port

9. 8086 (DOS) Interrupts Some examples: 02 write character to screen
05 write to printer
08 take character from keyboard
09 write string to screen
0D write buffer to disk

10. Use of i/o calls in Assembly & Higher Level Languages
Essential to invoke two commands:
Get right nibble contents into AH register
Invoke INT 21
e.g.
MOV AH,02
INT 21

11. Shutting down a program
Should be done formally
Use 4C as the trigger with INT 21
As with all INT 21 needs moving into AH register first
e.g.
MOVE AH, 4C
INT 21

12. I/O devices sorted by data transfer times
10 B/s B/s 1kB/s 10 kB/s 100 kB/s 1 MB/s 10 MB/s MB/s
Keyboard
Audio
Mouse
Joystick
Scanner
IDE HDD
VDU
TV Camera
CD Rom

13. Typical Slow devices
Keyboard
Mouse
Joystick
Audio

14. Fast devices (connect straight into motherboard)
VDU
Hard drive
CD-ROM
Scanner

15. Even faster devices.. CPU Memory (static/dynamic RAM & ROM)
Graphics processors (GPU)

16. i/o Connectors Slow (off motherboard via ports) Serial Parallel
Firewire
PS/2 mouse & keyboard (legacy)
VGA
RJ-45: Network connection
USB: getting faster & becoming the standard

17. Motherboard connectors from http://www. techiwarehouse

18. North Bridge & South Bridge
North: control chipset for fastest onboard devices
ROM & static RAM
South: control chipset for slower onboard devices
SATA & IDE connectors
hard disk & CD-ROM/DVD
RAM connectors
many types, differing no. of pins

19. Layout of component connections
Extremely fast components talking directly to each other
Connection
“North Bridge” chipset
Fast components talking directly to each other
Connection
“South Bridge” chipset
Slow components talking directly to each other

20. Buffers Areas of memory/storage…
where data is stored before forwarding
Message from slow device received and gradually fill buffer…
then sent quickly to fast device
Message from fast device quickly fill buffer
then sent slowly to slow device

21. Resulting arrangement
Pentium III
440 North Bridge
South Bridge
Main Memory
Cache
IDE Disk
Network
Mouse
KBd
USB
Printer
SCSI
Sound
PCI Bus
ISA Bus
Organizing components by their speeds
Incredibly Fast
Very Fast
Fast
Slow
Graphics

22. Buses and on-board communications
Bus - physical link between computer components that electrical impulses (i.e. data as 0s and 1s) can travel through
Only one device can send a message at any one time
other devices have to wait until the line is clear before sending

23. Smaller Motherboards So far…
considered Intel 8086 series CPU
large instruction set & power requirements
Other CPUs use much less power, smaller instruction set
therefore motherboard requirements miniaturised
e.g. Intel Atom: Netbook & Tablet PCs
ARM: Smartphones & Tablets

24. Motherboard-on-a-chip
Started with Smartphones
Spread to Tablet PCs…

25. Architecture of Motherboard chip
With further miniaturisation…
“motherboard” self-contained
mounted on a board to provide i/o connectors

26. Arduino Board (i/o) Microcontroller… not “motherboard on a chip”
therefore not expensive..
Based on i/o control, not apps
used for “physical” computing (real devices)
EPROM for embedded programming (“C”)
USB-computer for power (a few mA)
USB provides scope to use i/o for many purposes

27. Raspberry Pi (computer)
Similar size (and price) to Arduino BUT
needs specific power supply (micro USB, 700 mA)
i/o based on wider range of ports
Microprocessor…
uses ARM
with GPU
read to run an
operating system
(Linux)
Can run apps…

28. Smaller Motherboards So far…
considered Intel 8086 series CPU
large instruction set & power requirements
Other CPUs use much less power, smaller instruction set
therefore motherboard requirements miniaturised
e.g. Intel Atom: Netbook & Tablet PCs
ARM: Smartphones & Tablets

29. Motherboard-on-a-chip
Started with Smartphones
Spread to Tablet PCs…

30. BBC Micro:Bit