1. Bus structures Unit objectives:
Describe the primary types of buses, and define interrupt, IRQ, I/O address, DMA, and base memory address
Describe PCI and PCIe buses, and PCI and non-PCI video standards

2. Topic A
Topic A: Buses
Topic B: The PCI bus

3. Buses Communication pathway Defined by Three types
How many bits it transmits at one time
Signaling technique
Data transfer speed
Three types
Address
Data
Expansion (I/O)
continued 3

4. Buses, continued Address and data buses enable: Expansion bus
Basic CPU operation
Interactions with memory
Expansion bus
Communication pathway for non-core components to interact with the CPU, memory, and other core components
Adapter cards add functionality
PCIe is taking over from PCI
Older buses: ISA, EISA, Micro Channel, and PC bus 4

5. PCI bus slots 5

6. The riser bus
Brings the basic wiring and control of a function to a motherboard
Decreases cost
Two main riser standards:
Audio/Modem Riser (AMR)
Communications and Networking Riser (CNR)

7. Activity A-1
Examining buses

8. System interaction Gain the attention of the CPU
Access shared memory locations
Extend the system BIOS
Transfer data across the bus 8

9. Interrupts Signal CPU that attention is needed
CPU stops what it was doing
Services the device request
Returns to its previous task 9

10. IRQs Numerical identifiers Help CPU identify interrupt source
Enforce priority of interrupts
Common IRQs
IRQ 1: Keyboard
IRQ2: Cascade IRQs 8-15
IRQ4: COM1
IRQ6: Floppy
IRQ12: PS/2 mouse
IRQ14: Primary IDE hard drive 10

11. Device Manager: IRQs 11

12. Examining IRQ assignments
Activity A-2
Examining IRQ assignments

13. I/O addresses Identify devices
Have a range of numerical addresses for each device
Allow CPU to communicate multiple commands
Use 16-bit hexadecimal numbers
User or BIOS configures the number ranges 13

14. Device Manager: I/O addresses14

15. Viewing your computer’s I/O address assignments
Activity A-3
Viewing your computer’s I/O address assignments

16. DMA channels DMA controller relieves CPU Dedicated channels
Largely replaced by other techniques, such as bus mastering 16

17. Viewing your computer’s DMA channel assignments
Activity A-4
Viewing your computer’s DMA channel assignments

18. Memory addresses Devices extend system BIOS with new routines
Display adapters
SCSI controllers
IDE controllers
System BIOS locates and loads BIOS extensions using mapped memory location
Historically in upper memory block (UMB) – space between 640KB (0x000A0000) and 1MB 18

19. Device Manager: Base memory19

20. Viewing your computer’s memory address assignments
Activity A-5
Viewing your computer’s memory address assignments

21. Topic B
Topic A: Buses
Topic B: The PCI bus

22. PCI bus 32- or 64-bit bus 33 or 66 MHz clock speed
Pentium PCs
33 or 66 MHz clock speed
MBps maximum data transfer rate
Up to 8 functions on a single card
Up to 5 cards/slots per system
Requires PnP 22

23. PCI adapter 23

24. PCIe Newer standard Uses serial communication Lanes
2.5 Gbps in each direction using 8b/10b encoding (0.25 GBps)
x1 (by one), x2, x4, x8, x12, x16, and x32 bus widths
Links – bidirectional switched lanes
Can up-plug (e.g., x1 card in x16 slot)
Can’t down-plug (not officially)

25. Multifunction cards PCI spec supports multifunction cards
Up to 8 functions per card
Five slots/cards per system
Total of 40 expansion devices

26. Activity B-1
Identifying a PCI bus

27. Video adapters Generates signals sent to monitor
Graphical interfaces involve massive amounts of graphics data
Can be built into motherboard or adapter card
Three types of video slots
PCI
PCIe
AGP

28. PCI-based video Low-end systems: video adapter built into motherboard
PCI is slowest of three types
Share bus with all other PCI-based devices
Work well for two-monitor system

29. PCIe-based video Designed to replace AGP cards
x16 PCIe card has 4 GBps bandwidth
Bidirectional nature allows up to 8 GBps
Simultaneous data movement upstream and downstream
Ideal for multimedia applications, such as gaming, photography, and videography
See for comparison among PCI standards

30. A PCIe video card

31. AGP video adapters Technically a port, not a bus
Provides direct connection between video adapter and CPU
Referred to as #X
Original performance benefit was accessing and using main system memory
Direct Memory Execute (DIME)
Modern AGP cards use onboard memory, except in laptops
Multiple-monitor support
Being phased out for PCIe 31

32. AGP adapter
Note the hook 32

33. AGP characteristics 32-bit bus Multiple of 33 MHz clock speed
Speed “pumped” to as much as 533 MHz
MBps data transfer rate
PnP configurable

34. AGP slots Typically brown; sometimes maroon or other dark color
Separated from other bus slots to help cooling
High-end systems include multiple, independent AGP slots

35. Identifying graphics connections
Activity B-2
Identifying graphics connections

36. Unit summary
Described the primary types of buses, and defined interrupt, IRQ, I/O address, DMA, and base memory address
Described PCI and PCIe buses, and PCI and non-PCI video standards