Bus structures Unit objectives Describe the primary types of buses, and define interrupt, IRQ, I/O address, DMA, and base memory address Describe the features and functions of the PCI bus Describe the features and functions of the various video buses

Topic A Topic A: Buses Topic B: The PCI bus Topic C: Video buses

Buses Communication pathway Defined by –How many bits it transmits at one time –Signaling technique –Data transfer speed Four types –Address –Data –Expansion –Video continued

Buses, continued Address and data buses enable: –Basic CPU operation –Interactions with memory Expansion bus –Communication pathway for non-core components to interact with core components –Adapter cards add functionality –PCI bus predominant –Older buses: ISA, EISA, Micro Channel, and PC bus

PCI bus slots

Video bus Generates signals sent to monitor Can be built into motherboard or adapter card Communicates over expansion or video bus Enormous amount of data strains expansion bus Graphic buses –VESA or AGP –Transmit video data at high speeds

An AGP video bus slot AGP slot

The riser bus Brings the basic wiring and control of a function to a motherboard Decreases cost Three riser standards: –Advanced Communication Riser (ACR) –Audio/Modem Riser (AMR) –Communication and Networking Riser (CNR)

Activity A-1 Examining buses

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

Interrupts Signal CPU that attention is needed –CPU stops what it was doing –Services the device request –Returns to its previous task Polling –Inefficient alternative to interrupts

IRQs Numerical addresses Help CPU identify interrupt source Enforce priority of interrupts Common IRQs –IRQ 1: Keyboard –IRQ2: Cascade IRQs 9-15 –IRQ4: COM1 –IRQ6: Floppy –IRQ12: PS/2 mouse –IRQ14: Primary IDE hard drive

Device Manager: IRQs

Activity A-2 Examining IRQ assignments

I/O addresses Identify section of shared memory Range of memory addresses Hexadecimal

Device Manager: I/O addresses

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

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

Device Manager: DMA channels

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

Base 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

Device Manager: Base memory

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

Topic B Topic A: Buses Topic B: The PCI bus Topic C: Video buses

Bus types PCI currently most popular Historical bus types –PC/XT –PC/AT –ISA –EISA –MCA

PC/XT bus 8-bit bus –IBM PC and IBM XT 4.77 MHz clock speed 1.6 Mbps maximum data transfer rate (0.4 MBps) Supported IRQs 0-8 Configured with DIP switches or jumpers

PC/XT card

PC/AT and ISA bus 16-bit bus –IBM AT, clones, 80386/486, current PCs 8 MHz clock speed 8 MBps maximum data transfer rate

ISA adapter

ISA expansion bus slot ISA slot

PCI bus 32- or 64-bit bus –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

PCI adapter

PCIe Newer standard Uses serial communication Link Lanes x1 (by one) x1, x2, x4, x8, x12, x16, and x32 bus widths Can up-plug Can’t down-plug

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

Activity B-1 Identifying a PCI bus

Topic C Topic A: Buses Topic B: The PCI bus Topic C: Video buses

Need for video buses Older PC designs just used expansion bus Graphical interfaces involve massive amounts of graphics data Specialized buses were developed to be fast enough

VESA local bus 32- or 64-bit bus –Pentium PCs 33 or 66 MHz clock speed Popular on based PCs Generally software configurable No longer used

VLB adapter

PCI-based video Low-end systems: video adapter built into motherboard Three type of video slots –PCI –PCIe –AGP PCI is slowest of three types Share bus with all other PCI-based devices Work well for two-monitor system

AGP standards AGP 1.0 AGP 2.0 AGP bit AGP Ultra-AGP AGP Pro Ultra-AGPII

AGP 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

AGP adapter Note the hook

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

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

PCIe 16x PCIe card has 4 Gbps bandwidth Dual line technology allows up to 8 GBps Simultaneous data movement upstream and downstream Ideal for gaming and photography, videography

A PCIe video card

Activity C-1 Identifying graphics connections

Unit summary Described the primary types of buses, and defined interrupt, IRQ, I/O address, DMA, and base memory address Described the features and functions of the PCI bus Described the features and functions of the various video buses, and installed and configured an AGP adapter card