Input/Output Organization III: Commercial Bus Standards

CE 140 A1/A220 August 2003

Bus

Pathways of interconnections between different computer components

Three general types; data, address, control

Bus characteristics

Bus width – how many bits can be transmitted at a time

Bus speed – how many bits can be transmitted across each wire per second

Bus bandwidth – bus width x bus speed (same as maximum throughput)

IBM PC/XT Bus

Used on 8088-based systems 8-bit bus Copied by clone vendors for

compatibility with third-party I/O boards

IBM PC/XT Bus

Source: Phil Storrs PC Hardware book <http://members.iweb.net.au/~pstorr/pcbook/showtell/show2.htm>

IBM PC/AT Bus

Used on the 80286-based PC/AT Maintained compatibility with the XT

bus Added an edge connector to increase

bus width to 16-bits

ISA

Industry Standard Architecture Same as the PC/AT Bus 16-bit, 8.33 MHz Maximum

throughput 16.7 MB/s Limited bus master support

ISA

Source:<http://www.rackmountnet.com/ipc/isa_bk/isa_bk.htm>

Problems with ISA

Slow Limited number of interrupts Lack of bus master support Specific to Intel architecture cards

built using ISA will not work on non-Intel platforms

IBM-specific problem: no more monopoly on the hardware market

MCA (IBM’s response) MicroChannel Architecture Developed by IBM for the PS/2 line 16-bit/32-bit computer bus 10-16 MHz Intended to replace the ISA bus Allows bus mastering Limited plug and play Limited to IBM hardware Incompatible with XT, ISA boards

EISA (Industry’s response)

Extended Industry Standard Architecture

Extends ISA bus to 32 bits Maximum throughput: 33.3 MB/s Increased bus mastering support Maintains compatibility with old ISA

boards

EISA

Source:<http://www.atmarkit.co.jp/fpc/slotsocket/indexpage/>

Need for a faster bus

Original IBM PC: text-based applications

Advent of GUIs (Windows, et al) demand high performance

Need for a faster bus

Example 1024 x 768 display 24-bit color 30 frames per second 67.5 MiB/s ISA: 16.7 MB/s EISA: 33.3 MB/s

Local Bus Concept

Demand for higher bandwidth and increased throughput

Bus placed near (or on) the processor’s memory bus

“Local” to the processor Does not have to go through the

slower ISA bus

VESA Local Bus

Developed by Video Electronics Standards Association (VESA)

High-speed conduit for memory-mapped I/O and DMA

Intended for high-bandwidth peripherals (video, storage, etc.)

33 MHz, 32-bit Extension of the 486 memory bus

VESA Local Bus

Source:<http://www.lco-college.edu/classes/pc-ware/chap4b.html>

PCI

Peripheral Component Interconnect (PCI)

Developed by Intel (90’s) but standard was made public platform independent

33 Mhz, 32-bit Maximum throughput 132 MB/s

Plug-and-Play

PCI

Source:<http://www.ontrack.com/hardwareinfo/input-output.asp>

PCI Variants

PCI 2.2: 64-bit, 66 Mhz Maximum throughput: 533 MB/s

PCI-X: 64-bit, 133 Mhz 1066 MB/s PCI-X 266 (PCI-X DDR) 2133 MB/s PCI-X 533 4 GB/s Mini PCI – small form factor PCI cards

for use with embedded systems/portable systems

Problem with using PCI alone

Still not fast enough for memory Not compatible with ISA cards

Intel’s Solution: Northbridge/Southbridge Architecture

Uses bridge chips PCI Bridge (Northbridge)

Connects CPU, memory, and PCI bus ISA Bridge (Southbridge)

Connects PCI bus to the ISA BUS and also supports one or two ATA disks

Advantage: High-bandwidth memory bus (Front Side Bus) PCI bus available for high-bandwidth peripherals

Next generation: Intel Hub Architecture

Northbridge/Southbridge Architecture

Source: Structured Computer Organization by Tanenbaum

AGP

Accelerated Graphics Port High-speed computer bus designed

for 3D computer graphics acceleration

AGP 1X: 32-bit, 66 MHz Also available: 2X, 4X, 8X

AGP

Source: http://www.watch.impress.co.jp/pc/docs/article/991008/hotrev30.htm

PCI-Express

Next generation PCI implementation from Intel

Intended to replace AGP and PCI altogether

Not fast enough as a memory bus Alternatives: HyperTransport

SCSI Small Computer Systems Interface Pronounced “scuzzy” Higher transfer rate than ATA disks Used in workstations and servers More than just a hard disk interface, a full-

fledged bus Also supports CD-ROMs, CD-recorders,

scanners, tape units, etc. Devices are daisy-chained in a linear

manner Terminated at the end to prevent reflection

SCSI TypesName Data Bits Bus MHZ MB/sec

SCSI-1 8 5 5

Fast SCSI 8 10 10

Wide Fast SCSI

16 10 20

Ultra SCSI 8 20 20

Wide Ultra SCSI

16 20 0

Ultra2 SCSI 8 40 40

Wide Ultra2 SCSI

16 40 80

SCSI Typical 8-bit SCSI cable

50 wires, 25 ground, 8 for data, 1 for parity, 9 for control

IEEE 1394 Developed primarily by Apple Commonly referred to as Firewire (Apple),

i.Link (Sony) or digital video (DV) port Used for data storage devices and digital

video cameras Does not require a host IEEE 1394a: up to 400 Mbps IEEE 1394b: up to 800 Mbps Allows daisy-chaining, plug-and-play, and

hot-swapping

USB Universal Serial Bus Developed as a replacement to the serial

and parallel ports USB 1.1 – Up to 12 Mbps USB 2.0 – Up to 480 Mbps Up to 127 devices (THEORETICAL!) Daisy-chained in a tree structure Requires a host computer Upcoming: USB On the Go

Storage Interfaces

ATA Serial ATA SCSI IEEE 1394 USB

ATA

Advanced Technology Attachment Standard interface for connecting

storage devices Transitioned from PIO to DMA modes With the advent of Serial ATA, it has

been retroactively renamed Parallel ATA

ATA Types

Most new drives support Ultra DMA Modes (in contrast to Programmed I/O modes)

Ultra ATA/33 – 33 MBps Ultra ATA/66 – 66 MBps Ultra ATA/100 – 100 MBps Ultra ATA/133 – 133 MBps

ATA-VI

Supports 48-bit addressing that allows system to address 144 PB

Breaks the 137 GB size barrier imposed by older ATA standard

ATA Cables

Serial ATA

Higher speed than Parallel ATA Hot-swappable Cable: 7-wire cable versus 40/80-wire

cable Power cable: 15 pins Initial speed: 150 MBps Later implementations: 300 MBps,

600 MBps

Serial ATA Cables