Input/Output Organization III: Commercial Bus Standards CE 140 A1/A2 20 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

IBM PC/AT Bus  Used on the 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:

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  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:

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:

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:

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:

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 Types NameData BitsBus MHZMB/sec SCSI-1855 Fast SCSI810 Wide Fast SCSI Ultra SCSI820 Wide Ultra SCSI Ultra2 SCSI840 Wide Ultra2 SCSI

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