PC Bus Types

• Data transfer rates of communication modalities
• External device connectivity and drive connectivity (internal or external):
  • serial port
  • parallel
  • SCSI
  • IDE drive
  • PCMCIA
  • USB
  • firewire
• Internal expansion bus:
  • ISA
  • VESA Local Bus
  • PCI
• Video card connexions:
  • VESA VGA connectors
  • AGP slot
• see also:
  • networks
  • PCMCIA devices
  • image/video sizes & data transfer rates needed

Data Transfer Rates:

• see also: image/video sizes & data transfer rates needed
• Bit Rates (bits/sec):
  • Fax 4-14K telephone/videophone 14-28K
  • videoconference 128K MPEG1 1.5M
  • MPEG2 4M Dig. HDTV distribution 16M
  • TV studio 34M HDTV Studio 140M
  • TV Studio uncomp. 216M HDTV studio uncomp. 1G
  • CDROM video playback possible @ data transfer rates 90-200Kb/sec:
    • 160x120pixels@8-10fps & 11kHz sound rate with audio blocks (the Every field) at 1/2 or 1sec, using MS Video1 compression;
    • Key Frame option = selected; temporal quality = Low (2,3)
    • Data Rate option = CDROM @ 150kps or 80kps;
  • modems:

    • Modem	bit rate kbps	Mb/min	Min for 1Mb
      digital cell phone	9.6	0.072	14
      14.4 fax	14.4	0.108	9
      28.8	28.8	0.216	4.6
      ISDN 1 line	56	0.432	2.3
      ISDN 3 line	168	1.3	0.7

      •  

External device connectivity and drive connectivity:

• Serial Port:
  • RS-232C:
    • Can only send 1 bit per I/O but adequate for 1st generation modems with up to 2400bps.
    • Becomes a bottleneck when faster modems used such as V.32(38.4kbps) & V.32bis(57.6);
  • newer chipset:
    • 115,000bps to allow for modems faster than 9600bps.
• Parallel Port:
  • Normal:
    • Can send 8bits at a time but can only receive 4bits;
  • Bidirectional Portone:
    • Can send & receive 8bits at a time - used by some devices nor EPP compliant;
    • Used mainly by older LAN devices;
  • Enhanced:
    • Xircom/Intel/Zenith created a specification called the Enhanced Parallel Port (EPP) which became part of the IEEE 1284 standard & increased the port's throughput dramatically to be equiv. to an internal ISA 8bit bus but not as good as PCMCIA;
    • The computer & the device must conform to the EPP std.
    • Intel has built the EPP circuitry into its 386SL chip
    • Used mainly by LAN devices for portables without PCMCIA;
• SCSI:
  • Interface for PC's to SCSI hard drives, scanners, etc.
  • 1979: Shugart Assoc. introduce SASI (Shugart Assoc. Systems Interface)
  • 1981: Shugart & NCR propose SASI become an ANSI standard interface
  • 1986: SCSI-1 becomes an ANSI standard but in reality too many versions
  • 1994: SCSI-2 finally approved as a standard, ending incompatibility probs
    • plug'n'play compatibility in Windows95 (built-in drivers, etc);
    • unique ID#s for 8 devices per host adapter (0-7)
    • each device can directly communicate with any other.
  • 1996?: SCSI-3 expected to be approved as a standard
    • support for 15 devices per host adapter
  • SCSI-adapter cards:
    • 8-bit SCSI-1:
      • on sound cards - OK for CD-ROM but too slow for hard drives;
      • transfer 2-5MB/sec; cables up to 6m;
    • 16bit SCSI-2:
      • 50pin "Fast SCSI-II", 10MB/sec; supports 7 devices per card;
      • cables up to 3m.
    • Wide-SCSI-2:
      • 68pin high density, 20MB/sec; 16 or 32 bit data path;
      • also called fast wide; some support 15 devices per card;
    • Ultra SCSI-3:
      • allows 20MB/s 16bit or 40Mb/s across Wide or 16bit paths;
  • PIO type:
    • Programmable I/O - uses host CPU for data transfers
    • Cheaper & almost as fast as bus-mastering for single-threaded operating systems such as Windows 3.11
  • Bus Mastering:
    • Uses card's onboard processor to handle data transfers;
    • Some have onboard cache memory;
    • Expensive but should be much faster in multi-threaded OS's.
  • CorelSCSI software:
    • Non-disk SCSI devices often need their own SCSI ASPI drivers.
    • If your host SCSI card doesn't offer these drivers then can install CorelSCSI which detects equipment installed on system, updates DOS/Win files automatically, contains Windows tools - eg. Audio CD, SCSI diagnostics, TSR CDROM file
    • similar to MS MSCDEX.
• IDE: Integrated Drive Electronics
  • Not really a BUS but initially devised as a cheap way to develop HDDs for the AT.
  • Only support for up to 2 internal HDDs, no other peripherals.
  • The HDD actually contained the disk controller circuitry not the adapter board.
  • Based on a Cylinder Head Sector (CHS) Scheme derived from:
    • XT 13h interrupt hard disk subroutines developed by IBM:
      • 1 byte/head ID, 10bits/cyl#, 6bits/sector component;
      • allowed disks using up to 256heads, 1024 cylinders, & 63 sectors
        • given standard sector size of 512bytes, this makes max. disk 8.4Gb
  • AT Attachment (IDE's ATA) interface designed by IBM & Western Digital:
    • 16bits/cyl, 8bits/sector but ONLY 4bits/head
    • theoretically could build drives up to 137Gb BUT as this scheme did not mesh well with the 13h INT, max. drive only 528Mb (16heads, 63sectors, 1024cyl) !!
    • To enable drives greater than 528Mb, the 13h INT BIOS routine must be replaced at boot by another driver.
  • PIO modes 0,1 and 2 only as based on AT ISA bus.
  • 3 DMA modes.
  • Enhanced IDE (1995):
    • Support for:
      • dual-channel:
        • up to 4 internal HDDs or other devices eg. CDROM
    • Win3.x supports only 32bit disk/file access on 1st EIDE channel and only if < 528Mb size
    • logical block addressing (LBA) via address translation (like SCSI) as well as CHC
    • ATA-2 specifications
    • proposed ATAPI specification supports CDROM/tape backup devices
    • host interfaces on newer motherboards (eg. Intel Triton chipset)
    • higher performance modes (but requires upgrade of BIOS & LB/PCI):
      • PIO mode 3 - max. transfer rate 11.1MBps
      • PIO mode 4 - max. transfer rate 16.6MBps
        • (not supported in mid'95 BIOS yet - ? 1996)
      • Multiword DMA:
        • Mode 1 - transfer rate 13.3MBps
        • Mode 2 - transfer rate 16.6MBps
      • Ultra DMA 33.3MBps?
• PCMCIA Interface:
  • 16bit PCMCIA external expansion slots:
    • PC Memory Card International Assoc. estab. Jun'89 - credit card size PC peripherals;
    • Main features of this archictecture agreed to by JEIDA in '91:
      • host independence - can be run on any computer with PCMCIA-compliant port;
      • "plug & play" - automatic configuration but not always??
      • "hot swapping" - able to swap cards without rebooting computer;
      • execution in place (XIP) - once software loaded into ROM on a PCMCIA card, it can be run directly without being loaded into RAM!
      • Architecture:
        • Interface chip on M/B (most use Intel 82365SL chip) called host adapter that connects tthe expansion bus to 1 or more 68pin PCMCIA sockets;
          • handles PCMCIA interrupts & accepts card-config. commands from Socket Services;
        • Socket Services - the lowest layer of PCMCIA system software archit.
          • prime function is to relay commands b/n Card Services & host adapter.
        • Card Services - highest-level software layer in PCMCIA arch.
          • manages PC resources from a system-wide perspective;
          • ideally should do so directly with card's CIS but in reality, usually via
          • Card Services client drivers which determines needs, etc;
      • PCMCIA device drivers:
        • generic - initialise PC cards that perform well-defined functions
          • eg. SRAM or ATA hard disk cards;
          • these usually shipped with computer;
        • card services client drivers - tend to be card-specific;
        • enablers - bypass Card/Socket Services - also tend to be card-specific;
          • don't allow hot swapping;
        • super client drivers - can recognise & configure many cards with assistance of Card Services, usually shipped with PC;
      • ExCA specification:
        • Exchangeable Card Architecture - defined by Intel to assist PC Card & system interoperability for its 82365SL Host Adapter.
        • defines minimum set of requirements. Given to PCMCIA by Intel.
      • Problems as at '94:
        • PCMCIA manufacturers interpreted specifications differently ->incompatibilities;
        • notebook makers can include only PCMCIA host adapter chip on a M/B,
        • currently, these chips can't address all cards or all drivers;
        • most peripherals shipped with a driver disk that requires I/O info.;
        • most cards assume their resource allocations are correct rather than find out!
        • hot swapping depends on same type of software implementation:
        • different makers ship different BIOS:
          • Phoenix Technologies - Phoenix system BIOS + IBM PC-DOS;
          • SystemSoft - SystemSoft BIOS - in MSDOS since Nov'93;
          • Ventura Micro - other?
          • thus card makers often ship their own special PCMCIA client drivers called "enablers" which have own versions of Card/Socket Services built-in & thus can talk to host adapter directly, allows quick config. but not hot-swapping!
        • only 16bit bus - 32bit bus may not be possible with 68pins but may need 120!
          • PCMCIA guarantees backward compatibility whatever happens.
        • run at 5/12V but new notebooks run at 3.3V -> c'tee to address this prob.
        • although PCMCIA has said there will be no new official slot height, Toshiba has introduced its own 16mm slot - allows hard disks with bigger capacities, but was designed for modems with RJ-11 plugs;
      • Fixes to these problems:
        • makers of both PCMCIA cards & notebooks are publishing lists of compatible products - the systems sticking to a specific host adapter chip & 1 type of PCMCIA Card & Socket Services implementation, while the card makers promise to be compatible with it.
      • Release 1.0 ('90):
        • type I PCMCIA:
          • 3.3mm high sockets with 68 pin-out; footprint 54x85.6mm;
          • specifications for memory technologies only;
      • Release 2.0 (Sept'91):
        • type II PCMCIA:
          • 5mm high
          • additional support for I/O cards - modems/LAN/etc;
      • Release 2.01:
        • bug fixes for Release 2.0 plus support for:
          • type III PCMCIA:
            • 10.5mm - mainly for miniature hard disks;
  • 32bit CardBUS:
    • backwardly compatible with 16bit PCMCIA cards
    • marketed in high end laptops in 1996 & in most by 1998
  • Zoomed Video:
    • usually one of the 2 PCMCIA slots has direct access to video card allowing vastly improved video performance for video-type PCMCIA cards
    • initially on Toshiba laptops in 1996 but becoming widespread in 1998
• Universal Serial Bus (USB):
  • starting to be put into computers in 1997 but devices not marketed until 1998
  • can daisy chain up to 127 devices
    • may need a hub if devices do not have 2 USB ports to continue chain;
      • these hubs are being incorporated in monitors
  • supply power to devices;
  • plug & play;
  • 2 speeds: 1.5Mbps (10x serial port speed); 12Mbps;
    • still not fast enough for > 6x CDROMs or CD-rewritables
    • Kodak DCV300 video camera 10fps @ 320x240
  • plug & play compatibility only supported by Win95 OSR2.1 or later operating systems
  • can be used for:
    • creating other ports: serial, parallel, etc
    • printers, scanners, modems, CDROMs, video cameras, keyboards, joysticks, mouse, speakers
• FireWire:
  • transfers up to 200Mb/sec

Internal expansion bus:

• ISA:
  • 8bit - the original PC-XT internal expansion bus;
  • 16bit - the original PC-AT internal expansion bus - 8MHz; 5MB/sec;
• EISA:
  • 32bit - extended ISA internal expansion bus - 8-10MHz
  • didn't take off
• MCA:
  • 32bit - IBM PS/2 internal expansion bus - 8-10Mhz
  • didn't take off
• NuBus:
  • 32bit Mac.
• VESA local bus:
  • 32bit at full CPU speed rather than 8MHz;
  • But can only use certain peripherals such as Video card, HDD controller;
  • obsolete, replaced by PCI
• Extended VESA LB:
  • still on drawing board (May'94) - 64bit 50Mhz;
  • obsolete, replaced by PCI
• PCI:
  • 64bit 33MHz internal expansion bus for 64bit Pentium & RISC systems;
  • PCI is a mezzanine bus rather than a local bus & thus can operate at speeds independent of the processor cycle speed & can handle up to 6 slots cf max 3 for VL-BUS;
  • Another advantage over VLBus is that the cards & the CPU don't compete for use of the BUS which in VLBus means that CPU has to wait while expansion card using BUS;
  • PCI in contrast has concurrency - it can queue data until the CPU bus is idle;
  • Both PCI & VLBus can transfer data at max. 132Mb/sec - fast enough for 30fps video, etc;
  • PCI incorporates Plug & Play self-configuration;
  • PCI has 64bit data & address bus extension allowing overall bandwidth of 264MB/sec;
  • The 132MB/sec refers to PCI's 32bit implementation;

Video card connexions:

• VGA feature connector:
  • 1987: 26-pin 8bit 256-color 640x480 max. VGA card to other video-related cards;
• VESA Advanced Feature Connector (VAFC):
  • 1994: 80-pin 16-32bit bandwidth allows up to 1024x768;
  • But unlike VM-Channel, doesn't allow cards to share onboard components such as memory - it simply provides cards access to the display.
• VESA media channel (VM-Channel) :
  • 1994: 24bit? 100Mbps connector allowing up to 15 simultaneous devices to connect to graphics card & share the frame buffer of the host graphics card. Allows low-cost high-performance video peripherals such as video capture cards;
• AGP slot:
  • 1998: 100MHz slot designed for AGP video cards