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Computer ArchitectureComputer Architecture
Part IV-B: I/O Buses
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ChipsetsChipsets
Intelligent bus controller chips found on the motherboard
Enable higher speeds on one or more buses and the utilization of new facilities (e.g. faster, larger RAM)
Suppliers include Intel, SIS, Opti, Via, ALi
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Chipsets and the Other ComponentsChipsets and the Other Components
CPU
Caches
System Bus / FSB
Memory
I/O Devices:
Controllers
Adapter
DisksDisplaysKeyboards
Networks
Peripheral Bus
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Internal Bus OrganizationInternal Bus Organization
Same bus for all (e.g. HP-PB) Separate bus for CPU-memory and
I/O (whether I/O to CPU or I/O to memory, e.g. CIO)
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I/O Bus ArchitectureI/O Bus Architecture
Four (4) main I/O bus architectures in the modern PC Industry Standard Architecture (ISA) Peripheral Component Interconnect (PCI) Accelerated Graphics Port (AGP) Universal Serial Bus (USB)
Each may have internal or external ports
May be used to connect other I/O buses
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Internal vs. External PortsInternal vs. External Ports
Internal I/O ports LPT, COM1, COM2, EIDE, etc.
External ports Includes expansions slots in motherboard
which can accept various types of controllers
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I/O Buses in the PCI/O Buses in the PC
Source: www.mkdata.dk
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Source: www.mkdata.dk
Devices on each I/O BusDevices on each I/O Bus
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ISAISA
16-bits wide, 8 MHz Works synchronously with the CPU
clock If the system bus is faster than 10 MHz
then the ISA bus frequency is reduced to a fraction of the system bus frequency
Theoretical maximum: 8 Mbps, Reality: Only 1 – 2 Mbps
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ISA Internal and External PortsISA Internal and External Ports
Source: www.mkdata.dk
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ISA DrawbacksISA Drawbacks
16-bits, 8 MHz Too narrow and slow, not enough
bandwidth No intelligence
Every component requires a specific IRQ and possibly a DMA channel
Tuning of IRQ and DMA needs to be done manually – limited or no Plug-and-Play (PnP) features
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ISA FutureISA Future
Obsolete! No longer used in current motherboards Intel’s 810 chipset was the first not to
include any support for ISA
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PCIPCI
Started 32-bits wide, 33 MHz, maximum data transfer rate of 132 Mbps -> PCI-X supports 64-bits, 66 MHz
Processor independent Can be used with any 32- or 64-bit CPU
Buffered architecture
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Buffered ArchitectureBuffered Architecture
CPU delivers data to the buffer and proceeds with other tasks; PCI bus handles the rest of the operation
PCI adapters transmits data to the buffer, regardless of whether the CPU is free to handle request, i.e. requests are placed in a queue
Plug-and-play is supported in PCI specifications
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PCI Internal and External PortsPCI Internal and External Ports
Source: www.mkdata.dk
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PCI FuturePCI Future
PCI-X Supported by IBM, 3Com, Mylex,
Adaptec, HP and Compaq PCI-X 1.0: 64-bits, 66/133 MHz (133
provides around 11 MB/s bandwidth) PCI-X 2.0: 64-bits, 266/533 MHz PCI-X 1066: 1066 MHz (available 2004),
8.5 GB/s bandwidth
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PCI FuturePCI Future
PCI Express (Next Generation I/O or NGIO) Supported by Intel, Dell, NEC, Sun, etc. Codenamed 3GIO Can provide a theoretical maximum of 16
GB/s bandwidth
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AGPAGP
Designed exclusively for video Relieves PCI bus of graphics data 66 MHz, 64-bits
Introduced by Intel on Pentium II boards (440LX and later).
AGP standards 1x – 266 Mbps 2x – 533 Mbps 4x – 1.07 Gbps 8x – 2.1 Gbps
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ISA, PCI and AGP slotsISA, PCI and AGP slots
ISA
PCI
AGP
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USBUSB
12 megabits per second (Mbps) bus Can connect up to 127 devices in one
long “daisy chain” Devices can be plugged and
unplugged easily
USB
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USB DevicesUSB Devices
Meant to connect devices such as the keyboard, mouse, joystick, speakers, printers, modems, scanners, camera, etc.
Source: www.mkdata.dk
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USB VersionsUSB Versions
USB v1.1 (USB) Data rates of 12 Mbps (full-speed) and
1.5 Mbps (low-speed) USB v2.0 (Hi-Speed USB)
Theoretical maximum data transfer rate of 480 Mbps
Supports the three data transfer rates for backward compatibility
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Enhanced IDE (EIDE)Enhanced IDE (EIDE) IDE – Intelligent/Integrated Drive Electronics Also known as Advanced Technology
Attachment (ATA) Each channel has a master and slave
device
Source: www.mkdata.dk
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EIDE DevicesEIDE Devices
Hard disks (ATA-33/66/100) CD-R, CD-RW drives DVD drives Zip drive Tape Backup units
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SCSISCSI
Small Computer System Interface Utilizes host adapter to control 7 (or
15) devices using only one IRQ SCSI has its own CPU system frees
the main CPU from the I/O workload
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The SCSI Host AdapterThe SCSI Host Adapter
Intelligent controller at the heart of a SCSI system
Controls several SCSI units including various types of drives (hard disks, CDROM, Zip disks, MO drives, etc.), backup tape units, scanners
Has its own BIOS Some motherboards feature an on-
board SCSI host adapter
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SCSI ChainSCSI Chain
Regular SCSI systems can handle 8 devices (including the adapter); wide SCSI can handle 15 devices
Each device has to be assigned a unique number from ID0 to ID7; host adapter is typically assigned ID7
SCSI devices can be internal (inside the computer casing) or external
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SCSI Chain ExampleSCSI Chain Example
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SCSI TerminatorsSCSI Terminators
The devices at both ends of a SCSI chain must be terminated.
The host adapter is one end of the chain.
Source: www.mkdata.dk
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SCSI IntelligenceSCSI Intelligence
SCSI utilizes its own protocol to assure maximum utilization of the bandwidth.
Basis of SCSI is a set of commands Each device has its own intelligent controller
which can interpret these commands.
Source: www.mkdata.dk
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SCSI StandardsSCSI Standards
There are various other variations of SCSI SCSI standards are confusing to say the least!