Computer Architecture

1. Computer Architecture Part IV-B: I/O Buses

2. Chipsets • 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

3. CPU Caches System Bus / FSB Adapter Memory Peripheral Bus Controllers Disks Displays Keyboards I/O Devices: Networks Chipsets and the Other Components

4. Internal 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)

5. I/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

6. Internal 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

7. I/O Buses in the PC Source: www.mkdata.dk

8. Devices on each I/O Bus Source: www.mkdata.dk

9. ISA • 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

10. ISA Internal and External Ports Source: www.mkdata.dk

11. ISA 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

12. ISA Future • Obsolete! • No longer used in current motherboards • Intel’s 810 chipset was the first not to include any support for ISA

13. PCI • 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

14. Buffered 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

15. PCI Internal and External Ports Source: www.mkdata.dk

16. PCI 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

17. PCI 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

18. AGP • 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

19. ISA PCI AGP ISA, PCI and AGP slots

20. USB • 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

21. USB Devices • Meant to connect devices such as the keyboard, mouse, joystick, speakers, printers, modems, scanners, camera, etc. Source: www.mkdata.dk

22. USB 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

23. 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

24. EIDE Devices • Hard disks (ATA-33/66/100) • CD-R, CD-RW drives • DVD drives • Zip drive • Tape Backup units

25. SCSI • 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

26. The 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

27. SCSI 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

28. SCSI Chain Example

29. The devices at both ends of a SCSI chain must be terminated. The host adapter is one end of the chain. SCSI Terminators Source: www.mkdata.dk

30. SCSI 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

31. SCSI Standards • There are various other variations of SCSI • SCSI standards are confusing to say the least!