Computer Systems Architecture Historical Perspective The Universal Serial Bus was originally developed in 1995 by a group of industry leading companies Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC and Philips were involved in USB 2 developments USB defines an external expansion bus which makes adding peripherals to a PC relatively easy See: Wikipedia (Link) [ See:

Computer Systems Architecture Historical Perspective Major goals of USB 1.0 were ease-of-use and low cost USB version 1 was not designed to be a high speed bus – it’s for mice, keyboards, printers, scanners etc. In 2006, Intel estimated that over 3.5 billion USB interfaces had shipped NB that may include 2-10 “interfaces” per PC!

Computer Systems Architecture USB Connections The external expansion architecture of USB is shown below, which highlights: PC host controller hardware and software Robust connectors and cable assemblies “Peripheral friendly” master-slave protocols Expandable through multi-port hubs

Computer Systems Architecture USB host Client Describes all the software entities that are responsible for USB devices USB System Translation between the client data and USB transaction on the interconnect Managing USB resources(bandwidth, power …) USB Bus interface Handles interactions for the electrical protocol layer

Computer Systems Architecture Role of USB h/w and s/w Uniform view of I/O system for all application software Hides hardware implementation details Manages the dynamic attachment and detachment of peripherals “Enumeration” – initial communication with peripherals to discover device and driver identity Unique “address” for each peripheral Host PC software incorporates attached peripherals into the system power management scheme

Computer Systems Architecture Role of USB1.1 Hubs Provides additional, bi-directional connectivity for USB peripherals and works as bi-directional repeater Provides managed power to attached peripherals Recognises dynamic attachment of a peripheral Provides power during initialisation and later (0.5W to 2.5W max) May be cascaded up to five levels deep Monitors signals and handles transactions addressed to itself Supports both 12Mbits/sec (so-called “full-speed”) and 1.5Mbits/sec (“low-speed”) peripherals

Computer Systems Architecture USB1.1 Peripherals All USB peripherals are uniform slave devices that obey a defined protocol Peripherals respond to control transactions which may request detailed information about the device may request device configuration information may allocate a device ID Peripherals send and receive data to/from the host using a standard USB data format Standardized data movement to/from the PC host gives USB great flexibility and simplicity

Computer Systems Architecture USB 2.0 Same cables, same software interfaces, full support for USB1.1 devices Plus support for high- speed devices up to 480Mbits/sec Hub complexity increased to handle situations intelligently Became available some time after mid-2000

Computer Systems Architecture USB Topology Star- tiered topology Supports up to 127 devices Hot swappable Plug and play capabilities Host (Root Hub) Hub 1 Hub 2 Hub 3 Hub 4 node

Computer Systems Architecture USB devices HUB Serve to USB connectivity Can detect attach and detach Hub Controller + Hub repeater Functions USB device that is able to transmit or receive data

Computer Systems Architecture USB Cables D+ and D- carry data signal The signals on these two wires are referenced to the (third) GND wire VBUS carries a nominal 5V power supply, which may be used by a device for power – up to 2.5 Watts.

Computer Systems Architecture USB Cables “A” receptacles point downstream from a Host or Hub, while "B" receptacles point upstream from a USB device or hub A mini-B plug and receptacle-an alternative to B connector on handheld and portable devices The mini-B has a fifth pin, named ID, but it is not connected

Computer Systems Architecture Wireless USB High speed personal wireless interconnect technology Connects up to 127 devices Up to 480Mbps at 3 metres Up to 110Mbps at 10 metres Based on the WiMedia Alliance “ultra- wideband common radio platform” See

Computer Systems Architecture USB 3.0 – added optical channel Specifications released August 2008, chips by May 2009 USB 3.0 Promoters Group members: Intel, Microsoft, Hewlett-Packard, Texas Instruments, NEC and NXP Semiconductors USB 3.0 products expected to arrive in 2009 or 2010 About 5Gbps, copper connection, mostly backwards compatible with USB2 Originally intended to be part-optical, dropped due to costs More energy efficient than USB2

Computer Systems Architecture USB On-The-Go In standard USB, communication is controlled by the PC There is no way to connect peripherals together without the PC The USB On-The-Go (OTG) initiative specifies some additional capabilities to USB2.0 It adds some host capabilities to USB peripherals for direct interconnection See

Computer Systems Architecture Why USB? Ease of use – relatively simple for the user Better than existing connectors (2S/1P…) Single standard for manufacturers Design time will be reduced after initial learning period, broadens market Cost to manufacturers reduced by standardisation but raised by added complexity? Changes to PC design are reducing internal expansion capability

Computer Systems Architecture FireWire Many motherboards come with IEEE1394 (a.k.a FireWire or i.Link) for DV camera connection FireWire is a high performance, versatile LAN- style connector Runs at about 400Mbps (similar to USB2) Latest 800Mbps (2007)

Computer Systems Architecture USB and FireWire Similarities Many people confuse IEEE 394/FireWire/i.LINK and USB Both are modern digital data connection technologies capable of linking multiple peripherals to a computer Both permit “hot plugging” of peripherals (adding to or disconnecting from a computer without the need to reboot) Both use thin, flexible cables which employ simple, durable connectors

Computer Systems Architecture Differences FireWireUniversal Serial Bus Max no. of devices:64127 Hot-Swap:YesYes Max cable length between devices:4.5 metres5 metres Data transfer rate:200Mbps12Mbps (1.5MB/sec) Bandwidth Roadmap:400Mbps [std]480Mbps [late 2000] 800Mbps [rare?]4.8Gps (USB 3.0) 1Gbps+ [never happened] Internal peripheral connection:YesNo Network protocol:YesNo Power provider:Yes, >20WattsYes, just 2.5Watts

Computer Systems Architecture Original Target Markets 1394/FireWire/i.Link (200/400Mbps) DV Camcorders Professional High-Resolution Digital Cameras Some HDTV applications (HDTV?) Set-Top Boxes Hard Disks DVD-ROM Drives Professional-level printers Professional-level scanners Universal Serial Bus (v1.1) Keyboards Mice Monitors Joysticks Consumer Digital Cameras Low-Speed CD-ROM Drives Modems Speakers Consumer-level printers Consumer-level scanners

Computer Systems Architecture Different Markets and Approach 1394 offers a data transfer rate that is many times faster than USB1 and this was expected to continue, even with newer, faster versions of each technology But IEEE1394 development stalled… Some industry commentators asked “Can IEEE1394 win the interface war with USB?” Most IT analysts expected IEEE1394 and USB to coexist peacefully in modern computers USB was expected to be reserved for lower-bandwidth and less time-sensitive peripherals – but then came USB2 IEEE1394 is still used to connect to higher-bandwidth electronics where guaranteed bandwidth is key

Computer Systems Architecture What killed FireWire? Still not dead - IEEE1394 flourishes in niche areas of media communication But why the poor market penetration in personal computers? IEEE1394 is a fully developed networking protocol It is relatively complex and expensive Specialist markets don’t bring huge chip sales, so prices stay high It is “overkill” for most current PC applications

Computer Systems Architecture SATA Serial Advanced Technology Attachment SATA is the current generation storage interface for PCs and low- end Servers The old Parallel ATA bus was not able to meet the increased bandwidth and performance demands of current and future PC designs This standard replaces the 40 pin ribbon connector with a small flexible signal cable SATA can be directly connected (hot plugged) to motherboards and back planes similar to current SCSI applications eliminating the need for cable completely

Computer Systems Architecture Serial ATA Serial ATA overcomes the problems of parallel ATA. The features of Serial ATA are: 1.5 Gbps (real speed 150MB/s) 3 Gbps (300 MB/s) 6 Gbps released in May 2009 Hot plugging Two power saving modes, Low voltage requirement 7 wire cable (8 mm wide) up to 1 m long. Serial ATAParallel ATA

Computer Systems Architecture eSATA Port External Serial Advanced Technology Attachment or eSATA is an external interface for SATA technologies. Maximum cable length of 2 metres eSATAp is a newer standard with provision for power to be supplied through data cables