BUS

•  A data connection between two or more devices connected to the computer.

•  For example, a bus enables a computer processor to communicate with the memory or a video card to communicate with the memory.

• A bus is capable of being a parallel or serial bus

• An Industry Standard Architecture bus (ISA bus) allows additional expansion cards to be connected to a computer's motherboard.

• It is a standard bus architecture for IBM compatibles. Introduced in 1981, the ISA bus was designed to support the Intel 8088 microprocessor for IBM’s first-generation PC. •

In the late 1990s the faster peripheral component interconnect (PCI).

Soon afterwards, use of the ISA bus began to diminish, and most IBM motherboards were designed with PCI slots.

• Although there are still a few motherboards being made with ISA slots, these are generally referred to as the legacy bus motherboards

ISA (Industry Standard Architecture)

Block Diagram

Features

• 16-bit characteristics.

• It supported 16-bit peripheral devices.

• Five devices with 16-bit interrupt request (IRQ) could be connected at the same time.

• Also, three additional devices could be connected parallel to five devices with 16-bit IRQ.

• 16-bit direct memory access (DMA) channel.

• The CPU clock speed varied from 16 to 20 MHz.

Advantages

• Low cost• Compatibility• Used widely

Disadvantages• Low speed• Jumpers and DIP switches• Becoming out-dated

The ISA bus allowed the computer to automatically detect and setup computer ISA peripherals, such as a modem or sound card. 

Applications

Using the PnP technology, an end-user would have the capability of connecting a device and not having to configure the device using jumpers or dip switches.

• Extended Industry Standard Architecture (EISA) is a bus architecture that extends the Industry Standard Architecture (ISA) from 16 bits to 32 bits.

• EISA was introduced in 1988 by the Gang of Nine - a group

of PC manufacturers. 

• These competitors were AST Research , Compaq, Epson, Hewlett Packard , NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems.

• EISA was designed to compete with IBM’s Micro Channel Architecture (MCA) - a patented 16 and 32-bit parallel computer bus for IBM’s PS/2 computers.

• EISA extended the advanced technology (AT) bus architecture and facilitated bus sharing between multiple central processing units (CPU).EISA is also known as Extended ISA.

EISA (Extended Industry Standard Architecture)

Block Diagram

Bus width 32 bit

Compatible with 8 bit ISA, 16 bit ISA, 32 bit EISA

Pins 98 + 100 inlay

Vcc +5 V, −5 V, +12 V, −12 V

Clock 8.33 MHz

Theoretical data rate (32 bit) about 33 MB/s (8.33 MHz × 4 bytes)

Usable data rate (32 bit) about 20 MB/s

Features

Advantages• ISA Compatibility: ISA cards will work in EISA slots.

• 32 Bit Bus Width: Like MCA, the bus was expanded to 32 bits.

• Bus Mastering: The EISA bus supports bus mastering adapters for greater efficiency, including proper bus arbitration.

• Plug and Play: EISA automatically configures adapter cards, similar to the Plug and Play standards of modern systems

Disadvantages

It never became widely used .

It is no longer found in computers today.

• Stands for "VESA Local Bus." (VESA stands for "Video Electronics Standards Association").

• The VLB, or VL-bus is a hardware interface on the computer's motherboard that is attached to an expansion slot.

• By connecting a video expansion card to the VLB, you can add extra graphics capabilities to your computer.

• The interface supports 32-bit data flow at up to 50 MHz.

• Though the VLB architecture was popular in the early 1990s, it has since been replaced by the newer and faster, but still three-lettered, ISA, PCI, and AGP slots.

VESA (Video Electronics Standard Association)

Year created 1992

Created by VESA

Superseded by PCI (1993)

Width in bits 32

Number of devices 3

Speed 33 MHz

Style Parallel

Hotplugging interface no

External interface no

Features

Bus width 32 bits

Compatible with 8 bit ISA, 16 bit ISA, VLB

Pins 112

Vcc +5 V

Clock

486SX-25: 25 MHz486DX2-50: 25 MHz486DX-33: 33 MHz486DX2-66: 33 MHz486DX4-100: 33 MHz486DX-40: 40 MHz486DX2-80: 40 MHz486DX4-120: 40 MHz5x86@133 MHz: 33 MHz5x86@160 MHz: 40 MHz486DX-50: 50 MHz

Advantages

• VLB video cards provide, in general, much better performance than ISA cards.

• This is primarily due to the fact that the 32-bit local bus used by VLB cards allows for several times more data throughput between the card and the processor than ISA allows.

• VLB has however had its own share of problems. In particular, VLB video cards may cause reliability problems in motherboards running at 40 or 50 MHz .

• Many VLB cards are very good performers, but are hampered by their general age, along with that of the motherboards they run in; most are at least four years old and new development of better and faster chipsets is entirely in the PCI world now.

• Still, despite the fact that VLB is older than PCI, it can provide quite acceptable performance (although probably fewer features and less video memory).

• VLB is much closer to PCI than it is to ISA. Any system that will support VLB should be using it for the video card .

• The performance improvement over ISA is substantial in most cases.

Disadvantages

• 80486 dependence. The VESA Local Bus relied heavily on the Intel 80486 CPU's memory bus design.

• Limited number of slots available. Most PCs that used VESA Local Bus had only one or two VLB capable ISA slots from the 5 or 6 available (thus 4 ISA slots generally were just that, ISA only).

• Reliability problems. The strict electrical limitations on the bus also reduced any "safety margin" available - negatively influencing reliability.

• Limited scalability. As bus speeds of 486 systems increased, VLB stability became increasingly difficult to manage.

• Installation woes. The length of the slot and number of pins made VLB cards notoriously difficult to install and remove.

• PCI (Peripheral Component Interconnect) is an interconnection system between a microprocessor and attached devices in which expansion slots are spaced closely for high speed operation.

• Using PCI, a computer can support both new PCI cards while continuing to support Industry Standard Architecture (ISA) expansion cards, an older standard

PCI (Peripheral Component Interconnect)

Year created July 1993

Created by Intel

Supersedes ISA, EISA, MCA, VLB

Superseded by PCI Express (2004)

Width in bits 32 or 64

Speed 133 MB/s (32-bit at 33 MHz – the standard configuration)266 MB/s (32-bit at 66 MHz or 64-bit at 33 MHz)533 MB/s (64-bit at 66 MHz)

Style Parallel

Hotplugging interface Optional

Features

Block Diagram

PCI (Peripheral Component Interconnect) is an interconnection system between a microprocessor and attached devices in which expansion slots are spaced closely for high speed operation.

Using PCI, a computer can support both new PCI cards while continuing to support Industry Standard Architecture (ISA) expansion cards, an older standard

For image processing, PCI lets applications stream live video to a display or system memory, virtually eliminating the need for costly onboard memory.

For example, a video camera that sends 30 frames/s produces data streams of 10 to 40 MB/s, far outpacing ISA’s capacity of 3 to 5 MB/s of continuous data.

Advantages

• very high speed.

• Plug & Play.

• Dominant board-level bus

Disadvantages

• Incompatible with older systems

• Can cost more

Year created 2004Created by •Intel

•Dell•HP•IBM

Supersedes •AGP•PCI•PCI-X

Width in bits 1–32Number of devices One device each on each endpoint of

each connection. PCI Express switches can create multiple endpoints out of one endpoint to allow sharing one endpoint with multiple devices.

Style SerialHotplugging interface Yes, if Express Card, Mobile PCI Express

Module or XQD cardExternal interface Yes, with PCI Express External Cabling,

such as Thunderbolt

PCI-E

Year created 1998

Created by IBM, HP, and Compaq

Superseded by PCI Express (2004)

Width in bits 64

Speed 1064 MB/s

Style Parallel

Hotplugging interface yes

PCI-X

PARAMETERS PCI PCI-E PCI-X

Stands For Peripheral ComponentInterconnect

Peripheral ComponentInterconnectExpress

Peripheral ComponentInterconnectExtended

Format 32-Bit OR64-Bit

32-Bit 64-Bit

Style Parallel Serial Parallel

Hot PluggingInterface

Optional Optional Required

Speed 133MBps 250MBps-31.51GBps

1084MBps

• The pc provides fully-programmable asynchronous communication capabilities , through two standard EIA RS-232C connections to the Multi I/O card.

• This adapter features programmable baud rates from 50 to 9600 baud, a fully programmable interrupt system and variable character lengths(5,6,7, or 8-bit characters).

• In addition, the adapter adds and removes start, stop and parity bits, has false start-bit detection, line-break detection and generation, and possess build-in diagnostics capabilities.

RS-232(Recommended Standard)

1. Communication:asynchronous full duplex series data communication.

2.Speeds:150 bps to 19.2 kbps3. Length: typ. 75 ft (@ 9600 bps) min. 50ft (@ 19.2 bps) max. 2000 ft (@ 150 bps)4.Voltage levels : Logic 0 -> +3 V to +25 V (typ.+12V) Logic 1 -> -3 V to -25 V (typ. -12V)5.Cable : Multi-cored shielded.

Features

Advantages

• Electrical signal characteristics such as voltage levels, signaling rate, timing and slew-rate of signals, voltage withstand level, short-circuit behavior, and maximum load capacitance.

• Interface mechanical characteristics, pluggable connectors and pin identification.

• Functions of each circuit in the interface connector.

• Standard subsets of interface circuits for selected telecom applications

Disadvantages• The large voltage swings and requirement for positive and negative

supplies increases power consumption of the interface and complicates power supply design. The voltage swing requirement also limits the upper speed of a compatible interface.

• Single-ended signaling referred to a common signal ground limits the noise immunity and transmission distance.

• Multi-drop connection among more than two devices is not defined. While multi-drop "work-arounds" have been devised, they have limitations in speed and compatibility.

• Asymmetrical definitions of the two ends of the link make the assignment of the role of a newly developed device problematic; the designer must decide on either a DTE-like or DCE-like interface and which connector pin assignments to use.

• The handshaking and control lines of the interface are intended for the setup and takedown of a dial-up communication circuit; in particular, the use of handshake lines for flow control is not reliably implemented in many devices.

• No method is specified for sending power to a device. While a small amount of current can be extracted from the DTR and RTS lines, this is only suitable for low power devices such as mice.

• The 25-way connector recommended in the standard is large compared to current practice.

• Short for Universal Serial Bus, an external bus standard that supports data transfer rates of 12 Mbps.

• A single USB port can be used to connect up to 127 peripheral devices, such as mice,modems, and keyboards.

• USB also supports Plug-and-Play installation and hot plugging.Starting in 1996, a few computer manufacturers started including USB support in their new machines.

• It wasn't until the release of the best-selling iMac in 1998 that USB became widespread. It is expected to completely replace serial and parallel ports.

USB(Universal Serial Bus)

Features

•The Personal Computer works as a Host.

•The Low-powered devices can draw their power from the host via USB. If we have to connect a high power device then we have to use external adapter.

•USB cable has two twisted pairs of wires. One for the data transfer and the other for power transfer.

•We can connect maximum 127 USB devices to a host via USB hubs.

•USB devices are hot swappable  That means we do not have to turn off, On or restart our computer when connecting or disconnecting a USB device.

•When the computer enters in power saving mode, USB devices also put to sleep by the computer.

Diagram

Advantages

• Much more resistant to scratches unlike CD Roms and floppies.

• Much more convenient, will work with almost any computer as long as there is a flash drive.

• Great storage space.

• It's small size is convenient for carrying, and takes little space.

• One can purchase a USB that more reflects them through its colors and design.

Disadvantages

• It's small size also means it can be lost easily and/or forgotten.

• Its life span can be short, about several hundred thousand cycles.

• As the device ages the speed of writing process gradually slows.

• Only a few USB flash drives are equipped with a write-protect mechanism, meaning those that don't have the protection could be contaminated by what ever virus the computer it was connected to has.

• If inappropriately removed from the USB drive without being ejected, it become damaged or lose the data saved to it.

Application

• Today, SuperSpeed USB 3.0 provides the highest standard in USB performance—up to 10 times faster than High-Speed USB 2.0, with a design data rate of five Gbps. In addition, Super Speed USB dramatically reduces the power necessary to transfer large amounts of data.

• This latest version of USB retains full backward compatibility with previous generations, so existing platforms and devices will plug-and-play equally well with newer platforms and devices that support Super Speed USB.

• Portable devices such as handhelds, cell phones, and digital cameras that connect to PCs as USB peripherals benefit from having additional capabilities to connect to other USB devices directly using USB On-The-Go (OTG) technology.

FIREWIRE

• FireWire is a method of transferring information between digital devices, especially audio and video equipment.

• Also known as IEEE 1394, FireWire is fast -- the latest version achieves speeds up to 800 Mbps.

• At some time in the future, that number is expected to jump to an unbelievable 3.2 Gbps when manufacturers overhaul the current FireWire cables.

• You can connect up to 63 devices to a FireWire bus. Windows operating systems (98 and later) and Mac OS (8.6 and later) both support it.

Block Diagram

Features

• A simple common plug-in serial connector on the back of your computer and on many different types of peripheral devices

• A thin serial cable rather than the thicker parallel cable you now use to your printer, for example

• A very high-speed rate of data transfer that will accommodate multimedia applications (100 and 200 megabits per second today; with much higher rates later)

• Hot-plug and plug and play capability without disrupting your computer

• The ability to chain devices together in a number of different ways without terminators or complicated set-up requirements

• Simple cabling.

• Lower cost compared to parallel and Camera Link standards.

• Does not require camera files.

• Supports a variety of frame rates and image sizes.

• Supports multiple cameras on a single frame grabber.

• Available on PCMCIA cards for laptop us.

• Does not require National Instruments hardware.

Advantages

Disadvantages

• Slower data transfer rate - up to 400 Mbps for 1394a, up to 800Mbps for 1394b (dependent on camera, IEEE 1394 interface hardware, and operating system support).

• No onboard memory for saving images.

• Less triggering support.

• Difficult to synchronize with other devices.

Application

• FireWire helped fuel a revolution for digital content creators, and was awarded a 2001 Primetime Emmy Engineering Award by the Academy of Television Arts & Sciences for its contribution.

• Due to its high bandwidth and support of both isochronous and asynchronous data delivery, FireWire has found a very successful place in both the computer and consumer electronics industries.

• Whether connecting game consoles, personal video recorders, home stereo equipment, digital TVs, hard drives, CD/DVD-RW drives, printers, scanners, tape drives or other digital hardware equipment, FireWire is well-suited to handle all these various requirements.

• With the advent of the new FireWire 800 standard, the revolution created by the original will only grow.

• For those working with digital video, the new standard will enable new bandwidth-intensive applications, such as multiple-stream, uncompressed, standard-definition video.

SCSI (Small Computer System Interface)

The Small Computer System Interface (SCSI) is a set of parallel interface standards developed by the American National Standards Institute (ANSI) for attaching printers, disk drives, scanners and other peripherals to computers. SCSI (pronounced "skuzzy") is supported by all major operating systems.

Symbol

Features

• The first version (SCSI-1), adopted by ANSI in 1986, was an 8-bit version with a 5 MBps transfer speed that allowed up to eight devices to be connected with a maximum cable length of six meters.

• The latest version, 16-bit Ultra-640 (Fast-320) SCSI, was introduced in 2003 and has a 640 MBps transfer speed, connecting up to 16 devices with a 12 meter cable length. Other versions include:

• SCSI-2: 8-bit bus, six meter cable length, 5-10 MBps; connects 8 or 16 devices. 50-pin connector

Block Diagram

Advantages

1. SCSI can handle a wide variety of devices: hard drives, scanners, plotters, CD drives, and the list goes on.2. A SCSI controller can communicate with up to 7 or 15 devices depending on the version. I am sure work is being done to add more.3. It is often easier to install and setup a SCSI device than with many other device interfaces. (This comment is not limited to the SCSI vs. IDE issue. See Advantage #1 for the scope of what I mean by "device." I also say it is "often easier," not "universally easier.")4. SCSI controllers and devices are intelligent, they have microcontrollers, if not full blown processors, inside them. They do not require software-base controller drivers like some Windows devices, putting less load on the CPU.5. SCSI has proven itself to be a good platform for moving and storing large amounts of data. Recent developments with SCSI have focused on exploiting this feature even further.6. Newer SCSI devices and controllers are supposed to be backward compatible with older SCSI devices and controllers. (from my own personal experience, this is about 95% true)7. Recent SCSI controller and devices currently offer the highest through-put for any peripheral connection scheme currently available.8. SCSI drives are, on the whole, more reliable than ATA/IDE drives

Disadvantages

1. SCSI has never been cheap.

2. There are at least a dozen different versions of SCSI: narrow, wide, fast, ultra, SCSI-2, ultra-wide, Ultra 320, fibre-channel and more.

3. There are 3 different port interfaces for connecting internal SCSI devices: 50-pin, 68-pin, and 80-pin. You can buy adapters to convert from one kind of connector to another.

4. There are even more port interfaces for connecting external devices. I know of at least 4. You can buy cables that convert from one port interface to another.

5. SCSI drives generally run at higher RPMs than ATA/IDE drives which creates more heat and noise than their lower RPM counterparts.

6. When something breaks, SCSI drives are more difficult to repair than ATA/IDE drives. (or so I was told by a colleague who used to do physical repairs on hard drives)

Application

• SCSI is used to connect peripherals to an computer.

• It allows you to connect hard disks, tape devices, CD-ROMs, CD-R units, DVD, scanners, printers and many other devices.

• SCSI is in opposite to IDE/ATA very flexible.

• Today SCSI is most often used servers and other computers which require very good performance. • IDE/ATA is more popular due to the fact that

IDE/ATA devices tend to be cheaper.

Centronics(Parallel Port)

The Centronics interface is a standard input/output (I/O) interface designed in the 1970s for connecting printers and other devices. It was developed by the Centronics printer company which is now defunct. The Centronics interface, also known as a Parallel Port, became the standard means of connecting printers to personal computers for decades.

The technology that the Centronics interface developed into included a number of incarnations of the Parallel interface including the ECP (Extended Capabilities Parallel) and EPP (Enhanced Parallel Port) versions. The technology required a 25 way connector of which up to 17 wires were used in the specification and bi-directional communications became possible in the enhanced versions like ECP and EPP.

Today, the Centronics interface has been largely replaced by the universal serial bus (USB). For the most part, many manufactures have entirely omitted the parallel interface. However, a USB-to-parallel port adapter is available for PCs without a parallel port. These can be used for parallel printers and other peripheral devices that have a parallel interface. 

PARALLEL SERIAL

A parallel bus is one where each bit has its own copper wire.

A parallel bus is one where each bit has its own copper wire.

There is usually a strobe line that says when the data bits are valid.

There is usually some framing information to identify the start of a frame of data, such as a long gap. 

Examples of parallel bus: PCI, IDE, SCSI 

• Examples of parallel bus: PCI, IDE, SCSI