Universal Serial Bus (USB) (Understanding Expansion Buses)

Universal Serial Bus (USB)

Universal serial bus (USB) is an external peripheral bus standard designed to bring plug and play capability for attaching peripherals externally to the PC. The bus supports up to 127 devices simultaneously. 

This Icon/ symbol is use to identify USB cables, connectors, hubs, peripherals.



USB conforms to Intel’s plug and play (PnP) specification, including “Hot” plugging, which means that devices can be plugged in dynamically without powering down or rebooting the system. Simply plug the device, and the USB controller in the PC detects the device and automatically allocates the required resources and drivers. USB supports following data transfer rate, depending on the amount of bus bandwidth a peripheral device requires.

§ 1.5 mega bits per second (Mbps) for devices, such as a mouse or keyboard, that do not required large amount of bandwidth.

§ 12 Mbps transfer rate for high-bandwidth devices such as modem, speakers, Scanners etc.

USB sends signals over simple four-wires the physically two series are specified for USB.

§ Series “A” connector is designed for devices in which the cable remains permanently attached, such as hubs, keyboard, and mice. The USB ports on most motherboards are normally a series “A” connector.

§ Series “B” connector are designed for devices that required data cable, such as printers, scanners, modems and telephones. The physical USB plugs are small and unlike a typical serial or parallel cable connector.

Note: Maximum cable length between two USB full-speed (12Mb/sec) devices is 5-Meters; while for lower speed (1.5Mbp/sec) devices are 3meters.

Types of USB Sockets Type A and Type B

PCI Express (Understanding Expansion Buses)

PCI Express

The PCIe physical layer consists of a network of serial interconnects much like twisted pair Ethernet. A single hub with many pins on the mainboard is used, allowing extensive switching and parallelism and the serial interconnects (known as lanes) can be grouped to provide higher bandwidth. This design was chosen because as clock rates increase, synchronization of parallel connections is hindered by timing skew. PCI-e is just one example of a general trend away from parallel buses to serial interconnects. For other examples, see Hyper Transport, Serial ATA, USB, SAS or FireWire. A multichannel serial design also increases flexibility; slow devices can be given a single lane with a relatively small number of pins while fast devices can be given more lanes as necessary up to a maximum of 32.

Accelerated Graphic Port (AGP)(Understanding Expansion Buses)

Accelerated Graphic Port (AGP)

The AGP was created by Intel as a new bus specifically designed for high-performance graphics and video support. AGP is based on PCI, but it is physically, electrically, and logically independent of PCI. PCI is a true bus with multiple connectors (slots), while AGP is more of a point-to-point high performance connection designed specifically for a video card in a system because only one AGP slot is allowed for a single video card. The AGP specification 1.0 originally was released by Intel in July of 1996 and defined a 66MHz. Clock rate with 1X, 2X (1x means single signal send in 1 cycle, 2X means two signals are send in one cycle and so on.) signaling using 3.3 volts. AGP version 2.0 was released in May 1998 and added 4X signaling as well as a lower 1.5v operation capability.
The latest version of AGP specification for PC,s is AGP 8X, which was announced in August 2000. It defines a faster 8x transfer mode for ever-greater performance then before. AGP command is found only on Pentium II and late compute systems The standard AGP 1x/2x, AGP 4x and AGP pro slots are compared to each other in the pictures.

Accelerated Graphic Port

Peripheral Component Interconnect (PCI) (Understanding Expansion Buses)

Peripheral Component Interconnect (PCI)

The PCI bus specification was released in June 1992 as version 1.0 & since then have several upgrades. PCI bypasses the standard I/O bus, it uses the system bus to increase the bus clock speed and take full advantage of the CPU's data path.


The best features of the PCI slots are as bellow.

1. PCI cards do not have any jumpers, switches and are configured through the software.
2. PCI designs use special bus and chip set for advance bus mastering techniques. This allows to supports more then three PCI slots.
3. The PCI bus has its own set of Interrupts number for each slot, if a PC have more then four PCI slots, some of them will be sharing interrupts and IRQ,s 

The EISA Bus(Understanding Expansion Buses)

The EISA Bus

EISA is an abbreviation for Extended Industry Standard Architecture. IBM announced this Standard in September 1988 AT systems. The EISA bus essentially a 32-bit version of ISA. EISA is still use older 8-bit or 16-bit ISA cards in 32-bit EISA slots, providing for full backward compatibility. EISA also allowed for automatic configuration of EISA cards via software.

EISA bus added 90 new connections (55 new signals plus grounds) without increasing the physical connector size of the 16-bit ISA. The 32-bit EISA slot looks a lot like the 16-bit ISA slots. The EISA adapter, however, has two rows of stacked contacts. The first row is the same type use in 16-bit ISA cards, while the other thinner row extends from the 16-bit connector.

ISA bus(Understanding Expansion Buses)

ISA bus

ISA is abbreviation of Industry Standard Architecture, which was introduced as an 8-bit bus with the original IBM PC in 1981. It was later expanded to 16-bus with the IBM PC/AT in 1984.

ISA BUS

Understanding Expansion Buses

Understanding Expansion Buses

Expansion cards are integrated circuit card that plug into an expansion slots on a motherboard to provide access to additional peripherals or features (such as video, sound, image capture cards, etc.) not built into the board. Also referred to as an add-in-board Expansion slot is a slot on the motherboard that physically and electrically connects an expansion card to the motherboard and the system buses.

CPU speeds increased as technology improved, while the speeds of expansion cards remained relatively constant. It was not practical to redesign and replace every expansion card each time a new processor was released—this would have been complicated and expensive for manufacturers..

To resolve this problem, designers have divided the external data bus into two parts:

System bus: 

This supports the CPU, RAM, and other motherboard components. The system bus runs at speeds that support the CPU.

Expansion bus:

 A bus/slot on the motherboard that physically and electrically connects for expansion card to the motherboard and system buses. Expansion bus also called I/O buses. 

The main difference among buses consists primarily of their architecture the amount of the data they can transfer at a time and speed at which they can do it. Following section describes the different types of the PC buses.

Buses of Computer

BUSES:

“A collection of conducting wires which is responsible for communicating signals from one place to another place in a computer system.”
 “A bus is a “highway” of digital signal it consist of a set of physical connection (printed circuit tracks and wires) over which the data and other information are moved for one place to another place”.

Address Bus:

The address bus requests the memory location from the memory or I/O location from an I/O device. If an I/O is addressed, address bus contains 16-bit I/O address. The 16- bit I/O address selects one of the different I/O locations.

Data Bus:

The data bus transfer the information between microprocessor and its memory an I/O locations. Data transfers vary in size depending upon the microprocessor.

Control Bus:

The control bus contains lines that select the memory or I/O and cause them to perform read or write the operations.