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A+™ Essentials  Technologies


Given below are important bus types and their characteristics:

Bus Type

Data bus width








Use jumpers to configure





Backward compatible with ISA, uses software/ jumpers for configuration


VL bus




Backward compatible with ISA cards





Supports Plug and Play

64-bit PCI




Supports Plug and Play





Used in laptops, also know as PC card



Speed of Processor


Used in video cards

Common Buses and their Max Bandwidth

Common Buses

Max Bandwidth


132 MB/s


2,100 MB/s

PCI Express 1x

250 [500]* MB/s

PCI Express 2x

500 [1000]* MB/s

PCI Express 4x

1000 [2000]* MB/s

PCI Express 8x

2000 [4000]* MB/s

PCI Express 16x

4000 [8000]* MB/s

PCI Express 32x

8000 [16000]* MB/s

IDE (ATA100)

100 MB/s

IDE (ATA133)

133 MB/s


150 MB/s

Gigabit Ethernet

125 MB/s


100 MB/s


PCIe busses for 3x and 5x are not available. Since PCI Express is a serial based technology, data can be sent over the bus in two directions at once. Normal PCI is Parallel, and as such all data goes in one direction around the loop. Each 1x lane in PCI Express can transmit in both directions at once. In the table the first number is the bandwidth in one direction and the second number is the combined bandwidth in both directions. Also please note that in PCI Express bandwidth is not shared the same way as in PCI, so there is less congestion on the bus.


A standard FireWire connection will support 100,200 and 400 Mbps. The important features of IEEE1394 (also known as FireWire 400) are:

1. 100 Mbit/s, 200Mbit/s, and 400Mbit/s supported.
2. Works without control, devices communicate peer-to-peer.
3. Cable up to 4.5 m.
4. Up to 63 devices supported.
5. Power supply to external devices is 1.25A/12V (max.).
6. The only computer bus used in digital video cameras
The IEEE 1394b specification supports data rates up to 400 Mbit/s in half-duplex mode, and even higher in full duplex. It can support optical connections up to 100 metres in length.

SCSI Types:


Transfer speed




8 bit bus

Fast Wide SCSI


16 bit bus

Wide Ultra SCSI


16 bit bus

Ultra2 SCSI


8 bit bus

Wide Ultra2 SCSI


16 bit bus

Ultra3 SCSI or Ultra 160


16 bit bus


320 MBPS

16 bit bus

SCSI ID - 0=bootable drive, 7=controller, 1-6=any other devices
Wide-Ultra SCSI - 16 devices, 0=bootable drive, 15=controller

Each device in a SCSI chain need to have unique ID. For a 16-bit Wide SCSI, there are 16 possible SCSI Ids, 0-15. A standard 8-bit SCSI can support only 8 devices (including SCSI card), the Ids allowed are 0-7.

SCSI bus termination:

If the termination is not done, a SCSI devices on the bus will not function properly. This is due to reflection of the signals at the end of the bus. To prevent this, both ends of the SCSI bus need to be terminated. If one end of the SCSI bus is terminated, you may find intermittent problems. Never terminate the bus at a device connected in between.

USB (Universal Serial Bus):

- USB supports up to 127 devices simultaneously.
- USB enables you to daisy chain up to 127 USB devices. A USB hub is used for this purpose.
Also, USB devices can be plugged in without turning on/off power. I.e. USB devices are hot swappable.

USB 2.0

The important features of USB 2.0 are given below:

1. 1.5 Mbit/s 12Mbit/s 480Mbit/s supported.
2. USB controller is required to control the bus and data transfer.
3. Cable up to 5 m.
4. Up to 127 devices supported.
5. Power supply to external devices is 500 mA/5V (max).
6.Full compatibility with USB 1.1 devices.

To achieve proper USB connectivity six basic system elements must be present 

1) Support from the BIOS
2) Support from the Operating System
3) Physical USB ports
4) A USB Device
5) The correct USB cable for the device
6) Drivers either from the OS and/or the peripheral maker
USB 2.0 has a raw data rate at 480Mbps, and it is rated 40 times faster than its predecessor interface, USB 1.1, which has 12Mbps max speed.

External Serial Advanced Technology Attachment or eSATA is an external interface for SATA technologies. It is faster compared to USB 2.0 or PATA technologies, and suitable for backing up large amounts of data using external hard drive. 
Even though eSATA is part of the SATA interface specifications, it uses a very different physical connector from the internal SATA connectors. The reason for this is to better shield the high speed serial lines used to transfer the signals from EMI protection. It also provides a 2m overall cable length compared to the 1m for internal cables. As a result the, the two cable types can not be used interchangeably.

Speeds achievable by different technologies 

* USB 1.1 – 15 Mbps
* FireWire (1394a) – 400 Mbps
* USB 2.0 – 480 Mbps
* FireWire 800 (1394b) – 800 Mpbs
* SATA 1.5 – 1.5 Gbps
* SATA 3.0 – 3.0 Gbps

System board connectors of a PC:

1. 9-pin male connector on system board is serial and usually COM 1 (mouse)
2. 25-pin male connector on system board is serial and usually COM 2 (modem)
3. 25-pin female connector on system board is parallel and usually LPT 1 (printer)
Northbridge Southbridge Chipset

The Northbridge chipset controls communications between the CPU, memory, PCI and AGP busses. The Southbridge actually uses the PCI bus to handle the I/O ports, USB and the IDE controller.

Real Time Clock:

The Complementary Metal-Oxide Semiconductor (CMOS) allows the computer to store the Real Time Clock (RTC)and other device information even after the computer is switched off and on. This is achieved by using a battery back, just for CMOS.

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