Parallel Ports

Printers, image scanners, and other external data storage devices such as Zip drives are common peripherals that connect to parallel ports. The physical interface standards for parallel communications are 25-pin D-Sub (DB25) connectors, and the modern communications protocol is defined as the IEEE-1284 standard. Of the 25 pins in a DB25 connector, 17 are used for signaling and 8 are used for ground. Of the 17 signaling lines, 8 are used for data, 4 for control and 5 for status. The IEEE-1294 Parallel communication standard supports both forward and reverse data transmission directions, as well as bi-directional modes. EPP/ECP (Enhanced   Parallel  Port / Enhanced   Capability   Port)  are  part  of  IEEE

Standard 1284. EPP/ECP is a standard signaling method for bi-directional  parallel communication between a computer and peripheral devices that offers the potential for much higher rates of data transfer than the original parallel signaling methods. EPP is for non-printer peripherals. ECP is for printers and scanners. The new standard specifies five modes of data transfer.  Three of them support the older mono-directional modes (a forward direction method from PC to Centronics printer and two reverse direction methods from  peripheral   to   the  PC). 

DB25 Female



Centronics 36 Female



Centronics 36 Male

The fourth and fifth modes, EPP and ECP, are bi-directional (half-duplex) signaling methods, meaning that they are designed for back-and-forth communication. Partly because these are being implemented in hardware, EPP and ECP will provide much faster data transfer. The first three methods offer an effective data transfer rate of 50 to 115 kilobytes per second. 

Serial Ports

Mice, modems, programmable logic controllers, and handheld pocket organizers such as Palm Pilots are common peripherals that connect to

serial ports. Serial interfacing requires only a single line to transmit data and is therefore theoretically better for long distance transmissions. Since only one transmit or receive line is used, the maximum data transfer rate is not as high as parallel data transmission. Data is sent bit after bit, along the same line, causing timing and framing of bytes to be important so that the end of each bit and each byte can be determined accurately. This data transmission protocol used is known as RS-232 Serial. The typical RS-232 serial connector is the 9-pin D-Sub (DB9) connector, where 2 lines are used for data, 1 for ground, and     6     for     control.     The 

DB9 Male



DB25 Male



DB37 Male

maximum RS-232 serial cable length for reliable data transmission of 115 kilobits per second in a common hardware configuration is approximately 16 meters (50 feet) . 

USB is allows users a no-hassle way to connect just about every peripheral made without IRQ settings or hardware to configure.  There is no need to shut down and restart your PC to attach or remove a USB peripheral, thanks to a feature called hot-swapping. This feature is especially useful for users of multi-player games, as well as notebook PC 

users who want to share peripherals. The PC automatically detects the peripheral and configures the necessary software. USB also lets you connect many peripherals at one time.  Most modern computers come with two or four USB ports. USB utilizes 7-bit addressing allowing you to daisychain up to 127 peripheral connections. USB distributes electrical power  to    many    peripherals

USB A-Type Male



USB B-Type Male

automatically sensing the power that is required and deliver it to the device eliminating the need for power converter adapters. The USB 2.0 standard developed by Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC and Philips supports data speeds up to 480 megabits per second (Mbps).  This is 40 times faster than the USB 1.1 specification of 12Mbps.  USB 2.0 is backward compatible.

IEEE-1394 (FireWire) is very similar to USB and also uses uses advanced serial data interfaces at much higher speeds than conventional RS-232 serial with advanced power management.   The IEEE-1394 standard (also

branded as Apple FireWire and Sony iLink) was designed to replace SCSI and supports higher transfer speeds than USB 1.1. FireWire utilizes 6-bit addressing, allowing 63 devices to be connected. The 100-Mbps, 200-Mbps, and 400-Mbps transfer rates currently specified in IEEE 1394.a and the enhancements in IEEE  1394.b   are    well    suited   to 

 
IEEE-1394 4-pin Male



IEEE-1394 6-pin Male

multi-streaming I/O requirements. Like USB , IEEE-1394 use an isochronous data interface, where time constraints determine when data must be delivered or received as demanded by multimedia streaming applications.

PS/2 and AT

Keyboards can use three different methods to connect to the computer, a small round  plug  called  the  PS/2  connector  (from  IBM's  old  computer 

brand of the same name), a larger round plug called the AT connector which traces its lineage to the IBM PC-AT, or the USB port.  Mice can also use three different methods to connect to the computer; Either by PS/2, serial or the USB  port.  PS/2  and  AT ports 

IDE / SCSI

IDE (Integrated Device Electronics) is also known as ATA (Advanced Technology    Attachment)    and    is    integrated   in   almost   all   modern

motherboards today to connect hard drives and other types of internal drives. IDE is slower than SCSI (Small Computer Systems Interface). SCSI allows faster transfer rates and lower CPU loading than is possible with ATA. However, this increase in performance does come at  a  cost   -   SCSI  is  much 

40-pin Male



40-pin Female

more complex as well as generally more expensive than comparable ATA/IDE technology. 

The floppy disk interface is integrated in almost all modern motherboards today and supports two floppy drives and a tape device. The floppy cable is twisted at pins 9 to 16 which swap Motor Enable A and Drive Select A with Motor Enable B and Drive Select B signals, so the drive connected after the change receive signals for the A drive instead of signals for the B drive.