Serial Ports

• An external modem is a modem that plugs into a serial port on the computer.
• Internal modems plug into an expansion slot on the computer. They have the serial port that they require to function, built in.
• When using external modems are 2 things you need to consider, the number of available serial ports in the computer, and the UART type of each serial port.

Parallel Ports

• IEEE Standard 1284.
• 10 feet max. Max speed is 150KBs (1200 Kbs)
• Parellel ports are SPP (Standard Parallel Port), EPP, and ECP. Enhanced Parallel Port. Enhanced Capability Paralle port. Degree of sophistication between ECP and EPP corresponds to reverse alphabetical order. That is, ECP is more sophisticted than EPP. EPP more sophisticated than SPP. EPP is for non-printer peripherals. ECP is for printers and scanners. EPP-ECP standards are part of IEEE Standard 1284. ECP can use direct memory access. Both have been displaced by usb, but mostly only in consumer models.

PCI, PCIe, AGP, ISA, IrDA Busses, Ports

• PCIe (PCI express): 1x, 2x, 4x, 8x, 12, 16, 32x. Higher number, faster speed, longer slot. PCIe-16 is now commonly used for video. See chapter 2.
• Other expansion slots besides PCI (peripheral component interconnect) are AGP (accelerated graphics), ISA (Industry Standard Architecture). Both are outdated.
• Speed order slow to fast: PCI, AGP, PCIe. PCI is 127 mBps. AGP is 508.6 mBps
• IrDA port is an Infrared Data Association Port. A kind of infrared port. Max 2 meters, line of sight! Really only practical at 1 meter or less. Slow. About the same speed as parallel port.

IRQ and IO addresses for Serial and Parallel Ports (Section 4.1)

• Memorize the following port IRQ’s and IO’s (Input Output addresses)
• Serial Ports:
• Com 1 and 3 are both IRQ 4.
• IO for Com 1 is 03F8 – 03FF. IO for Com 3 is 03E8 – 03EF. 4-1=3.
• Com 2 and 4 are both IRQ 3.
• IO for Com 2 is 02F8 – 02FF. IO for Com 4 is 02E8 -02EF. 3-1=2.
• Odd com port number with even irq number, even com with odd irq.
• Parallel Ports:
• LPT1 is IRQ 7, IO is 0378 - 037F.
• LPT2 is IRQ 5, IO is 0278 - 027F

SCSI bus (Section 4.2)

• SCSI bus types are narrow 8-bit, wide 16 bit.
• In addition to width there is also speed. Fast, ultra.
• Up to 320 megabytes per second (MBps). Newer SATA tends to be faster and cheaper than scsi, and also just as good for RAID.
• 7 generations of SCSI, plus some variations within each generation
• Used with pc servers and high-end workstations. Tagged Command Queuing (TCQ) protocol helps with servers accessing many files for many users, at once.
• QAS: TCQ was not the Holy Grail for SCSI. With Ultra320 (SPI-4) comes the draft proposal for Quick Arbitrate and Select (QAS), which began appearing in drives and controllers in the second half of 2001
• IDE fought back with RAM on IDE controller card, enabling IDE to have 90% the speed of SCSI in multiaccess situations.

SCSI Standards

• X SCSI-1, regular SCSI, 1986
• X SCSI-2, fast, or fast wide SCSI, 1994
• X SCSI-3, ultra SCSI, 1995
• The first official SCSI is now known as SCSI-1. It supported 5MB/second transfers, and used an 8-bit bus.
• SCSI-2, the next generation, was Fast SCSI, and supported 10MB/second transfer.
• The release of CPU's such as the 80286, made the option for sixteen-bit available. This is known as Wide SCSI.
• Combining Fast and Wide yields Fast Wide SCSI. (Some versions of Fast-Wide are equal to SCSI 3). Some references optionally will denote not-wide SCSI as Narrow SCSI. If wide is not specified, narrow is assumed. Narrow is 8 bit. 8 bit allows for 8 devices (0-7). 16 bit allows for 16 devices.
• The modifier Ultra was used after Fast-Wide. Generally the SCSI-n designations are not used anymore after SCSI-3, however some merchants may use numbers, albeit incorrectly. There is SCSI Ultra, and then…
• Ultra 2 came into being after Ultra.
• See http://www.certiguide.com/aplush/cg_aph_XSCSIGenerations.htm
• The latest method for using Ultra is to use the maximum throughput in megabytes as a number after Ultra. An example of this would be Ultra 160, which would yield 160MB/second transfer rates.
• This is from: http://www.certiguide.com/aplush/cg_aph_VISpeedsandFeeds.htm

SCSI connectors

• SCSI-1 uses DB-25 connectors or 50 pin Centronics (like that used for a parallel port to attach at the printer end, however the cables are different - be careful not to smoke your printer by plugging in to a scsi port on a computer instead of into a parallel port, or by plugging your printer into parallel port but using a scsi cable.
• SCSI-3, Wide SCSI, uses 68 pin connector.
• Ultra2 SCSI uses HD-80 connector. SCA. This is the only one that has power in addition to data.
• 50 wire ribbon used by SCSI-1, 2, and 3, internally. One end for scsi adapter card, multiple ends for devices, much like IDE.
• Externally SCSI uses round cable. Daisy chained. Devices need power cable as well as data cable. Except for 80 pin connector.
• Differential signaling: 2 wires, 0 is represented by 0 v on both wires. 1 is represented by one voltage on wire 1 and another voltage on wire 2, or vice versa. Allowed for longer cable lengths. Later renamed High Voltage Differential, HVD. As compared to SE, single-ended signaling.
• Later LVD was introduced. Combined SE and HVD. Low voltage. Allowed longer cables. 12 meters. Watch out, lvd and hvd cables and connectors look the same.
• LVD/MSE, sometimes abbrev MSE, called multimode or Multimode Single Ended, allows both se and lvd drives to be attached. However SE cable length limits apply. SE has larger distance.
• All Ultra SCSI specifications use differential SCSI:
• Unfortunately, the only way to tell SE and LVD cables and connectors apart is to look at the symbols or documentation. Failing to do so could result in damage to components.
• SCSI ID numbers and assigning priorities: ID numbers are for device addressing and they also assign priority.
• 3 pin-sets. Allow binary expression of numbers 0-7. 4 pins, 0-15. 5 pins, 0-31.
• By default, ID0 used for the device (such as the hard drive) containing an op sys. Adapter card is ID 7. Adapter card has highest priority.
• ID usually set with jumpers.
• ID7 is always the highest priority, regardless of bus width. 32-bit bus (ultra2?), priority is 7,6,5,4,3,2,1,0; 15,14,13,12,11,10,9,8; 23,22,21,20,19,18,17,16; 31,30,29,28,27,26,25,24.
• Generally hard drive is 0, cd drive is 3, floppy is 2.
• In high-traffic settings, you will typically want to set the slower devices (scanners, tape drives) to the higher-priority IDs, to ensure that they are not crowded off the bus by the faster devices like hard disks.
• Termination done with resistor packs, auto termination, jumpers.
• Active termination works by using a small voltage regulator.
• SCSI terminators are usually integrated into the same type of connector used to daisy chain the devices.
• SCSI terminator type must match the bus type (1, 2, or 3), as opposed to matching the most advanced device in the chain. This bit of info is frequently needed to answer a test question correctly.
• SCSI 1 has 6 m cable length, rest are 1.5 to 3 meters.
• Speeds: SCSI-1, 5 mB/sec. Fast SCSI-2, and Wide SCSI-2, 10 mB/sec. Wide-Fast, 20 mB/sec. SCSI-2, Wide-Ultra, 40 mB/sec.
• 5, 10, 20, 40. 1; fast or wide; wide-fast; Ultra. ??
• Compare with USB and firewire. SCSI 5, 10, 20, 40. Newer versions have 80, 160, 320 and 640.
• USB 1.5 mB/sec and 60 mB/sec for vs 1, 2. The 60 mBps speed of USB is slower than PATA speed (EIDE). Ultra ATA is the same as ATA/133, has speed of 133 mBps.
• Firewire 50 mBps = 400 mbits/sec.
• Bootable hard disk, SCSI ID 0. CD-ROM, ID3.