In order to connect any MIDI equipment up to a PC, you first need a MIDI interface.  Luckily, every sound card that I know of has a built-in MIDI interface, using the game port.  Other types of MIDI interfaces available include ISA cards, parallel port plug-ins, serial port plug-ins, USB (Universal Serial Bus) plug-ins, and possibly some that plug into a PCI slot.  I will give more details on each.

    The most common type is the one built into every sound card that I know of.  In order to make this work, you must use a "MIDI adapter," which plugs into the game port.  While most sound cards may function fine with a generic MIDI adapter (around 10-20 dollars), some brands of sound cards insist on that brand of MIDI adapter.  This is especially true with the cards from Creative Labs.  Use of a generic MIDI adapter on some cards can cause gargled data (and sounds) or no activity at all.  Here is a word of warning for new users.  BE SURE TO INSERT THE CABLE LABELED "IN" INTO THE MIDI OUT ON THE MIDI DEVICE AND THE CABLE LABELED "OUT" INTO THE MIDI IN ON THE MIDI DEVICE.  You can think of this labeling as going INto the sound card or going OUT from it.  The reliability of this type of connection varies greatly from one card to another and also on not having too many desktop icons and/or fonts installed.  While the Sound Blaster AWE-64 Gold and Live Value have been proven to be quite reliable, the full-edition AWE-32 is NOT USABLE FOR SERIOUS EXTERNAL MIDI!!!  Proprietary MIDI adapters max out around $30 or so.

    The next category include those that plug into the serial port, parallel port, or USB port.  In theory, the serial port type would have the poorest reliability.  Likewise, the parallel port variety would seem to have the highest reliability in this group.  However, the use of a parallel port MIDI interface renders most printers useless while it is connected.  On the flip side, parallel port models can have the most channels/buses.  Be sure to install the software drivers that come with these devices.  This category is best for people who want to connect large MIDI systems easily.  Serial port units are limited to no more than two buses (32 channels) in and four buses (64 channels out).  These are called "2x4's."  Parallel port units can be designed to handle 8 IN's, and 8 OUT's (8x8).  I don't have enough data on the USB type.

    The last type include ISA cards and possibly PCI cards.  While these may be the most reliable (especially PCI MIDI interfaces if they exist yet), they require opening up your PC and possibility going through a fight against your PC over IRQ's and such.  In theory, these (especially PCI units) would have the highest reliability and number of MIDI buses.  Again, you must install drivers for these devices.

    Please note that some MIDI interfaces have SMPTE time code generators and/or readers.  However these units generally start out at least $200 and go up over a whopping $1,000!  Serious users that also go into video production may wish to consider this.  For the rest of us, it is a very expensive feature that will probably never be used.  Some units also have "tape-sync" and/or "drum-sync".  Again, consider your uses, for these tend to add greatly to the cost.

    As for best buys and such, I recommend the Portman variety for external units, and the Winman variety for internal cards.  These units are feature-loaded, but have good prices.  You can get a Portman 4x4/S, which plugs into the parallel port for around $200.  This has four MIDI IN's and four MIDI OUT's (all separately addressable), as well as SMPTE read/write.  However, this unit is flaky under DOS use.  The oddest part with this unit is that it often fails the DOS diagnostic test, but runs flawlessly under Windows.  This unit also functions as a stand-alone patch bay, but must be connected to the parallel port for changes in programming.
 
 

    After the hardware is installed, you must run the software/hardware setup software, which installs the necessary drivers to make your interface functional.  The instructions are generally included with the hardware.  If you are supposed to re-boot your computer in order to auto-detect new hardware, be sure to click on "Have Disk" when you get to that point (and have the disk and/or CD inserted).

    In EACH program that you use with MIDI (except for most MIDI file players), you will need to go to the Options, Preferences, or Devices menu and enable all this good stuff that you have on the system.  WARNING:  Do NOT enable "MIDI Mapper" on sequencers and such, or you will risk not being able to enable one or more other MIDI devices, because of the MIDI Mapper already addressing those devices.
 
 

    As for MIDI input, these are usually merged when using a Windows based sequencer.  In order to enjoy your new "5-manual organ", be sure to have each keyboard and/or device set to transmit on a different channel.  If one or more keyboards have a "split-keyboard" option, be sure to allow one or more extra channels for this, too.

    Luckily, Windows seems to behave nicely when to comes to outputting to multiple MIDI buses.  Yes, each bus is treated as a separate "device."

    Please note that not all MIDI sequencers support the use of multiple output buses.  If this is the case, then ALL tracks must go to the SAME device regardless of hardware configuration.  An exception include selecting "MULTIPLE INSTRUMENTS" on the MIDI section of the Multimedia part of the Control Panel, and then using the MIDI Mapper as the output device.  Another exception is a software mutli-route driver, such as "Instrument Mapper" that is included with the Sound Blaster AWE-64.
 
 

    The virtual MIDI device called "MIDI Mapper" is accessible under Multimedia properties within the control panel.  This device simply acts as a default router of MIDI output when no output device is specified, such as by a MIDI file player.  Unless you have external MIDI hardware that is at least General MIDI compliant (MIDI GS and XG are even better), you should set the MIDI Mapper to "Single Instrument" and use "Wavetable Synthesis" (or something to that effect).
 
 

    If  you set your MIDI Mapper to route MIDI to the sound card, it is ideal to go through HARDWARE wavetable synthesis.  The second best option here is through software wavetable synthesis (often labeled as SWT or SW Wavetable).  However, this route uses the MOST processor time and is the MOST likely to suffer from cutting in and out under heavy processor usage.  Even my brother's 475 MHz AMD K6 processor falls victim to this!  The worst route (and still available on many new PC's and cheap sound cards) is FM synthesis.  FM Synthesis is NOT General MIDI compliant, and it SUCKS!  If under MIDI Devices under Multimedia properties in the control panel, you see only two devices and these being something like "External MIDI OUT" and "FM Synthesizer", I'm sorry to be the bearer of bad news, but you need either a NEW SOUND CARD, software wavetable synthesizer (and possibly a new CPU or WHOLE NEW SYSTEM), or a keyboard or sound module that is at least General MIDI compliant.