2. Hardware

To connect the two computers you need some sort of cable, called a nullmodem. The simple version uses software handshaking to control the data flow. The "deluxe" version does this using the modem control signals (RTS/CTS). If possible, use hardware handshaking. The risk to lose data packets will decrease and the data throughput will rise.

It is also very useful to have a serial chip with FIFO support. A 16550 for example can store up to 14 bytes in it's fifo chain until it signals an interrupt to gather the data.

2.1 The simple nullmodem cable

    DTE 1                                        DTE 2
  
  9pol 25pol (female)                          25pol 9pol (female)
  
   5    7  ]--GND--------------------GND------[  7   5
  
   2    3  ]--RxD--------. ,---------RxD------[  3   2
                          X
   3    2  ]--TxD--------' `---------TxD------[  2   3

2.2 The full-featured nullmodem cable

    DTE 1                                        DTE 2
  
  9pol 25pol (female)                          25pol 9pol (female)
  
   5    7  ]---GND--------------------GND------[  7   5
  
   2    3  ]---RxD--------. ,---------RxD------[  3   2
                           X
   3    2  ]---TxD--------' `---------TxD------[  2   3
  
   7    4  ]---RTS--------. ,---------RTS------[  4   7
                           X
   8    5  ]---CTS--------' `---------CTS------[  5   8
  
   4   20  ]---DTR--------. ,---------DTR------[ 20   4
                           X
   6    6  ]---DSR--o-----' `------o--DSR------[  6   6
                    |              |
   1    8  ]---DCD--'              `--DCD------[  8   1