Notes regarding large systems

A single digital I/O card will provide a limited number of lines: typically 96 (for Advantech cards) or 72 (for Amplicon cards).

If you need more lines than this, you will need more than one IO card. PC-compatible computers have a limited number of ISA and PCI slots: you will need some slots for sound, serial or multimonitor cards.

Even if you have enough lines in total, do you have enough inputs and enough outputs?

Input/output mixes on Amplicon cards

With 24V devices, which we use, lines are configured in blocks of 24. Each block of 24 may be all inputs, all outputs, or 16 inputs and 8 outputs. So each 72-line card can take the following input/output mixes: 72/0, 64/8, 56/16, 48/24, 40/32, 32/40, 24/48, 16/56 (the only combination not possible is 8/64).

Input/output mixes on Advantech cards

Lines are configured in blocks of 8, to be input or output.

Very large operant control systems

Our intravenous self-administration boxes have up to 6 inputs and 8 outputs each. So a full 8-card system should be able to run 41 of these boxes, and if you have fewer devices attached, you'll get more boxes. So you could build systems that are very large by common behavioural neuroscience standards.

For a system this large, it might be a bit cheaper to get an 'industrial' computer (1 @ <£1,500?) than the necessary number of smaller-capacity PCs (4–5 @ £500 each). On the other hand, I generally prefer to have lots of cheap PCs scattered around running smaller systems – if one system is damaged you lose less; also, you have more computers hanging around to do other things with.

Whether you can actually use up the software limit of 8 cards depends on the other devices in the computer. Each card will need a unique I/O base address, and very probably a unique interrupt. Base addresses and interrupts are also used by things like serial ports, Ethernet cards and so on. But if you use a PS/2 mouse and keyboard, disable the serial (COM) ports, use a networked printer and disable the printer (LPT/PRN) port, use PCI or on-board video, a PCI network card, and as many as possible of your PCI devices share interrupts, you should certainly manage 5 or 6 cards in an industrial computer (360 or 432 lines). Note that multimedia Whisker setups will often need to use PCI slots and interrupts for Audio outputs (one PCI slot for each 2 channel sound card), Display outputs (at least one slot for a multimonitor adapter), and Touchscreen inputs (one slot for a multi-serial card).