原创 The pre-USB era (Part 1)

Let me take you on a trip down memory lane to remind you of how wonderful USB really is.

As far as I know, USB (which stands for Universal Serial Bus) was originally conceived only in the context of computers and their peripherals, such as mice, keyboards, printers, scanners, and external storage devices. Once it had been introduced, however, USB proved to be so useful that it now appears in all sorts of devices, including smartphones, digital cameras, e-Book readers... the list goes on and on and on...

Now, before we plunge into the fray with gusto and abandon, let's remind ourselves as to the key things USB provides that most of us don't even think about anymore:

* Any USB-enabled device can be connected to any USB port on the computer.
* The same USB device can be connected to different computers (PCs, Macs...).
* If this is a new device for which a driver has not yet been installed, then the host system will locate and install the driver without the user having to reboot the system.
* The host system automatically configures itself and the USB device without forcing the user to play around with esoteric settings like numbers of bits and bit rates.
* USB provides "hot swap" capabilities, which means it isn't necessary to power-down the computer before connecting or disconnecting a USB device.
* If you have more devices than you have USB ports on your computer, all you have to do is plug a cheap-and-cheerful USB hub into one of the ports on the computer and then plug other devices into the hub.

Today, USB is the interconnect of choice for a wide variety of devices

The bottom line is that USB makes things incredibly easy for end-users. One strange thing to me is that, although USB hasn't been around all that long in the scheme of things, many younger users have never known a time before USB. And even those of us who were present in "ye olden days" tend to forget just how painful things used to be...

In a moment I'm going to talk about things like PS/2 connectors, RS-232 connectors, Centronics interfaces, SCSI interfaces, and goodness knows what else. One problem is that it's hard to visualize these things without pictures. Another problem is that – not surprisingly – all of the equipment in my office is now USB-based; any older computers and peripheral devices were hauled off to my local technology recycling center long-ago.

Thus it was that I recently found myself visiting the technology recycling center purchasing a bunch of old computers and peripherals that I may well have donated to them myself (as always, it's a funny old world when you come to think about it). The folks at the center did say that after I'd taken my pictures I could return these units and they would refund my money. But these things are getting harder and harder to find so I decided to keep them because I may wish to take additional pictures in the future.

Let's start by considering the sort of thing we might have seen looking at the back of a generic tower computer circa the mid-1990s. Basically we would have been faced with a whole bunch of connectors and expansion cards as illustrated in my Visio sketch below:

The back of a generic tower computer circa the mid-1990s

So what sort of devices and connectors would we be looking at here? Well, first of all there would be a PS/2 connector for the keyboard. This was a 6-pin mini-DIN connector, where the letters D-I-N stand for Deutsches Institut für Normung, which is the German national standards organization that originally standardized this type of connector.

A keyboard with a PS/2 connector

Just to make sure we're all tap-dancing to the same drum beat, a lot of these photos may look a little strange at first because we set them up to have the connector in the foreground and its corresponding device further back. A graphic artist friend called Nick took these pictures for me. Keeping things in focus proved to be harder than I had expected. In many cases Nick had to take two photos – one with the connector in focus and another with the device in focus – and then merge them together (I love learning how to do things like this – this technique would never have occurred to me on my own). But we digress...

The name "PS/2" comes from the IBM Personal System/2 series of personal computers. These computers – along with the PS/2 connector – were first introduced in 1987. The PS/2 keyboard connector replaced a larger 5-pin/180° DIN connector used in the earlier IBM PC/AT design.

In fact, there would be two PS/2 sockets on the back of the computer, where the second was used for a mouse. This PS/2 mouse connector generally replaced the older 9-pin RS-232 "serial mouse" connector that was used on earlier machines (we'll return to RS-232 connectors in a moment).

A mouse with a PS/2 connector

The PS/2 designs on keyboard and mouse interfaces were electrically similar and employed the same communication protocol. However, a given system's keyboard and mouse port might not be interchangeable since the two devices use a different set of commands. Thus, in order to avoid confusion, the two connectors on the back panel would typically (hopefully) have little images of a keyboard and a mouse associated with them. These were jolly useful if your computer was sitting on top of your desk, but not quite so useful if you were squirming around on the floor under your desk trying to connect things up in the dark.

Over time, these two connectors started to be color-coded – as were the plugs on the ends of the keyboard and mouse cables. I remember thinking that this was an incredibly clever idea the first time I saw it (before that everything was the same color, which didn't exactly help the situation).

[To be continued on The pre-USB era (Part 1)]