Although software synthesizers are undoubtedly versatile, and mostly inexpensive, there is still something about classic hardware synthesizers that still appeals. If you had an original Minimoog in your studio, for example, you would want to use it every day.
However, the 'classic' era prior to around 1983 was also prior to MIDI. MIDI, as you know, is the universal means of data communication between keyboards, synthesizers, sequencers and even effects units. So if an instrument doesn't feature a trio of MIDI connectors, what can you do?
The simple answer is just play it live and record it into your audio sequencer. In an era of programming, yes this really is possible! And any wrong notes or mis-timings can easily be fixed with a little editing or punching-in.
But if you are dead set on programming your classic analog gear, then there is a solution. Even prior to MIDI, synthesizers could communicate with each other. So for example you could play one synth from the keyboard of another.
This was achieved by means of voltages. Analog synths could convert an input control voltage into a note. Also, a gate signal indicated the start and end of the note. So if somehow MIDI messages can be converted into control voltage and gate signals, then you can indeed sequence your analog synth via MIDI.
Fortunately a company called Kenton Electronics can supply MIDI to CV converters to various levels of specifications, and none too expensive in comparison with the value and utility of these instruments.
The Kenton PRO-2000 for example offers fast response times, options of volts/octave (Moog) and hertz/volt (Yamaha) control, and two separate channels for control over two instruments, among many other features.
There are some classic analog synths without the necessary CV and gate connections. For these, Kenton also supply 'socket kits' for classics such as the Roland TB-303, Korg Mini 700, and additional control sockets for other such as the Roland SH-101 (a real musical classic that one).