# How many hours of labor did it take to assemble a minicomputer?

A minicomputer like the PDP-8 contained several thousand discrete transistors and other components, all of which had to be soldered by hand, and that was among the simplest computers on the market; larger minicomputers and mainframes could contain hundreds of thousands of hand-assembled components. How many hours of labor did it take to do this assembly? (All labor input, from when components are delivered to the factory, to when finished machines roll out.)

Ideally I would like to gain a comprehensive understanding of how labor cost varied as a function of component count, but finding statistics for this will be potluck, so I will happily accept an answer that finds numbers for any computer or calculator prior to when wave soldering changed the picture. Failing that, I would be interested in figures for other electronic devices such as radios or TV sets of that era, if accompanying component counts are available to make them comparable.

• Serious this is about computers? Sounds more like a general question about manufacturing. Also, wave soldering has been in large scale use since 1950. So way before any mini computer. Next, soldering isn't the only, not even the most time consuming process in building a machine. Last but not least, anyone in production planing will tell you that without a detailed product definition no meaningful even less comparable numbers can be given. So any number here would be about comparing apples and oranges. Feb 25, 2020 at 18:37
• @Raffzahn I'm hoping for an answer like 'the PDP-8 took X hours of labor to make each unit' - that would be a detailed product definition! but upvoting your comment because it just told me a couple of interesting things I didn't know, that wave soldering happened a lot earlier than I thought; was it used for the PDP line? And that soldering isn't the most time-consuming process, even when you're doing it by hand; what is, then? Feb 25, 2020 at 18:42
• Sie this picture of a PDP-8 flip-chip. It shows all signs of wave soldering. You may not like it, but all was time consuming. There is no single-most point. Feb 25, 2020 at 18:49
• While I'm not sure about the original PDP-8, the PDP-8/I and later models had backplanes that were wire-wrapped by machine. The modules were soldered by machine, too. There was perhaps less literal manual construction involved, even in the 60s, than what you're thinking. The first major customer for a new embedded computer at the time was often that company's own factory. Feb 25, 2020 at 19:13
• Pick and place also existed for Through hole components. First I saw was 1986, but I'd guess that machine was 5 to 10 years old at that time. Feb 26, 2020 at 17:04

Most PDP-series machines of this era were built using a large number of cards (with soldered components) connected by a wire-wrap backplane and a series of cables. I think the cables were mostly used to interface major components together, such as the CPU to the RAM, storage drives, terminal multiplexers, etc.

The cards were considered standard components which could be interchanged relatively easily within type, and could be produced in volume. I would be surprised if as much as a man-hour was required to produce each one, on average. If PCBs and automatic soldering equipment were used, the main time consuming tasks would be to place the right components in the right holes, trim the leads, and test the finished result.

Some cards were actually core memory arrays, which required specialist assembly techniques and represented a substantial proportion of the final system cost. Until the advent of semiconductor RAM ICs, this was still the most cost-effective type of system memory available.

The cables were also standard components which could be produced and stocked up against needs in the field. A customer might reasonably want to keep disk and tape drives in a particular configuration, which may require longer cables to reach between racks or even through an under-floor trough.

The single most complex component would have been the wire-wrap backplane. Assembling one of these by hand would have been a monumental task, but DEC used automatic machines for this. I'm sure it still took a while, but a machine can be set up and then left with minor supervision, instead of requiring many hours of craftsman-level skilled labour.

• I am quite sure I've seen references for DEC to use automatic wire-wrap machines. A backplane is quite nice to such a process. Feb 26, 2020 at 6:20
• Denver-Gardner wire-wrap machines were used at DEC, possibly starting with the PDP-8. From Bell, et. al., Computer Engineering, page 58: Automatic wire-wrap technology was used to reduce printed circuit board interconnection cost. This also eliminated errors and reduced checkout time
– dave
Feb 29, 2020 at 15:48