[syhprum (OP)]

I rather resent people claiming they haves "built a computer" when what they have done is purchase a commercially built mother board and plugged a few circuit boards into it and loaded commercially available software.
Any one who has built even a calculator from TTL to their own design knows this is a task of much greater magnitude than "building a computer".

[evan_au]

Everyone has to start building a computer from some components:

• The TTL chips mentioned above were components originally developed for the ICBM programme.
  
• Some of the early electromechanical calculators used relays from telephone exchanges as components
  
• The components of Colossus included vacuum tubes that were originally designed for radios.
  
• Babbage tried to build his analytical engine "from scratch" - and failed. 

One person who built a calculator from scratch was John Napier. (The origins of the abacus are lost in history...)

I think that these days, the computer is itself a component; what matters is not the fact that you built a computer, but what you are able to do with that computer.

What a computer can do is quite often determined by the software.

[syhprum (OP)]

Babbage did not lack intellectual skills to design a computer what he lacked were the business skills to get it into production.
His designs were later built by other engineers one as recently as the nineteen nineties.
TTL chips were not really required some early computers were built with pseudo TTL with transistors glued onto chips

[nicephotog]

From all of that it appears you mean the electronic components and design more than joining components below clip in ready style on a circuit board(that coincidentally require to match by frequency harmonics and voltage as much clip in design).
Perhaps it requires chemistry for the capacitor types and resistors, physics for the crystal harmonics oscillator to keep the beat,
bu' for the "operations" upon data given a computer can modify or recognise data and do work upon it using instructions repetitively over a set there are index registers and operation circuits and counter register to shuffle instructions or data through,
abbreviated is an "Architecture" for the CPU.

There are also "slave computers" for managing and retrieving , placing, readying , cleaning data transfer and setup to be ready to push through the CPU operation circuits From data storage devices,
Robotics for disc head controllers.
Alike network data transfer, internally "signals"(non binary arranged pulses and frequencies) are used to trigger and halt and control hardware activity when manipulating data to a useful/correct position.
e.g. the "term signal" for halt in Linux is not binary though the halt instruction is responding to a program that can access the signal generators to transmit to hardware signal receiver filters.

--

What level were you considering means truly "built" as e.g. DIY ?

[chris]

I rather resent people claiming they haves "built a computer" when what they have done is purchase a commercially built mother board and plugged a few circuit boards into it and loaded commercially available software.

Hmm - I really resent the guy who allegedly "built" my house too; all he did was to order a few pallets of bricks from the brickworks, some timber from the woodyard and a few dozen bags of cement, and when it was finished he installed some off the peg furniture from Ikea. What a cheapskate eh? I feel totally deceived. He should have made those bricks himself, and grown, felled and prepped the timber. As for the cement, buying that in bags was a total cheat...

[syhprum (OP)]

I think you can consider you have built a computer if you construct it from TTL chips on circuit boards you have designed and constructed your self.
I know this is like buying the bricks from the brick yard but it is the minimum amount of DIY that will produce what we think of as a computer today.
The most DIY intensive effort I can think of is to build a simple computer with electromagnetic relays that can be constructed in the home workshop but even then one would need a source of insulated wire!.
Perhaps we should speak of assembling a computer and not building it. 

[chris]

You're probably right, but the point I was trying to highlight is that not many things these days are really built, according to your strict definition.

[Bored chemist]

Well, I don't know if it counts, but my brother built a computer way back in the 80s
It was based on a design he got from a book. It used an 8080 processor and the inputs and outputs were switches and LEDs. If I remember rightly, the "glue" circuitry was a mixture of 74 series TTL and some 4000 series CMOS.
As far as I know, it never (directly) served any useful purpose but it did give him something to talk about in job interviews.

[quandry]

Building a computer entails designing the logic required to perform the function required, determining the components required to perform the function and then assembling the components.
The last step is often considered to be 'building a computer'.
The first step is the creative part.