why did Amstrad use sockets for the CPU and GateArray?

[eto]

This question bugs me since I looked the first time into a CPC:

Amstrad did not bother to use sockets for most ICs as it was much cheaper to go without sockets. 

But what would be the reason to use sockets for the CPU and the GateArray?

Any ideas/insights?

[pelrun]

They're far more expensive parts and it probably saved money to do large production runs with the asian factories with the parts they had access to, before shipping the boards to the UK, and then they could decide how many devices to fully assemble based on the current state of the market.

[McArti0]

And PAL.
That is, things that may not have been available at the time of soldering the board.
PAL programmable, ( in another place)
GA programmable,  (in another place)
Z80 difficult to obtain or in large, rare series.

That's how I imagine it.

[eto]

They're far more expensive parts

Gate Array for sure. But wasn't the Z80 also just a cheap and simple IC? I would expect that the FDC was more expensive than the Z80 - but that might be wrong.

[McArti0]

Z80 Hard to obtain in large quantities.

[Bryce]

The PAL and GA are custom chips that could have required late changes even after production had started, so these were of course socketed to allow for easy replacement if an issue was found. The Z80A cost around $10 for a hobbyist in the early 80's, which is equivalent to about $40 today. So Amstrad were probably paying equivalent $20 a piece and they were known to have failures, so that's probably why Amstrad chose to socket them. Neither really surprises me. What surprises me is what ISN'T socketed: The ROMs. Amstrad must have been extremely confident about the code on these, confident enough not to socket them.

Bryce.

[pelrun]

Confident or "We can't afford to respin the ROMs anyway so they'll just have to go out as is"

[andycadley]

Probably a case of "If it ships with ROM bugs, so be it. Better known bugs than programmers trying to work around a dozen variations."

Which is what happened, until BASIC 1.1 came around on later models.

[eto]

paying equivalent $20 a piece and they were known to have failures,

wouldn't that have been the case for the FDC and AY also? Or were those cheaper and more reliable?

The PAL and GA are custom chips that could have required late changes even after production had started

Sure, that makes sense. However does it also make sense for later motherboard revisions when the ICs were known to work well?

[Bryce]

paying equivalent $20 a piece and they were known to have failures,

wouldn't that have been the case for the FDC and AY also? Or were those cheaper and more reliable?

The PAL and GA are custom chips that could have required late changes even after production had started

Sure, that makes sense. However does it also make sense for later motherboard revisions when the ICs were known to work well?

The FDC had been around since 1978 and was used in millions of computers, so both the price and reliability were most likely better.
The AY was also around since 1978 and widely used in Pinball and Arcade machines. I'm not sure what it costed, but it would have been considered reliable at least.
The CPU was also directly connected to the expansion port with zero protection, so maybe they were expecting regular failures from static discharge?

Bryce.