Probably a little bit of both.

How can it be both.

They either needed that many because they were selling that many.

Or bought way more to stop others from buying.

You can order parts today that you'll need in four, eight, twelve, sixteen months. You can do that even though both you and the competition plan to release new models in a few months, if you're willing to decide on the storage capacity of your next product already.

So how much you need is a forecast, or more precisely, a range of forecasts that depend on what you and your competitors will sell. Your order will say "I commit to buying x and want an option on y more" and a larger x gets you a lower unit price for the first x you buy.

If the vendor's production capacity is within your forecasts, or near it, why shouldn't you just commit to order everything and get a nice low unit price? You'll lose if your forecasts are very wrong, but then that's true whatever you do. It sucks for your competitors, who did not order according to their own forecasts.

Once they were selling a large enough quantity to begin with they can gamble their profits on overstock for future production, wiping out future supplies for competitors... at which point it's more of a guarantee, if there are multiple viable products and you remove all but one, consumers have no choice.

These are separate things (getting to the point of large scale production and blocking your competitors), e.g they could have played fair with the same initial success without excessive overstocking, allowing their competitors to continue competing and letting market forces decide, and letting suppliers gradually match current demand.

In short, there is no advantage to overstocking to such an excess other than to block your competitors. But you can only do so once you have a foot in the door and enough money to do so.

But there wasn't and will never be any overstock at Apple since Tim Cook started working there. In 2008 Apple still had Texas warehouses with old beige Mac but all of the Mac produced in the Tim Cook era do not last more than a 2 - 3 weeks in a warehouse. This includes components and this is why every January after an iPhone release the business journalists start predicting Apple's downfall because they lower their part orders for display, memory, etc. They don't let any of that stuff sit in a warehouse... EVER.

But did they overstock?

What I recall is them being production limited over and over again because their best wasn’t always good enough to stay ahead of demand. Nobody has talked about them hoarding.

Blocking competition was a benefit, but not the goal.

But they probably discussed it happening in a meeting. Therefore it also became a goal.

I think they bought what they needed, but that was enough to block others from getting produced.

Yes, unintentional side effect. I'm sure it crossed the minds of some the executives that they might be screwing their competition by buying out all the chips.

Apple is obviously not going to buy less so their competition can have more when Apple needed the supply.

Intentional effect.

The fact that it's one of severel effects and one of several motivations does not make it unintentional, or even necessarily just a side effect.

It could just as well be simply one of multiple fully considered effects, and surely was.

No one was demanding those hard drives, Toshiba was close to shelving it before going into production. Jon Rubenstein convinced Steve Jobs to invest in them for the music device they were building and 8 million was given to Toshiba so they can start producing these drives.