4K and 5K iMacs Support 10-Bit Color Depth on OS X El Capitan

Why Apple go to all this trouble with amazing technology and then cripple it by shoving in a 5400RPM drive is beyond me. You've made 11 billion dollars profit in 3 months. Just make SSDs standard in all your computers already.

The average human eye registers... 7 bits of color. By using ten bit color you go from one bit of color you can't see to three bits of color you can't see (per channel, per pixel). So I am asking my graphics processor to process 9 bits per pixel that make no discernible difference in the quality of the image. Why not leave it at 8 bits and maybe OpenCl can make use of the unused graphics card clock cycles/processing?

Well, given that we can ALL see gradation issues with 8 bit, they must be on to something right?

The secret is that reproduction of light intensity by pixels, as well as the capturing of light intensity by photosensors, is linear. Half the value, half as much light.

The eye, on the other hand, does not process light information linearly. We tend to be able to pick out detail in medium dark areas better than those in very dark or very light areas.

As such, if you were to use 7 or 8 bit color, the eye can easily see incremental changes in color in the middle brightness band, whereas incremental changes in very bright parts of the band are nearly impossible to discern.

By increasing the bit level, you better cover this gap in the perceptual gamut of the eye. You could get the same value in 7 pixels by applying a mapping function equivalent to the eye's discrimination to the hardware pixels and to the light signal in memory.

However, you'd find this used a LOT more resources and was incorrect far more often than simply pushing some extra bits. That's because mapping is computationally expensive, every eye is different and it's unlikely a mapping function on commodity hardware and in commodity software is going to meet your exact need.

I don't think anybody I know should buy the base model.

Correction: Nobody should buy the base model. And they shouldn't even sell it because that dupes unwitting customers. Any version with a 5400 disk is truly a crappy computer. That disk is a bottleneck that cripples an otherwise excellent machine. Whatever dollars you save buying that version, they aren't worth it. The dollars you're still spending are being spent on junk at that point.

It seems like every iMac discussion going forward, no matter what cool feature it is they added, is going to quickly diverge into complaints about how crappy the disk is and how that completely overshadows anything else they do.

And SSDs do not yet have the same capacities. Just attach an external SSD and be happy already, eh? :)

If the fix to the performance problems on a £1500 iMac is to run the OS through an external drive — well, I think that gives a stronger argument than I can ever articulate.

What you're actually complaining about is that you think its too expensive to buy the drive you want and you expect it for less.

No. That's not it at all. The point is that the Apple brand is associated with a certain amount of quality and prestige. They refused to jump on the netbook bandwagon way back when because netbooks, whether $200 or $2, were garbage. At any price, the user experience was so terrible that it would be cruel to subject a person to them. Apple recognized this and held themselves to a higher standard.

They no longer hold themselves to that higher standard. They are now selling a computer which truly is garbage. Their 5400 disk iMacs are so frustrating to use that the experience damages their brand and reputation. And non-tech consumers just don't know enough to avoid this trap. They'll buy the base model because it's cheapest or simply in stock, and assume that no matter what, they can rely on Apple to give them a solid product. That's what Apple is known for, after all. But they will feel swindled as soon as they start using it. It offers a horrible user experience right out of the box.

As an Apple fan and shareholder, I do not like where this is headed. I don't think it's in the best interest of Apple to degrade its reputation by sacrificing the quality of their products. I want them to keep being awesome, not become yet another computer maker willing to sell whatever cheap drivel they can.

Apple invested in the supply chain in astronomical numbers. Until the stock of the 5400RPM drives are gone, and the cost of a sizable SSD comes down, and Apple can corner that part of the market for their own longevity/sustaining, we won't see it. 2 years ago, I paid ~$370 for a 480GB SSD. I've never worried about running out of space.

Yep, I know the feeling. 4 years ago I paid £240 for an OCZ 240GB SSD that had read/write speeds of 150MB/s either way. I buggered it after I stupidly enabled TRIM. Luckily they later replaced for a 256GB.

Now I can buy a 500GB Samsung 850 EVO SSD for less than £120. Apple could easily get that far cheaper, that's not in question.

5400RPMs in 2015, with those specs, and at that price, is a joke. You can't even swap it out for an SSD. No appreciation of longevity, or value for money. Raise the price by £100 if you have to, and throw in a 256GB PCI-e SSD on the base model. Just don't offer 5400RPM drives for Christ's sake.