Could easily have been a drive that had been in his main work machine for quite some time. He no doubt had the good sense to have backups on other local drives and remote services[1], but this could still be his primary store. It isn't like holding the text of books in progress is a task that needs the speediest of SSDs so if that drive just kept working why would he replace it?

[1] presumably these have also been purged if his wishes were so written or interpreted, probably by more conventional means[2]

[2] the bulldozer being used for this one drive for ceremonial purposes

SATA drives replaced IDE drives (which this appears to be) more than ten years ago, somewhere around 2004-2006.

PATA drives were still common enough ten years ago, maybe not in brand new machines but certainly in active ones and readily available as replacements/upgrades. Using a machine from ~10 years ago for document authoring isn't unusual. A good keyboard screen is more important than the rest of the machine for that sort of job - you don't need something new, fancy, & powerful, and many authors prefer an older machine because they can't run distractions well!

He could have been on an old computer - GRRM, for example, still writes on an MS-DOS machine

Yes, strange indeed, I expected Terry to only roll with the latest in tech.

Sarcasm? There has been interviews with him where he discusses his "writing equipment" and like many authors he preferred a basic system that kept mostly out of his way. I mean it's just as easy to write a novel in Word for DOS* as it is in the latest software and hardware tech, so why would authors want to waste their time always running the latest tech when it's a distraction from their day job?

* I'm not advocating people write novels in DOS. Just making an exaggerated point that since the medium is text only you don't need to be upgrading frequently.

Isn't GRR Martin famously writing on a DOS computer ?

Using Wordstar no less, must drive his editor and publisher bonkers.

Not that i can't relate. If i could find a CLI browser that kept up with latest CSS and JS stuff, i would be doing everything in a framebuffer CLI.

Indeed: http://www.bbc.co.uk/news/technology-27407502