Hard disk capacity vs. performance
 

(Not sure if this is the right forum...)

I've heard that larger capacity hard disks offer better throughput and less latency than small ones with similar performance specs. Is this true? I would vaguely expect it to be true due to lower seek times (i.e. the head wouldn't have to move as far to access data on an unfragmented partition), but I'm not really sure...

(For the record, my main laptop's hard disk failed, and I'm shopping for a replacement. I don't need more than ~80GB, but if higher capacity means better performance that might sway my decision.)

From the benchmarks I have seen there is some validity to that claim, but the difference in performance is usually small.
http://www.harddrivebenchmark.net/hdd_list.php

You'll have to decide for yourself if the price is worth it. In general, I don't get less than 100GB. I usually get 150 - 250 GB range.

Bigger is newer and that alone may be the reason behind subtle improvements in speed. The old thought was larger spaces between data caused slower speeds.

I think I'd consider a SSD instead of a mechanical drive unless this is pretty old laptop. A ssd fills two issues. One is the poor speed of most laptop drives and lower power use.

Only in the sense that larger is probably (quite a poor) proxy for newer, as jefro points out, and newer is a vague proxy for higher performance, all other things being equal. To give an obvious contra-example, if you look at enterprise SAS drives, they are almost always small, high rotational speed (10k or 15 k) and fast, with respect to conventional hard drives. So, in that particularly case, larger is not going to correlate with faster particularly well when compared against 'standard' hard drives (&, btw, they aren't what you'd want for your laptop).

And it depends somewhat (depending on what sort of speed is important to you) on areal data density; the more tightly data is packed, the more data passes a head per second, so the more data that can be retrieved (or written) per second. And that's nice if you want sustained bandwidth (and areal density will again correlate a little with newer), but that probably isn't the most important thing to you, for what you consider to be speed.

Full stroke seek times are a function of how far the head might have to move (ie, the physical size of the disk) and how good the head is at moving. In practice, most of your data is rather less than a full stroke away, but you can make this problem worse with fancy partition schemes (plus a latency of of half a rotation, on average, of course).

Also, you miss the factor that most hard drives are multi-platter jobs and there is an amount of marketing that goes into what gets offered. If, to reach some particular popular capacity, a hard drive manufacturer needs two and a half platters, you'll get three and, after excluding any bad blocks, if necessary, the drive manufacturer has a big lump of area to exclude (to hit that all important capacity point), what will get excluded are the slower parts of the disk. So, you might get less capacity for your money than you otherwise might, but at least it'll be faster capacity, and the full stroke distance will be reduced.

Generally-
Newer HDDs are faster (for any given size).
Higher data density/bigger capcity HDDs are faster than smaller HDDs.
Higher RPMs HDDs are faster (which is why a 10,000/15,000 RPM 'small' SAS drive can be faster than 7200/5400/etc. HDDs which are bigger).

Theres lot of other factors, like number of platters, so its pretty hard to know which dirve will be faster unless you can see a direct comapison betweent eh drivers you are interested in.

For a laptop where you only need 80GB, forget HDDs and get an SSD. They will run rings around a HDD, in particualr for access times. Well worth it....unless your laptop is so old it only has IDE or SATA1, in which case getting a SSD will be pretty much impossible (IDE) or pointless (SATA1).