With the ready availability of really big hard-disks these days, many people will be thinking of replacing (or adding-to) that pokey little disk you got with the computer a year or two back. Question is, what size of disk will work, and what's likely to give trouble?
The answer is that historically, computers have suffered various limits on maximum hard-disk size, ranging from 512MB through to 32GB. Unless your computer is a good few years old you won't hit any of these, though. The one you need to be concerned about on recent machines is the 128GB limit.
In order to take a disk larger than 128GB, the hardware AND operating-system software must support what is known as '48-bit LBA' addressing of the disk. If either cannot support this mode of working, then very large disks are not for you. If your computer is less than two years old then it's highly unlikely there will be a problem. If older, again there may be no problem (some five-year-old computers are OK with terabyte-capacity disks) but you should not assume so.
-How do I know if my box meets this requirement?
For the hardware, you need to identify the computer or motherboard type, and look this up on the manufacturer's site. Most manufacturers are quite helpful in this respect, and will allow you to download information of this kind. Where the board does not meet the large-disk requirements, there may be a a BIOS upgrade available. Do be aware that upgrading (aka 'flashing') the BIOS carries the risk of leaving you with a useless board if it goes wrong, though. Your call as to whether to try this!
Tip: If your mobo has SATA disk-connectors (whether used or not) you can almost take it for granted it's large-disk compatible. These were introduced round-about the same time as disks >128GB.
The operating-system software can also be checked on the supplier's site. Microsoft state that Windows XP Service Pack 2 (by far the most common OS in use today) supports large disks, as does Vista. If you have Windows XP but it isn't Service Pack 2, or if you are using an earlier version of Windows, then check the specs. You still might not need to upgrade -for example Windows 2000 SP4 just needs a simple settings-change to make it large-disk compatible. Linux- here it's the kernel that matters more than the actual distro, and again the latest kernels (2.6) will have no problem. Earlier kernel.. Check on the distro's website.
-Can I get round this by partitioning the disk into smaller segments?
No. This is an issue of the total disk size. Partitioning will not help. At least, not unless you're prepared to forego using the space above 128GB.
-What will happen if my box isn't suitable for a large (>128GB) disk?
Three things may happen:
The computer may refuse pointblank to boot with the disk connected.
It may be that all you can 'see' of the disk is the first 128GB.
The disk may register in its full glory, and appear to work perfectly. But, when it becomes 128GB full, disaster strikes.
The first two may be a trifle disappointing, but at least they are obvious, and cause no harm. It's the third that we need to be fully aware-of as it could lead to major data-loss. What actually happens here is known as 'Address roll-over' -since the computer cannot handle the large numbers needed to address disk-sectors above 128GB, when that point is reached the counter which determines the position of the heads on the disk's surface rolls-back to zero. (Think of a car odometer if you want an analogy) Result is that the next piece of data over-writes track zero of the disk. Track zero contains the information pertaining to what data-partitions are on the disk, and what they contain. Once this vital data is over-written, the whole contents of the disk will become inaccessible. So, the disk will appear work fine, perhaps for months, until you download just one more mp3. Then, it's like the disk suddenly and totally fails. In fact it hasn't failed, it is still perfectly serviceable. But, the entire contents have been rendered useless. Instantly. And for all intents and purposes, irretrievably.
Because the consequences of address-rollover are so severe (the sudden, instant and entire loss of data on the disk) it's not something we want to risk, if we can possibly avoid it. Therefore IF YOU ARE NOT SURE YOUR COMPUTER WILL TAKE A DISK OVER 128GB IN SIZE, PLAY SAFE AND STICK WITHIN THAT LIMIT.
The other option (if you cannot get a definitive Yes or No on large-disk compatibility from your computer-supplier) is to fit the disk as a secondary, and then test for address-rollover by deliberately filling it past 128GB with unimportant data, say multiple copies of a DVD-worth of data. (140GB should be enough) Might be a painstaking process, but it's better than losing all your data sometime later.
-Does this apply to very large disk-in-a-box (USB or NAS) units?
As far as I can tell, the only requirement here is that the operating-system shall support such disk sizes.
-Is there another size-limit above 128GB?
Yes, but it's huge. Might take us a while to reach it.
http://www.48bitlba.com is a very good information-resource.