# Selling laptops



## Daffodil (3 Jan 2013)

I have a few old laptops that are still working but would like to get rid of them for a bit of cash and buy a decent new one.  Is there anywhere that would buy second hand laptops either in the Dublin area or online?


----------



## vandriver (3 Jan 2013)

Www.donedeal.ie or www.adverts.ie are two that spring to mind.


----------



## Sue Ellen (3 Jan 2013)

Make sure to clear any personal info before selling.


----------



## dub_nerd (4 Jan 2013)

Sue Ellen said:


> Make sure to clear any personal info before selling.


 
I would go one further. OP, you may or may not be aware that a knowledgeable buyer of your laptops will be able to access not only files that you leave on it, but also potentially anything that was _ever_ on it, even if it has been deleted. Recovering/undeleting files is straightforward and as far as I'm aware (from hearsay) that is the sole purpose for which some unscrupulous people purchase second hand equipment. If you have ever had any sensitive personal data on the laptop, the only fully safe option is to either sell it without its hard drive, or to properly erase/format the hard drive and reinstall the operating system (and other software) from scratch.


----------



## DrMoriarty (4 Jan 2013)

+1. There's a good guide here.

I'd go for adverts.ie over donedeal.ie — fewer users, but more your "target audience", and you'll probably waste less time on scammers and timewasters. The format allows buyers to ask questions and make offers, and it's free to place a basic ad.

Be prepared for a bit of a shock on what these will fetch — the "perfectly good" laptop you spent >€500 on just a few years ago may fetch only a fraction of that on the secondhand market, simply because €500 now gets you so much more, specs-wise.


----------



## Leo (4 Jan 2013)

dub_nerd said:


> a knowledgeable buyer of your laptops will be able to access not only files that you leave on it, but also potentially anything that was _ever_ on it, even if it has been deleted.


 
They'll be able to recover deleted files (or portions thereof) so long as the areas on the disk where they were stored have not been overwritten by something else. So while recovering files is possible, it's not possible to recover everything that was ever on it.


----------



## dub_nerd (5 Jan 2013)

Leo said:


> They'll be able to recover deleted files (or portions thereof) so long as the areas on the disk where they were stored have not been overwritten by something else. So while recovering files is possible, it's not possible to recover everything that was ever on it.


 
That's why I used the word "potentially" 

Joking aside, modern drives with large block sizes are prone to leaving sensitive data recoverable in a fragmentary manner. Even if file level recovery is impossible because blocks from deleted files have been reallocated, a block level sniff around the disk may turn up interesting stuff. If the file system block size is a multiple of the drive physical block size, then fragments of old files are in principle recoverable, and they are not necessarily prone to overwriting because they are protected by being allocated to an existing "real" file. You will have up to one full block "wasted" per file, and its several KB size is plenty for containing fragments with old passwords etc.


----------



## Leo (7 Jan 2013)

dub_nerd said:


> That's why I used the word "potentially"


 
Only potentially if no write activity has taken place since files were deleted...so bordering on the scare-mongering there.


----------



## Boyd (7 Jan 2013)

Would "restore factory settings" (basically re-install windows) do the trick re: deleting all sensitive data?

You could also try ebay to sell it OP....


----------



## dub_nerd (7 Jan 2013)

Leo said:


> Only potentially if no write activity has taken place since files were deleted...so bordering on the scare-mongering there.


 
No, you didn't read the rest of my post. Old data at the block level can remain unerased inside the contents of new files. They are protected from future overwrites because they are allocated as part of an existing file, but do not form part of its contents because of the difference between file system block size and physical disk block size. What happens is that disk blocks beyond the end-of-file marker are allocated to the file.

Consider this scenario. I create a new text file and stick a single letter X in it. When I save and look at the file size it is "1 bytes, 4096 bytes on disk". 4096 is the file system block size - the minimum size of any file. That 4K block will never get overwritten while my file exists, because it is allocated. The contents of the 4K block are not all nicely blank. They contain whatever contents were on that block the last time it was allocated, less the new file contents I have just saved. The file system knows the logical length of the file -- 1 byte -- so it doesn't care that there is garbage at the end. The disk driver did not erase the contents because it has a smaller physical write size than the file system block size. There could be a bunch of unerased passwords in that 4K block. You could never recover them as part of a file recovery because the knowledge of their former participation in a file _has_ been erased. But if I examine the disk with a block level analyser I will find them. A block level search tool will find them if there's a likely search string ("password"?) without having to do this by hand, just in case you're wondering who would bother! (I've done it before myself; the police would certainly do it as part of a forensic examination; so it would be naive to think a criminal wouldn't).

Furthermore, even blocks that are not part of new files are not guaranteed to be overwritten by new file activity. That's because the block allocation mechanism will favour contiguous groups of blocks for new allocations of large chunks. So the normal disk fragmentation phenomenon will ensure that there are lots of unerased old blocks. A defrag will erase these of course, but how many people even know what that is, let alone do it on a regular basis?


----------



## Leo (7 Jan 2013)

dub_nerd said:


> No, you didn't read the rest of my post.


 
I did. You implied in your first post that it is possible to fully restore any file ever deleted from an old laptop, that is untrue and misinformation like that tends to frighten people who are not as computer literate.


----------



## AlbacoreA (7 Jan 2013)

Deleteing, formating or re-installing the OS, isn't enough. You need to do a secure one pass overwrite using a tool that can access all sectors including damaged and hidden Partitions/sectors. http://techlogon.com/2012/07/07/securely-erase-a-hard-drive-dban-may-not-be-sufficient/. Once you've done that its not recoverable.


----------



## TarfHead (7 Jan 2013)

Time involved in readying some old laptops for sale, versus cash to be received from sale of old laptops .. may not be worth it ?


----------



## dub_nerd (8 Jan 2013)

Leo said:


> I did. You implied in your first post that it is possible to fully restore any file ever deleted from an old laptop, that is untrue and misinformation like that tends to frighten people who are not as computer literate.


 

My exact words were "potentially anything that was _ever_ on it". That is not untrue or misinformation, it is a fact. I did not refer to "any file". A file is a logical construct. Fragments of files are recoverable, even when they have ostensibly been overwritten. You either understand this or you don't -- either way I doubt if the elaboration already entered into added anything useful for the OP, and I don't intend to go into it any further to humour you.

People who are not computer literate should take away exactly one conclusion -- *do not sell any computer with its original disk drive intact*. If you think that's scaremongering and you feel you're in a position to offer more nuanced advice, be my guest.


----------



## AlbacoreA (8 Jan 2013)

Daffodil said:


> I have a few old laptops that are still working but would like to get rid of them for a bit of cash and buy a decent new one.  Is there anywhere that would buy second hand laptops either in the Dublin area or online?



They generally give you very little for them.


----------



## AlbacoreA (8 Jan 2013)

dub_nerd said:


> ...People who are not computer literate should take away exactly one conclusion -- *do not sell any computer with its original disk drive intact*. ..



Most non techies won't know what to do with that. So if I say securely wipe them as per the instructions above, or remove the disk and drill a few holes through it. They won't know how to do either.


----------



## Leo (8 Jan 2013)

dub_nerd said:


> My exact words were "potentially anything that was _ever_ on it". That is not untrue or misinformation, it is a fact.


 
On a several year old laptop, you absolutely will not be able to recover 'anything that was ever on it. End of story, let's not drag this any further off topic.


----------



## AlbacoreA (8 Jan 2013)

From a regular persons point of view the easiest thing is to remove the disk. Would most people know how, or be willing to do that. I don't think so.

I wasn't aware that many disk wiping tools didn't touch the hidden/damaged sector. I always assumed they did. Lesson learnt.


----------



## dub_nerd (8 Jan 2013)

Laptop drives can usually be removed by taking out a single screw. But you're right, most people still won't know how, and in any case who's going to want to buy it -- unless they know how to purchase and install a new drive and reinstall all software.

Disk wiping tools DO erase all blocks, as long as we are not just talking about deleting files or deleting the drive allocation table (sometimes referred to as a "quick format"). Again, is your average person going to do this and reinstall all software?

Corporate users in my experience have their IT department look after reformatting drives before giving away old machines or sending them off to be junked.


----------

