Please consider clearing all data from disc drives so that computers are safe to be recycled. While it may be possible to delete only personal data, I always totally wipe all data from hard discs and then check them for faults. It can take some time, but once started each step of the process can be allowed to run until completed and the disc access light goes out. It is even possible to run the same process on several discs at he same time, each in its own text console window.
Secondhand computers usually require obsolete RAM which is much more expensive than the current varieties, please do not remove it and make the box worthless.
I normally use a Knoppix bootable DVD or CD running the Linux operating system to check the number of drives fitted, then for each individual drive write all zeros to at least the start of the drive, create a new Master Boot Record (MBR), test by writing and then reading test patterns to every individual Byte location and re-format each drive using a standard formatter. This will report any faulty area. You can download a Knoppix .iso image from the University of Kent at
http://www.mirrorservice.org/sites/ftp.uni-kl.de/pub/linux/knoppix
The machine BIOS must be configured to boot from CD/DVD. This is often the default, or there are several alternate methods provided to enter the BIOS configuration facility, usually involving pressing a key such as <delete>, <f2>, or <f10> during the Pre Operation Self Test (POST) immediately after switch-on, or if necessary delete the BIOS configuration using the link provided on the motherboard or remove the back-up battery for a few minutes.
Discs are cleared using text commands while working as the administrator called root. Boot from the Knoppix disc, open a text console, (there is usually a clickable icon at the bottom of the screen), and type
su -
(an alternative is to type
<Ctrl><Alt><F1>
to enter the text only console mode and login as root), there is no password set so you will not be required to enter one.
df
will show the device names used by Knoppix for individual disc partitions such as /dev/sda1 or /dev/hda1, their initial, used, and free capacities, and the names used when they are mounted by Knoppix, such as /media/disk where the important information is the initial device name (without the trailing number) for each disc.
If for example a disc is called /dev/sda (no number!) then clear the Master Boot Record (MBR) by Writing all zero bytes from the start of the disc using
dd if=/dev/zero of=/dev/sda
to at least the first few sectors of the disc and either stop after a minute or so using [Ctrl]C or leave it to finish and the disc access light goes out.
then run
cfdisk /dev/sda
Move the cursor to the line showing the now empty disc and create a new DOS MBR (the default)
Move the cursor to the line showing Free Space and create a new partition using the entire disc space, then close cfdisk.
Format the new partition using
mke2fs -c -c /dev/sda1
where the -c -c instructs the formatter to write then read patterns to every disc Byte location, the patterns being binary 01010101, 10101010, 11111111, and finally 00000000 which leaves the disc empty. Any disc errors will be shown on screen.
The same Knoppix disc can be used to perform a simple write then read test of machine RAM. Place the Knoppix disc in the drive and re-start the computer, then as soon as the first static screen appears, instead of allowing the disc to boot enter
memtest