This is a nice entry for a disk - relative path - no spaces - name describes contents: perfect!
If the filename points to a *.vmdk you can skip the device type

This connects an iso-file as a CDrom.

Silent default when *.present is set to true

if you don't want that CDs or ISOs are connected
at boot-time you have to add this.
Don't use with virtual disks

only set deviceType when you need a CD/ISO.
"disk" usually appears when you swapped a CDrom and a vmdk.

Use this for CDroms only - I don't recommend to use this entry at all - as it produces unpredictable results on hosts with more than one CDrom.

If you have problems with Virtual CD-drives like Daemon Tools - check this first.

Depending on the device type you selected one of this entries is appropriate.
instead of using autodetect you can also give the driveletter or device-name

This mode makes a vmdk behave like a good-old-real-metal harddisk. If you accidentaly format it, the only way to restore your files is the use of forensic tools.
All changes are written to the vmdk directly and the disk will not be included in snapshots.

This mode writes all changes to a temporary file which will be deleted when you power off the virtual machine.
The temporary files are named like this
2k-ide-system.vmdk.REDO_a02144
Obviously this setting makes no sense for a brand new VM.
Disks useing this mode are not included in snapshots.

WARNING: for experts only

This mode writes all changes to a temporary file. This time the file will not be deleted when you power off the virtual machine.
The temporary file are named like this 2k-ide-system.vmdk.REDO_a02144

Current VMserver doesn't offer this mode via GUI - though he can use it.
Be very careful with this mode: this is not the mode used for snapshots!
Snapshots nowadays are created per VM - the REDOlogs created by the 'undoable mode' are created per disk.
Never use this in combination with a snapshot !!!

At first sight this mode looks like the one we had in WS 3 and GSX 2.5 - but you can not commit/ discard/ keep these REDOlogs when you power down a VM with current VMserver.
To commit or discard these REDOs you need a special hack that should be used by experts only ...

I use them in case I want to use very old guests - early Dos for example. Be careful - may have strange and un-expected side-effects.