You will need a partition on the external drive that has been freshly erased.
For some people Time Machine will be more than adequate. Time Machine is part of OS X. There are two components:
1. A Time Machine preferences panel as part of System Preferences;
2. A Time Machine application located in the Applications folder. It is
used to manage backups and to restore backups. Time Machine
requires a backup drive that is at least twice the capacity of the
drive being backed up.
Alternatively, get an external drive at least equal in size to the internal hard drive and make (and maintain) a bootable clone/backup. You can make a bootable clone using the Restore option of Disk Utility. You can also make and maintain clones with good backup software. My personal recommendations are (order is not significant):
2. Data Backup
3. Deja Vu
5. Synk Pro
Visit The XLab FAQs and read the FAQ on backup and restore. Also read How to Back Up and Restore Your Files. For help with using Time Machine visit Pondini's Time Machine FAQ for help with all things Time Machine.
Although you can buy a complete external drive system, you can also put one together if you are so inclined. It's relatively easy and only requires a Phillips head screwdriver (typically.) You can purchase hard drives separately. This gives you an opportunity to shop for the best prices on a hard drive of your choice. Reliable brands include Seagate, Hitachi, Western Digital, Toshiba, and Fujitsu. You can find reviews and benchmarks on many drives at Storage Review.
Enclosures for FireWire and USB are readily available. You can find only FireWire enclosures, only USB enclosures, and enclosures that feature multiple ports. I would stress getting enclosures that use the Oxford chipsets especially for Firewire drives (911, 921, 922, for example.) You can find enclosures at places such as;
1. Cool Drives
All you need do is remove a case cover, mount the hard drive in the enclosure and connect the cables, then re-attach the case cover. Usually the only tool required is a small or medium Phillips screwdriver.
You can backup multiple computers on ONE HD with Time machine. just choose the destination, ....
it will make multiple time machine backups in different folders inside the MAIN folder marked Backups.backupsdb
keep it simple. Also makes 2 copies (not meaning time machine) of ALL important data. 2 copies is 1, and one is none.
I already have SuperDuper for my iMac and the App is on the AirMac.
I do have a second backup (Portable HD) for my iMac photos and iTunes.
I have hooked it (2nd HD) up to the AirMac via USB to B/U a few files temporarily.
The simple choice would be to buy another portable HD and partition it in 3 sections:
(1) Permanent Storage of photos and iTunes and special files.
(2) Weekly B/U of iMac via Firewire/USB
(3) Weekly B/U of AirMac via USB/Thunderbolt.
Is that possible with buying one (1) new HD or Time Capsule?
OR do I need 2 HD's, in which case, I would keep what I have and just buy a portable HD for the AirMac.
theres no need for all that partitioning actually. multple TM backups will auto dirrect to new bacupdb folders
can you. yes. need to. no
just get a superslim 500GB HD 7mm for your macbook Air. for TM backups and personal files and folders
More important than peripherals or ramm or larger SSD. is that of multiple redundant backups
The biggest mistake everyone makes about computers is considering them data storage devices. the pros never make this mistake. multiple backups on multiple HD and optical archival DVDs
Enjoy your new Air
One last question, I think!
If I get a Time capsule, can I partition it so that I have a section (Partition) as a permanent storage section along with the 2 Time Machine erasable/update sections for the two Computers (iMac & AirMac)?
In other words: 3 sections: 2 @ 500GB and 1 @ 1TB. OR I couls do 4 500GB for any future needs.