Apple’s diminuitive Mac mini has been an enduring classic, ever since it launched seven years ago. It’s the most affordable of all Macs, takes up next to no desk space, and quietly gets on with its job. No fuss in a cute package.

For the first year of its life, the Tupperware box-sized computer ran a PowerPC G4 processor, but was swiftly transitioned to Intel Core Duo when Apple moved all its Macs to Intel chips in 2006.

Today more than ever the Apple Mac mini represents an incredible feat of hardware engineering, to squeeze very fast processors, memory and storage, and now even the complete power supply into one low-profile aluminium armoured case.

Packing so much into a small space makes it the anathema of the typical Windows desktop PC, a wheezy box as high as your knees – but one that's relative doddle to nip inside and replace the memory, the hard drive, and more.

The original generations of Mac mini didn’t even let you upgrade the RAM, unless you got jiggy with a putty knife and were willing to take a leap of faith as you prised the box apart, probing inside with the broad flat blade.

The new Unibody-style Mac mini at least gives you ready access to the RAM. Flip the Mac mini over, and neat tank-turret cover can be removed to reveal memory chips and a very dapper layout of wireless antenna and its perforated guard. The new Mac mini is as beautiful inside as it is sleek and svelte from the outside.

And upgrading the memory is as far as Apple will let you go before invalidating the warranty. To go beyond this point and delve inside requires a little knowledge and some nerve. But why would you want to, beside maybe upgrading the hard disk?

The answer is of course in the headline: to add a second drive.

Taking the slot

When the Apple Mac mini went Unibody in 2010, Apple created an option for a DVD-less Server edition. In place of the slot-load optical drive was a second hard disk, not just swelling capacity but enabling faster or more robust RAID storage options.

With the latest Apple Mac mini (Mid-2011), released last summer, Apple has made the slotless mini the only option, joining the MacBook Air as another computer to lose the integrated optical drive..

This leaves a nice empty space inside to add your own second drive in these non-server editions. All the pieces are in place in every modern mini – except a custom SATA ribbon cable and mounting screws for the hard drive.

Catering for these needs is the iFixit Mac Mini Dual Hard Drive upgrade kit

Mac mini upgrade kit

This includes all the necessary components, along with a natty set of Torx drivers to help you on your way. While you may have a good toolset already, you’re unlikely to have one specialised piece: a U-shaped tool that makes the task of removing the logic board a cinch.

The job involves a compete disassembly and rebuild of the Apple Mac mini. With good light and an hour or so of methodical work, you too can have a dual-drive Mac mini.

The upgrade is particularly compelling to add a small but affordable solid-state drive (SSD), while keeping the original 500GB hard disk for good storage capability. For OS X, a 30GB SSD is sufficient to run the operating system and install many applications.

If you intend to keep your OS X Lion user directory on the boot drive, you'll probably need considerably more space. If you can stretch to it, a 256GB capacity solid-state drive makes a good compromise between space to breath while keeping price within reach.

 Mac mini upgrade step 1

1. Down the hatch

With the Mac mini powered down and disconnected, turn upside down and remove the black plastic hatch by rotating it a few degrees anti-clockwise. Now’s a good time to attach an ESD strap to yourself to ensure you don’t destroy the delicate electronics with a tiny static spark while working inside.

Mac mini upgrade step 2

2. Cooling off time 

After marvelling at the beautiful symmetry within, start the disassembly by first removing the cooling fan, held in place with three T6 screws. After lifting carefully, pry off its power connection from the board with a spudger. Next remove a plastic cowling to the left of the fan, held in place with one T6 screw. This plastic piece will require a little wiggle to extract.

Mac mini upgrade step 3

3. Antenna plate-off

The antenna plate supports Bluetooth and one of the mini’s three Wi-Fi aerials. Remove its four T8 screws and carefully pull out, then disconnect the signal lead that attaches it to the board. Note how the semi-circle edge fits into the mini’s chassis: this will also require some alignment when you replace it later.

Mac mini upgrade step 4

4. Drive away

The installed SATA hard disk (‘lower drive’) connects to the system through a press-to-fit flat ribbon cable on the edge of the logic board. Pry this off with the spudger. At a push, you can just get the drive out now, but better to wait a few steps when it slides out much easier. You will also need to disconnect the remote IR sensor, by lifting its connector from the board, by the RAM.