Getting Started with Raspberry Pi: Installing Raspbian
Now that you have a Raspberry Pi and want to set it up with an operating system (need to buy a Raspberry Pi? Get one on Amazon), you have several choices. If you're primarily using the Raspberry Pi as a media center, you may want to consider installing RaspBMC, a custom distribution of XBMC. This will allow your Raspberry Pi to boot directly into a media center interface.
But if you're looking to use your Raspberry Pi as a general computer, you may want to consider the Raspbian distribution. Raspbian is a version of Debian Linux specifically configured to run on the Raspberry Pi and is recommended by the Raspberry Pi Foundation as the operating system to install.
You may also want to learn about NOOBS, an even easier way to install operating systems on your Raspberry Pi.
Downloading Raspbian
Raspbian is available for free from the Raspberry Pi website. Under the header "Raspbian 'wheezy'", download either the torrent or direct download. The torrent has the potential to be faster, but some firewalls may block the required ports and you may have to use the direct download instead.
Once you have the ZIP file downloaded to your computer, unarchive it. There will be a single .img file inside. This is the disk image you will flash to the Raspberry Pi's SD card. To install Raspbian, you will need an SD card that has 2 GB of space or more-- this cheap 16 GB Class 10 SD card works great on the Raspberry Pi, and gives you plenty of room to add media and other programs once Raspbian is installed.
Mac OS X
On Mac OS X, we will use a utility called dd. This is a Unix tool for flashing disk images, among other things.
Once you've plugged in the SD card to your Mac, Open the "Disk Utility" application from the Utilities folder in Applications. You'll see a screen similar to the one below, listing your Mac's hard drive, any external hard drives plugged in, and your SD card. You can see my Raspberry Pi SD card is a 4GB SD card.
Format the SD Card
If you haven't already, format the drive to FAT-32. This can be done from Disk Utility by clicking the "4.01 GB APPLE SD Card Reader Media" item in the list on the left. On your computer, it may be called something different if your SD card model or capacity is different than mine. Make sure you select the SD card and not your hard drive.
Once you've highlighted the SD card in the list, click the "Erase" tab that appeared on the right hand pane. You'll see a "Format" option and a "Name" field. Choose "MS-DOS (FAT)" as the format and enter a name. For the FAT-32 format, the name must be uppercase and you will not be able to enter lowercase letters. I chose "RASPBIAN."
After you've verified the selected item is actually your SD card and you have entered a name and selected "MS-DOS (FAT)," click the erase button to begin the format process. This should be fairly quick as long as you do not use a Secure Erase.
At this point, make sure you have a little bit of time to keep your computer on or awake. This process will likely take ten to twenty minutes or more.
Find the Disk Image
Open the Terminal application from the Utilities folder in Applications, and navigate to the directory where you extracted the .img file earlier. For those that used Safari, it will likely be the ~/Downloads folder. If you are unfamiliar with the Terminal and used Safari or another web browser that placed the file in your Downloads folder, you can use the following command: cd ~/Downloads.
Now, type ls in the Terminal and hit enter to list all of the files in the directory, If you see the Raspbian image file (not the .zip file-- this one will end in .img), you're in the right place. If not, try the step above again and make sure you cd into the right directory. Remember or write down the exact file name of the .img file.
We're going to list all of the attached disks to find the SD card's mount point. We do this with the command df -h. You'll see a list like the one below. Notice how I have a ton of different disks, but only one has a cell with the value /Volumes/RASPBIAN. If you named your drive something else, look for that instead.
The item I am looking for is the bottom row. Make a note of the first column value, which is /dev/disk1s4 for me. Now, because we want to write to the raw disk, we need to change the value we're going to use. Essentially, you want to add an "r" before "disk" and remove the "s4" at the end. So, while we see the value /dev/disk1s4, we'll need to remember the value /dev/rdisk1.
Once you've made a note of this value, we can now unmount the partition so that dd can flash the disk image.
Unmount the Volume
Open Disk Utility again and you'll see the SD card in the list to the left with the name you chose earlier. Right click the name of the SD card this time. In my case, it is "RASPBIAN." Do not click the "4.01 GB APPLE SD Card Reader Media" list item, because we are selecting the partition in this case. In the menu that pops up, click "Unmount."
Flash the Disk Image
Go back to the Terminal and type the following command, ensuring you replace the "[FILESYSTEM]" value with the one you noted earlier and the "[DISK IMAGE NAME]" with the proper file name obtained above.
sudo dd bs=1m if=[DISK IMAGE NAME] of=[FILESYSTEM]
For me, the command would look something like this:
sudo dd bs=1m if=2012-12-16-wheezy-raspbian.img of=/dev/rdisk4
Hit enter, and wait until the command completes. Once dd flashes the disk image, you can remove it from your Mac and plug it into your Raspberry Pi. The default username is pi and the default password is raspberry.
Troubleshooting
Q: I receive the error "dd: bs: illegal numeric value"
A: Ensure the value of the bs parameter in the command above is 1m (e.g. lowercase "m"). For those curious, the bs value is the "block size" of the partition.
Q: I receive the error "dd: /dev/disk4s1: Resource busy"
A: Make sure you unmounted the SD card's partition through Disk Utility.
Windows
The recommended method for flashing an SD for use in a Raspberry Pi is a program called Win32DiskImager. The latest version can be found on the official website. Personally I recommend version 0.5, since the latest version (0.6) has a bug that may cause your entire hard drive to be flashed instead of the SD card.
Once you've downloaded the Win32DiskImager application and extracted the ZIP file, download the Raspbian distribution. This can be found on the Raspberry Pi website under the heading "Raspbian 'wheezy'". Once the ZIP file downloads, extract the .img from the .zip.
In Win32DiskImager, ensure you select the correct drive letter for your SD card. In my case, the SD card was drive F:/. Yours may be different, so check in Windows Explorer to make sure you have the correct letter. Do not choose C:\, since that is your main hard drive.
Also, select the .img file you extracted from the Raspbian distribution above using the file picker. Once you have made sure you have the correct .img file and drive letter for your SD card, click "Write" (not read) to flash the SD card. This will take less than five minutes on average and you can see the current progress in the Win32DiskImager window. Once the flash completes, you can exit the program.
Setting Up Raspberry Pi
Once you've flashed the disk image using the methods above, place the SD card into your Raspberry Pi, plug in the HDMI monitor, any keyboards and mice, and then the power cable. Your Raspberry Pi should begin to boot and you should be able to see Raspbian on your screen.
Complete the Raspbian setup, and your Raspberry Pi is now ready to be used!