If you purchase the xbox arcade console then you will get one of these 512mb memory units free with the console. However if you opt to go for either the premium console or the elite console you will get the main hard drive for free and will have less need for these. These small memory units are both advantageous as they are small and compact and suitable for certain tings. However they are on the other hand quite pathetic compared to the 20gb or 120gb hard drives which are also available on the market. I currently own both a 20gb hard drive and one of these 512mb memory units as well.

This is a 512mb memory unit for use in xbox 360 consoles - all of them whether they are the arcade or the elite. It is white to fit in with the typical colour of the console. It simply slots into a little slot which is appropriately labeled on the front of the console. You just push open the flap and push the memory unit inside the console until it stops and it will of course stick out from the console.
It is also very small and sleek and is probably similar size to a credit card - though of course a bit thicker. I think it looks really cool and is great and compact.

This memory unit being of only 512mb can be used in the whole for storing game saves which of course can be very important and need to be saved and kept somewhere safe - and this is the perfect option. You can also store your xbox live account on here as well as putting some pictures and maybe some music on here. This will all of course be limited to 512mb. You can also download and save stuff from the xbox live marketplace, but again you will be limited to how much you can download.
The unit being very small is great for carrying around with you and taking to a friend's house for example in order to take your game saves (and your games) to play round their house and nopt have to worry about losing any unlocked content or having to start the game all over again.

The fact that this is so small in storage size is not so much as a disadvantage but just something it lacks. Without as much space you are restricted to what you can put on it and use on your xbox 360. For example you will be unable to benefit from a lot of the features on the console.
You will only be able to store a small amount of music and won't be able to put any films from your computer onto this unit.
You won't be able to benefit from all the great stuff available to download from the xbox live marketplace such as arcade games and xbox originals which are great fun to play on your console - but of course will often take over 500mb of space. You will also be restricted as to downloading themes, gamer pictures and especially downloadable content. You may have the game needed and enough microsoft points but with no memory space you won't be able to get this content that could greatly improve your playing experience and add new levels and modes to some of your games, for example.
Another potential problem is that it is very small, which although has its benefits, also means if taken out of the console it can be easily lost and prove rather difficult to fin compared to a large hard drive unit!