Usually a "laptop bag" includes pockets and gussets, where to store your documents, papers, pens and so on, while "second skins" have one main pocket where to store your laptop (and sometimes one or two small pockets).
There is no fixed terminology but if one wishes to differntiate then case is for protecting the computer/laptop when it is at a place and bag is for carrying it around.
It's best to use a laptop bag that is the right size for your laptop. A proper sized laptop bag can cushion and protect the laptop. A bag that is too large can allow the bag to shift around too much.
You use it to carry your laptop around without your bag. When in your bag it protects your laptop from scratches.
The difference between a Fossil bag and a Mineral bag is that they are both purses and handbags manufactured from two different companies, and are priced differently as well.
A bag has a strap and a sack has a handle.
A discount laptop bag may sufficiently protect your laptop depending on which bag has been discounted and what sort of protection your laptop needs. Will a discount bag protect your laptop from a volcano? Most likely not. Will it protect it from a small bump? Probably.
Messenger are usually larger and wider than a shoulder. Messenger usually have a space for a laptop as well. Shoulder come in all sizes and shapes where messenger usually are all the same.
All laptop bags have clip-on should straps, and should be interchangeable between brands.
A duffle bag is usually smaller than a suitcase. The biggest difference between a duffle bag and a suitcase is that a suitcase usually has hard sides while a duffle bag has soft sides.
The types of briefcases used to carry a laptop include: portfolios, a protective laptop bag, and a messenger bag. The key is that whichever bag is used is padded to protect the laptop.
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