When it comes to computer storage, judging from many questions friends and readers send me, there's quite a bit of confusion among general users as to what it actually is. And it's not your fault; digital storage can be as messy as my desk. This is the reason for this series, where I sort out the basics and more, in layman's terms.
That said, some information in this might be too basic for advanced users. Home and novice users, however, give yourself some uninterrupted time and dive in. You'll survive.
1. Understanding the units
No matter how boring this is, you can't grasp digital storage without know its measurement unit, which is byte.
Byte (symbol: B): Byte is generally the smallest unit in digital storage. You can think of 1 byte as one character in a document. For example, we actually need to use 4 bytes to store just the word "byte." In real life, we use larger units, including kilobyte, megabyte, gigabyte, and terabyte.
Kilobyte (KB or kB): By general definition, one kilobyte is 1,024 bytes. In many cases, for the sake of simplicity, 1 kilobyte is understood as 1,000 bytes.
Megabyte (MB): By general definition, 1 megabyte is 1,024,000 bytes. Similarly, it can also be understood as 1,000,000 bytes.
Gigabyte (GB): By general definition, 1 gigabyte is 1,000,000,000 bytes.
Terabyte (TB): By general definition, 1 terabyte is 1,000,000,000,000 bytes, or 1,000GB.
Currently, the largest 3.5-inch hard drive (commonly found inside a desktop computer) offers 4TB of storage space. Most computers come with drives with capacities of somewhere between 120GB and 2TB. Most mobile devices, such as tablets or smartphones, offer between 8GB and 120GB of storage space.
Generally, a typical photo taken by the iPhone 4 takes up about 2MB of storage space. A digital song uses about 5MB. A compact disc (CD), which has the capacity of 700MB, can hold about 350 iPhone photos or some 140 songs. The actual size of digital content varies a great deal, however, depending on the format and the compression level. The common rule is the richer (and/or higher quality) the content, the larger storage space it requires. A 10-minute audio podcast needs anywhere between 4MB and 10MB, but a 10-minute high-def movie requires a few hundred megabytes or even a gigabyte of storage space.
Storage vs. memory
These are two terms that are often mistakenly used for each another, though they are two very different things.
Storage, in a nutshell, is where the information (such as Word documents, photos, movie clips, programs, and so on) is stored. In a computer, the whole operating system itself, such as Windows 7 or Mac OS, is also stored on the internal storage device. Storage is nonvolatile, meaning that the information is still there when the host device (a computer, for example) is turned off and is readily accessible when the device is turned back on. It's like a book or a paper notebook that's always there, ready for you to read or write on.
Memory (aka system memory, random access memory, or RAM), on the other hand, is where information is being processed and manipulated. Data in the system memory is volatile, meaning that when the computer is turned off, it's gone; the memory becomes blank, as if nothing has been there before. It's somewhat like the short-term memory part of your brain, where images or ideas are being formed and processed when you read a book -- those that disappear the moment you stop reading.
Source: by Dong Ngo, CNET.
