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 tech talk file sizes

File Sizes

This is part two of my series on hard drives. If you missed it, go back and read my first post which explains the different kinds of hard drives, and how you can use them. In this continuation I’ll talk about how we measure file sizes and how we measure how fast we can move them around. Hard drives used to be very expensive, but as the cost of storage has plummeted, we can now store large music collections, or massive databases. Something that was unthinkable even just a few years ago.

Size Matters

As you’re probably aware, computers love the numbers 1 and 0. In fact, everything they do is at its base level just adding 1s and 0s. And when computers store information (spreadsheets, holiday photos, the White Album, anything!) it’s also stored in 1s and 0s. This is called a bit, and eight of them together make a byte. We measure how much storage a file requires in bytes. Each letter in each word in this blog post is one byte, so these bytes add up quickly. A thousand bytes we call a kilobyte or kB (actually it’s a 1024 bytes in a kilobyte, because you get there by doubling the size; 1 bit + 1 bit = 2 bits. 2 + 2 = 4…. 8… 16… 32… 64… 128… 256… 512… 1024). A thousand kilobytes are a megabyte (1 MB). A thousand megabytes are a gigabyte (1 GB). A thousand gigabytes are a terabyte (1 TB). So a 1 TB hard drive can store a trillion bytes. That’s a lot of information!

Pedal to the metal

When we move files around we measure the speed in how much data is moved per second. Unfortunately, there are two ways to measure this, and they are written confusingly similarly. If a file can be moved from one place to another at a speed of 1 megabyte per second, we would write this as “1 MB/s”. A 600 megabyte CD would take 10 minutes to copy at 1 MB/s because it would be 600 seconds. 5 GB/s is 5 gigabytes per second. Sometimes, however, speed is measured in “bits” not “bytes”, which you’ll remember there are 8 bits per byte. Unfortunately, the way we write this is with a lowercase “b” instead of uppercase, which means “byte”. So “8 Mb/s” means that a file can transfer at 8 megabits per second, which is the same as 1 megabyte per second. Ridiculous, I know. Internet speeds are often measured in megabits, not bytes. You may be paying for a 5 megabit connection to the internet, which actually means 625 kilobytes per second.
So now that we’ve established how we measure file sizes and transfer speeds, let’s look at how we transfer those files and what that looks like.

Putting it together

There are really only two ways to move files around in your computer; from one hard drive to another, or from a CD/DVD to a hard drive. Optical drives and hard drives both use a cable called SATA to transfer files. A SATA cable can move files at up to 6 Gb/s (older computers use a slower 3 Gb/s speed). This is pretty fast! In this case, the limiting factor is the speed of the drive, not the speed of the transfer cable. Spinning hard drives are pretty slow, often as slow as 1 Gb/s. CDs and DVDs are even worse, and max out at around 250 Mb/s. This is where an SSD really gets to shine! An SSD can transfer up to 7 Gb/s, so the limitation is the pipe going in and out. Even though SATA was designed for internal use, there also exists eSATA, which you can use to connect to external SATA drives.


Now you should have a better understanding of how files are measured and how transfer speeds are timed, you can better understand what your storage needs might be, and when you need fast transfer speeds.

At Bit-Wizards we offer Managed IT Services for your business, and we can make sure your company PCs have everything they need for your employees to do their job effectively, and even integrate cloud storage directly into your network. So even if after reading this spectacular blog post, you are still a bit confused, just give us a call we’re good at it!


Samuel O. Blowes, Director of IT
Samuel O. Blowes

Director of IT