What size drive do I need?

MB, GB and TB explained, what actually fits on a drive once Windows has taken its share, and which size SSD or backup drive to buy.

// THE UNITS

How many MB in a GB?

Each step up is 1,024 times bigger than the one before. Drive and phone makers round that to 1,000, which is why a new drive always looks a bit smaller in Windows (see the table further down).

KB1 kilobyte = 1,024 bytesA short email without attachments is about 20 KB.
MB1 megabyte = 1,024 KBA phone photo is about 3 MB. A song is about 8 MB.
GB1 gigabyte = 1,024 MBAbout 340 photos. An hour of HD streaming uses about 3 GB.
TB1 terabyte = 1,024 GBAbout 350,000 photos. Backup drives are usually 1 to 4 TB.
PB1 petabyte = 1,024 TB, about 1 million GBThe storage of about 8,000 phones of 128 GB each. Data centres work in petabytes.
EB1 exabyte = 1,024 PB, about 1 billion GBThe whole world’s internet traffic is about 13 EB a day.

One gigabyte, as 1,024 squares of 1 MB

1 GB holds about 341 phone photos (3 MB each).

// DRIVE SIZES

What fits on a 240 GB drive?

Pick a size. Windows and your programs take their share first, and you should keep some space free so updates install and the drive stays quick.

It’s the computer’s main drive, with Windows on it

Windows, Office and updates Keep free (15%) Space for your files

Your of space would hold about…

Each figure assumes you filled the space with just that one thing. Real life is a mix.

// CHOOSING A SIZE

How big a drive do I need?

Put in roughly what you have. The figures below are an example, so change them to match yours.

Photos

Minutes of phone video

Songs

Documents and PDFs

Big games

Anything else (GB)

Your files come to aboutbefore you add anything new

Computer drive

Backup driveAt least twice your files, so there’s room for older versions

Not sure what you’ve got? On Windows, right-click your Pictures, Documents or Videos folder and choose Properties to see its size. On an iPhone, go to Settings, General, iPhone Storage.

Email, web and documents256 GBPhotos mostly kept in the cloud or on your phone.

Family photos and music on the computer512 GBThe sensible choice for most home laptops.

Video, big photo libraries or games1 TB or morePlus a backup drive at least as big.

// DRIVE TYPES

SSD or hard drive?

SSD (solid-state drive)

Use one for the computer’s main drive. Windows starts in seconds rather than minutes, programs open quickly, and with no moving parts it’s silent and copes better with a laptop being knocked about. It costs more per GB, which is why sizes are smaller.

Hard drive (HDD)

Fine for backups and storing lots of files. It’s much cheaper per TB, so a 2 or 4 TB backup drive is affordable. It’s slower and doesn’t like being dropped, so it’s not a good main drive in a modern computer.

Why does Windows show my drive as smaller?

Drive makers count 1 GB as 1,000 MB. Windows counts in 1,024s, so the same space shows as a smaller number. Nothing is missing.

On the box	Windows shows

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