Tuesday, 4 October 2011

size matters...

Do you know your bytes and pixels from your mega/kilo/giga/tera bytes? If not, read on...

Quite a few teachers have approached me, who are worried about using up their hard drive space, but fret not dear educators, your MacBook has a HUGE hard drive - but how huge? Generally when I excitedly point out that you have maybe 200 to 500 Gigabytes of space (depending on the age of your Mac), I invariably get a look that looks like I have just emitted a noxious fume from my nether-parts. So here goes...

The smallest unit of memory is a bit, then a byte, and they go up in thousands from there, so a thousand bytes in a kilobyte, a thousand kilobytes in a megabytes... and so on.

Here's a simpler way to imagine it...

1 bit (short for binary digit) = teeny tiny, the smallest size you can get, and yes, useless to you.

1 byte (b) = 1 character in the alphabet, eg the letter 'a'. = still useless

1 kilobyte (Kb) = 1000 bytes = 1000 characters, eg, a page of text = now we're getting somewhere...

1 megabyte (Mb) = 1000 Kilobytes = 1000 pages of text = 1 large digital image = 1 minute of music (mp3)

5 megabytes = 5,000 kilobytes = 5,000 pages of text = 1 very large digital image = a 5 minute song (mp3) This is pretty much the upper limit for email attachments.

10 Megabytes = 10,000 KB = 10 large photos = 10 minutes of music = 1 minute of video.

1 gigabyte (Gb) = 1000 megabytes (MBs) = an entire film/movie

1 terabyte (Tb) = 1000 GBs = MASSIVE = Pretty much only relevant for storage, external hard-drives etc.

Yes there are more...


In a nutshell

bytes - pretty much useless, like a few peas.

kilobytes (KB) like pages of text (text emails and small images would be measured in kilobytes) the most useful size online, not too small not too big.

megabytes, now we're getting heavy - large photos, music, 10 MBs or more for video

Maybe these analogies can help?

ant, mouse, dog, elephant, blue whale

a grain of rice, a bowl of rice, a bag of rice, a sack of rice, a truck load of rice

a coin, hand bag/back pack, carry on luggage, suitcase, a plane load of luggage

To confuse things, images use more memory than text, and are measured in pixels, which do relate to size, but are not the same thing. Your MacBook Pro screen is at least 1200-1500 pixels wide, so that gives you an idea...

With the kids it can be helpful to get them to think of pixels in similar ways to mm, but this will lead to confusion later as they're actually smaller, but at least it's in the right ballpark. Like the image above looks about 8 cm wide on my screen, but is actually 400 px wide, not 80mm, but because higher resolution screens have smaller pixels you can't just compare using a ruler against the screen, this is obvious to geeks like me, but to normal people this is the kind of essential information that is rarely obvious.

As a rough guide:
  • 10 pixels square = tiny, the size of 1 font character, like the letter 'o' = 1kb 
  • 100 pixels square = the size of about 4 desktop icons = 10kb 
  • 1000 pixels square = small/standard monitor (screen) size = 1 Mb 
  • 10,000 pixels square = large or 'high definition' (size of a window), high resolution image/poster = 10 Mb 

So when Googling images, a pixel size of about 500px is ideal, 50px is too small (blurry) and images in the 1000s are probably too big (takes ages to load, and display).