While it's true that we're all different and have slightly different needs when it comes to what lives on our smartphones, there are some common strands and requirements. Each of which has been growing over the last few years, begging the question of how large internal storage needs to be in today's (and tomorrow's) Windows Phones? The answer, as you can imagine, is especially relevant to those designed with no microSD expansion.

Using my own experiences as my example, as I tend to do, I lived for ages with the Lumia 920 and then 1020 in turn, each with sealed/capped storage at 32GB. In fact, around 29GB, since you have to take off space used to store the OS itself. In each case, I had no showstopping issues, but I was plagued with 'your space is running low' after a few months and in each case found that I had to trim my phone's contents, usually by removing a large game or a sideloaded video 'for that trip', etc.

However, we shouldn't really have to compromise in 2015. I'm not talking about trying to take every song and video you own with you - that's unrealistic, but I don't think it's unreasonable to want to take a dozen albums of favourite music, for playback offline when on coaches, trains and planes, I don't think it's unrealistic to take a documentary or two, for similar offline use, and so on.

In fact, even leaving aside wanting some content offline that could otherwise be 'streamed' when you have connectivity, it turns out that space can still be an issue for some phones. As an extreme example, you'll all remember the farce of the HTC 8S, which came with only 4GB of internal storage and which became unusable after only a few days of use? 

When is a Windows Phone not a Windows Phone? When it's completely unusable - meet the HTC 8S...

So, let's break down, using guesstimates, what the 2015 smartphone user will need in terms of storage. As this is All About Windows Phone, I'm using Windows Phone 8.1 Update 1 as my baseline:

• Operating System - currently needing 3GB, but this will rise slightly as all devices get transitioned to Windows 10 Mobile. Still, let's be optimistic and assume that this won't rise too much. Say 4GB for the OS.
• Working space - the 4GB above is to, quite literally, store the OS. There also the matter of all the settings files, temporary files, caches, and so on. Best to keep this at 1GB or above - many people will have experienced their phone grinding to a halt as the free space dwindles towards zero.
• Updates to core applications - think Store, Podcasts, Calendar, Maps, Music, Video, and much more. These will be updated regularly and there needs to be room to store the new binaries on the internal disk. Probably half a gig, but let's play safe and stay future proof with another 1GB allocation.
• PIM data for the user, contact details, calendar entries, any notes, artwork. Not huge, but still let's call it 200MB, again to be safe.
• Email database, at any one time keeping hundred, if not thousands of emails, some with attachments, each of which may run into the Megabytes. 1GB is a good guess here.
• Internet Explorer cache, downloads and associated files, the workings of a 2015 web browser accessing sites with potentially high resolution graphics. Typically this is in the order of 1GB, but let's allow 2GB, just in case, not least because newer phones tend to have higher resolutions and get served bigger images and other resources.
• Third party applications and games installed by the user. Technically, on phones with expandable storage, some of these can be installed on card, but I rarely recommend this, since it can confuse things if the card is taken out later. Best to put all apps on internal storage where possible. Now, how much space to allow for applications is like asking how long a piece of string should be, it will depend hugely on the user, but I'll take my own figure, for around 40 apps, including half a dozen games of various sizes, as typical. 7GB. I really don't think this is unusual, and it could be quite a bit higher.

So that's just over 16GB so far, and we haven't touched any media (including photos) yet. Immediately then, we have a conclusion that space is going to be tight, but probably manageable, on a device with 16GB internal disk, but only with the proviso that there's a card slot (for media) as well. A good example of this is the Lumia 830, which manages to make all the bare minimums across the board, and with some style. But the older Lumia 925 (aside from the 32GB Vodafone variant), for example, is completely at sea nowadays, unless it's used as a feature phone with little use and precious few applications. 

The microSD slot, maxed out happily, in the Lumia 830...

More serious is that the multitude of budget Lumias (and other OEM devices) with 8GB internal disks are compromised. With around 5GB free out of the box for all the stuff listed above, they're now very limited in what can be installed and expansion cards will be a necessity for games, as well as media, of which more in a moment.

Flagships like the Lumia 1020 and 930 (and the 920 before them), each with 32GB internal storage, have more room to move, in theory. Though as I stated above, with no expansion card, the 16GB 'buffer' (i.e. 32GB minus the 16GB above) goes remarkably quickly, since photos, videos and music are notorious space hogs.

Let's quantify this. And again apologies for using my own devices as the example (though I'm not atypical):

• Music. Say 20 favourite albums, an hour each, stored locally for easy and free listening when not within range of fast 4G data/Wi-fi. Around 3GB, depending on the encoding and bitrates used.
• Podcasts. I'm a bit of a podcast nut and subscribe to over a dozen, so at any one time that's around 1GB of MP3 audio sitting in my phone waiting to be heard (and it goes without saying that any podcatcher you choose should be set to keep just the last ONE episode of each feed!)
• Movies. Now, not everyone keeps video files offline like I do, but it's very handy. Stuck in the car waiting for family or on a long train journey, usually starved of decent mobile bandwidth, it's really fun to have a handful of my favourite music concerts stored as (e.g.) 720p MP4s for enjoying as and when needed. In my case 4 or 5 hours means about another 3GB worth of storage needed.
• Photos. This is something that everyone can get onboard with, which of us doesn't take loads of snaps with our phones? And the files are getting bigger. Where a photo taken on a phone back in 2005 used 100Kb or so, we're now talking 8MP and 13MP photos, or 'dual' shots with underlying 20MP or 34MP versions, or 'Rich Capture' shots with up to another three full resolution photos in the background. Phew. A 'rich capture' shot on the humble Lumia 640 XL, for example, uses up to 10MB per image. On the Lumia 930 this rises to 20MB per shot. So with about five hundred captured photos (a typical collection for a smartphone user over a six month period, even by conservative estimates), we're talking around 2.5GB. And a lot more if Rich Capture and RAW (etc.) are used a lot.
• Videos - as in captured videos on the phone. Most Windows Phones now capture at 720p, at least, and quite a few at 1080p and even 4K, in the case of the Lumia 930 and 1520. Again, shooting videos on the phone is something which lots of people do, and it's remarkably easy to use up phone storage with the files. At 1080p, video from Lumia Camera or similar uses up around 130MB per minute of footage. Allow (say) just 45 minutes of footage across a dozen captured clips and you're looking at almost 6GB.

Again, adding up that last media-centric batch of 'stuff' gives us almost another 16GB of content. And shows exactly why those Lumia 1020s, 920s and 930s are running out of room, in typical user hands. 

One solution, of course, is to build devices with larger internal disks - there were some limited edition 64GB Lumia 1020s, for example (produced for O2 in the UK, for one), but these are very rare in the Windows Phone world. (Though in the wider Android world, quite a few manufacturers are now following Apple down the 'charge a lot, provide a lot' strategy for their premium 64GB and 128GB phones.)

Far more cost effective - and flexible - is to put the whole of that last 16GB (and part of the former?) on a microSD expansion card. The majority of Windows Phones now include a microSD slot (in fact, it's far quicker to list the devices without a microSD slot, i.e. Lumia 930, 920, 1020, Icon, 925) and cards are now incredibly cheap - I just bought a 64GB card for under £20 on Amazon (other suppliers are available, but make sure you get the real thing and not some clone of a big brand!), instantly doubling or quadrupling the storage on any of my compatible Windows Phones for not much more than the cost of a case.

[A huge, but noteworthy, side benefit of putting media on a microSD is that you can load it up separately from using Wi-fi or a microUSB lead from a computer. If you've ever been stuck, about to head out the door and waiting for 5.4GB of movies to transfer over a wire then note that you can halve this time (or even better) by 'removing' a microSD card and inserting it into an integral card reader/writer on a PC or Mac, or using one of those USB card adapters.]

Phew. That's a lot of options and numbers. Let's break it down into a few takeaways:

1. If you have a 32GB 'sealed' device then you're OK, but do expect to have to seriously manage your media and applications more as time goes on (as per the diagram above!) Try not to let free space dip below 1GB.
2. If you have a '16GB plus microSD' device (like the Lumia 830) then you're good to go, with no compromsises, as long as you set everything large or media-related up on the expansion card - I'd suggest a 32GB card as a bare minumum.
3. If you have a '8GB plus microSD' (far more common), then your options are far more limited. In addition to setting everything large or media-related up on the expansion card, (and I'd advise perhaps a 64GB card if possible) you're still going to hit problems. As applications are updated, as temporary files grow, as the browser cache grows, as emails build-up, you'll want to spend more and more time in the 'Storage sense' application.

Of course, the vast majority of regular AAWP readers won't have to worry about no. 3 above, since you experiment with applications, enjoy games and generally use your Windows Phone a lot, and as such will have hit the limits of your internal storage a while ago. Hopefully you've already upgraded to something a little more capacious. While casual Windows Phone users will be less ambitious with their phones and may indeed survive with just 8GB for their internal disk, but I'd still bet that they see 'Free up some storage' warnings on a semi-regular basis.

If all this sounds alarmist then I don't mean it to be. For a start, I'm going to follow up with a tutorial or two on making more of an expansion card, on supported devices. I'd also urge anyone concerned by this to think about the Lumia 830 as the lowest-priced Windows Phone that is the most future proof - or, if budget allows, maybe a Lumia 1520 if you can still find one (i.e. second hand)?

For the future, I'd like to see every non-budget Windows Phone, certainly those from Microsoft, come with a 16GB internal plus microSD, as this really is the most flexible and powerful solution - in terms of storage, at least.

Comments welcome, of course - how badly have you been affected by any of this, and on which device?