How much disk space did Snow Leopard really save?

Like apparently hundreds of thousands of others, I upgraded my machines running Mac OS X from version 10.5 (Leopard) to 10.6 (Snow Leopard) last Friday. I'm now a Snow Leopard user, and I like it just fine.

I was excited about this upgrade, because I love the notion that the people who released it care about optimizing the performance of my system. One of the optimizations I looked forward to was reclaiming over 6 GB of disk space after the upgrade (see Bertrand Serlet's announcement at 00:20:48 to 00:21:11 in the WWDC 2009 keynote video).

Lots of people in the Twittersphere were excited about the space savings, too. Before I upgraded, I checked to see what people were tweeting, just to make sure I wasn't about to walk off a cliff. Many people mentioned tremendous disk space savings that were well in excess of the 6 GB that Apple promised. Pretty exciting.

We have two Mac computers. Here's how the savings went for us:

Mac #1      10.5      10.6      Savings
-------  ---------  ---------  ---------
Total    148.73 GB  159.70 GB
Free      47.70 GB   59.71 GB   12.01 GB

Mac #2      10.5      10.6      Savings
-------  ---------  ---------  ---------
Total    185.99 GB  199.71 GB
Free      68.66 GB   83.95 GB   15.29 GB

So, ...wow, we saved over twice as much space as Apple had advertised. But there's a curiosity in the numbers. Do you see it? How did my total capacity get bigger as the result of a software upgrade? The answer is that my capacity didn't really get bigger; it's just that Apple now measures disk space differently in 10.6.

I knew this was coming because of this article called "Snow Leopard's New Math." Snow Leopard still uses the abbreviation "GB" to refer, now, to 10⁹ bytes, whereas, before, Leopard used the abbreviation "GB" to refer to 2³⁰ bytes. The problem, see, is that 10⁹ ≠ 2³⁰. In fact, 2³⁰ is bigger. So in Snow Leopard, Apple is dividing by a smaller unit than it used to, which results in disk capacities and file sizes looking bigger than they used to. (Here's a good article about that.)

It is misleading that Apple used the same abbreviation—"GB"—to refer to two different units of measure. However, Apple is well justified in using "GB" in Snow Leopard. IEEE 1541-2002 says the right abbreviations would have been "GiB" (gibibytes) in 10.5 and "GB" (gigabytes) in 10.6. By that standard, Snow Leopard is right, and Leopard was wrong. All's well that ends well, I suppose.

Now, back to the space savings question. How much space did I really save when I upgraded to Snow Leopard? To answer that, I need to convert one of the two columns in my analysis (labeled "10.5" and "10.6") to the other column's unit, so I can subtract. Since when I watched the WWDC keynote film, my mindset was of 10.5-style "gigabytes" (properly gibibytes), I'll convert to GiB. Here's the answer:

Mac #1      10.5        10.6      Savings
-------  ----------  ----------  ---------
Total    148.73 GiB  148.73 GiB
Free      47.70 GiB   55.61 GiB   7.91 GiB

Mac #2      10.5        10.6      Savings
-------  ----------  ----------  ---------
Total    185.99 GiB  185.99 GiB
Free      68.66 GiB   78.18 GiB   9.52 GiB

That's still spectacular, and I'm plenty happy with it. I have basically bought a whole bunch of performance enhancements and 17 GiB of disk space for $49 plus tax (I bought the Snow Leopard upgrade family pack). I think that's a pretty good deal.

This whole story reminded me of the old days when I used to install Oracle for a living. People would buy, say, a brand-new 100,000,000-byte disk drive and then be upset when the df utility showed considerably less than 100 "MB" of free space. Part of the explanation was that df reported in mibibytes, not millions of bytes.

It's interesting to note that in Snow Leopard, df -h now reports in Bi/Ki/Mi/Gi units, and df -H reports in B/K/M/G units (defined as IEEE 1541 defines them). Smart.

Syncing..., Part 3

In a couple of prior posts, I described some of my requirements for syncing my iPhone with my laptop computer. A couple of months ago, I solved the problem (and a whole bunch of other ones, too). I'm very pleased with the solution I chose, which I'll share with you here.

I bought a new MacBook Pro. Not one of the new solid-brick-of-aluminum ones, but one of the slightly older aluminum ones held together with screws. It has a beautiful 15-inch matte-finish monitor, and it's faster than any portable I've ever used. It runs Windows XP applications in my Fusion VM about 33% faster than the native XP laptop I replaced.

It was a big investment, but I love it. Every time I open up my MacBook, I feel good. Thirty seconds later after it has booted completely from scratch, I love it even more.

VMware Fusion, by the way, is a brilliant penetrant to the barriers I had perceived about moving from Microsoft Windows to Mac OS X. With Fusion, you can make your whole Windows PC run on your Mac if you want to. As you gain comfort in OS X, you can migrate applications from Windows to the native Mac operating system. I digress...

So, now I use iCal, which gives me the ability to subscribe to iCal feeds like the one from TripIt. And ones like webcal://ical.mac.com/ical/, which automagically populate your calendar with US holidays, so you won't accidentally book a course on Labor Day. (Visit iCal World for more.)

My new system completely solves the travel problems I was talking about. Now, I do this before I travel:

1. Book travel.
   
2. Forward the confirmation emails to plans@tripit.com.
   
3. Print my TripIt unified itinerary for my briefcase. (Or not.)
4. Sync my iPhone with my laptop.

And that's it. No data double-entry. None.

One more requirement I had, though, was syncing my iCal calendar with Google Calendar. I found a solution to that one, too. I tried using the Google Calaboration, but I really didn't like the way it forced me to deal with my separate calendars. The tool I chose is called Spanning Sync. I used their 15-day trial, liked it a lot, and bought a subscription. I love the way I can map from my list of Google calendars to my list of iCal calendars. However, I don't like the way it syncs my contacts, so I just turn that feature off.

I'm intrigued by the Spanning Sync business model as well. You can save $5 on Spanning Sync by clicking here. It works like this (I'm quoting here a Spanning Sync web page)...

After a 15-day free trial period, Spanning Sync usually costs $25/year, but you can save $5 by using my discount code if you decide to buy it:

39PKXV

Also, if you use my code I'll get a $5 referral fee from Spanning Sync. Once you're a subscriber you'll get a code of your own so you can make money every time one of your other friends subscribes to Spanning Sync. Pretty cool!

Anyway, I'm very pleased with the new system, and I'm happy to share the news.