The Unfairness in the Surface Pro vs. MacBook Air Argument

A lot has been written and echoed about the Surface Pro and the limited amount of available storage space out of the box. In case you are confused, this isn’t the first time that people are having this discussion. Back in October of 2012, when Microsoft launched the Surface RT, people were complaining about the same issue. Long story short, in the case of the Surface RT device:

A 32GB Surface [RT] has a lot less usable disk space than a 32GB Android or iOS tablet, and while this can be expanded with SD, that’s not as clean or convenient as one would like. If you want to load up your Surface [RT] with media, this makes the 64GB device more compelling—but you pay a hefty price premium for the privilege.

Now back to February 2013. Microsoft has just released the Surface Pro tablet-notebook hybrid, and critics are at it again: “Microsoft’s Surface Pro is a [storage] hog”.

However, this time, Ed Bott chimes in with a really good point. The Surface Pro shouldn’t be compared to the iPad, but to the MacBook Air:

“They’re both ultraportable devices that run full-strength operating systems. Both use similar CPUs, offer similar amounts of RAM, and advertise 128 GB of storage. The Surface Pro has touch capabilities and can be used as a tablet, but at its heart it is a full-strength PC designed for extreme mobility.”

Then Bott goes on to compare the out-of-the-box storage requirements of both the Surface and the Air. And while I agree that such a comparison is less dishonest than a comparison with a true tablet like the iPad, I do have a problem with his sloppy analysis of the MacBook Air. To be clear, I’m not implying Bott is being dishonest, but as he himself admits in the article:

I don’t have a MacBook Air to do the same calculation, but I confirmed from several online sources […]

It turns out there are a of lot online sources that are saying many different things, and without a MacBook Air on your desk, it’s really hard to verify these sources or understand what’s really going on1.

Unfortunately, the Air I’ve got here in front of me isn’t the 11-inch model, but rather the 13-inch one with the same 128GB Apple SSD (TS128E). However, I don’t see any reason to believe that this has an impact on the storage requirements of OS X.

In this discussion, I will address the exact some points as in Bott’s article: the difference in disk size reporting, the less-than-advertised disk size on the Apple SSD, the disk space configuration on the Air under Mountain Lion, and finally, how much space is really left on the Air?

1. The difference in disk size reporting

The difference in disk size reporting is, as Bott explains, related to marketing, but also to this little thing called international standards.

These standards state that there are two ways of scaling a unit —in this case the byte— either by using a decimal prefix (base-10) or a binary prefix (base-2). The decimal prefixes we are most familiar with are the kilo-, mega-, giga-, and tera-, and they represent x 10^3 (a thousand), x 10^6 (a million), x 10^9 (a billion), and x 10^12 (a trillion), respectively. In the context of our discussion, 128 gigabyte is 128,000,000,000 bytes. These scaled units of bytes are often abbreviated, using their corresponding international symbols: KB, MB, GB and TB.

In the case of binary prefixes, we are dealing with x 2^10 (or 1024), 2^20 (or 1024 x 1024), 2^30 (or 1024^3), etc. The standards prescribe the use of the terms kibi, mebi, gibi, and tebi to indicate that they are, in fact, different from the kilo, mega, giga and tera. Using these prefixes, 128,000,000,000 bytes is only 119 gibibyte or 119 GiB when abbreviated using its symbol.

This allows us to conclude that Apple is complying with the standard, while Microsoft is not. Apple uses the KB, MB, GB and TB units and measures in a 10-base system, while Microsoft uses the same symbols, but measures in a 2-base system.

That is not to say that Apple switched to the 10-base system in 2009 just to comply with the standards—as the standards had been around for several years by then. There is certainly some marketing strategy involved. Since Apple ships industry-standard disks in many of its machines, it is bound by the disks that its partners produce, and the way they measure size. If Apple hadn’t switched to the 10-base system, it would have to sell 59 Gib and 119 GiB MacBook Airs, possibly confusing a lot more customers in the process.

2. The less-than-advertised disk size on the Apple SSD

Now we’ve come to the point where Apple’s practice could be called unfair or misleading. A point that Bott got totally wrong in his article, as it is unrelated to the difference between 10-base and 2-base.

In the previous point I explained why Apple is indeed allowed to use the size measurement of 128 GB to indicate 128,000,000,000 bytes, and the difference with 119GiB. In this point, however, I will briefly touch on why I believe it’s unfair for Apple to put even the 64 GB and 128 GB labels on it’s MacBook Airs.

If you buy a hard disk or SDD from a third party vendor that lists a storage capacity of 128 GB on the box, it will come with 128 gigabytes, or 128,000,000,000 bytes, of useable space in a 10-base system. The Samsung SSD I have in my MacBook Pro is shown having a capacity of 256GB in Mountain Lion:

Capacity:   256.06 GB (256,060,514,304 bytes)
Model:      SAMSUNG SSD 830 Series
Revision:   CXM03B1Q

However, looking at the Apple SSD—which Apple is calling flash storage on its website, because it doesn’t have the standard 2.5″ SSD form factor— in the MacBook Air 13-inch, we can see that it is about 7GB shy of 128GB:

Capacity:   121.33 GB (121,332,826,112 bytes)
Model:      APPLE SSD TS128E
Revision:   TPSABBF0

This is the physical size of the storage device that is available to the machine. It is unaffected by EFI (boot) and Recovery Partitions, and any space reserved for the operating system. Based on my own understanding and some internet sources, I’d say this lost space is related to the spare blocks that Apple mentions in its support article. Maybe Apple’s Flash-chip partners don’t factor this in by creating chips that are a bit larger than 128GB to account for these spare blocks. Who knows?

In the end, Apple is selling laptops with less available total space as advertised. The Surface Pro 128 comes with 127.90 GB (represented as 119.12 GB), and that is indeed 7 GB more than the MacBook Air’s 121,33 GB, but for reasons that are different from those that Bott states in his article. Fact remains, Bott has a point here that the Air is at a 7 GB disadvantage.

3. The disk space configuration on the Air with Mountain Lion

At this point, Bott’s numbers are all wrong.

This is an overview of the three partitions on the SSD of the MacBook Air 128 GB:

/dev/disk0
#:                      TYPE NAME              SIZE
0:     GUID_partition_scheme                  *121.1 GB
1:                       EFI                   209.7 MB
2:                 Apple_HFS Macintosh HD      120.47 GB
3:                Apple_Boot Recovery HD       650.0 MB

As you can see, some partitioning overhead gives us a total space of 121.1 GB (down 0.2GB from the 121.3 GB total physical space):

  1. 209.7 MB (0.2 GB) is allocated to the EFI boot partition.
  2. 120,47 GB is left for the operating system, applications and documents.
  3. 650 MB (0.6 GB) is allocated to the Recovery partition, which includes tools to recover and reinstall Mountain Lion.

This makes a total of about 1GB (rounded) allocated to “the EFI and Recovery partitions and other system items” that is about 7 times less than the 7.53 GB that he has in his article. This compares very favorably to the 8.61 GB of boot and recovery partitions on the Surface Pro.

4. How much space is really left on the Air?

At this point the Surface Pro is down to 119,29 GB of free space (before the operating system), while the Air is down to 120,47 GB. This is still a draw, but that’s about to change.

From Bott’s article: the available space on the Surface Pro out of the box is 96,3 GB. This puts Windows 8 and included applications at about 23 GB. This is comparable to a Windows 8 installation on a desktop computer.

In comparison, a MacBook Air with Mountain Lion and iLife out-of-the-box comes in at about 12 GB, which brings the Air down to 108 GB.

Given that the recovery partition on the MacBook Air is only 650 MB, compared to 7,81 GB on Windows, removing it on the MacBook will not result in much reclaimed space. In addition, Bott’s claim that it is not possible to remove the recovery partition on the MacBook Air is false. It is possible, though a little less fool-proof than on the Surface Pro.

In conclusion, a stock MacBook Air 128GB has about 108 GB of available space, while the Surface Pro has 96,3 GB. That’s a difference of 11,7 GB or 12 percent. Let’s also not forget Apple is shipping the Airs with about 7 GB of physical space less as advertised, which is arguably more unfair than Microsoft’s failure at reducing the size of Windows.

But I’ll quote Bott’s last statement:

Of course, neither device can compare to a tablet or phone OS in terms of efficiency. Tablet operating systems are designed to be small, and they sacrifice all sorts of capabilities that you expect in a full-strength PC. But if you’re going to complain about operating systems using too much of the available storage, you’d better make sure your letter to Redmond is cc’ed to Cupertino.


  1. This is why I’m not criticizing any of his Surface Pro numbers.