The 2013 MacBook Air Review (13-inch)
by Anand Lal Shimpi on June 24, 2013 12:01 AM ESTThe CPUs
Apple keeps things simple across the 2013 MacBook Air lineup by configuring both 11 and 13-inch models with the same base CPU: a Core i5-4250U.
To understand Apple’s CPU choice, you have to understand that Apple is primarily concerned about improving battery life this generation. The line between MacBook Air and MacBook Pro has to be well defined. The Air is about portability, while the Pro is about performance. When faced with a power/performance tradeoff, it’s clear on which side of the fence Apple will fall whenever the MacBook Air is concerned.
| Apple 2013 MacBook Air CPU Comparison | |||||
| 1.3GHz dual-core | 1.7GHz dual-core | ||||
| Standard On | 11 & 13-inch MBA | Optional on Both | |||
| Intel Model | Core i5-4250U | Core i7-4650U | |||
| Base Clock Speed | 1.3GHz | 1.7GHz | |||
| Max SC Turbo | 2.6GHz | 3.3GHz | |||
| Max DC Turbo | 2.3GHz | 2.9GHz | |||
| L3 Cache | 3MB | 4MB | |||
| TSX-NI | No | Yes | |||
| TXT | No | Yes | |||
| AES-NI | Yes | Yes | |||
| VT-x/VT-x EPT | Yes | Yes | |||
| VT-d | Yes | Yes | |||
| TDP | 15W | 15W | |||
| Processor Graphics | Intel HD 5000 | Intel HD 5000 | |||
| GPU Clock (Base/Max) | 200/1000MHz | 200/1100MHz | |||
The lower base clock alone shouldn’t mean much, but the max TDP of the CPUs in the new MacBook Air falls as well - from 17W down to 15W. The thermal limit is even more dramatic since with Haswell ULT, the 15W includes the CPU/GPU as well as the on-package PCH. In Ivy Bridge the PCH was off package and wasn’t included in the 17W TDP.
Max turbo clocks are identical between the Haswell ULT CPUs Apple picked this round and the Ivy Bridge models before, but with a lower TDP it’ll be harder to always sustain the same frequencies given the right workload.
Haswell does feature a not insignificant gain in IPC compared to Ivy Bridge, which should help offset the power constraints that could otherwise force a larger regression in performance.
Both 2013 MBAs ship with the same CPU by default, and both can be upgraded to the same higher end SKU: a Core i7-4650U. The 4650U retains the same 15W TDP as the i5-4250U, but it increases its base clock speed to 1.7GHz and max turbo to 3.3GHz. The L3 cache also grows from 3MB to 4MB. All in all, this should be a very healthy upgrade in performance. Intel likely maintains the same TDP by binning for power; the i7-4650U is probably capable of running at higher frequencies without any appreciable increase in voltage. The max GPU clock also goes up by 10%.
Haswell ULT, Courtesy iFixit
What's arguably coolest about the i7-4650U is it enables Haswell's Transactional Synchronization Extensions (TSX-NI), a feature which is unfortunately disabled on the i5-4250U. I don't suspect this will matter much for most MBA users, but anyone looking to play around with Haswell's TSX instructions will want to opt for the higher end SKU. The upgrade costs $150 regardless of base model. Intel charges $454 for the i7-4650U and $342 for the i5-4250U, a difference of $112; Apple is adding another $38 onto the 1KU pricing, which isn't unreasonable.
Many have asked me what the impact of the i7 will be on battery life. I'm hoping to get my hands on an i7 based machine when I return from the UK in a week, but for those of you making immediate decisions I'll offer the following. Sustained operation at higher frequencies will likely draw more power, and negatively impact battery life. Light to medium workloads will enjoy a mix of race to sleep benefits as well as higher power consumption under load. Idle power should be roughly similar between the parts however. For most workloads I'd expect a modest impact to battery life, but it won't be enough to regress to 2012 levels of battery life. All of this is said without knowing key details like operating voltage for most 4650Us. I plan on addressing that shortly.
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seapeople - Tuesday, June 25, 2013 - link
Brightness is pretty much the number one power consumer in a laptop like this (which is actually mentioned in the review). If you expect to run anything at 100% brightness and get anywhere near ideal battery life then you are bound to be disappointed.name99 - Monday, June 24, 2013 - link
"802.11ac ... better spatial efficiency within those channels (256QAM vs. 64QAM in 802.11n). Today, that means a doubling of channel bandwidth and a 4x increase in data encoded on a carrier"This is a deeply flawed statement in two ways.
(a) The modulation form describes (essentially) how many bits can be packed into a single up/down segment of a sinusoid wave form, ie how many bits/Hz. It is constrained by the amount of noise in the channel (ie the signal to noise ratio) which smeers different amplitudes together so that you can't tell them apart.
It can be improved somewhat over 802.11n performance by using a better error correcting code (which essentially distributes the random noise level over a number of bits, so that a single large amount of noise rather than destroying that bit information gets spread into a smaller amount of noise over multiple bits).
802.11ac uses LDPC, a better error correcting code, which allows it to use more aggressive modulation.
Point is, in all this the improved modulation has nothing to do with spatial encoding and spatial efficiency.
(b) The QAM64 and QAM256 refer to the number of possible states encoded per bit, not in any way to the number of bits encoded. So QAM64 encodes 6 bits per Hz, QAM256 encodes 8 bits per Hz. the improvement is 8/6=1.33 which is nice, but is not "a 4x increase in data encoded on a carrier".
We are close to the end of the line with fancy modulation. From now on out, pretty much all the heavy lifting comes from
(1) wider spectrum (see the 80 and 160MHz of 802.11ac) and
(2) smaller, more densely distributed base stations.
We could move from 3 up to 4 spatial streams (perhaps using polarization to help out) but that's tough to push further without much larger antennas (and a rapidly growing computational budget).
There is one BIG space for a one-time 2x improvement, namely tossing the 802.11 distributed MAC, which wastes half the time waiting randomly for one party or another to talk, and switching to a centrally controlled MAC (like the telcos) along with a very narrow RACH (random access channel) for lightweight tasks like paging and joining.
My guess/hope is that the successor to 802.11ac will consist primarily of the two issues I've described above (and so will look a lot more like new SW than new DSP algorithms), namely a central arbiter for a network along with the idea that, from the start, the network will consist of multiple small low-power cells working together, about one per room, rather than a single base station trying to reach out to 100 yards or more.
bittwiddler - Monday, June 24, 2013 - link
• The keyboard key size and spacing is the same on the 11 and 13" MBAs.• The 11" MBA is exempt from being removed from luggage during TSA screenings, unlike the 13.
• The 11" screen is lower height than most and doesn't get caught by the clip for the airplane seat tray table.
• When it comes to business travel computing, I'm not interested in a race to the bottom.
Sabresiberian - Monday, June 24, 2013 - link
One thing I would NOT like is for Apple to make a move to a 16:9 screen. I'd certainly rather have 1440x900 on a 13" screen than anything denser that was 16:9. I mean, I'm one of the guys that has been harping on pixel density and refresh rates since before we had modern smart phones (the move to LCDs set us back a decade or more in that regard), but on a screen smaller than 27", 16:9 is just bad. In my not-so-humble opinion.4:3 is better for something smaller than 17", but I can live with 16:10. :)
Kevin G - Monday, June 24, 2013 - link
Re-reading trough the review I have a question about the display: does it use panel self refresh? I recall Intel hyping up this technology several years ago and the Haswell slides in this review indicate support for it. The question is, does Apple take advantage of it?Kevin G - Monday, June 24, 2013 - link
I think that I can answer my own question. I couldn't find the data sheet for the review panel LSN133BT01A02 but references on the web point towards an early 2012 release for it. Thus it looks like it appeared on the market before panel self refresh was slated for wide spread introduction alongside Haswell.hobagman - Monday, June 24, 2013 - link
Hi Anand & all -- could I ask a more CPU related question I've been wondering about a lot -- how come the die shots always look so colorful and diverse, when isn't the top layer all just interconnects? Or are the die shots actually taken before they do the interconnects, consisting in the top 10-15 layers? Would really appreciate an explanation of this ...hobagman - Monday, June 24, 2013 - link
I mean, what are we actually seeing when we look at the die shot? Are those all different transistor regions, and if so, we must be looking at the bottom layers. Or is it that the interconnects in the different regions look different ... or ... ?SkylerSaleh - Tuesday, June 25, 2013 - link
When making the ASIC, thin layers of glass are grown on the silicon, etched, and filled with metal to build the interconnects. This leaves small sharp geometric shapes in the glass, which reacts with the light similarly to how a prism would, causing the wafer to appear colorful.cbrownx88 - Monday, June 24, 2013 - link
Please please please revisit with the i7 config - been wanting to make a purchase but have been waiting for this review (and now waiting on the update lol).