The CPU Selection

Like the 2011 MacBook Pro upgrade, the iMac gets the Sandy Bridge treatment. Given the heat-dissipating volume of the iMac's all-in-one form factor, Apple only offers a quad-core CPU throughout the lineup. Just a couple of years ago quad-core CPUs weren't mainstream but I believe today it's safe to say that four cores are going to be the standard going forward. We'll see two cores stick around for small form factors and budget systems but everything else is moving to four. Intel is still toying with the idea of 6-cores for the high end but I'd say there's likely even less traction for 6-cores today than there was for 4-cores a few years ago. While high end desktop users could easily make the argument for 4 cores, it's much more difficult to do the same for 6 unless you're building more of a workstation.

I've described Sandy Bridge several times in the past so I won't belabor the advantages here, but the advent of aggressive turbo modes basically rids the OEM of any reason to make a trade off between more cores and higher clock speeds. Sandy Bridge offers you the best of all worlds - high clock speeds in lightly threaded applications or more cores when you need them.

The iMac is less TDP constrained than the MacBook Pro so we get higher base clock speeds to begin with. In fact, Apple opts for lower priced desktop CPUs than the mobile chips. They are clocked higher and put out more heat but they do help Apple maintain that healthy profit margin. Take a look at Intel's price list:

2011 iMac Comparison
Mobile CPU Price Desktop CPU Price
Intel Core i7-2820QM (2.3GHz quad-core) $568 Intel Core i7-2600 (3.4GHz quad-core) $294
Intel Core i7-2720QM (2.2GHz quad-core) $378 Intel Core i5-2400 (3.1GHz quad-core) $184

The $2199 15-inch MacBook Pro comes with a 2.2GHz mobile Core i7, the 2720QM to be specific - the CPU itself costs $378. The $1999 27-inch iMac comes with a 3.1GHz desktop Core i5-2400, the CPU here is priced at a much lower $184. The most expensive CPU you can buy in the 27-inch iMac is a Core i7 2600, which Intel charges $294 in 1,000 unit quantities. There's physically more hardware in the iMac, but using desktop CPUs is a no brainer for Apple here.

The CPU lineup is a bit strange:

2011 iMac Comparison
iMac Model $1199 21.5-inch $1499 21.5-inch $1699 27-inch $1999 27-inch
Base CPU Intel Core i5-2400S (2.5GHz quad-core) Intel Core i5 2500S (2.7GHz quad-core) Intel Core i5 2500S (2.7GHz quad-core) Intel Core i5 2400 (3.1GHz quad-core)
CPU Upgrade Offered None Intel Core i7 2600S (2.8GHz quad-core) None Intel Core i7-2600 (3.4GHz quad-core)

The 21.5-inch iMac comes with a Core i5-2400S or 2500S by default. You can upgrade to the Core i7-2600S but only if you buy the $1499 system. Based on iFixit's teardown you should be able to do a CPU upgrade on your own since these are just standard socketed parts. Note that the 21.5-inch iMac only uses 65W TDP CPUs, the S suffix drops base clock speed a bit in exchange for lowering the max TDP from 95W down to 65W. Remember how turbo works, with lots of cores sharing a low TDP the base clock might be low but that means that you've got more room to turbo up when you start powering cores down. Despite the 2.5GHz base clock speed, the Core i5-2400S can turbo up to 3.3GHz with a single core active. The 2500S reaches a staggering 3.7GHz at max turbo.

The 27-inch iMac starts with a Core i7-2500S, but the upgraded model moves to a 95W Core i5-2400 clocked at 3.1GHz. Believe it or not but the i5-2400 can only turbo up to 3.4GHz. Running single threaded applications, the cheaper iMacs will actually be a little faster. There's also a Core i7 upgrade offered here, but again only for the more expensive iMac: Apple will sell you a Core i7-2600 for an additional $200.

Apple 2011 iMac CPU Comparison
  2.5GHz Core i5 2.7GHz Core i5 2.8GHz Core i7 3.1GHz Core i5 3.4GHz Core i7
Intel Model Core i5-2400S Core i5-2500S Core i7-2600S Core i5-2400 Core i7-2600
Base Clock Speed 2.5GHz 2.7GHz 2.8GHz 3.1GHz 3.4GHz
Max SC Turbo 3.3GHz 3.7GHz 3.8GHz 3.4GHz 3.8GHz
Max DC Turbo 3.2GHz 3.6GHz 3.7GHz 3.3GHz 3.7GHz
Max TC Turbo 2.8GHz 3.2GHz 3.3GHz 3.3GHz 3.6GHz
Max QC Turbo 2.6GHz 2.8GHz 2.9GHz 3.2GHz 3.5GHz
L3 Cache 6MB 6MB 8MB 6MB 8MB
Cores/Threads 4 / 4 4 / 4 4 / 8 4 / 4 4 / 8
AES-NI Yes Yes Yes Yes Yes
VT-x Yes Yes Yes Yes Yes
VT-d Yes Yes Yes Yes Yes
TDP 65W 65W 65W 95W 95W

Now let's talk architecture. All of the Core i5s come with a 6MB L3 cache, while the upgraded i7s come with an 8MB L3. The even bigger difference? None of the Core i5s come with Hyper Threading enabled - they are four core, four thread chips. Only the upgraded Core i7s have HT enabled, giving them a total of eight threads. By comparison, all 15-inch MacBook Pros are mobile Core i7s with 8MB of L3 cache, four cores and eight threads. In other words, given the right workload, a high end 15-inch MacBook Pro could actually outrun one of these iMacs.

Hyper Threading only really matters with heavily threaded workloads (video encoding, offline 3D rendering) so I doubt most users would notice a difference, but it's still a shame that the iMac can't claim total superiority over the MacBook Pro.

I turned to MSR Tools once again to verify turbo operation. Running a single threaded instance of Cinebench the tools reported a maximum clock frequency of 3.3GHz. Assuming MSR Tools itself is keeping a second core awake, turboing up to 3.3GHz makes sense. I have no reason to believe that Apple is artificially limiting max turbo speeds, at least on the 27-inch 3.1GHz Core i5 model. Given how much room there is inside the iMac to dissipate heat, I don't see any reason for Apple to limit clock speeds here.

The quad-core CPU idles at 1.6GHz under OS X

Quick Sync is of course one of Sandy Bridge's biggest features and once again it goes relatively unused within the iMac. FaceTime HD supports it but iMovie, which ships with the system, has yet to be updated to take advantage of Quick Sync. If you want to upgrade to Sandy Bridge in order to get better video transcoding performance courtesy of its hardware decode/encode engines, I'd recommend waiting until Apple actually updates its software before making the move to Sandy Bridge on OS X.

Two Models Intel's Z68 Chipset, Thunderbolt & Display IO
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  • utlragear - Monday, June 11, 2012 - link

    And here's the thing. It shouldn't cost any more than the difference for the monitors. But iPeople usually can't comprehend that.
  • khimera2000 - Monday, May 30, 2011 - link

    No 2000$ is not a big deal, and those people that are complaining are the ones that actually want the most out of there money.

    Sorry man hard as it is for me to brake it to you, especially since you have to hear it hear... but nerds know how to shop for computer parts, and they know whats it worth.

    If you want to buy a 2000$ rig only to throw it away two years later and buy another 2000 rig go ahead.

    I will take that same cash, keep the moniter and have 2000$ to spend on my next computer. where as you will have 1000$

    i dont know about you, but I baught a really good moniter when i rebuilt my computer last, and am looking forward to spending that 1k that you will have to spend on a moniter on other cool tech :D

    O ya im also looking forward to the following...

    Upgrading my CPU, GPU, HDD, all me RAM, My Motherboard, and if a deal comes around adding two more moniters :)

    Then again where all broken nerds right? and the above dosent really matter in your world.

    You are right on them not targeting us though. We care about how long the life of our PC will be, what softwear goes into it, and the quality of the componants, where as a mac can be baought off the shelf by any shmuck off the streat.

    Don't beleave me? then you are what Mac is targeting. For everyone else they understand what im talking about. Especialy the part where we research every peace that goes into our rig.
  • rubaiyat - Wednesday, September 7, 2011 - link

    I've seen plenty of PC users blow much more than $2000 on their computers, WITHOUT a display. They tend to do it in bits and pieces and never add up the total cost because maths (and spelling) are not their strong points.

    They also have big trouble with equivalency. Perpetually claiming something quite inferior is equal to something distinctly superior, either through ignorance (never seen better) or price-tag fixation.

    I bought my iMac 27" for about $1540. I didn't dumbly pay retail for it any more than you claim you do on your PC parts. No wasting massive amounts of time hunting down parts in magazines, dodgy PC fairs, eBay etc. hastling to fix the eternal problems, then sweating out the repairs because they have essentially no support.

    My time can be better spent getting work done (not hanging out in rank dark rooms wasting the days away playing games). The iMac is beautifully svelte, fast, quiet and works out of the box. Not just a brilliant workstation but also a fantastic media station for after work.

    You can't say I haven't shopped around. I did it for the iMac and got a very fast great deal in an afternoon. I know I got a bargain soon as I negotiated it and took. I had spent vastly more unproductive time going through the PC parts sites and shops, looking for the 'bargains' I could never find.

    Just how do the higher prices you pay in these places, for sometimes cheaply made components, work out to be a "deal"?
  • utlragear - Monday, June 11, 2012 - link

    mostly from broke nerds"? Is that why I have a 5500 square foot home paid for along with over 700k in savings? Keep in mind that some people don't buy apple because they were actually smart enough to understand it's mostly over rated, over priced, slow and outdated hardware out of the box. i7 based PC's came out a YEAR before apple even released them.

    Some people simply don't throw their money like water down a sewer as some college students do while trying to look hip, cool and pretend they are "rich" while they occupy an apartment. Another clue for you, people with lots of money that stay that way, usually aren't iSuckers. Do you know how many times I've heard that dumb, "People don't buy apple because they are broke bs?" Too many times. If you want to buy apple because the marketing is effective on apples credulous marketing demographic, then fine. But don't try to act like it's a great value because it isn't.

    I'd rather buy my family 2 or 3 superior PC's with windows 7. And you are right. For MANY people $2000 isn't a big deal. But again, I don't believe that because that is true I should burn money to apple's delight. If I'm going to drop some cash it might be $15,000 for recording studio gear. Or a new car. Something you can't usually get a break on. .
  • Tros - Friday, May 27, 2011 - link

    "Keeping your old monitor that is still good to save money makes sense but not on an all in one unit."

    Did you know that the 27-inch iMac works as a driven monitor? This is a new feature that I've yet to see on any other all-in-ones, esp. laptops, tablets, smartphones. The screens I could have saved on laptops, if they were able to be driven by a hardware solution.
  • Penti - Friday, May 27, 2011 - link

    It's certainly useful when using it together with a MacBook Pro so you can connect it to your screen (iMac) at home or your workstation at work, and still use the built in workstation for other work. But it doesn't have use outside of that. It's not compatible with much else sadly (don't expect it to play nice with your video game console and so on). Neither is it independent from the on board motherboard.

    Neither is it a solution to save the screen. Which you can just get a new one three years later or so with your new iMac any way as Apple doesn't seem to be interested in release a Mac Medium stationary workstation with fast desktop parts. Sure a good external screen will last pretty well for 4-5 years and still be pretty high-end (if it doesn't break). But if your replacing your computer with a new iMac it's pretty pointless argument. If you run a MBP as workstation, a Mac Pro or a PC then you could argument for your external displays though, and the iMacs video in solution wouldn't be worth any thing just as a screen in those setups any way. Not when you can't tear out the motherboard.
  • KoolAidMan1 - Friday, May 27, 2011 - link

    Mac Pros are too expensive for the vast majority of people, given the performance you're getting. I switched from PowerMacs to iMacs for my Final Cut Studio machine a few years ago and I'm never looking back. Cheaper, nearly as fast, and with a $1000 display built in.

    If a new model comes out, resale value is insanely high so you just ship off the old one and get a new iMac with faster components and an even better display. The move from the 24" iMac to the 27" iMac was one of the most economical upgrades I've ever made. I wish my PC upgrades were as simple and returned as much money.

    Other plus is that it also works as a monitor for my gaming PC. Sadly that isn't an option anymore unless your computer has a Thunderbolt port, but that is my only real criticism of the 2011 models. If you don't intend on using it as a monitor as well as a Mac like I do, then it is really great.
  • Penti - Friday, May 27, 2011 - link

    And just to clarify the 2011 iMac only works as a target display with 2011 MacBook Pro's, and prior to that you were limited to the mini-displayport input and what the monitor could do with that input. You could with the previous model connect a Mac Pro, MBP, MB, Mac Mini, PC or gaming PC with displayport and possibly consoles with an adaptor but not native. It's preferable if you can feed it with a 2560x1440 TDMS signal. (Computers can be connected with Dual-link DVI-to-DisplayPort adapter for like $200 USD too)

    So it's pretty useless today for use as input if you don't plan on a dual mac configuration with iMac 2011 and MBP 2011. No expensive adaptors that work with the Thunderbolt Mac yet too. Certainly not a great convenient solution for use of your screen with all your favorite electronics at least. That said, I wouldn't use the external 27" Cinema Display with Blu-ray players and consoles either. The previous solution with 2009 late and 2010 mid iMac 27" models wasn't good with gaming consoles and BD-players either it had to use and pass-through the 720p signal to your screen and didn't support 1080i or 1080p. The monitor/iMac didn't accept 1080p signals at all. Which meant you needed a separate $299 USD scalerbox for that. Or get by with 720p. Which basically meant you needed $500 US Dollars worth of hardware with the old model in order to connect a none DP PC/Mac Pro high-res and a BD-player and or console scaled to native res. They could do it better. But that would mean a separate driver/controller board for the monitor/panel.
  • headbox - Friday, May 27, 2011 - link

    unlike your Alienware/PC hardware, you'll be able to sell the iMac for close to what you paid for it years later. I bought a Macbook Pro for $1800 and sold it TWO years later for $1500, and 50 people people called wanting to buy it. Try putting a 2 year old Dell online for sale- you won't get 50%, if at all.
  • The0ne - Friday, May 27, 2011 - link

    The fact is people buying Macs are NOT your conventional user, in the least. They will love it because it's sleek, it's compact thus saving space, and as far as the people I know that like them money is not a concern even if it is. Apple consumers are a strange lot, you either accept it or not.

    The example given by headbox is a prime example. Why would anyone pay close to the original paid price for a 2 year old Mac? It's not logical at all in any sense except to own a Mac yet people do it all the time. I can understand if there were benefits to this but there really aren't. It's just "I have a Mac" thingy.

    But make no mistake though, if you are going to get one and keep it for a long time might as well get one with a nice big screen. I have 3 Dell 30"s that I saved up and bought and wouldn't go back to anything less. My eyes are grateful until I use my M17xR2. My eyes aren't that young anymore!

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