virtualbox.org

I am considering purchasing an iMac 27" and I am trying to decide between the i5 or the i7 quad core. Does anyone have any experience or insight? I realize the i7 is better than the i5 with its faster clock speed and the hyper threading. However, is it really worth the extra money? Since the i7 is HT, will i actually see 16 cores when i allocate CPU's to a VM due to the HT versus 8 for the i5 (i am guessing VirtualBox doubles available CPU's due to my dual core MBP showing 4 available CPU's)?

If this is true, then it would be a solid reason for selecting the i7 over the i5. Any insights out there?

HT is a very bad for VMs, don't consider logical core as "good to use" for Virtualization. Only consider physical cores availalbe

I just bought a 27" iMac with the fastest i7 available as you can see by my signature. I've been running VirtualBox for a long time now and it didn't even occur to me to base my buying decision on VirtualBox. The bottom line is, a faster machine will run VMs faster. For the most part you don't want to run more than one core in a virtual machine. It screws up USB support for one thing. The only thing I would say is buy what you can afford.

I don't know too much about what hardware variety is offered by Macs, but IMHO when buying any PC, pay more attention to front side bus speed, L2 cache size, hard disk size and RAM size. These will have a much bigger effects on VM performance than the choice of CPU. Having said that the CPU should have VT-x support, and should ideally have enough cores so that one can be dedicated to the host, and one for each VM you want to run simultaneously. If you only ever run one VM then dual core is fine. Oh, and as mentioned, hyperthreading is not a substitute for actual independant cores.

mpack is correct. both the i5 and i7 iMacs have the same 5 GT/s bus speeds. However, the i5 L2 cache is 32k per core vs 256k per core for the i7. The i5 comes with a 6MB L3 cache vs 8MB for the i7. both can be expanded to 32 GBs of RAM. I personally opted for the Fusion drive because it combines a 128 GB SSD drive with either a 1 TB or 3 TB conventional drive which gives you approx 3.5 times the read/write speed.

now we all know way more than we ever wanted to know in a VirtualBox forum.

I just got my second iMac, a late 2012 with 8GB of memory and standard drive.

The i7 is like 50% faster than the i5.

I've just spent the last two days discovering how to use VirtualBox to install Ubuntu and have found that 12.04 32bit works great when you give it 2048GB of memory and a fixed virtual disk. I also told the VM to simulate a 128MB video card with 3D support. It doesn't do 3D games too well but everything else works fantastic.

I strongly recommend you go for the i7.

The SSD Fusion drive is a nice idea and I'm still 50/50 on Apple's implementation of it. I'm thinking in a couple years you'll be able to swap in your hard disk for a SSD drive without the confangled way Apple did it. So I saved myself $250 bucks.

Also, Thunderbolt will allow me to have a SSD externally. It won't be as fast as a SATA-SSD internal drive, but it'll be pretty close.

Perry wrote:I just got my second iMac, a late 2012 with 8GB of memory and standard drive.

The i7 is like 50% faster than the i5.

I've just spent the last two days discovering how to use VirtualBox to install Ubuntu and have found that 12.04 32bit works great when you give it 2048GB of memory and a fixed virtual disk. I also told the VM to simulate a 128MB video card with 3D support. It doesn't do 3D games too well but everything else works fantastic.

I strongly recommend you go for the i7.

The SSD Fusion drive is a nice idea and I'm still 50/50 on Apple's implementation of it. I'm thinking in a couple years you'll be able to swap in your hard disk for a SSD drive without the confangled way Apple did it. So I saved myself $250 bucks.

Also, Thunderbolt will allow me to have a SSD externally. It won't be as fast as a SATA-SSD internal drive, but it'll be pretty close.

Congrats on the new iMac. I'm very happy with the Fusion drive. Of course you could have purchased the iMac with just an SSD drive, or a regular drive + an SSD drive, or an SSD drive and a Fusion drive etc.

Perry wrote:and have found that 12.04 32bit works great when you give it 2048GB of memory and a fixed virtual disk.

I'm sure that a lot of configurations work great. However, using a fixed size disk is usually a mistake IMHO. I'll bet you made yours too small, and resizing it will be a hassle. To make matters worse, performance is no better than a dynamically allocated disk. This is a common newbie mistake.

mpack wrote:

Perry wrote:and have found that 12.04 32bit works great when you give it 2048GB of memory and a fixed virtual disk.

I'm sure that a lot of configurations work great. However, using a fixed size disk is usually a mistake IMHO. I'll bet you made yours too small, and resizing it will be a hassle. To make matters worse, performance is no better than a dynamically allocated disk. This is a common newbie mistake.

I agree. I haven't ever made a fixed disk. Seems to be rather limiting and takes up space if you never fill it.

It's possible that the Dynamic drive option wasn't the problem. The original install called for a 384 or 512 MB and the Ubuntuu installation ran horribly. I changed two things on the next install, one being the Fixed disk and the other setting aside at least 2GB of memory. I'm going to try a 64 bit install of 12.04 with a Dynamic disk just for argument sake.

In any event, my 32bit install with a fixed disk is running almost as fast as if it were installed natively.

As for the Fusion drive, I kinda wish that I had gotten it however I'm also kinda glad that I didn't given that it's a proprietary solution. I got two options, using a SSD drive via the Thunderbolt interface which is boasting 80% efficiency or in three years when the warranty runs out and the cost of SSD drives is much lover to have a SSD hard disk installed.

And as for "noobie mistakes" are concerned, it takes like a 1/2 hour to set a new install and something tells me the Fixed disk might be a much better option considering that iDefrag reported the initial Dynamic virtual disk to have something like 100 to 150 fragmentations.

Dynamic vs. fixed has been thrashed around here a lot. I can tell you it has been my experience that in a virtual environment there is little to no difference. Not enough to justify the long wait to make it fixed and if you make it too small to begin with the ease of increasing the dynamic outweighs everything else.

While you can run Ubuntu and most modern Linux distros at 512 the lack of performance will be noticeable, unless you are not running X. 1GB seems to make them happy and 2GB is almost too much (no noticeable improvement) but that is what I use.

Perry wrote:And as for "noobie mistakes" are concerned, it takes like a 1/2 hour to set a new install and something tells me the Fixed disk might be a much better option considering that iDefrag reported the initial Dynamic virtual disk to have something like 100 to 150 fragmentations.

I'm not sure why you would try and use iDefrag, a Mac defrag program to check a .vdi since it wasn't designed for that and any readings would be meaningless. As far as the 1/2 hour to install a guest the only reason that would be true is if you set a guest to use a fixed disk. I think most Linux guests take between 5-10 minutes to install. if you took a poll of all VirtualBox users, I would guess 95% of them do not use a fixed disk and there are many reasons for that. and Ubuntu 12.04+ will definitely have all sorts of issues trying to run in under 2048MB if you are going to try and run Unity.

Well I decided to try an install with Dynamic disk and 2GB of memory and it appears the 512MB was the bottleneck. With this new revelation I'll do another install with perhaps 128GB Dynamic virtual disk.

Learn something new everyday.

In any event, setting up virtual machines on an iMac like this is a dream come true. I can have a 32 bit install along side of a 64 bit install and have a Windows 8 next to it as well. As I am into software development I really don't need 2D or 3D acceleration in the virtual boxes. So this configuration gives me a number of options and is very flexible. It's quite the dream machine.