Three years ago, I decided not to get an iMac. Now I'm rethinking that decision.

And it's not because CNET gave the iMac an Editor's Choice award, though that's helpful. What tipped the scales is an ability to use the machine as a lowly external monitor years from now. Let me explain.

For years now I've oscillated between a Mac and Windows existence. In the 1980s, it was Mac for me. After college, Windows moved in. Then at the newspaper where I used to work, we installed Macs. Then at CNET, it was Windows, until more recently, when I adopted a bi-OS existence. I'm not religious about these matters.

In my life today, Macs are ascendant for reasons of reliability, grace under pressure, and the ability to snooze and wake up fast. But I've steered away from iMacs for a few reasons:

&149' I wanted a quad-core processor. That's not a problem anymore, with new iMacs sporting Intel's latest.

&149' I wanted more hard drive capacity for copious photo and video data and for backups. That's not a big problem with Thunderbolt's fast connections for external drives, though there will be cable clutter and perhaps a port shortage until Thunderbolt hubs arrive.

&149' I had software I'd paid for on Windows that I didn't want to buy again for Mac OS X. I now lead a largely cloud-based existence for much of my work and personal computing, though, and the native software I need can be transferred to the Mac without a price penalty. (OK, my son would miss building racetracks with TrackMania, but I'm not going to junk the Windows machine.)

&149' I don't like all-in-one designs, because I prefer to buy an external monitor with a longer useful lifespan than the processor and graphics chip.

But here's a nice thing you can do with an iMac: when it gets old and tired, you can turn it into an external monitor. That means you can buy another machine and get some handy screen acreage. That idea is what got me thinking about the new iMac seriously for my home machine that I use for photo and video editing.

But wait--that Thunderbolt complicated matters. There's been confusion about whether the external-monitor feature, called target display mode, works with the new high-speed ports.

Apple today published the official word on the subject: You can't use the new Thunderbolt iMacs as an external monitor with a DisplayPort cable. You can, however, do so with a Thunderbolt cable, which means a new MacBook or another new iMac could use it as an external monitor.

Apple&39's new 27-inch iMac includes two Thunderbolt data ports, in addition to 4 USB 2.0 inputs and a FireWire 800 port.

So somebody who wants to use an iMac as an external monitor for, say, a Blu-ray drive or game console or laptop probably needs to look elsewhere unless somebody figures out an adapter of some sort. But that's not my problem. I'm trying to figure out what to do with an elderly iMac a few years from now, when, I imagine, Thunderbolt ports won't be such a rarity.

Thunderbolt is now what's got me stewing.

A 10Gbps bidirectional interface is a great idea, and Thunderbolt gives you two such channels for each connector. But today, we're in the early days with the chicken-and-egg problem: computer makers wait for more Thunderbolt peripherals before adding the expense of a Thunderbolt port, while peripheral makers wait until there are more computers before creating Thunderbolt-capable products. Intel's endorsement may encourage some, but Apple's apparent period of exclusivity may discourage others who'd prefer to tap into a broader market.

Even interfaces that got serious traction, such as IEEE 1394, aka Firewire, never really attained the high market penetration and attendant low costs of that king of interfaces, USB. Which leads me to ask: Why not put a USB 3 port on the new iMacs

Sure, Intel has yet to build in USB 3, so computer makers must use more costly special-purpose chips to support it. But when I look at most of the throughput-challenged devices in my future--external drives, flash card memory readers, video cameras, and cameras--USB 3 seems like the likely answer to USB 2's shortcomings, even though it's only got half the data-transfer speed of Thunderbolt.

Here, though, I'm still not too worried. I figure somebody will come up with a USB 3 hub that plugs into Thunderbolt. It is, after all, designed to be an all-purpose high-speed connector.

So overall, an iMac looks more compelling to me than in years past. Still, I have to say, an iMac is a second choice to a nonexistent machine I call the Mac Pro Lite.

As long as I'm buying something that puts processing power and expandability over portability, I'd like the Mac equivalent of a cheap tower. Note that the Dell XPS 8300 beats the 27-inch iMac on Photoshop tests.

Sure, it might be harder to come up with the profit margins in this highly cost-sensitive tower computer market, but surely Apple engineers are clever enough to imbue a single-socket, dual-drive machine with the company cachet.

My guess is Apple steers clear because it's trying to stay distinctive, to keep the product line from sprawling too much, and to provide clean integration rather than something amenable to tinkering with the innards. Overclocking, expansion ports, unsupported video cards--it's not the Apple ethos.

Nor is it with me, for the most part. I mostly just want a better price-performance ratio and hard drive expansion. The iMac is the closest thing Apple's got short of an expensive Mac Pro. And now, the iMac is a strong contender.