NEW YORK (CNN/Money) - The fourth quarter was good to companies' bottom lines, but the goodness didn't get doled out in equal portions.

About half of the companies in the S&P 500 have already reported, and so far earnings growth over the year ago period is running around 25 percent, according to First Call. Because many of the nation's retailers have yet to report, the final result will likely be better than that, setting us up for the best earnings period in a decade.

It's technology, with earnings up around 50 percent versus the fourth quarter the previous year, that's made for the lion's share of the gains. What's more, the sector that everybody left for dead a year ago is beating analyst estimates by a wider margin than any other.

Basic materials companies are also posting big gains, thanks to the run up in commodity prices, as are financials, which are benefiting from a steep yield curve.

On the other side of the coin, communications services continue to struggle, posting lower earnings than a year earlier. Consumer staples companies have put up modest growth, but many have also fallen short of estimates.

Meantime, as earnings season begins slow its pace in the week ahead, it's important to remember that there's a difference between the pro forma results companies and analysts highlight and what earnings look like when you include charges for restructuring and asset write-downs and the like.

Earnings according to generally accepted accounting principles are running about 16 percent below pro forma profits -- a gap that is a bit wider than the historic norm -- according to First Call's Joe Cooper

Companies in this report: Tyco; Cisco; PepsiCo.

Everybody heaps praise on Tyco (TYC: Research, Estimates) CEO Ed Breen for doing a tough job well, but in one respect he's got it easy. It's not difficult to look straight edge when investors' point of comparison is the antics of former CEO Dennis Kozlowski.

But we digress. Tyco had a busy year in 2003, cleaning up the mess that Dennis made. It's been scuttling businesses that didn't make sense, restructuring others, shoring up its pension plan and working down debt levels. The stock market has rewarded to company for these efforts. More important, so have the credit markets, making it easier for Tyco to tap the money it needs for day-to-day operations.

Now that its house is more in order (although there's work to be done yet) Tyco's challenge is beginning to shift. It needs to start being more than a mishmash of various corporate entities and start working as a company. Breen's next job will be to develop more of a corporate identity at Tyco, and develop all those (ten-cent 1990s word coming) synergies that are supposed to exist between its businesses.

Why it matters: It's not entirely clear that Tyco's model really works. Much of the vaunted growth it achieved through the 1990s came through acquisitions and, as we found out later, accounting tricks.

Tyco investors, and corporate-types everywhere, very much want to know if the model can work, and they'll be focusing on that in the quarters to come. They'll also be watching to see how much ground Tyco can put between it and its past, on the view that the sooner the company transforms itself, the sooner we can put general worries about financial shenanigans behind us.

First Call estimate: 32 cents a share versus 32 cents a year ago.

No, Cisco (CSCO: Research, Estimates)'s stock is nowhere close to the high it reached in March 2000. It has to rise nearly 200 percent before that happens. But it did recently tick above its March 1999 high -- an event which serves to simultaneously remind us of how silly things got in 2000 and how very far (more than 200 percent) Cisco has come from its 2002 lowpoint.

Enthusiasm for Cisco continues to run high on the belief that in 2004 business spending on tech is really going to cook. Companies are flush with cash, say the bulls, and a tax break on capital spending, set to expire at the end of the year, will prompt many of them to purchase Cisco's wares.

Why it matters: Investors, keen to know whether the bull case on tech spending is beginning to unfold, will be listening closely to Cisco's conference call for signs of light.

CEO John Chambers, badly burned for overpromising in the past, has learned to play it a bit closer to the chest. Any sign of enthusiasm from him on capital spending prospects would be greeted with glee across the tech sector -- particularly since Cisco's January quarter end means its results will give a closer to real-time read on what's going on.

Cisco's bread and butter remain the servers and routers that it made its name on, but it will be particularly important to watch how its emerging technology businesses are faring. Good growth in areas like voice over IP would suggest, first, that Cisco is successfully positioning itself for tech's next wave and second, that companies are beginning to invest in less proven technologies -- a sign that they're getting ready to really spend.

First Call estimate: 17 cents a share versus 15 cents a year ago.

The stock market keeps bubbling higher, but PepsiCo (PEP: Research, Estimates) shares have lost their fizz.

Sure, investors appreciate that it and companies of its ilk offer steady growth through good and bad times, but these days that sort of growth just isn't strong enough. They want to buy companies that make cell phone chips, not corn chips.

Then there are the inevitable questions over what sort of growth rate Pepsi is going to be able to post in the future. Competition is stiff across all of Pepsi's product categories and Gatorade is the only one of its brands that holds a clear No. 1 position.

The bottled water business -- Pepsi owns Aquafina -- is particularly tough. A slew of big companies (Coke, Nestle, etc.) and smaller outfits fighting for share and a low barrier to entry (it's, um, water) have made for price and margin erosion across the board. Meantime, many Americans' belief that the carbohydrate molecule is the root of all evil bodes poorly for Frito Lay.

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Why it matters: As with other global consumer companies, Pepsi must find ways to grow within markets that seem increasingly saturated.

The company's apparent tactic for doing this is, first, to further promote the Pepsi brand, creating associative links in people's minds across all its product categories and, second, to expand brands, like Tropicana, that fit in with the trend toward healthier eating.

First Call estimate: 52 cents a share versus 50 cents a year ago.