Today: Tech-focused Nasdaq composite index is latest to hit a milestone number, closing higher than 4,000 for the first time since the dot-com boom collapsed. Also: Hewlett-Packard (HPQ) earnings arrive after Workday and Palo Alto Networks surge higher on their reports.

The Lead: Nasdaq closes higher than 4,000 for the first time since 2000

As Twitter's explosive Wall Street debut and the performance of momentum stocks such as Tesla spur technology-stock bubble talk, the Nasdaq composite index Tuesday reached a milestone unseen since the original tech bubble popped at the beginning of the millennium.

The tech-heavy stock index closed higher than 4,000 on Tuesday, the first time it has reached that high since 2000, when years' worth of exuberance for Silicon Valley technology companies suddenly collapsed.

The index first passed that mark just as Y2K concerns had engineers furiously working overtime: Dec. 29, 2000. However, those eager to compare the current explosion in valuations for technology companies are going to find that the growth this time around is much different, and certainly not just focused on tech: The blue-chip Dow Jones industrial average hit a record round number last week, and the Standard & Poor's 500 followed a day later.

When the Nasdaq reached the 4,000 mark at the end of 1999, it was completing a year that saw the index nearly double, growing 85.6 percent. While the Nasdaq index has had a solid year in 2013, it can't even sniff those results: After Tuesday's 0.6 percent gain to 4017.75, it has increased 33 percent so far this year.

What happened next more than a decade ago seems even more out of reach in today's markets: After reaching 4,000 at the end of 1999, the Nasdaq took less than three months to cross 5,000, gaining 25 percent in fewer than 50 sessions and closing at an all-time high of 5,048.62 on March 10, 2000.

"The euphoria just isn't there on a mass scale today." Drew Nordlicht, managing director at wealth-management company HighTower, told USA Today after the Nasdaq crossed 4,000 in intraday trading Monday.

The difference shows in investors' ability to differentiate between a good tech investment and a questionable one. At the end of the last millennium, technology companies with questionable business models and sketchy prospects were arriving on Wall Street to huge valuations and fanfare pretty much across the board. Now, while Twitter and a host of enterprise-software companies have found resounding demand for early shares, Silicon Valley companies such as Violin and Chegg have experienced a far different welcome to Wall Street.

"This time, the market is differentiating between business models that are working and those that are not," Dan Veru, chief investment officer at Palisade Capital Group, told USA Today.

Despite the differences, this year's gains can rattle nerves in Silicon Valley.

"Everyone feels like the valley has been in a boom cycle for quite some time. That makes people nervous," Yelp CEO Jeremy Stoppelman told The New York Times for an article titled, "In Silicon Valley, Partying Like It's 1999 Again."

Beyond that Times headline, however, few feel that a bubble similar to the late '90s has officially formed around the valley, with the lessons of that time still fresh in many minds.

"It's taken 13 years to get back," Jack Ablin of BMO Private Bank told USA Today. "It just shows the magnitude of that bubble we expanded back in 1999 and 2000."

SV150 market report: Hewlett-Packard gains after earnings report

Aside from the Nasdaq's rise, Silicon Valley's pre-Thanksgiving news has focused on earnings reports, with Hewlett-Packard releasing the biggest of the week Tuesday afternoon and enjoying after-hjours gains on Wall Street.

HP's revenues continued to suffer year-over-year declines in the most recent quarter, but the Palo Alto tech giant's sales easily topped analysts' projections and the announcement of a fresh dividend cheered investors to drive up the company's stock price. Hewlett-Packard reported a $1.4 billion profit, or 73 cents a share, on revenues of $29.1 billion, a decline from $30 billion last year but well above the average analyst forecast of $27.9 billion, according to a Thomson Reuters survey. "There is some hope given that the company was able to jump over what was admittedly a pretty low hurdle," Edward Jones analyst Bill Kreher told Reuters. After shares closed with a 0.9 percent decline at $25.09, they shot up to near $27 in after-hours trading.

TiVo and Infoblox joined HP in announcing quarterly results Tuesday, but reactions to the two SV150 companies' reports was quite different. San Jose-based TiVo earned $12.5 million, or 10 cents a share, on revenues of $117.3 million, easily defeating analysts' average forecast; The company's stock, which ended Tuesday's session with a two-cent gain at $13.24, gained as much as 3 percent in late trading. Santa Clara's Infoblox was not as fortunate, with shares falling more than 20 percent after a report that met analyst expectations for the previous quarter but included a forecast that was much weaker than expected.

Monday's earnings reports led to big gains Tuesday for Workday and Palo Alto Networks. Workday shot 12.7 percent higher to $82.60 after the Pleasanton cloud-software company announced that revenues increased 76 percent in the quarter that marked the anniversary of its initial public offering. Palo Alto Networks, which excised its IPO just three months ahead of Workday, gained 7.4 percent to $49.49 after showing Wal Street its own strong revenue gains.

Apple (AAPL) and Google (GOOG) were two of the most important factors in Tuesday's positive push by the Nasdaqnad SV150. Apple gained 1.8 percent to $533.40 a day after confirming the acquisition of PrimeSense, as the Cupertino company won a patent battle with a man who claims to have invented the smartphone and received a patent for post-picture focusing technology similar to the Lytro. Google advanced 1.2 percent to $1,058.41 after announcing that its low-priced Motorola smartphone, the Moto G, would be available in the United States well before the expected launch date. Pandora also gained Tuesday, increasing 3 percent to $28.79 as its quest for federal legislation to reduce the rates webcasters like the Oakland company pay to artists seemed to come to an end, and Facebook moved 2.4 percent higher to $45.89.

Intel (INTC) headed the other way Tuesday, losing 0.4 percent to $23.65 after Bloomberg News reported that the Santa Clara chipmaker was seeking $500 million for its struggling TV unit. eBay (EBAY) declined 0.6 percent to $48.76 as investors seem inclined to believe Amazon will have a stronger holiday shopping season, and Tesla Motors (TSLA) fell 0.3 percent to $120.50.

Up: Workday, Palo Alto Networks, Yelp, SunPower (SPWRA), Pandora, LinkedIn, Splunk, Twitter, Facebook, Apple, SanDisk, AMD, Applied Materials, Netflix (NFLX), Google, SolarCity, Yahoo (YHOO), Nvidia, VMware

Down: Symantec, Juniper, Electronic Arts (ERTS), HP, Zynga, Salesforce, eBay, Adobe (ADBE), Intel, Gilead, Cisco (CSCO), Tesla

The SV150 index of Silicon Valley's largest tech companies: Up 11.84, or 0.84 percent, to 1,416.49

The tech-heavy Nasdaq composite index: Up 23.18, or 0.58 percent, to 4,017.75

The blue chip Dow Jones industrial average: Up 0.26 to 16,072.8

And the widely watched Standard & Poor's 500 index: Up 0.27, or 0.01 percent, to 1,802.75

Check in weekday afternoons for the 60-Second Business Break, a summary of news from Mercury News staff writers, The Associated Press, Bloomberg News and other wire services. Contact Jeremy C. Owens at 408-920-5876; follow him at Twitter.com/jowens510.