At the Linux Foundation's annual conference in August, IBM VP Brad McCredie told the crowd something that was probably unthinkable when Linus Torvalds created his new operating system kernel two decades ago.

"The Linux market now is bigger than the Unix market," he said.

As recently as Q4 2010, Unix server revenue was 25.6 percent of the worldwide market, with Linux at 17 percent, according to IDC. By the first quarter of 2012, Linux commanded 20.7 percent of worldwide server revenue compared to Unix's 18.3 percent. And in IDC's most recent report covering Q2 2013, Linux was up to 23.2 percent of all revenue with $2.8 billion, while Unix fell 21 percent year over year to $1.8 billion. Unix's Q2 server revenue of 15.1 percent was its lowest ever reported by IDC. (Windows servers account for nearly 50 percent of revenue, while IBM's mainframes took nearly 10 percent.)

Linux surpassing Unix is no surprise. Red Hat and other vendors have been trumpeting their ability to move customers from old Unix servers to Linux ones for years now. Open source operating systems based on Linux are prevalent on everything from Web servers and small business workloads to the world's biggest supercomputers. "Linux server demand continued to be positively impacted by cloud infrastructure deployments" in the second quarter, IDC said.

But Unix isn't dead yet, analysts and vendors are quick to note.

“Near-ultimate availability”

Press coverage was already declaring the death of Unix back in late 2011, at which time Forrester analyst Richard Fichera wrote a blog post saying, "the extinction of UNIX is not going to happen in our lifetime... UNIX on proprietary RISC architectures will stay around for several reasons that primarily revolve around their being the only close alternative to mainframes in regards to specific high-end operational characteristics."

For performance, "near-ultimate availability," and "isolated bulletproof partionability"—the ability to run workloads on "dynamically scalable and electrically isolated partitions with the option to move workloads between them while running"—Unix was still king, Fichera wrote in that October 2011 post.

Linux has closed much of the gap, Fichera wrote in an update in July this year. The kernel's scalability to 4,096 x86 CPUs and up to 16TB of memory puts it "well into high-end UNIX server territory," he wrote. I/O performance, virtualization, clustering, and high availability are also improving. "Modern Linux is looking an awful lot like UNIX," with the "number of workloads that cannot be effectively served by Linux on x86 systems continu[ing] to shrink," he wrote.

But again, Unix still isn't dead and may never kick the bucket in our lifetimes. While migrations from Unix to Linux continue, a core group of customers continues to upgrade hardware on which existing applications run. Unix may not attract as many new customers as Linux, but new deployments do exist.

"People expect that Unix will go away like turning a light switch, and it simply won't happen that way," IDC Research Vice President Jean Bozman told Ars. "This decline should taper to some level. I don't think we're there yet, but it's going to hit a level where those core workloads are going to be refreshed, and there are net new customers as well. We don't expect [Unix] to disappear at all, and we haven't hit the number where it's going to plateau yet."

Migrations from Unix to Linux have been "primarily driven by cost, or perception of cost over time," Bozman said.

Still, Databases, and data warehousing in particular, remain strong on Unix, she said. Unix also remains hugely important in the telecommunications industry, no surprise since Unix was developed at AT&T and Bell Labs in the late 1960s and early 1970s. "A lot of that is software that companies write for themselves to control the way calls are routed," she said.

In IDC's market data, Unix systems include RISC, Itanium, and x86 systems running Unix operating systems (like IBM AIX, HP-UX 11, or Oracle Solaris). "The entire Unix system's ecosystem is composed of servers, storage, software, and services. Thus, there is a multiplier effect in which Unix servers are the foundation of a Unix ecosystem worth several times the server revenue alone," Bozman said.

Rivals hope IBM won’t dominate Unix like it does the mainframe

IBM has extended its market share lead, although, like other vendors, its revenue has declined. IBM made $5.7 billion on Unix servers in 2011 for a 50.4 percent revenue share and $5.1 billion in 2012 for a 56.1 percent share, according to IDC data Bozman provided to Ars.

Oracle and HP took 19.2 percent and 18.6 percent of the Unix market in 2012, respectively. Hitachi and Fujitsu rounded out the top five with 2.2 percent and 2.1 percent. The total Unix market dropped from $11.3 billion in 2011 to $9.1 billion in 2012.

Mission-critical applications are still attracting customers to Unix systems, IBM's McCredie told Ars. McCredie recently visited a few customers in "very large retail, some in banking, very large enterprises, and they're still putting new workloads on the Unix systems," he said. Unix is doing particularly well with databases and enterprise resource planning applications, he said.

IBM came to the LinuxCon conference this year to tout an increased investment in Linux for its Power servers, which also run Unix. That doesn't mean the company is going to let its Unix technology stagnate though.

"I would not portray this as a disinvestment in Unix," McCredie said. "IBM is a big company. We have a lot of resources, and we can do more than one thing. The investment in Linux is not to say we need to migrate people off. We've had zero customers say, 'we don't like Unix, we need to go somewhere else.'"

Oracle is similarly trumpeting both Linux and Unix. "While we're seeing that some customers are moving workloads off of UNIX servers, we also see many moving back to UNIX servers to fulfill their up-time, performance, and data integrity requirements that the other platforms can't give them," Oracle VP of software development Markus Flierl told Ars in an e-mail.

Unix customers could suffer if the continued drop in revenue pushes vendors out of the market, leaving only one or two viable options. Fujitsu says it's going to try to prevent that from happening, despite being one of the smallest vendors, with annual Unix server revenue dropping from $303 million to $188 million between 2011 and 2012.

Fujitsu server head Noriyuki Toyoki warned last month that letting IBM dominate Unix the way it dominates mainframes would be bad for everyone (except IBM), according to the IDG News Service.

“Two cash cows would make IBM much, much stronger. We have to stop it. That would not be good for us, and it’s never good for the customer," Toyoki said.