IBM Corp. rolled out a new mainframe computer Tuesday boasting a 50-percent performance boost and dramatically lower energy costs than its predecessor.

The new System z10, with a starting price at about $1 million, comes as IBM focuses on lowering the price tag for running its storied line of data-crunching workhorses.

The Armonk, N.Y.-based company said it designed the new machine to help companies and government agencies that rely on mainframes — usually for critical data processing such as bank transactions or census statistics crunching — save money on energy bills and better handle a flood of Internet information.

The size of IBM’s investment — the company spent five years and $1.5 billion developing the new mainframe — also underscores its commitment to the long-term viability of the mainframe and efforts continue adapting the decades-old product line to the Internet age.

For years some IT experts predicted the demise of the mainframe, bulky and expensive machines that face competition from smaller, less-expensive servers. But IBM says mainframe revenue is growing, rising in 5 out of the last 7 quarters, thanks in part to interest from emerging markets like Brazil, China, India and Russia.

IBM says it incorporated a number of technological upgrades into the new machine to appeal to cost-conscious companies looking to consolidate the number of servers in their data centers.

The z10′s capacity is equivalent to 1,500 servers based on the popular x86 design, IBM says, though it has 85 percent lower energy costs and takes up 85 percent less space than the batch of x86 servers.

The new machines also boast more processing horsepower, using 64 processors compared to the 54 processors used in its predecessor, the z9.

Those chips are better at multitasking — the new machine is IBM’s first mainframe to use so-called “quad-core” chips, or microprocessors with four computing engines on a…