IBM and four other companies have joined the Pittsburgh Digital Greenhouse in recent months, bringing the number of members in the nonprofit organization to 27.

President and chief executive officer David Ruppersberger said Monday that the additions will help "make the Greenhouse network stronger and more valuable."

Two of the new member companies joined the Greenhouse during the fourth quarter last year. They include:

• Aeptec Microsystems, which is also known as 3e Technologies International Inc., a Rockville, Md., wireless communications company that has a satellite office in Blairsville, Pa.; and
• Novocell Semiconductor Inc., a provider of memory products for the semiconductor industry, based in Pittsburgh's Oakland neighborhood.

The remaining companies joined the Digital Greenhouse since the beginning of the year, including:

• IBM Corp., of Armonk, N.Y.;
• Accipiter Systems Inc., in Wexford, a maker of computer network products; and
• Vesper Networks, a computer network equipment developer founded in Pittsburgh in 2002.