Born in what is now Lviv, Ukraine, Lempel studied at Technion — Israel Institute of Technology, earning a BS, MS, and doctorate in electrical engineering and computer science. He stayed at Technion to teach, but on the side he founded a research lab for Hewlett-Packard in Haifa, and was its director for 14 years. Lempel was interested in data compression. Some compression technologies are “lossy” — a tradeoff of fidelity to achieve smaller file sizes, such as with JPG images. But some digital data must be compressed with lossless techniques, such as computer programs and digitized music. This was especially important as microcomputers were first getting popular: they were lacking in both memory and data storage.
Lempel, with his Technion colleague Dr. Jacob Ziv, developed lossless compression algorithms, known as LZ1 (1977) and LZ2 (1978). “The LZ algorithm can be found in virtually every modern computer,” said the Association of Computing Machinery in 1998, when it presented them an award for the idea. “Most workstations run with one or more LZ compression algorithms in its software, hardware or both. We use the LZ algorithm often without being aware of it, archiving files; installing software that is compressed on a disk; backing up hard drives; and going online. These examples are of the practical impact added to the well-recognized theoretical significance of the work of Dr. Lempel and Dr. Ziv.” Dr. Lempel is “considered one of the greatest researchers who worked in the Technion in the 100 years of its existence,” said its current president, Uri Sivan. “The Lempel-Ziv algorithm contributed to the world an unprecedented technology that enables fast and lossless data transfer.”
It’s still in use today as the basis for several derivatives, such as in GIF image files, MP3 sound files, and software installer distribution. In 1977 the algorithm was named by the Institute of Electrical and Electronics Engineers as an IEEE Milestone (“key historical achievements in electrical and electronic engineering”), and in 2007 awarded Lempel the IEEE Richard W. Hamming Medal for “pioneering work in data compression, especially the Lempel-Ziv algorithm.” Dr. Ziv is still alive, at 91. Dr. Lempel died on February 4, at 86.
Author’s Note: Dr. Ziv died March 23, 2023, at 91.