Panasonic on Tuesday introduced a write-once Blu-ray disc with a writing speed that's faster than other discs available today in the high-definition format. The consumer electronics company said the write-once disc has a 4x writing speed, versus 2x for most other Blu-ray discs. In addition, the single-sided disc is available in 25 Gbytes and 50 Gbytes. The latter version is dual layer, which means the disc doesn't have to be turned over while recording data. Panasonic, which is the brand name of Matsushita Electric Industrial, plans to release the 25-Gbyte version this month and the larger disc in September. The discs have a maximum data transfer speed of 144 Mbytes per second, which means a 1 Gbyte of data can be written onto the disc in a minute. Panasonic claims to be the first company to develop a 4x Blu-ray disc that can store 50 Gbytes.