The LaserJet 4 was HP's first 600 dot per inch laser printer. It was based on the Canon EX engine and had a maximum print speed of eight pages per minute. The LaserJet came standard with a 100-sheet multipurpose "lip" tray and a 250-sheet main input tray which sat under the machine. The construction of the multipurpose tray was somewhat "tinny" compared to previous lasers, but it was reliable. An optional 500-sheet input tray was also available. For the first time, the LaserJet 4 could also listen on both its serial and parallel interfaces at the same time. It included an interface slot for optional MIO LAN cards. The Postscript/Mac connect version of the LaserJet 4 was the LaserJet 4M, also introduced in 1992. Its part number was C2021A and it was priced at $2995. The LaserJet 4 Plus and 4M Plus were introduced in 1994 with almost identical features to the 4/4M, but with a faster, 12 ppm print speed. The part number of the 4 Plus was C2037A, priced at $1849; the part number of the 4M Plus was C2039A, priced at $2479.