300, 350, 500, 2900) were external boxes that could be connected through an optional serial interface to many of the ET series office typewriters, the others were fully integrated with an external monitor which could be installed on a holder over the desk. Most of the ET/ETV/Praxis series electronic typewriters were designed by Marion Bellini. By 1994, Olivetti stopped production of typewriters, as most users had transitioned to personal computers. Computers Between 1955 and 1964 Olivetti developed some of the first transistorized mainframe computer systems, such as the Elea 9003. Although 40 large commercial 9003 and over 100 smaller 6001 scientific machines were completed and leased to customers to 1964, low sales, loss of two key managers and financial instability caused Olivetti to withdraw from the field in 1964. In 1965 Olivetti released the Programma 101, considered one of the first commercial desktop programmable calculators. It was saved from the sale of the computer division to GE thanks to an employee, Gastone Garziera, who spent successive nights changing the internal categorization of the product from "computer" to "calculator", so leaving the small team in Olivetti and creating some awkward situations in the office, since that space was now owned by GE. In 1974 the firm released the TC800, an intelligent terminal designed to be attached to a mainframe and used in the finance sector. It was followed in 1977 by the TC1800. During the 1970s Olivetti also manufactured and sold two ranges of minicomputers. The 'A' series started with the typewriter-sized A4 through to the large A8, and the desk-sized DE500 and DE700 series. Olivetti's first modern personal computer, the M20, featuring a Zilog Z8000 CPU, was released in 1982. The M20 was followed in 1983 by the M24, a clone of the IBM PC using DOS and the Intel 8086 processor (at 8 MHz) instead of the Intel 8088 used by IBM (at 4.77 MHz). The M24 was sold in North America as the AT&T 6300. Olivetti also manufactured the AT&T 6300 Plus, which could run both DOS and Unix. The M24 in the US also was sold as Xerox 6060. The Olivetti M28 was the firm's first PC to have the Intel 80286 processor. The same year Olivetti produced its M10 laptop computer, a 8085-based workalike of the successful Radio Shack TRS-80 Model 100, which it marketed in Europe. These were the first laptops to sell in million-unit