The HP-150, a "compact, powerful and innovative" computer made by Hewlett-Packard in 1983 and based on the Intel 8088, was one of the world's earliest commercialized touch screen computers. The machine was not IBM PC compatible, although it was MS-DOS compatible. Customized MS-DOS versions 2.01, 2.11 and 3.20 were available. Its 8088 CPU, rated at 8 MHz, was faster than the 4.77 MHz ones used by the IBM PC of that period. Using add-on cards, main memory could be increased from 256 KB (256 KiB) to 640 KB. However, its mainboard did not have a slot for the optional Intel 8087 math coprocessor due to space constraints. The HP-150 with an optional hard disk was called the "Touchscreen MAX".