Weighing approximately 23 Kg (50 pounds) and sized slightly larger than an IBM typewriter, the 5100 Portable Computer was announced by the company’s GSD (General Systems Division)  in September 1975. The Portable Computer was intended to put computer capabilities at the fingertips of engineers, analysts, statisticians and other problem-solvers. Available in 12 models providing 16K, 32K, 48K or 64K positions of main storage, the 5100 sold for between $8,975 and $19,975. The 5100 was available with either APL or BASIC — or both — programming languages.

When the PC was introduced in 1981, it was originally designated as the IBM 5150, putting it in the “5100″ series, though its architecture wasn’t directly descended from the IBM 5100. 

If the size and weight of the 5100 seems vrey huge by today’s standards, then the Portable Computer was more slender compared to a late-1960 ’s IBM computer with the equivalent capability. Such a machine would have been nearly as large as two desks and would have weighed about half a ton. (www-03.ibm.com)