Image:SSEM_Replica.jpg The '''Manchester Small-Scale Experimental Machine (SSEM)''', nicknamed '''Baby''', was the first stored-program Computer to run a program, on June_21, 1948. It was developed by Frederic C. Williams and Tom_Kilburn at the University_of_Manchester. The computer was built around a Williams_tube, which was developed by Williams and Kilburn. The Williams tube stored 32 words of 32 Bits each. This was used for the computer's memory, which had the advantage of allowing Random_access to memory, rather than the Sequential_access of the Delay_line_memory units. It was a Serial_machine, operating on one bit at the time. The Input was a bank of switches to set any bit in memory, and the output was a bit pattern on the Williams tube (a Cathode_ray_tube). The SSEM was a very limited machine, apparently more for the purposes of testing the Williams tube and other hardware than for producing a practical computer. It was limited because (1) it could store a total of only 32 numbers and instructions, and (2) the Instruction_set was very limited. The instructions available were: * jump indirect * relative jump indirect * take a number from memory, negate it, and load it into the Accumulator * write the number in the accumulator back to memory * subtract a value from the accumulator * skip next if accumulator if negative * stop A division program was written, using pencil-and-paper method, operating on one bit at the time. It was used to divide 2³⁰-1 by 31, giving the answer in about 1.5 seconds. Then this routine was used in a program to show that 314,159,265 and 217,828,183 are relatively prime. Finally, a program was written to find the largest divisor of integers, by testing all numbers from a starting point down as possible divisors, with repeated subtraction used for division. This program was comprised of seventeen instructions and it was written by Kilburn. (A nineteen instruction amended version of it has been published.) It ran successfully on June 21, 1948, first on small integers. Within a few days it was run on 2³⁰-1 by trying every number from 2¹⁸-1 down. It ran for 52 minutes, executing 3.5 million accesses to memory and 2.1 million instructions, and produced the correct answer. The SSEM developed into the Manchester_Mark_I, which led to the Ferranti_Mark_I, the world's first commercially available general-purpose computer. At around the same time EDSAC was being developed at the University_of_Cambridge_Mathematical_Laboratory. A working replica of the SSEM was created in 1998 to celebrate the fiftieth anniversary of its first program. This is on display at the Museum_of_Science_and_Industry_in_Manchester. Reference: *''A History of Computing Technology'', by Michael A. Williams, IEEE Computer Society Press, 1997. *''Annals of the History of Computing'', Vol 27, No. 3, Jul-Sep 2005, IEEE Computer Society ==External links== *Computer 50 *Computer Conservation Society Category:One-of-a-kind_computers Category:Early_computers Pl:Small-Scale_Experimental_Machine