English: Operating en:IBM 1620 computer (Model 1 Level H) at the Computer History Museum. I took this photo and edited it.

This computer was restored by a team of volunteers over a two year period after having sat idle for over 15 years. This machine was originally built in about 1964 (based on part datecodes). The only severe problem encountered was that the en:core memory is completely inoperative due to corrosion (caused by incorrect solder flux when the machine was built) and had to be replaced with SRAM chips. As an illustration of the change in price of computers; the original core memory (60,000 decimal digits) cost about $90,000 in 1964 (this would be over $500,000 in 2000 dollars due to inflation), we replaced this with 1MByte of SRAM totaling $40 and used only about 4.25% of this memory (the rest is unused due to the decimal based addressing of the 1620 and only 6 bits of each byte are used due to the decimal data format of the 1620). In other words, $90,000 of core was effectively replaced by less than $2 of SRAM storage (with the remaining $38 dumped as waste)... memory is almost free now. Less than a dozen transistors were replaced (of the about 5,000 in the computer) to repair the electronics; except for one, all were original IBM transistors from the period.

I was a member of this team.

Photo by RTC.