Editing IBM 1620 (section)

===Memory===
The IBM 1620 Model I was a variable "[[word (data type)|word]]" length decimal ([[binary-coded decimal|BCD]]) computer using [[core memory]]. The Model I core could hold 20,000 decimal digits with each digit stored in six bits.<ref>"...  arranged as a 100x100 array of 12-bit locations, each holding 2 decimal digits. (Each decimal digit was encoded in binary using 6 bits.)"</ref><ref name=ChulaStat/> More memory could be added with the IBM 1623 Storage Unit, Model 1 which held 40,000 digits, or the 1623 Model 2 which held 60,000.<ref name=IBM.intro59/>

The Model II deployed the IBM 1625 core-storage memory unit,<ref>{{cite book
|chapter-url=https://link.springer.com/content/pdf/10.1007/978-3-642-03757-3_16.pdf |archive-url=https://web.archive.org/web/20171222052358/https://link.springer.com/content/pdf/10.1007/978-3-642-03757-3_16.pdf |archive-date=2017-12-22 |url-status=live   |author=Oddur Benediktsson  
|title=History of Nordic Computing 2  
|volume=303  
|pages=149–155  
|doi=10.1007/978-3-642-03757-3_16  
|series=IFIP Advances in Information and Communication Technology  
|year=2009  
|isbn=978-3-642-03756-6  
|chapter=FORTRAN II – the First Computer Language Used at the University of Iceland  
}}</ref><ref name=NordBook>{{cite book
|title=History of Nordic Computing 2: Second IFIP WG 9.7 Conference
|url=https://books.google.com/books?isbn=3642037577  |isbn=978-3642037573  |date=2009
|author1=John Impagliazzo   |author2=Timo Järvi  |author3=Petri Paju}}</ref> whose memory cycle time was halved by using faster cores, compared to the Model I's (internal or 1623 memory unit): to 10&nbsp;μs (i.e., the cycle speed was raised to 100&nbsp;kHz).

While the five-digit addresses of either model could have addressed 100,000 decimal digits, no machine larger than 60,000 decimal digits was ever marketed.<ref>Although there are descriptions of a single 100,000-digit machine, designed in the late 1960s, using heavily modified hardware.</ref>
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