[Cryptography] Why full-fledged quantum computers might always be five years away

[Steven M. Bellovin]

On 2 Aug 2026, at 21:29, Jerry Leichter wrote:

> What is a digital computer?
>
> The IBM 1620 - late 1960's - was missing all the following features that someone today would likely list if asked to define a digital computer:
>
> - No binary arithmetic - the machine worked in decimal.  Yes, the internal gates were binary but that was essentially invisible in the device as presented to a user.
> - No hardware floating support
> - No interrupt mechanism
> - No separate user/supervisor mode
> - No support for graphics
> - No support for a mouse
> - No support for a network connection
> - No time/date reference - the machine (and in fact even machines built years later) had no internal way to determine the current date and time; you entered that at boot
> - No real-time clock.  The 1620's operating system didn't ask you for the current date and time as it even lacked a mechanism to increment the time at regular intervals to create a clock.
>
> And yet the 1620 was described as a digital computer, and was used for the kinds of things we use digital computers for to this day.  It even came with a FORTRAN compiler.
>
Well, early 1960s. (Wikipedia claims 1959 introduction.) But you missed the biggie: it couldn't do arithmetic on its own. Rather, there were tables in RAM giving the results of addition and subtraction operations.


        --Steve Bellovin, https://www.cs.columbia.edu/~smb