When I was in college, computers used core memory that was made up of small doughnut-shaped ferrite cores strung like beads on an abacus … each doughnut held one bit. A friend of mine took a 7.76 gigapixel photo of a one kilobit memory unit (1,024 bits or 128 bytes). On his web page, you can zoom and pan to see the details up close … amazing technology for its time 
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What was the actual size?
It looks as if it was handmade/soldered!
Simply amazing.
@TDahl : did the Marslander had any of these?
@MikeWayzovski The Viking '75 Mars landers did not have core memory, but they did have something similar - plated-wire memory - in the main Guidance Control and Sequencing Computer (GCSC). According to NASA Special Publication SP-4212 On Mars: Exploration of the Red Planet 1958-1978, a contemporaneous history written about the Viking program, the GCSC consisted of two Honeywell HDC 402 processors, each with 18K words (24-bits per word) of 2-mil plated-wire memory. Here is an overall view of the GCSC unit:
And here is a scan of page 257 from the above book, showing a bit of the plated-wire memory:
These computers represented a difficult design and manufacturing challenge for the program, in part because the computer (along with the entire lander) was subjected to ~240 degree F heat sterilization for some 40 hours prior to launch (with the goal of preventing forward contamination of Mars by Earth spores or microbes).
No other Mars surface-bound spacecraft has been entirely sterilized. All subsequent landers and rovers sent to Mars have only been sterilized in certain critical parts; the bulk of those spacecraft have been mechanically and chemically cleaned to a vey high degree but not truly sterilized. Heat-sterilizing (chosen as the most effective and practical method) was a huge challenge for the Viking program.
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There is a measuring tool included (lower right hand corner). It would seem that the “doughnuts” are about 1.38 mm.
Very cool @jimhami42 thank you for posting this.
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