Monrobot XI
[6] However, in 2021, a collector in North Carolina revealed that he owns half a dozen complete Monrobots, along with ancillary items, manuals, and tape programs.
Even at the time it was introduced, it was not rare for electronic digital computers to use magnetic-core memory for RAM; the price (per bit) of which would eventually fall[8] from over $1 in the early 1950s to about $0.20 by the mid-1960s.
Thus, physically it bore some resemblance to the theoretical Turing machine of computer science, albeit with the idealized data tape being of finite length and joined end-to-end, and then finally replicated 32 times in parallel.
[citation needed] The long latency of memory access, which followed from exclusive reliance on a macroscopic moving part, made the Monrobot XI operate very slowly,[vague] despite the use of non-mechanical electronics for logical functions.
The Monorobot XI might best be thought of as a modernized (solid-state), low cost version of the IBM 650, which had been the world's first mass-produced computer.
[10]: 35 The Monrobot XI's rewritable, persistent ("nonvolatile") memory consisted of a rotating magnetic drum storing 1,024 words of 32 bits, each of which could record either a single integer, or a pair of zero- or single-address instructions.
A perforated metal screen at the side or back of the cabinet could be removed, affording a direct view of the reddish-brown iron oxide-coated drum, surrounded by multiple stationary magnetic read/write heads.
[1] This astoundingly small active component count (383) – little more than in the Manchester Baby (250), the world's first stored-program Turing-complete computer produced in 1948 – contrasts starkly with the many billions of transistors present in modern microprocessors used in handheld cellphones.
The low component count was a key benefit of its slow electromechanical memory, which exploited synchronization with a spinning drum's rotational angle, rather than adding electronic switches, to accomplish multiplexing of bits.
Construction used pluggable printed circuit boards, allowing partial replacement of a defective module as the principal means of repair.
This continued an electronics construction tradition pioneered when the relatively unreliable vacuum tubes had been used as active components, prior to the advance to more modern transistors used in the Monorobot XI.
The arithmetic unit performed computations using the binary number system, with machine-language programming using hexadecimal digits (called "sexadecimal" in the programmer's manual),[10]: 3 and employing the unusual character set of {0,1,2,3,4,5,6,7,8,9,S,T,U,V,W,X}.
The longer durations reflected the mean latency (6 ms) of accessing a persistent memory location, rather than a register, to retrieve the second of the two operands.
An option was a heavy-duty Flexowriter, which rattled and shook the entire machine, especially when the heavy carriage forcefully returned to the beginning of a new print line.
