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Royal McBee RPC-4000

Overview

The RPC-4000 (Royal Precision Computer 4000) was a transistorized drum computer announced by Librascope (General Precision) in 1960 as a more powerful successor to the LGP-30. Sold and serviced by Royal Precision (the joint venture between General Precision and Royal McBee), it was structurally similar to the LGP-30 – still a bit-serial machine built around a magnetic drum – but transistorized with significantly more memory and a dual-address instruction scheme. Commercially it was disappointing: only 104 units were reported in operation by 1964 (per the BRL market report), far fewer than the LGP-30’s ~500 units.

Key People

  • The design team at Librascope/General Precision
  • Mel Kaye – a legendary RPC-4000 programmer whose exploits were immortalized in “The Story of Mel” (recounted by Ed Nather), a celebrated piece of computer folklore about hand-optimized machine code

Technical Specifications

Parameter Value
Word size 32 bits
Memory type Magnetic drum
Memory capacity 8008 words total
Drum organization 123 tracks x 64 sectors per track
Main memory 7872 words (average access 8.5 ms)
Dual-access storage 128 words (secondary access 4–6 ms)
High-speed storage 8 words on track 127 (average access ~1 ms)
Drum rotation speed 3600 RPM
Clock speed ~125 kHz
Word time 0.26 ms (260 microseconds)
Operating speed 230000 operations per minute (~3833 operations/second)
Technology Transistorized (500 transistors, 4500 diodes)
Addressing Dual-address (one-plus-one): each instruction contains operation code + operand address + next instruction address
Registers 4: upper accumulator, lower accumulator, command register, index register
Extended accumulator Lower accumulator expandable to 8 one-word accumulators under program control
Instruction set 32 commands (codes 00–31)
Weight 500 pounds (230 kg)
Power ~1 kW; standard 110–120V outlets; no air conditioning required
Price $87500 (~$952000 in 2025 dollars)

I/O Equipment

Device Speed
Model 4430 Reader/Punch 60 chars/sec read, 30 chars/sec punch
Model 4480 Tape Typewriter 10 chars/sec
Model 4410 Photo-Electric Reader 500 chars/sec
Model 4440 High-Speed Punch 300 chars/sec

Key Innovations

Dual-Address Instruction Format

Unlike the LGP-30’s single-address format, each RPC-4000 instruction contained two addresses: one for the operand and one specifying where on the drum the next instruction was located. This effectively automated part of the “optimum programming” technique that LGP-30 programmers had to manage manually, reducing the performance penalty of drum latency.

Fast Data Tracks

The drum included special fast-access tracks: 128 words of dual-access storage (4–6 ms access) and 8 words of high-speed storage (~1 ms access), providing a limited form of fast working memory.

Extended Accumulator

The lower accumulator could be configured as eight separate one-word accumulators under program control, providing flexibility for complex calculations.

Optimizing Assembler

An assembler that automatically placed instructions on the drum for optimal access timing.

Comparison with LGP-30

Feature LGP-30 (1956) RPC-4000 (1960)
Technology 113 vacuum tubes + 1450 diodes 500 transistors + 4500 diodes
Memory 4096 words 8008 words
Addressing Single-address Dual-address (one-plus-one)
Instructions 16 32
Weight 800 lbs 500 lbs
Power 1500W ~1000W
Price $47000 $87500
Drum speed 3700 RPM 3600 RPM
Clock 120 kHz ~125 kHz

Edward Lorenz Connection

Edward Lorenz’s famous chaos discovery was made on the LGP-30, not the RPC-4000. However, the RPC-4000 was a natural upgrade path for LGP-30 users, and Lorenz is sometimes described as having later used an RPC-4000 at MIT, though the precise timing of any such upgrade is not well documented in available sources. (Some accounts describe the chaos discovery computer simply as a “Royal McBee” without specifying the exact model.)

The Story of Mel

The RPC-4000 achieved lasting fame through “The Story of Mel”, a piece of computer folklore written by Ed Nather and posted to Usenet on May 21, 1983. It tells the story of Mel Kaye, a Real Programmer at Librascope who wrote hand-optimized machine code for the RPC-4000 that was so perfectly tuned to the drum timing that conventional programmers could not understand or improve it. The story celebrates the art of low-level optimization and became one of the most widely shared pieces of computing lore.

Key detail from the story: Mel exploited the RPC-4000’s dual-address instruction format and the drum’s physical timing so completely that his code ran at maximum speed without an optimizing assembler.

The “Auto-Beatnik” Program

The RPC-4000 also gained public attention through the “Auto-Beatnik” program, developed by the Librascope research team, which composed poetry algorithmically. The program was featured in Horizon magazine and LIFE magazine (March 3, 1961).

Commercial Performance

The RPC-4000 was a commercial disappointment. By 1964, only 104 units were in operation (compared to the LGP-30’s ~500). It competed unsuccessfully against:

  • IBM 1401 (2800 units installed by 1961)
  • DEC PDP-1 (53 units, but pioneering interactive computing)
  • Emerging machines with ferrite core memory offering random access, which made drum-based machines obsolete

The fundamental problem was that core memory replaced drums as the standard for main storage, eliminating the latency penalties that the RPC-4000’s clever dual-address scheme was designed to mitigate.

Notable Anecdotes

  • The RPC-4000’s dual-address scheme was simultaneously its greatest innovation and its obsolescence marker – it solved a problem (drum latency) that core memory eliminated entirely.
  • Mel Kaye’s programming exploits on the RPC-4000 made it perhaps the most famous drum computer in folklore, even though the LGP-30 sold four times as many units.
  • The Auto-Beatnik poetry generator appearing in LIFE magazine in 1961 was an early example of “AI” capturing public imagination.

Current Status

Only one original RPC-4000 is known to survive, located at the Computer History Museum in Mountain View, California, in non-working condition and in storage.

No original RPC-4000 software is readily available online. Known leads include Paul Pierce’s Control Data paper tape library (in poor condition) and digitized magnetic tapes from Munich University’s observatory system.

A detailed hardware replica project exists at e-basteln.de.

Sources