Demystifying The Computer

Optional Rules for GURPS Computers

by Michael J. Daumen

Though GURPS campaigns can range far into the future, in game terms they have progressed little since the advent of the personal computers of the late 1900s. Existing rules simulate a wide variety of computing devices with only a few variables: weight, volume, power, cost, and Complexity. All GURPS computers use today's technology; however, computers didn't work that way in the past, and they won't always do so in the future. GURPS Steampunk addresses machines that might have existed a century ago, offering some variations to traditional models. But the computers of tomorrow have been given little attention.

Alternate technologies for computers have many applications in modern-day and futuristic GURPS settings. Cutting-edge processors may power the advanced labs of a supers campaign, or be the target of corporate or government espionage. They may be the prerequisite for the self-aware AIs of the cyberpunk genre. A starfaring civilization relies on computers for astrogation and the storage of a galaxy of scientific knowledge. The future even holds a place for the analytical engines of GURPS Steampunk on planets that have regressed from galactic technology (as in Traveller's Long Night), or have developed along alternate scientific paths.

GURPS rules assume that a computer is electronic -- data is stored and manipulated through electrical control of binary switches and gates. In the last fifty years, successive generations of computers have become smaller, faster, and cheaper. But there are physical and chemical limits to the size and speed of microchips; as the twenty-first century begins these barriers are in sight. Advanced technology books in the GURPS system do not address the fundamental limits of current machines or the options available tomorrow.

The other major disadvantage of electronic computers is their vulnerability to electromagnetic interference, whether from a nuclear explosion or eavesdropping. In our world, most people use computers without this concern, but in some GURPS futures (especially those involving space combat and post-apocalyptic radiation) it is an important consideration. Current rules allow computers to be hardened against pulse damage at an increase in weight and cost. Machines from both the past and the future have varying degrees of protection from this problem.

GMs who want personal or vehicular computers with more detail can follow the design process outlined below. There are no new variables to add, just a description of the technology used to make computations.

  1. Select designing TL. Computers as most readers know them were envisioned in the mid-19th Century and attained familiar forms in the late 20th Century. However, mechanical calculators have existed for centuries. TL determines which technologies are available, and affects the Complexity of the computers that use them. Mechanical Computers can be built in any period, but reach their peak at TL5 and are outperformed by later technology. Vacuum tubes appear in TL6 and obsolete by TL7. Optical computers are perfected in TL8 and quantum devices in TL10. Neither advanced technology becomes obsolete at higher TLs.
  2. Select computer size. The weight, cost, volume, and power requirements of computers restrict their uses in vehicles and campaigns. Most of the sizes and specifications in Table 1 are "standard" sizes from G:VE61. The Tiny and Megaframe sizes appear in G:STM85; the latter is too unwieldy at high TLs! Many GURPS rulebooks have figures which differ slightly; consider this table as a guideline when confronted with inconsistencies. Once a GM knows a computer's size and TL, its Complexity is easily calculated.

    Table 1: Computer Parameters



    Weight (lbs.)


    Volume (cf)


    Cost ($)


    Power (kW)



    Tiny / Tablet











    Personal / Briefcase


































































    * Can runs independently on power cells (see p. S65)
    ** Unavailable after (early) TL7. Cannot be built with optical or quantum technology.

  1. Select computing technology. The specifications in Table 1 are based on electronic computers used in the present day. Table 2 shows how other technologies will affect the specifications of the computer. Alternate technologies have certain features built in to their computers.

    By TL7, the two primitive technologies are totally supplanted by electronic machines. This "early" obsolescence cuts off the cost and size benefits of designing machines at higher-than-minimum TLs. Mechanical computers built after TL6 and vacuum tube computers built after early TL7 are no better than their ancestors -- they are merely historical curiosities. In other circumstances, halve (or quarter) the cost, volume and weight of computers built at one (or two) TLs higher than a technology's minimum TL.

    GMs who desire even more detail can represent the wide variety of electronic computers by splitting TL7 into "early" (transistors), "middle" (integrated circuitry), and "late" (microchips) TL7. Multiply the parameters of early TL7 devices by 1.25 and late TL7 devices by 0.75 to reflect these developments.

  2. Table 2: Computing Method





    Vacuum Tube





    Weight Multiplier









    Volume Multiplier









    Power Multiplier









    Cost Multiplier











    Dedicated**; Hardened


    Dedicated; Hardened


    EMP Resistant***


    EMP Resistant***

    Minimum TL









    Maximum TL




    early 7





    * TL5 is optimum technology; see GURPS: Steampunk for mechanical devices at lower TLs.
    ** If not dedicated, reduce Complexity by 2.
    *** Resistant to pulse damage but not TEMPEST interception (but can be for double weight, volume & cost)

  1. Select terminals and special features. Computers be additionally made Compact, Dumb or Genius, Dedicated, or High Capacity (as outlined on p. VE61). Any computer made at TL6- is Dedicated at no change in stats; otherwise reduce Complexity by 2. Electronic computers can be hardened per the normal rules.

    The addition and use of terminals is unchanged -- see p. VE62.

  2. Complete description. The only additional peiece of information necessary to record is the designing technology. A useful format is:

             [TL] Name: [features] [technology] [size], weight, volume, power, cost, Complexity.

    It is not necessary to record negligible power requirements. If a TL6- machine is not dedicated, note this in parenthesis after the Complexity.

Example: A GM wants to create wrist-mounted computers for scientific use. The base size is Tiny/Tablet and the designing TL is 10. A design using optical technology would cost $500 times cost multiplier (7.5) and divided by 1/4 for two increases in TL ($937.50), weigh 1 lb., and have a complexity of (10-7=) 3. While its components will withstand the radiation from a nuclear blast, the handcomputers will still be subject to remote surveillance.

         TL10 Wristcomp: Optical Tiny/Tablet, 1lb., 0.02cf, $937.50, Complexity 3.

It's a bit more work to convert GURPS Space or GURPS Traveller ship modules. Replace the given computer system with its counterpart, then recompute cost, weight, and volume. Ignore hull space changes of less than 0.25 -- round up or down to the nearest half-space.

Example: The captain of the Melisande needs to replace his ship's combat-damaged TL8 mainframe. Unfortunately, his hasty retreat has brought him to a TL6 planet. Rather than staying stranded, he decides to replace the old electronic system with a vacuum tube clunker. To run his astrogation program of Complexity 3 he opts for a vacuum tube macroframe computer with genius capability. It will weigh 4,000 lbs., take up 400 cf of space, and cost $10.5 million of his high-tech cargo. The modification increases the weight of the small bridge from 2.9 to 4.5 tons and the hull spaces to 1.5. He can take some consolation that his system is still hardened with no extra cost. Complexity will be TL6 - 2 (for macroframe size) - 2 (he wants to run multiple programs, so takes the penalty for an undedicated system) + 1 (for the genius option) = 3, enough to run his hyperspace calculations and one other program. While the repairs are proceeding he'll have to hire native programmers for new software, and add tubewatching duties to the crew schedule!

         TL6 Astro-calculator: Genius vacuum tube mainframe, 2Tns, 400cf, $10,500,000, 40kW, Complexity 3 (not dedicated).

The computer technologies envisioned by this article are explained below:

Article publication date: October 19, 2001

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