The IBM 4020 Military Computer – Tracking Missiles with 6-Bit Bytes | Hacker News Reader

The IBM 4020 Military Computer – Tracking Missiles with 6-Bit Bytes

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The Wikipedia page for the IBM 4020[1] points to IBM's fairly detailed, 33-page description of this machine.[2]

[1] https://en.wikipedia.org/wiki/IBM_4020_Military_Computer

[2] http://bitsavers.org/pdf/ibm/4020/4020_Military_Computer_Gen... [PDF]

On the topic of odd bit computers I worked with a Harris H100 24-bit mini-computer until 2011 in military aviation. As mentioned elsewhere some old paradigms are still present in these arenas.

There isn’t much left out there about that machine anymore unfortunately. Every boot required inputting a specific set of digits into the registers via the front panels switches to bootstrap the physical storage device, which had been upgraded to a 3.5” HDD at some point.

i like 6-bit bytes because they can be represented by hexagram unicode, like so: ䷄䷅䷆䷇䷈䷉䷊䷋䷌䷍䷎

You can use braille for 8-bit bytes. Unlike hexagrams, they're even in order.

⡙⡯⡵⠠⡣⡡⡮⠠⡵⡳⡥⠠⡢⡲⡡⡩⡬⡬⡥⠠⡦⡯⡲⠠⠸⠭⡢⡩⡴⠠⡢⡹⡴⡥⡳⠮⠠⡕⡮⡬⡩⡫⡥⠠⡨⡥⡸⡡⡧⡲⡡⡭⡳⠬⠠⡴⡨⡥⡹⠧⡲⡥⠠⡥⡶⡥⡮⠠⡩⡮⠠⡯⡲⡤⡥⡲⠮

I’ve never seen those characters before. Have you got any more recommended references on that subject?

https://en.wikipedia.org/wiki/I_Ching#Hexagrams

The aricle deals more with the 6-Bit Byte than the missile tracking.

Shouldn’t that be called a word? Or are they afraid the youngsters won’t get it and thus won’t click?

Byte only became standardized as 8-bits later on, it had various numbers of bits depending on the particular architecture historically. Per the article, this particular system had 48-bit words, so 8x6-bit bytes.

A byte was the number of bits a particular system used to represent a character - 6 bits was common in the 1960s. 36 bit words were also common then, 6 bytes and handily a ‘sweet spot’ for representing a floating point number.

https://en.m.wikipedia.org/wiki/Word_(computer_architecture)

Just yesterday I was working with a data storage system that uses 6 bit bytes organized into 12 bit words.

Haha, this is one of many 6 bit byte systems still used in aviation every day.

I think you’re confusing bytes and words. A word is multiple bytes. In this case 8 bytes.

Yes and no - the term was used early to describe the native register size of a microprocessor. Later on, when microprocessors began offering instructions that could deal with varying data size, it became one of several terms used, e.g. the Motorola 680x0 which uses the terms bytes (8 bits), words (16 bits) and longwords (32 bits).

This computer had 48-bit words, composed of 8 6-bit bytes.

Contrary to what the author suggests, 8 bits / 1 byte is the most common specification since 45 years now, not just "the last 30 years or so". MOS 6502, Z80, Motorola 6800/6809/680x0 and Intel 8080 were the most popular CPUs of the 70s and most of the 1980s.

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