http://www.righto.com/2019/10/how-special-register-groups-invaded.html
Half a century ago, the puzzling phrase "special register groups" started showing up in definitions of "CPU", and it is still there. In this blog post, I uncover how special register groups went from an obscure feature in the Honeywell 800 mainframe to appearing in the Washington Post.
While researching old computers, I found a strange definition of "Central Processing Unit" that keeps appearing in different sources. From a book reprinted in 2017:1
"Central Processor Unit (CPU)—Part of a computer system which contains the main storage, arithmetic unit and special register groups. It performs arithmetic operations, controls instruction processing and provides timing signals."
At first glance, this definition seems okay, but a few moments thought reveals some problems. Storage is not part of the CPU. But more puzzling, what are special register groups? A CPU has registers, but "special register groups" is not a normal phrase.
It turns out that this definition has been used extensively for over half a century, even though it doesn't make sense, copied and modified from one source to another. Special register groups were a feature in the Honeywell 800 mainframe computer, introduced in 1959. Although this computer is long-forgotten, its impact inexplicably remains in many glossaries. The Honeywell 800 allowed eight programs to run on a single processor, switching between programs after every instruction.3 To support this, each program had a "special register group" in hardware, its own separate group of 32 registers (program counter, general-purpose registers, index registers, etc.).
(Score: 3, Informative) by Mojibake Tengu on Thursday October 24 2019, @06:05PM (2 children)
Special registers are such as Channel Control Word (CCW) or Channel Status Word (CSW) registers on mainframe processors. Often, they could be seen on the panel together with arithmetic registers and addresses. There are plenty of such, and they have a good use in virtualization too. On petty technologies like microprocessors and contraptions today known as CPU, they still exist as addressable registers bound to generic I/O ports for specific devices, known as controllers. However, proper generic channel architecture was lost to post-modern age.
Respect Authorities. Know your social status. Woke responsibly.
(Score: -1, Flamebait) by Anonymous Coward on Thursday October 24 2019, @06:17PM (1 child)
Ignore the primary sources while pulling a bullshit explaination out of your ass.
typical..
(Score: 2) by c0lo on Friday October 25 2019, @12:06AM
There still a valid point there, even if it's only a tangent one: the fact that the "primary sources" are no longer accurate for the majority of current CPU-es (thus the definition is not valid in the general sense), it doesn't mean [wikipedia.org] that the use of "special registers" cease to exist.
And that bears an Informative value.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford