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Liam Proven's thoughts on IT, especially FOSS
How to tell a mainframe from a minicomputer from a micro
How to tell a mainframe from a minicomputer from a micro
Oct. 6th, 2022 10:21 pm
liam_on_linux: (Default)
[personal profile] liam_on_linux
Mainframes: the first style of computer. Primarily designed as a
batch-oriented system, meaning that they are not directly
interactive. Jobs are queued up, run without interaction, results
stored, and then the next job processed. Later models added
interactivity as a secondary feature, usually like most mainframe I/O
handled by intelligent peripherals which in effect are networked to
the main processors. So, the terminal, on its own, shows a form and
then handles all user input as the user completes the form, without
communicating with the host at all. Then, when the user signals that
the form is complete, the entire contents, maybe many pages, are sent
as a single message to the host.
Separate processors in storage, in terminals, in networking
controllers, in printers, in everything. Typically the machine cannot
actually drive any output or input directly (e.g. mouse movements, or
keystrokes, or anything): peripherals do that, collect and encode the
results, and send them over a network. So as someone else commented,
a mainframe isn't really a computer, it's a whole cluster of
closely-coupled computers, many with dedicated functionality. Quite
possibly all implemented with different architectures, instruction
sets, programming languages, bit widths, everything.
Here's an article I wrote about a decade back about how IBM added the
new facility of "time sharing" -- i.e. multiple users on terminals,
all interacting with the host at the same time -- by developing the
first hypervisor and running 1 OS per user in VMs, because the IBM
OSes of the time simply could not handle concepts like "terminal
sessions".
Minicomputer: the 2nd main style of computer. Smaller, cheaper, so
affordable for a company department to own one, while mainframes were
and are mostly leased to whole corporations. Typically 1 CPU in early
ones, implemented as a whole card cage full of multiple boards: maybe
a few boards with registers, one with an adder, etc. The "CPU" is a
cabinet with thousands of chips in it.
Hallmarks: large size; inherently multitasking, so that multiple
users can share the machine, accessing it via dumb terminals on
serial lines. User presses a key, the keystroke is sent over the
wire, the host displays it. Little to no networking. One processor,
maybe several disk or tape drives, also dumb and controlled by the
CPU. No display on the host. No keyboard or other user input on the
host. All interaction is via terminals. But because they were
multiuser, even the early primitive ones had fairly smart OSes which
could handle multiple user accounts and so on.
Gradually acquired networking and so on, but later.
In some classic designs, like some DEC PDPs, adding new hardware
actually adds new instructions to the processor's instruction set.
Wildly variable and diverse architectures. Word lengths of 8 bit, 9
bit, 12 bit, 18 bit, 24 bit, 32 bit, 36 bit and others. Manufacturers
often had multiple incompatible ranges and maybe several different
OSes per model range, depending on the task wanted, so offering
dozens of totally different and incompatible OSes across half a dozen
models.
Microcomputer: the simplest category. The entire processor is
implemented on a single silicon chip, a microprocessor. Early
machines very small and simple, driven by 1 terminal with 1 user. No
multitasking, no file or other resource sharing, no networking, no
communications except typically 1 terminal and maybe a printer.
Instead of 1 computer per department, 1 computer per person.
Facilities added by standardised expansion cards.
This is the era of standardisation and commoditisation. Due largely
to microcomputers, things like the size of bytes, their encoding and
so on were fixed. 8 bits to a byte, ASCII coding, etc.
Gradually grew larger: 16-bit, then 32-bit, etc. In the early '80s
gained onboard ROM typically with a BASIC interpreter, on-board
graphics and later sound. Mid-'80s, went to 16-bit with multicolour
graphics (256+ colours), stereo sound. Lots of incompatible designs,
but usually 1 OS per company, used for everything. All single-user
boxes.
These outperformed most minis and minis died out. Some minis gained a
hi-res graphical display and turned into single-user deskside
"workstations", keeping their multitasking OS, usually a UNIX by this
point. Prices remained at an order of magnitude more than PCs, and
processors were proprietary, closely-guarded secrets, and sometimes
still implemented across multiple discrete chips. Gradually these got
integrated into single chip devices but they usually weren't very
performance competitive and got displaced by RISC processors, built
to run compiled C quickly.
In the '90s, generalising wildly, networking became common, and
32-bit designs became affordable. Most of the 16-bit machines died
out and the industry standardised on MS Windows and classic MacOS. As
internet connections became common in the late '90s, multitasking and
a GUI were expected along with multimedia support.
Apple bought NeXT, abandoned its proprietary OS and switched to a
UNIX.
Microsoft headhunted DEC's team from the cancelled MICA project,
merged it with the Portable OS/2 project, and got them to finish OS/2
NT, later Windows NT, on the N-Ten CPU, the Intel i860, a RISC chip,
then on MIPS, and later on x86-32 and other CPUs. This was the first
credible commercial microcomputer OS that could be both a client and
a server, and ultimately killed off all the proprietary
dedicated-server OSes, of which the biggest was Novell Netware.
That is a vastly overlong answer but it's late and I'm just
braindumping.
Mainframe: big tightly-clustered bunch of smart devices, flying in
close formation. Primary role, batch driven computing,
non-interactive; interactivity bolted on later.
Mini: departmental shared computer with dumb terminals and dumb
peripherals, interactive and multitasking from the start. Most
text-only, with interactive command-line interfaces -- "shells" --
and multiprogramming or multitasking OSes. Few had batch
capabilities; no graphics, no direct I/O, maybe rare graphical
terminals for niche uses. Origins of the systems that inspired CP/M,
MS-DOS, VMS, UNIX, and NT.
Micro: single-chip CPU, single-user machines, often with graphics and
sound early on. Later gained GUIs, then later than that networking,
and evolved to be servers as well.
If the machine can control and be controlled by a screen and keyboard
plugged into the CPU, it's a micro. If its CPU family has always been
a single chip from the start, it's a micro. If it boots into some
kind of firmware OS loader, it's probably a micro. The lines between
micros and UNIX workstations are a bit blurred.
Tags:
* mainframe,
* microcomputer,
* minicomputer
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Date: 2022-10-06 08:50 pm (UTC)
history_monk: (Default)
From: [personal profile] history_monk
Workstations are now dead. They were outcompeted by microcomputers
with faster processors (Intel/AMD) and better graphics (Nvidia/ATI).
Another way to view it is that desktop microcomputers morphed into
workstations.
So today's workstations run Windows NT (Windows 10 or 11), with Linux
and macOS as alternatives that are strongest in specific sub-markets.
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Date: 2022-10-07 04:17 pm (UTC)
liam_on_linux: (Default)
From: [personal profile] liam_on_linux
Indeed so.
Minis, arguably, evolved into workstations, and then were replaced my
micros that evolved into very slightly different, and rather more
standard, workstations.
It's a sort of convergent evolution.
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Date: 2022-10-07 07:49 pm (UTC)
From: [personal profile] cks
Many of the famous Unix machines of the 1980s and 1990s confuse this
taxonomy. For example, Sun Microsystems implemented its machines
using microprocessors (first Motorola, then SPARC), and sold the same
core designs as both workstations (graphical display and local
keyboard and mouse) and servers (multiple serial lines, serial
console that you weren't expected to use, etc). In some cases they
sold physical machines that could be both at once.
Silicon Graphics turns out to have an even more interesting history.
Their very first products were terminals for what were definitely
minicomputers (eg, VAXes), but they rapidly evolved into workstations
and servers based around microprocessors in the same approach as Sun
had.
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Date: 2022-10-07 09:25 pm (UTC)
liam_on_linux: (Default)
From: [personal profile] liam_on_linux
Interesting. OK, fair point.
How would you revise the taxonomy then? Most workstations were
micros, but a few were derived from minicomputer tech? Or the other
way round?
As [personal profile] history_monk says above, a valid interpretation
is that high-end PCs basically evolved into things that were
workstations in all but ancestry.
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Date: 2022-10-07 10:11 pm (UTC)
From: [personal profile] cks
I think I'd say that mainframe, minicomputers, and micros started out
as a division of all of technology, form factor, and usage, but this
joint division was only valid through the 1970s when single-chip CPUs
were not very good. As single-chip CPUs improved their capabilities
through the 1980s, everything came to be built with them, erasing the
technology distinction and leaving behind only an increasingly
blurred usage and form factor distinction. Effectively by the late
1980s minicomputers as such were mostly dead, replaced almost
entirely with 'servers' (implemented almost entirely with single-chip
CPUs), and CPUs had gotten so capable that there were no classical
micros left.
This replacement included classical minicomputer companies like DEC.
DEC still sold server VAXes, but they were increasingly implemented
with single-chip VAX CPUs, not with discreet components (although I
think they remained physically big). And these single-chip VAX CPUs
let DEC make VAX workstations that had the small form factor of Sun,
SGI, and so on workstations, a form factor that wasn't possible with
'minicomputer' discreet components. At one point we had both DEC
Ultrix VAX and MIPS workstations, and you mostly couldn't tell them
apart from the outside.
In the 1990s, the rising tide of x86 capability and volume erased any
remaining hardware advantage that Unix vendors had, first in
workstation size machines and then later in server ones. By the end
of the 1990s, x86 desktop machines were objectively better and
cheaper than Unix vendor workstations for anything except expensive,
high end graphics work. In 1999, we evaluated replacements for 1996
era SGI Indys and x86 desktops running Linux crushed the competition
(to a degree that was sad to see), even with Sun's workstations of
the era using a lot of PC hardware interfaces and hardware. And
obviously in the modern era the 'minicomputer' form factor is pretty
much dead because you can get a very powerful machine into the small
'1U' rack form factor.
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Date: 2022-10-07 10:20 pm (UTC)
From: [personal profile] cks
As an illustration of the blurring of the form factors and the
implementation, a 1984 Amiga A1000 is quite physically similar to Sun
workstations such as the Sun 2/50. Both have a central 'pizza box'
core unit, with a keyboard, mouse, and display plugged into them. The
Sun is more expensive and more capable (and has a better display),
but both are single-chip CPU machines (and with Motorola 68xxx CPUs,
although different ones). The Amiga is sort of in the 'micro' camp
(and later Amiga designs would shift back toward classical micro form
factors), while the Sun 2/50 is definitely a workstation.
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