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87 votes
Accepted

How much better was DEC Alpha than contemporaneous x86?

The Alpha team set out to create a high-performance architecture, planned to last for 25 years and allow for 1000-performance increase over those 25 years. So they placed some long bets, starting with ...
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77 votes
Accepted

Why did 1950s-60s computers have such wide words?

And if you go back further, e.g. to the ENIAC, you'll see a word size of 40 bits. And if you go back even further, to mechanical calculators, you'll see word sizes determined by the number of decimal ...
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63 votes
Accepted

How should we interpret Dave Cutler's criticism of Unix?

The I/O model on "Cutler systems" – RSX-11M, VAX/VMS, Windows NT – is an asynchronous packet-driven I/O model, rather than the fundamentally synchronous I/O model of Unix. At its core, you ...
  • 28.5k
58 votes

How much better was DEC Alpha than contemporaneous x86?

Stephen Kitt has done what seems to me an excellent job of outlining features and when they were introduced. I'll take a slightly different tack, instead picking a single point in time, and pointing ...
  • 3,892
42 votes
Accepted

Is this a real system? Which one?

TL;DR: Is this a real system? Which one? No, it's most likely not a specific machine but a setup to look contemporary. In Detail: I've come across several computers. (They all look extremely ...
  • 177k
38 votes

Why did DEC develop Alpha instead of continuing with MIPS?

The main thrust of the marketing behind the DEC Alpha was its 64-bit microprocessor architecture. They got there years before potential competitors, including MIPS. At the time DEC was shipping the 64-...
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28 votes

Why did DEC develop Alpha instead of continuing with MIPS?

and would have improved the chances of a single RISC architecture having wide enough industry support to achieve critical mass rather than being outcompeted by x86. It's important to remember that in ...
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24 votes
Accepted

Did the PDP-8 designers consider a stack?

Without detailed documentation on the PDP-8 design process, we cannot say for sure. I suspect that while they may have briefly considered it, it was never a serious prospect. The PDP-8 is just the ...
  • 10.2k
23 votes

How should we interpret Dave Cutler's criticism of Unix?

While I am sure that the merits of Cutler's stated "low opinion" could be debated, I'm interested to better understand exactly what he was referring to here. There's no citation, and I haven't ...
  • 11.1k
23 votes
Accepted

What was this mini-computer tape troubleshooting process

While I can't be certain, what you describe sounds like some variation on what's mentioned in the description of Techmoan's The Magnetic Tape Viewer - see the sound on a tape: Q) You can buy these ...
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21 votes

Why did 1950s-60s computers have such wide words?

Longer words mean more bits can be processed at once. An 8 bit processor can perform a 32 bit calculation, but it has to do it in 4 stages of 8 bits each. A 32 bit processor can do it in one stage. ...
  • 14.2k
20 votes

How should we interpret Dave Cutler's criticism of Unix?

At the operating system level – as seen by applications – files in VMS are very record oriented. Guide to OpenVMS File Applications (336 page, 2MB PDF) probably goes into far more detail than anyone ...
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20 votes
Accepted

Advantage of RS-232 over 20mA current loop

TL;DR: It's a classic case of technological advancement vs. installed base In the early days of electricity-based communication (i.e., telegraph and later TTY) there was no way to detect a voltage and,...
  • 177k
19 votes

How widely used was 0xDEADBEEF?

It can be found in implementations of zfs such as OpenZFS, inherited from the Solaris Kernel Memory C header file: https://github.com/openzfs/openzfs/blob/master/usr/src/uts/common/sys/kmem_impl.h ...
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18 votes
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Were there any LSI-11 like home computers outside of Russia?

The Heathkit H11 was available either as a kit or pre-assembled. It never became really popular in the West, but it was one of the most powerful PCs available in 1978. It used the LSI-11 small format ...
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17 votes
Accepted

DEC Alpha: why no 8/16-bit load/stores?

Support for byte writes throughout a memory system is expensive. Among other things, if one wishes to use error-corrected memory that can correct single-bit errors, a memory that can be written in ...
  • 29.2k
17 votes

Why did DEC develop Alpha instead of continuing with MIPS?

DEC's use of MIPS was only ever as basically a stop-gap. Before they used MIPS, DEC had started work on a project called Prism. It was intended to be their first commercial RISC processor. In June of ...
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16 votes
Accepted

How did 36-bit computers format ARPANET packets?

However, at that time, the world had not yet settled on octets. I beg to differ. If you look through brochures and manuals of next to all manufacturers, they tried hard to be IBM compatible at least ...
  • 177k
16 votes

DEC Alpha: why no 8/16-bit load/stores?

Apart from anything else, Alpha was the VAX replacement - indeed, it was internally called EVAX. It would be necessary to take VMS source code written in VAX MACRO-32 assembler and compile it into ...
  • 28.5k
16 votes

Is this a real system? Which one?

As @Raffzahn answers, this is probably a concocted image made to look like various real DEC setups. The attached image is of a PDP-12. You can see the heavy tilt towards DECtapes. You also see an ...
  • 4,538
16 votes
Accepted

IBM vs DEC and business partners

I don't agree with the answer you read on quora. DEC did have a partner relationship with a certain kind of customer, namely engineering and science labs. Ken Olsen and the engineering staff at DEC ...
  • 4,538
16 votes

Advantage of RS-232 over 20mA current loop

The current loop goes all the way back to classic telegraphy. If there's current flowing, then that's one state. If there's no current, then that's another state. It's as simple as it can be. You ...
  • 10.2k
15 votes
Accepted

Conditional skip instructions of the PDP-8

If you compare the octal opcodes for the skip instructions, a bcd | ||| 7500 SMA = 111 101 000 000 7440 SZA = 111 100 100 000 7420 SNL = 111 100 010 000 ...
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14 votes
Accepted

Performance characteristics of the DEC Type 30 graphical display

This might just be stating the obvious, but Type 30 manual linked in the question describes the device as a random-position point-plotting cathode ray tube. Nowhere does the manual suggest it's a ...
  • 28.5k
13 votes

How did 36-bit computers format ARPANET packets?

ARPANET isn't the only context in which the world of PDP-10 computing ran into data paths that used octets for framing. Four other contexts come to mind: 9 track magnetic tape, PDP-11 file exchanges,...
  • 4,538
13 votes

Why did 1950s-60s computers have such wide words?

A possible answer occurs to me: it might be precisely because of the slow memory. Say you want to add a pair of ten-digit decimal numbers, SUM += VAL, on a 6502. That chip has a BCD mode in which it ...
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12 votes
Accepted

DECNet physical connector

DECnet is more of a protocol suite than a physical hardware standard. So asking what kind of physical connector it uses is kind of like asking what kind of physical connector TCP/IP uses -- the ...
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12 votes
Accepted

What was the reasons for DEC engineers to choose MMU page size in VAXen?

The first and most important point to keep in mind is that the VAX wasn't initially designed as a new architecture, but an extension to the basic PDP-11 structure to break its 64 KiB boundaries. Early ...
  • 177k
12 votes

How much better was DEC Alpha than contemporaneous x86?

Alpha fizzled in the face of the HP/Intel partnership pushing their Itanium 64-bit architecture I think it's important to note that during this period, there was a widespread belief that the VLIW ...
12 votes
Accepted

What was the DEC Type 30 vector graphics display used for?

In that era you couldn't afford to build the raster displays that we have now. The RAM for the frame buffer would have been far too expensive. Vector displays were common, even though they had ...
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