Questions tagged [dec]

For questions regarding the hardware, software and peripheral products of DEC - The Digital Equipment Corporation.

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72
votes
8answers
21k views

How much better was DEC Alpha than contemporaneous x86?

The DEC Alpha, released in 1992, seems like an early implementation of a fully 64-bit microprocessor architecture. Its release led to quite a bit of both marketing hype and genuine vendor support in ...
45
votes
10answers
10k views

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

Modern general-purpose computers typically have a 64-bit word size, but looking back in time, we see narrower CPUs. In the early 80s, the 68000 dealt with 32-bit addresses but the ALU was only 16 bits ...
38
votes
6answers
10k views

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

Dave Cutler is well known for his contributions to operating systems, having led the effort on VAX VMS at DEC and Windows NT at Microsoft. According to his Wikipedia page, he is also known for ...
33
votes
8answers
5k views

Why did DEC develop Alpha instead of continuing with MIPS?

I have been rereading a fascinating discussion about why DEC replaced VAX with Alpha based on talks with people who were there at the time; in a nutshell, in the opinion of the VAX engineers, it was ...
29
votes
2answers
6k views

Is this a real system? Which one?

I was playing Remedy Entertainment's video game Control the other day. Inside the game world, I've come across several computers. (They all look extremely similar.) To me, it looks like some kind of ...
27
votes
2answers
3k views

How widely used was 0xDEADBEEF?

Inspired by some comments on the question "The history of the NULL pointer":- There was a practice in the '70s to use the hexadecimal code 0xDEADBEEF to indicate an invalid value. This could be to ...
24
votes
5answers
3k views

Were there any LSI-11 like home computers outside of Russia?

In my childhood I had one of these: https://en.wikipedia.org/wiki/Electronika_BK Note, that the CPU of this is based on LSI-11. This is rather surprising because PDP-11 took a room (I was lucky ...
22
votes
5answers
844 views

Where can I find software for the PDP-6?

We are planning to build a reconstruction of the PDP-6. The project is making a lot of progress, but currently we have a critical lack of software. Does anybody know where we can find software to run ...
21
votes
3answers
3k views

How did 36-bit computers format ARPANET packets?

The contract to develop ARPANET, the first version of the Internet, was awarded in 1969; usage of the system expanded exponentially through the seventies. The size and format of ARPANET packets were ...
18
votes
2answers
482 views

Why were TECO variables called Q-registers?

The TECO editor, (originally Tape Editor and COrrector, later Text Editor...) found in some form on just about every computer and operating system DEC ever made, provides variables in which you can ...
15
votes
2answers
1k views

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

The first version of the DEC Alpha had no load/store instructions for 8 or 16-bit values; if you wanted to deal with data of such sizes, you had to do it by shifting and masking values in registers as ...
15
votes
3answers
879 views

Conditional skip instructions of the PDP-8

I am interested in the SKIP instructions on the PDP-8. These test the accumulator and Link bit, and they skip the next instruction if the condition holds. The instructions are: OR GROUP SMA - Skip ...
14
votes
5answers
2k views

Advantage of RS-232 over 20mA current loop

According to https://en.wikipedia.org/wiki/VT52 Like other early DEC terminals, the VT50 series were equipped with both an RS-232 port as well as a 20mA current loop, an older serial standard used ...
14
votes
1answer
237 views

What happens on a VT102 when you use delete character on a reverse video line?

On a DEC VT102, suppose you have a line where all 80 characters (in particular, the rightmost character) are in reverse video. You then move the cursor to the start of that line and use DCH (ESC [ P) ...
12
votes
1answer
684 views

Can I use the DEC VT220 composite output to connect it to a TV?

I have a DEC VT220 from 1986, it has a composite output. Works great in all its max-19200Kbps monochrome glory. The composite output plug is a BNC, and it looks like BNC-to-RCA composite jack ...
11
votes
1answer
622 views

What does bold reverse video look like on a VT100/VT102?

My understanding is that bold text on a VT100/VT102 is more intense than ordinary text; I might say that normal text is 80% grey and bold text is 100% grey=pure white, for the sake of illustration. ...
11
votes
1answer
577 views

On-disk structures for Files-11 format (RSX11)

I'm looking for an explanation, or a link to documentation of the on-disk structures of the Files-11 format, that is, the format of disks used by RSX-11 on the PDP-11. Also known as ODS-1, the ...
10
votes
2answers
2k views

Did the PDP-8 designers consider a stack?

The PDP-8 was a remarkable exercise in minimalist computer design; some of the aspects of its design are discussed in detail at PDP-8 transistor count One feature it did not have was a stack. Instead, ...
9
votes
4answers
546 views

Is there a non-paging ITS for the PDP-6 or PDP-10?

In the late 60s, the Incompatible Timesharing System ran on a PDP-6 without any paging hardware (i.e. an MMU in modern terminology). See the Jargon entry for BLT, for example, which states (my ...
8
votes
2answers
213 views

Why was the VT05 resolution 72×20?

According to https://en.wikipedia.org/wiki/VT05 the VT05 presented the user with an upper-case only ASCII character display of 20 rows by 72 columns. At first glance this seems a reasonably natural ...
8
votes
1answer
531 views

Typical mid-scale business computer system of the late 70s

What was the most common business computer system of the late 70s, just before the Apple II and CP/M really started proliferating? For concreteness, let's say we are talking about a U.S. company on ...
8
votes
1answer
247 views

Was there an interactive macro/scripting language named PAGEN?

In a BESM-6 disk image I can see bits and pieces of something that looks like a strange interactive scripting language: [start of disk block] <LET=P11=%X01 <IEQ=P11=%377 <LET=P11=1 <END &...
7
votes
1answer
305 views

Origin of the NZVC condition codes scheme?

The NZVC condition codes scheme, and corresponding set of 14 conditions for branches, is the nearly only in current ISAs that utilizes condition codes at all. The first computer I know that used it is ...
6
votes
2answers
271 views

DECNet physical connector

DECNet was a network system for DEC computers, introduced in the mid to late seventies. What physical connector did it use? Was it possible to connect to such a network using just an RS-232 serial ...
6
votes
2answers
515 views

Understanding PALcode

Reading over some old articles on Alpha I realized I really didn't understand PALcode. So I did a little reading on that. PALcode is stored in main memory, is written in Alpha ML, and is called by a ...
6
votes
2answers
290 views

Behavior of DECDHL on single lines

The escape sequences ESC # 3 and ESC # 4 (DECDHL) are meant to be used on pairs on adjacent lines to request double height lines. As an example: echo -e "\e#3DOUBLE HEIGHT LINE\n\e#4DOUBLE HEIGHT ...
6
votes
2answers
308 views

Were the VAX eXtended Function Control (XFC) instructions ever used commercially?

The DEC VAX has a set of 256 instructions set aside for user addition via microcode edits. Were extension sets ever commercially produced and sold, or was this functionality mostly used in-house? ...
6
votes
2answers
382 views

VAX 11/780 16MB memory board - what was the physical size?

I'm trying to get a feel for what it looked like when you designed a computer to have a lot of memory chips stuffed into it. To that end, I found this: https://commons.wikimedia.org/wiki/File:...
6
votes
0answers
119 views

Restoring a self-inking printer cartridge

I've seen people ask about restoring printer or typewriter ribbons, but my situation's a little different. I have a self-inking ribbon for a DECwriter Correspondent. It's easy to open up the casing, ...
5
votes
3answers
675 views

Performance characteristics of the DEC Type 30 graphical display

The DEC Type 30 was an early vector graphics display, that was used for an astonishingly wide range of applications for the 1960s. It used a 16-inch circular CRT with high persistence phosphor ...
5
votes
3answers
730 views

Did DEC build their early computers out of the same parts?

Considering the PDP-8, PDP-7, PDP-9, PDP-1, even though they are completely different architectures (from a programmer's or compiler's point of view at least), they have some remarkable similarities ...
5
votes
3answers
568 views

Was there an analog of local labels in the IBM assembly language?

In the assembly language used in Unix on DEC machines (PDP-11, VAX), one can use numerical labels and refer to them with suffixes "b" and "f" meaning "backwards" and &...
5
votes
3answers
352 views

Was this FORTRAN "extension" originated by IBM?

This question has been prompted by a recent question about the assigned GOTO operator. It appears that some early FORTRAN implementations supported a non-obvious construct: using an indexed variable ...
5
votes
1answer
362 views

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

MMU page size in VAXen is just 512 bytes. Such a small size causes increased number of MMU page walks and leads to TLB thrashing more often. Current tendency is to have MMU pages as big as 2 Mbytes. ...
4
votes
4answers
1k views

IBM vs DEC and business partners

A Quora question Why did Digital Equipment Corporation (DEC) fail? has gathered some really interesting answers, including from former DEC people. There is one such answer I do not quite understand: ...
4
votes
4answers
487 views

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

The DEC PDP-1 had, unusually for its time, a vector graphics display. According to https://en.wikipedia.org/wiki/History_of_Digital_Equipment_Corporation Most systems were purchased with two ...
4
votes
1answer
281 views

How did the DEC RP06 respond to unscheduled power off?

The DEC RP06 disk drive was a remarkable piece of hardware. It seems to have been the last generation of drives that used rigid magnetic disks in removable packs, before their replacement by '...
3
votes
1answer
188 views

Porting of software from the m68k family architecture to the DEC VAX

I am looking for impressions, memoirs, articles, guidelines - everything that is possible about the unusual direction of software migration. I am interested in non-Unix related code, and preferably ...
3
votes
1answer
209 views

DEC "CI" bus, better known as?

Looking over a list of various VAX processors, I noticed a reference to a "CI" bus. Poking about in Google I can only find very passing mentions of this, and no details. I suspect this had ...
3
votes
0answers
153 views

What was a DEC PDP-11/85 intended to be, and why might it be able to use DECsystem-10 software?

In this DEC PDP-11 Strategy Memo from Sept 1974, there is this curious question. HOW MUCH OF THE DEC SYSTEM 10 SOFTWARE CAN THE 11/85 USE, OR DOES THE 11/85 HAVE TO START FROM SCRATCH? CONFLICTING ...