Hot answers tagged

81

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 the 64-bit design (which cost performance but ensured long-term viability). It wasn’t designed to compete with x86 (which wasn’t perceived as a viable long-...


74

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 digits they can represent. And that explains the approach: Computers originally were meant to automate calculations. So you want to represent numbers. With ...


57

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 fire off an I/O request, and get a notification of when it's complete. Meanwhile, execution continues. Of course, it's trivial for the system to provide synchronous I/...


56

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 out differences between the two at that time. I'm going to choose the 21164 as the Alpha to compare. It came out in January of 1995. It had a 266 MHz clock ...


42

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 similar.) The usual way of game designers to speed up development: Reuse of props. [or] is it just designed in the style of a DEC That seems to be the purpose. ...


38

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-bit Alpha, MIPS was just beginning to have success with the 32-bit MIPS R3000 being used by SGI. Given that DEC didn't just need to replace their aging Vax ...


28

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 the late 80's and very early 90's when Alpha was being developed, absolutely nobody was worried about x86 dominating high end computing. Not even Intel ...


22

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 found a good explanation critiquing his criticism. Honestly, at face value, it's a naive criticism. Cutler was not naive, so, it's likely just a sound bite poke ...


20

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. Since early computers had limited clock speeds due to slow electronics increasing the word size was one of the few options available to improve performance. In ...


19

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 line 80 #define KMEM_FREE_PATTERN 0xdeadbeefdeadbeefULL Quote from the magic number wiki page: "Dead beef", Famously used on IBM systems such as the RS/...


19

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 should be expected to know, but you can get a feel from the Introduction (emphasis mine): 1.1 File Concepts A computer file is an organized collection of ...


19

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, when needed, amplify it. Only current flowing in a closed circuit could be detected reliably—by having it run through a coil which in turn moved a lever—and ...


19

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 PDP-5 redesigned electronically. The PDP-5 was introduced in 1963 as an even-more-reduced version of a computer compared to the PDP-1 and PDP-4. The PDP-1/4 did ...


18

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 of the PDP-11, and came with 4 kwords of memory for $1295. (That is 8 kbytes, but DEC preferred to refer to memory as register size, which was 16 bits.) It ...


17

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 1988, however, there was a meeting of senior executives. The PRISM project was producing some interesting technology, but didn't have a chip set available yet (...


16

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 for data exchange. Being IBM compatible was effectively mandatory for the whole industry and with the /360 introduction in 1964 the size of a byte (for ...


16

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 independent 8-bit chunks byte-writable memory will require four extra bits per octet, or 16 bits per 32-bit word. A memory that is limited to writing 16-bit ...


16

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 object in the lower image that might be an oscilloscope. (Image taken from Ed Thelens great site)


16

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 all understood how scientists and engineers think and what they want. But this was without any marketing specialists to act as liaisons. Sometime in the 1970s, ...


16

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 don't need to manipulate voltages. That's the key. Just turn a literal switch on and off. It also has problems. Current losses are heavy even in short ...


15

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 | ||| 7510 SPA = 111 101 001 000 7450 SNA = 111 100 101 000 7430 SZL = 111 100 011 000 you see that in each group, there are three conditions that ...


14

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 Alpha machine code. VMS had a lot of dependency on 32-bit words. MACRO-32 code was explicit about length. Higher-level code, in BLISS-32, tended to be explicit ...


14

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 vector graphics display. It then further describes how the computer supplies the X,Y coordinates of a single point to be plotted. There is no facility to plot a ...


13

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, DECnet, and Kermit. 9 Track Magnetic Tape. 9 Track tape rapidly became the most popular standard as IBM transitioned from 36 bit processors to the 360. ...


13

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 can add two digits at a time; it has to do everything through an 8-bit accumulator. So we need a loop of five iterations, which we might unroll for speed. Each ...


12

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 approach was "the next RISC". Existing RISC approaches were growing into the millions of transistors and the outright performance gap that existed in the 1990s ...


12

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 disadvantages - at engineering time you had to make a fixed-for-all-time choice between how long of a vector you could write vs. the persistence time of the phosphor....


12

Using someone else's processor would fundamentally change the nature of the company, which historically was based on creating computer systems based on DEC-designed processors. I don't believe DEC was capable of such a radical change. That's not to pooh-pooh the technical reasons given in other excellent answers here. But historical inertia should not be ...


11

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 answer is, it uses whatever connector you need to use for the particular data link layer you're running DECnet on top of. If you are running DECnet over Ethernet, ...


11

In a similar vein, Algol-68R on ICL 1900 (a 24-bit machine) initialized memory to -6815700, which when displayed as text (four 6-bit characters), spelled 'F00L', as well as possessing numerous other virtues. https://en.wikipedia.org/wiki/ALGOL_68-R#F00L


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