Hot answers tagged

69

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-...


54

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/...


47

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 ...


21

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 ...


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 ...


18

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 ...


16

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/...


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 ...


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

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 ...


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 ...


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. ...


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

This information is based on information from the DEC VT220 Technical Manual. I've not actually tried this out myself, but it did work for the OP when he tried it. TLDR: Yes, it's likely to work, and quite cheap to try using a sub-$1 BNC to RCA adapter if you already have an RCA-RCA video cable. Section 1.4 says that the "BNC connector for composite video ...


11

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....


10

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


10

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 ...


9

I can only provide my memories of a dozen or so years of programming for these DEC terminals. The 'new' character at the right hand end of the screen is inverse video. If I recall correctly, on the VT320 onwards there was a configuration setting to change this, such that it would appear not inverted.


9

It's possibly a stretch, but the General Instruments CP1600 which was in the Intellivision, though otherwise unsuccessful, was based on the PDP-11 architecture. The Intellivision was a product of Mattel, not GI, so it's the one commercial machine that opted to use the chip rather than being the machine the chip was designed for. General Instruments designed ...


9

It's really more of a conjecture, but if it is considered suitable as an answer: Already in early TECO, the letter q ("quantity") was used to retrieve the value of a register. That might have been the reason to call them Q-registers. Trying to trace reasons for why things are named a certain way is always difficult; they way this usually goes is that ...


9

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 implementations even offered a hardware-based PDP-11 mode. MMU page size in VAXen is just 512 bytes Which is also the block size of most DEC disk drives (...


9

Yes, at a physical level there was some commonality, but not at as high a level the question references. In the mid 1960s, DEC sold a line of simple logic modules, known as flip chips. The PDP-7 and the original PDP-8 were built (at least partially) out of the R-series modules, though there were some custom modules created just for them (e.g. a W130 ...


9

36-bit computers were used to communicate through channels which were not 36-bit. ARPANET packets are not the only one, paper and magnetic tapes, connections to terminals, ... have also their frame which is not 36-bit. Protocols and OS of the time were used to define various ways to transform 36-bit words in smaller units (search here for SET TAPE FORMAT ...


8

TLDR: TECO uses single-character commands. When extending TECO to add registers to store numeric values, there was a limited set of unused characters left for the commands associated with this functionality. q was chosen as one of these command characters because it could serve as a mnemonic for "quantity." This led to the numeric registers being called "Q-...


7

There were obviously no same parts that were doing any of those operations. The DEC hardware evolved from transistor technology (PDP-1, PDP-8, etc.) to medium-scale IC logic like standard TTL (PDP-8/E, early PDP-11) and eventually to large-scale ASIC CPUs like LSI-11 or 6100 PDP-8 clone. The similarity of instruction sets has nothing to do with the actual ...


7

My take is that this scheme has been invented the same way everything has been invented: Slowly, by evolution and combining existing ideas, and not "from scratch" by a strike of genius. The carry flag has been around a long time before that (other PDPs, and previous computers). Branches or skips that test the carry flag have also been around (other PDPs, ...


7

There was Terak 8510/A - a graphic workstation with the LSI-11 compatible processor, a graphical frame buffer (hardware-scrollable the same way as in the BK-0010), and a text mode with downloadable fonts, although admittedly too expensive to be a home computer. In some sense BK-0010 looks like a stripped-down Terak (no text mode, less RAM, etc.), but the ...


7

In Israel, in the early 1980s (I started work as an accountant in 1982 so I don't know how long the system had been in use prior to this date), all the kibbutzim of an area used to connect to one PDP-11 which was run from a communal computing centre. Each kibbutz had one data line. We had programs for accounting and a precursor of what was to be ERP, as well ...


7

I'd like to add a few words on conditional branching. This is quite different from the conditional branching on the PDP-11 and the 6502 computers. It simply doesn't fit into the PDP/8 instruction scheme, the 12 bits aren't enough for that. A conditional branch needs two aspects in one instruction: defining the branch target (the jump address) ...


7

At that time, computing model was very rich API, complex CPUs, complex tools, etc. Filesystem were almost structured files oriented, etc. UNIX came with its "uniform" vision of I/O, everything is a file, a file is just a stream of bytes. That wasn't so easy for people trained on former OSes to understand why UNIX is a good model. While I loosely remember the ...


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