From - Sat Sep 9 19:57:12 2000 Path: reader4.news.rcn.net!feed1.news.rcn.net!rcn!cpk-news-hub1.bbnplanet.com!paloalto-snf1.gtei.net!news.gtei.net!newsgate.tandem.com!mailint03.im.hou.compaq.com!xdelta!hoffman From: hoffman@xdelta.zko.dec.nospam (Hoff Hoffman) Newsgroups: comp.os.vms,comp.sys.dec,vmsnet.alpha,vmsnet.misc,comp.answers,news.answers Subject: OpenVMS Frequently Asked Questions (FAQ), Part 5/5 Followup-To: poster Date: 17 Aug 2000 22:07:12 GMT Organization: Compaq Computer Corporation Lines: 1404 Approved: news-answers-request@mit.edu Distribution: world Expires: 17 Nov 2000 00:00:00 GMT Message-ID: <8nhnmg$3j0$1@mailint03.im.hou.compaq.com> References: <8nhni9$3hv$1@mailint03.im.hou.compaq.com> Reply-To: hoffman@xdelta.zko.dec.nospam NNTP-Posting-Host: 16.32.80.251 X-Trace: mailint03.im.hou.compaq.com 966550032 3680 16.32.80.251 (17 Aug 2000 22:07:12 GMT) X-Complaints-To: usenet@mailint03.im.hou.compaq.com NNTP-Posting-Date: 17 Aug 2000 22:07:12 GMT Summary: This posting contains answers to frequently asked questions about the OpenVMS operating system from Compaq Computer Corporation, and the computer systems on which it runs. X-Newsreader: mxrn 6.18-32 Xref: reader4.news.rcn.net comp.os.vms:280587 comp.sys.dec:87918 vmsnet.alpha:10604 vmsnet.misc:6633 comp.answers:42587 news.answers:191827 Archive-name: dec-faq/vms/part5 Posting-Frequency: monthly Last-modified: 17 Aug 2000 Version: VMS-FAQ-5.TXT(4) This is the OpenVMS Frequently Asked Questions Part 5/5. Please see Part 1/5 for administrivia, indexing, archiving, etc. ------------------------------------------------------------ ALPHA1. What do the letters AXP stand for? While there are many fanciful "definitions" which have circulated widely, the truth is that AXP is not an abbreviation nor an acronym; the letters do not mean anything. They are just three letters chosen to form a trademark. When it came time to chose a "marketing name" for the Alpha AXP line, the company was in a quandary. The internal "code name" for the project, Alpha, was widely known and would seem the ideal choice, but it was already in common use by a number of other companies and could not be trademarked. A well-known "name search" firm was hired and was asked to come up with two lists of possible names. The first list was intended to evoke the feeling of "extension to VAX", while the second list was to suggest "not a VAX". Unfortunately, none of the choices offered were any good; for example, "VAX 2000" was found on the first list while the second list contained "MONDO" (later to be used for a kids' soft drink). Shortly before announcement, a decision was made to name the new line ARA, for Advanced RISC Architecture. However, an employee in Israel quickly pointed out that this name, if pronounced in the "obvious" manner, sounded very much like an Arabic word with decidely unfortunate connotations. Eventually, AXP was selected; the architecture would be referred to as "Alpha AXP" whereas products themselves would use just "AXP". Use of the AXP term has been phased out in favour of using Alpha. For example, "OpenVMS AXP" is now officially refered to as "OpenVMS Alpha". ------------------------------------------------------------ ALPHA2. What are the OpenVMS differences between VAX and Alpha? Very few. As of OpenVMS V6.1, the VAX and Alpha platforms are very close to "feature parity". Most applications can just be recompiled and run. Some differences to be aware of: - The default double-precision floating type on OpenVMS Alpha is VAX G_float, whereas on VAX it is usually D_float. D_float is available on Alpha, but D_float values are converted to G_float for computations and then converted back to D_float when stored. Because the G_float type has three fewer fraction bits than D_float, some applications may get different results. IEEE float types are also available on OpenVMS Alpha. - Data alignment is extremely important for best performance on Alpha. This means that data items should be allocated at addresses which are exact multiples of their sizes. Quadword alignment will offer the best performance, especially for character values and those smaller than 32 bits. Compilers will naturally align variables where they can and will issue warnings if they detect unaligned data items. - Compaq C is the only C compiler Compaq offers on OpenVMS Alpha. It is compatible with DEC C on OpenVMS VAX, but is somewhat different from the older VAX C compiler most people are familiar with. Read up on the /EXTERN_MODEL and /STANDARD qualifiers to avoid the most common problems. - The page size on Alpha systems is variable, but is at least 8K bytes. This can have some effect on applications which use the $CRMPSC system service as well as on the display of available memory pages. The page size is available from $GETSYI(SYI$_PAGE_SIZE). There are also a number of manuals which discuss migration to OpenVMS Alpha available on the documentation CD-ROM media, both in the main documentation and in the archived documentation section. On more recent OpenVMS Alpha versions, OpenVMS Alpha has begun to add features and support not available on OpenVMS VAX. Salient new areas include the following: - 64-bit addressing in OpenVMS Alpha V7.0 and later - Multi-host SCSI support (SCSI TCQ) in V6.2 and later - PCI support (platform-dependent) - OpenVMS Galaxy support in V7.2 and later ------------------------------------------------------------ [ALPHA3 removed, information obsolete] ------------------------------------------------------------ [ALPHA4 relocated to VMS16, and out of Alpha hardware section] ------------------------------------------------------------ ALPHA5. Seeking performance information for Alpha (and VAX) systems? Compaq makes a wide range of performance documents available through its FTP and WWW Internet servers (see DOC2). The following contain information on current Alpha and VAX products: http://www.digital.com/alphaserver/products.html http://www.digital.com/alphaserver/vax/ The following sites contain information on various retired VAX and Alpha products: http://www.digital.com/alphaserver/archive/index.html http://www.digital.com/alphaserver/performance/perf_tps.html Also see CPU2000: http://www.spec.org/osg/cpu2000/ http://www.spec.org/osg/cpu2000/results/cpu2000.html ------------------------------------------------------------ ALPHA6. Where can I get updated console firmware for Alpha systems? Firmware updates for Compaq Alpha systems are available from: ftp://ftp.digital.com/pub/Digital/Alpha/firmware/ ftp://ftp.digital.com/pub/Digital/Alpha/firmware/readme.html The files are structured similiar to those on the firmware CD, and are separated by CD release. For example, the contents of the V3.7 firmware CD are located at: ftp://ftp.digital.com/pub/Digital/Alpha/firmware/v3.7/ The latest and greatest firmware (if released since the last firmware CD) is located at: ftp://ftp.digital.com/pub/Digital/Alpha/firmware/interim/ Please send your comments and feedback to alpha_server@service.digital.com For information on creating bootable floppies containing the firmware, and for related tools, please see the following areas: ftp://ftp.digital.com/pub/DEC/Alpha/firmware/utilities/mkboot.txt ftp://ftp.digital.com/pub/DEC/Alpha/firmware/utilities/mkbootarc.txt ftp://ftp.digital.com/pub/DEC/Alpha/firmware/utilities/mkntboot.txt [Stephen Hoffman] To check the firmware loaded on recent OpenVMS Alpha systems, use the command: $ write sys$output f$getsyi("console_version") $ write sys$output f$getsyi("palcode_version") SDA> CLUE CONFIG [Clair Grant] Also see ALPHA14. ------------------------------------------------------------ ALPHA7. How do I boot an AlphaStation without monitor or keyboard? The AlphaStation series will boot without a keyboard attached. To use a serial terminal as the console, issue the console command SET CONSOLE SERIAL - after that, it will use the terminal. Older Alpha workstations generally can't be booted without a keyboard. The usual settings for the console serial terminal (or PC terminal emulator acting as a serial console are: 9600 baud, 8 bits, no parity, one stop bit (9600 baud, 8N1). The AlphaStation and AlphaServer series use the PC DIN serial connector for the "COM1" and "COM2" serial lines, see MISC1 for details and pinout. ------------------------------------------------------------ ALPHA8. Will OpenVMS run on a Multia? AlphaPC 164LX? 164SX? Yes, there are a set of unsupported images that permit recent OpenVMS Alpha versions to bootstrap on the Multia UDB system. These images and the associated instructions are available at the OpenVMS Freeware website: http://www.openvms.digital.com/freeware/multia/ Instructions are included IN the kits. READ THE INSTRUCTIONS. Some of the restrictions involved when running OpenVMS on the Multia system include (but may well not be limited to) the following: o The PCMCIA support was completely removed, because the Intel chip on the Multia was not compatable with the Cirrus chip on the Alphabook. This means, of course, that you will not see and cannot use any PCMCIA cards on a Multia. o The Multia uses shared interrupts, and as a result, a special ZLXp-E series graphics device driver -- one that does not use interrupts -- is needed. This driver is provided in the kit. o The serial lines don't work. o If you have a Multia with a PCI slot, you can't use any PCI card that requires interrupts. o The SRM console on this system is very old and very fragile. (This SRM console was designed only and strictly for diagnostic use, and was not particularly tested or used with OpenVMS.) o If things don't work for you, don't expect to see any OpenVMS updates, nor SRM console updates, nor any support. The Multia images are not included on the OpenVMS Freeware V4.0 CD-ROM kit, the kit that was distributed with OpenVMS V7.2. (These images became available after Freeware V4.0 shipped.) Other sources of information for OpenVMS on Multia include: http://home.earthlink.net/~djesys/vms/hobbyist/multia.html http://home.earthlink.net/~djesys/vms/hobbyist/mltianot.html http://home.earthlink.net/~djesys/vms/hobbyist/support.html http://www.netbsd.org/Ports/alpha/multiafaq.html [Stephen Hoffman] [David J. Dachtera] OpenVMS Alpha is not supported on the AlphaPC 164LX and 164SX, and the OpenVMS CPU-specific routines and images necessary to bootstrap on these systems do not presently exist. Also see ALPHA13. ------------------------------------------------------------ ALPHA9. What is the least expensive system that will run OpenVMS? The cheapest systems presently offered by Compaq that will run OpenVMS are the AlphaServer DS10 server and the AlphaStation XP900 workstation. Other companies sell Alpha-powered systems and Alpha motherboards, some of which will run (and can be purchased with) OpenVMS -- see the OpenVMS Software Product Description (SPD) for details on the supported systems and configurations. There are also many used AlphaStation, AlphaServer, and DEC 3000 models available which are quite suitable. For more experienced OpenVMS system managers, the (unsupported) Multia can bootstrap OpenVMS -- see ALPHA8 for details. Depending on the OpenVMS version and configuration, the OpenVMS Software Product Description (SPD) is available at: http://www.digital.com/info/SP2501/ http://www.digital.com/info/SP4187/ http://www.digital.com/info/SPHOME/ When purchasing a system, ensure that the system itself is supported, that the system disk drive is supported or closely compatible, that the CD-ROM drive is supported or is closely compatable and that it also specifically supports 512 byte block transfers, and particularly ensure that video controller is supported. Use of supported Compaq hardware will generally reduce the level of integration effort involved. A CD-ROM drive is required for OpenVMS Alpha installations. [Stephen Hoffman] ------------------------------------------------------------ ALPHA10. Where can I get more information on Alpha systems? Compaq operates an AlphaServer information center at: http://www.digital.com/alphaserver/ Alpha Technical information and documentation is available at: http://www.support.compaq.com/alpha-tools/ documentation/current/chip-docs.html ftp://ftp.compaq.com/pub/products/alphaCPUdocs/ ftp://ftp.digital.com/pub/DEC/Alpha/systems/ http://ftp.digital.com/pub/Digital/info/ semiconductor/literature/dsc-library.html Platform product documentation: http://www.digital.com/info/lists/key-server_AL.HTM http://www.digital.com/info/lists/key-workstation_AL.HTM Information on Multia hardware is available at: http://www.netbsd.org/Ports/alpha/multiafaq.html [Stephen Hoffman] The NetBSD folks maintain some Alpha hardware information at: http://www.netbsd.org/Ports/alpha/models.html ------------------------------------------------------------ ALPHA11. What are the APB boot flag values? The following flags are passed (via register R5) to the OpenVMS Alpha primary bootstrap image APB.EXE. These flags control the particular behaviour of the bootstrap: >>> BOOT -FL root,flags bit description --- ---------------------------------------------- 0 CONV Conversational bootstrap 1 DEBUG Load SYSTEM_DEBUG.EXE (XDELTA) 2 INIBPT Stop at initial system breakpoints if bit 1 set (EXEC_INIT) 3 DIAG Diagnostic bootstrap (loads diagboot.exe) 4 BOOBPT Stop at bootstrap breakpoints (APB and Sysboot) 5 NOHEADER Secondary bootstrap does not have an image header 6 NOTEST Inhibit memory test 7 SOLICIT Prompt for secondary bootstrap file 8 HALT Halt before transfer to secondary bootstrap 9 SHADOW Boot from shadow set 10 ISL LAD/LAST bootstrap 11 PALCHECK Disable PAL rev check halt 12 DEBUG_BOOT Transfer to intermediate primary bootstrap 13 CRDFAIL Mark CRD pages bad 14 ALIGN_FAULTS Report unaligned data traps in bootstrap 15 REM_DEBUG Allow remote high-level language debugger 16 DBG_INIT Enable verbose boot messages in EXEC_INIT 17 USER_MSGS Enable subset of verbose boot messages (user messages) 18 RSM Boot is controlled by RSM 19 FOREIGN Boot involves a "foreign" disk If you want to set the boot flags "permanently" use the SET BOOT_FLAGS command, e.g. >>> SET BOOT_OSFLAGS 0,1 ------------------------------------------------------------ ALPHA12. What are Alpha console environment variables? Alpha systems have a variety of variables with values set up within the SRM system console. These environment variables control the particular behaviour of the console program and the system hardware, the particular console interface presented to the operating system, various default values for the operating system bootstrap, and related control mechanisms -- in other words, "the environment variables provide an easily extensible mechanism for managing complex console state." The specific environment variables differ by platform and by firmware version -- the baseline set is established by the Alpha Architecture: AUTO_ACTION ("BOOT", "HALT", "RESTART", any other value assumed to be HALT), BOOT_DEV, BOOTDEF_DEV, BOOTED_DEV, BOOT_FILE, BOOTED_FILE, BOOT_OSFLAGS, BOOTED_OSFLAGS, BOOT_RESET ("ON", "OFF"), DUMP_DEV, ENABLE_AUDIT ("ON", "OFF"), LICENSE, CHAR_SET, LANGUAGE, TTY_DEV. OpenVMS Galaxy firmware can add console environment variables beginning with such strings as LP_* and HP_*, and each particular console implementation can (and often does) have various sorts of platform-specific extensions beyond these variables... The contents of a core set of environment variables are accessable from OpenVMS using the f$getenv lexical and the sys$getenv system service. (These calls are first documented in V7.2, but have been around for quite a while.) Access to arbitary console environment variables is rather more involved, and not directly available. [Stephen Hoffman] ------------------------------------------------------------ ALPHA13. Will OpenVMS run on a NoName AXPpci33? Information on bootstrapping OpenVMS (using Multia files) on the (unsupported) NoName AXPpci33 module is available at: http://www.jyu.fi/~kujala/vms-in-axppci33.txt Tips for using the Multia files with the AXPpci33: o You have to use the Multia kit and follow the directions in ALPHA8, but do *not* load the Multia SRM firmware into the AXPpci33. Rather, download and use the latest firmware for the AXPpci33 from the Compaq firmware website instead. o 64 MB memory is generally necessary. o you cannot use any PCI cards, and if you plan on networking, you need to find an ISA Ethernet card supported by OpenVMS. o When the AXPpci33 board bootstraps, it will dump some stuff like a crash dump, but it will continue and -- so far -- this hasn't caused any particular hassles. o The system shutdown and reboot procedures do not work properly. o The serial console is reported to not work, though the serial ports apparently do work. The status of the parallel port is unknown. o Rumour has it that you have one of the AXPpci33 motherboards with the PS/2 mouse and keyboard connectors and a VGA card (one that will work under DECwindows) and you can run DECwindows on the system. [Robert Alan Byer] ------------------------------------------------------------ ALPHA14. How do I reload SRM firmware on a half-flash Alpha system? Some of the AlphaStation series systems are "half-flash" boxes, meaning only one set of firmware (SRM or AlphaBIOS) can be loaded in flash at a time. Getting back to the SRM firmware when AlphaBIOS (or ARC) is loaded can be a little interesting... That said, this usually involves shuffling some files, and then getting into the AlphaBIOS firmware update sequence, and then entering "update srm" at the apu-> prompt. To shuffle the files, copy the target SRM firmware file (as200_v7_0.exe is current) to a blank, initialized, FAT-format floppy under the filename A:\FWUPDATE.EXE From the AlphaBIOS Setup screen, select the Upgrade AlphaBIOS option. Once the firmware update utility gets going, enter: Apu-> update srm Answer "y" to the "Are you ready...?" Apu-> quit You've reloaded the flash. Now powercycle the box to finish the process. Also see ALPHA6. ------------------------------------------------------------ ALPHA15. Will OpenVMS run on the Alpha XL series? No. OpenVMS does not support the Alpha XL series. OpenVMS can not, will not, and does not bootstrap on the Alpha XL series. The Alpha XL series was targeted for use (only) with the Microsoft Windows NT operating system.  For the list of boxes officially supported by OpenVMS, please see the OpenVMS Software Product Description (SPD). If you are very lucky, sometimes a particular unsupported Alpha box or motherboard will resemble a supported box sufficiently closely and can thus mimic that system and bootstrap. (No such family resemblances exist for the XL.) If you are exceedingly lucky, somebody here in OpenVMS Engineering will have put together a bootstrap kit -- such as that for the Multia. (No Miata-like OpenVMS bootstrap kit exists for the XL.) ------------------------------------------------------------ ALPHA16. Describe Alpha instruction emulation and instruction subsets? The Alpha architecture is upward- and downward-compatible, and newer instructions are emulated on older platforms, for those cases where the compiler is explicitly requested to generate the newer Alpha instructions. In particular, OpenVMS Alpha V7.1 and later include the instruction emulation capabilities necessary for the execution of newer Alpha instructions on older Alpha microprocessors. Alpha instructions are available in groups (or subsets). Obviously, there is the base instruction set that is available on all Alpha microprocessors. Then, the following are the current instruction extension groups (or subsets) that are available on some of various recent Alpha microprocessors: byte/word extension (BWX): LDBU, LDWU, SEXTB, SEXTW, STB, and STW. floating-point and square root extension (FIX): FTOIS, FTOIT, ITOFF, ITOFS, ITOFT, SQRTF, SQRTG, SQRTS, and SQRTT. count extension (CIX): CTLZ, CTPOP, and CTTZ. multi-media extension (MVI): MAXSB8, MAXSW4, MAXUB8, MAXUW4, MINSB8, MINSW4, MINUB8, MINUW4, PERR, PKLB, PKWB, UNPKBL, and UNPKBW. The typical instruction subset that provides the biggest win -- and of course, your mileage may vary -- is typically the instruction set that is provided by the EV56 and later; specifically, the byte-word instruction subset. To select this subset, use the following: /ARCHITECTURE=EV56/OPTIMIZE=TUNE=GENERIC The /ARCHITECTURE controls the maximum instruction subset that the compiler will generally use, while the /OPTIMIZE=TUNE controls both the instruction-level scheduling and also the instructions generated inside loops -- any code resulting from /OPTIMIZE=TUNE that is specific to an instruction subset will be generated only inside loops and will also be "protected" by an AMASK-based tesst that permits the execution of the proper code for the particular current Alpha microprocessor. Typically /OPTIMIZE=TUNE=GENERIC is the appropriate choice for tuning, and the /ARCHITECTURE selects the minimum target architecture for general use throughout the generated code. Code generated for later architectures and instruction subsets will run on older Alpha systems due to the emulation, but if /ARCHITECTURE is a significant benefit, then the emulation might be a performance penalty. Please see the OpenVMS Ask The Wizard area for the source code of a (non-privileged) tool that looks at the instruction subsets available on the particular Alpha microprocessor that the tool is run on. This tool demonstrates the use of the Alpha AMASK and IMPLVER instructions. ------------------------------------------------------------ ALPHA17. What is the Accuracy of the Alpha Time of Year (BB_WATCH) Clock? The specification for maximum clock drift in the Alpha hardware clock is 50 ppm, that's less than +/-.000050 seconds of drift per second, less than +/-.000050 days of drift per day, or less than +/-.000050 years of drift per year, etc. (eg: An error of one second over a day-long interval is roughly 11ppm, or 1000000/(24*60*60).) The software-maintained system time can drift more, primarily due to other system activity. Typical causes of drift include extensive high-IPL code (soft memory errors, heavy activity at device IPLs, etc) that are causing the processing of the clock interrupts to be blocked. Also see VAX8, TIME6. ------------------------------------------------------------ ALPHA18. So how do I open up the DEC 3000 chassis? After removing those two little screws, tilt the back end of the top shell upwards -- then you can remove the lid. [Felix Kreisel] ------------------------------------------------------------ ALPHA19. What is byte swizzling? "Swizzling" is the term used to describe the operation needed to do partial word IO on a pre-ev6 system. It involved shifting the offset into an address space by 5 (or 7 for one older system), and ORing this into the base address. It then required the size of the operation to be ORed into the low order bits. That is, because EV4 and EV5 did not bring bits 0 and 1 off the chip, to do programmed IO for bytes/words, the information on the size/offset of the transfer was encoded into the address data. The data itself then had to be shifted into the correct "byte lane" (i.e. it's actual position within a longword). EV56 (though not EV5) had byte/word operations, but OpenVMS did not directly support this for IO. EV6 systems (with the exception of the AlphaServer GS60 and AlphaServer GS140 series, for reasons of platform compatability) all support a flat byte addressable IO space. If device driver uses CRAM or IOC$WRITE_IO/IOC$READ_IO, then OpenVMS will do the right thing without changing the driver -- OpenVMS will swizzle and unswizzle as needed. To use byte/word operations on MEMORY, you need to tell the compiler to use the EV56 or EV6 architecture (/ARCHITECTURE=EV56). Memory operations did not swizzle, but the compiler would do long/quad access, and extract/insert bytes as needed. Using /ARCHITECTURE=EV56 allows smaller more efficient byte IO logic to memory. Beware: a few Alpha systems have EV56, but do not support byte/word to I/O space. If the application is directly doing IO access across a range of Alpha systems (like the graphics servers), then the driver will need to know how to do swizzling for old platforms, and byte access for new platforms. [Fred Kleinsorge] ------------------------------------------------------------ ALPHA20. What commands are available in the Alpha SRM console? In addition to the normal BOOT commands and such (see ALPHA11 for some details) and the normal contents of the console HELP text, operations such as I/O redirection and floppy disk access are possible at the SRM console prompt: 1. Format a FAT floppy, and insert it into the AlphaStation floppy drive. 2. Perform the following at AlphaStation SRM Console : >>> show * > env.dat >>> show conf > conf.dat >>> cat env.dat > fat:env.dat/dva0 >>> cat conf.dat > fat:conf.dat/dva0 3. You may use the SRM "ls" to display the contents of the floppy. >>> ls fat:env.dat/dva0 >>> ls fat:conf.dat/dva0 4. You can now transfer the FAT-format floppy to another system. ------------------------------------------------------------ ALPHA21. How do I switch between AlphaBIOS/ARC and SRM consoles? The specific steps required vary by system. You must first ensure that the particular Alpha system is supported by OpenVMS (see the SPD), that all core I/O components (graphics, disk controllers, etc) in the system are supported by OpenVMS (see the SPD), and that you have an OpenVMS distribution, that you have the necessary license keys (PAKs), and that you have the necessary SRM firmware loaded. A typical sequence used for switching over from the AlphaBIOS graphics console to the SRM console follows: 1. Press to get to the AlphaBIOS setup menu. 2. Pick the "CMOS Setup..." item. 3. Press to get to the "Advanced CMOS Setup" menu. 4. Change the "Console Selection" to "OpenVMS Console (SRM)". 5. Press , , then to save your changes. 6. Power-cycle the system. Most Alpha systems support loading both the AlphaBIOS/ARC console and the SRM console at the same time, but systems such as the AlphaStation 255 are "half-flash" systems and do not support the presence of both the AlphaBIOS/ARC and SRM console firmware at the same time. If you have a "half-flash" system, you must load the SRM firmware from floppy, from a network download, or from a firmware CD-ROM. Following the normal AlphaBIOS or ARC firmware update sequence to the APU prompt, and then explictly select the target console. In other words, power up the system to the AlphaBIOS or ARC console, use the supplementary options to select the installation of new firmware (typically from CD-ROM), and then rather than using a sequence which updates the current firmware: Apu-> update -or- Apu-> update ARC Apu-> verify Apu-> quit Power-cycle the system Use the following sequence to specifically update (and load) SRM from AlphaBIOS/ARC on a "half-flash" system: Apu-> update SRM Apu-> verify Apu-> quit Power-cycle the system Use the following sequence to specifically update (and load) the AlphaBIOS/ARC console from SRM on a "half-flash" system: >>> b -fl 0,A0 ddcu BOOTFILE: firmware_boot_file.exe Apu-> update ARC Apu-> verify Apu-> quit Power-cycle the system Once you have the SRM loaded, you can directly install OpenVMS or Tru64 UNIX on the system. Do not allow Windows NT to write a "harmless" signature to any disk used by OpenVMS, Tru64 UNIX, or Linux, as this will clobber a key part of the disk. (On OpenVMS, you can generally recover from this "harmless" action by using the WRITEBOOT tool.) If you have a "full-flash" system and want to select the SRM console from the AlphaBIOS or ARC console environment, select the "Switch to OpenVMS or Tru64 UNIX console" item from the "set up the system" submenu. Then power-cycle the system. If you have a "full-flash" system with the SRM console and want to select AlphaBIOS/ARC, use the command: >>> set os_type NT and power-cycle the system. For information on acquiring firmware, see ALPHA6. For information on OpenVMS license PAKs (for hobbyist use) see VMS9. For information on the Multia, see ALPHA8. Information on enabling and using the failsafe firmware loader for various systems -- this tool is available only on some of the various Alpha platforms -- is available in the hardware documentation for the system. This tool is used/needed when the firmware has been corrupted, and cannot load new firmware. ------------------------------------------------------------ VAX1. Please explain the back panel of the MicroVAX II The MicroVAX-series console bulkhead was used with the KA630, KA650, KA655 processors. There are three controls on the console bulkhead of these systems: Triangle-in-circle-paddle: halt enable. dot-in-circle: halt () is enabled, and auto-boot is disabled. dot-not-in-circle: halt () is disabled, and auto-boot is enabled. Three-position-rotary: power-up bootstrap behaviour arrow: normal operation. face: language inquiry mode. t-in-circle: infinite self-test loop. Eight-position-rotary: console baud rate selection select the required baud rate; read at power-up. There are several different bulkheads involved, including one for the BA23 and BA123 enclosures, and one for the S-box (BA2xx) series enclosure. The console bulkheads typically used either the MMJ serial line connection, or the MicroVAX DB9 (not the PC DB9 pinout), please see the descriptions of these in section MISC1. For available adapters, see MISC4. Also present on the console bulkhead is a self-test indicator: a single-digit LED display. This matches the final part of the countdown displayed on the console or workstation, and can be used by a service organization to determine the nature of a processor problem. The particular countdown sequence varies by processor type, consult the hardware or owner's manual for the processor, or contact the local hardware service organization for information the self-test sequence for a particular processor module. Note that self-tests 2, 1 and 0 are associated with the transfer of control from the console program to the (booting) operating system. [Stephen Hoffman] ------------------------------------------------------------ VAX2. What is the layout of the VAX floating point format? The VAX floating point format is derived from one of the PDP-11 FP formats, which helps explain its strange layout. There are four formats defined: F 32-bit single-precision, D and G 64-bit double-precision and H 128-bit quadruple precision. For all formats, the lowest addressed 16-bit "word" contains the sign and exponent (and for other than H, some of the most significant fraction bits). Each successive higher-addressed word contains the next 16 lesser-significant fraction bits. Bit 15 of the first word is the sign, 1 for negative, 0 for positive. Zero is represented by a biased exponent value of zero and a sign of zero; the fraction bits are ignored (but on Alpha, non-zero fraction bits in a zero value cause an error.) A value with biased exponent zero and sign bit 1 is a "reserved operand" - touching it causes an error - fraction bits are ignored. There are no minus zero, infinity, denormalized or NaN values. For all formats, the fraction is normalized and the radix point assumed to be to the left of the MSB, hence 0.5 <= f < 1.0. The MSB, always being 1, is not stored. The binary exponent is stored with a bias varying with type in bits 14:n of the lowest-addressed word. Type Exponent bits Exponent bias Fraction bits (including hidden) ========================================================================== F 8 128 24 D 8 128 56 G 11 1024 53 H 15 16384 113 The layout for D is identical to that for F except for 32 additional fraction bits. Example: +1.5 in F float is hex 000040C0 (fraction of .11[base 2], biased exponent of 129) [Steve Lionel] ------------------------------------------------------------ VAX3. Where can I find more info about VAX systems? Compaq runs a VAX "InfoCenter" at: http://www.digital.com/alphaserver/vax/ Jim Agnew maintains a MicroVAX/VAXstation FAQ at: http://anacin.nsc.vcu.edu/~jim/mvax/mvax_faq.html James Lothian maintains a VAX-11/750 FAQ at: http://www.dcs.napier.ac.uk/~oose5002/750faq.html The VAXstation 3100 Owner's Guide: http://www.whiteice.com/~williamwebb/intro/DOC-i.html A field guide to PDP-11 (and VAX) Q-bus and UNIBUS modules can be found at: http://metalab.unc.edu//pub/academic/computer-science/ history/pdp-11/hardware/field-guide.txt Various VAX historical information (also see VMS1) can be found at: http://telnet.hu/hamster/vax/e_index.html ------------------------------------------------------------ VAX4. Where can I find information on NetBSD for VAX systems? Gunnar Helliesen maintains a NetBSD VAX FAQ at: http://vaxine.bitcon.no/ ------------------------------------------------------------ VAX5. What system disk size limit on the MicroVAX and VAXstation 3100? System disks larger than 1.073 gigabytes (GB) -- 1fffff hexidecimal blocks -- are not supported on any member of the VAXstation 3100 series and on certain older members of the MicroVAX 3100 series, and are not reliable on these affected systems. (See below to identify the affected systems -- the more recent members of the MicroVAX 3100 series systems are NOT affected.) Various of the SCSI commands used by the boot drivers imbedded in the console PROM on all members of the VAXstation 3100 series use "Group 0" commands, which allow a 21 bit block number field, which allows access to the first 1fffff hexidecimal blocks of a disk. Any disk references past 1fffff will wrap -- this wrapping behaviour can be of particular interest when writing a system crashdump file, as this can potentially lead to system disk corruptions should any part of the crashdump file be located beyond 1.073 GB. More recent systems and console PROMs use "Group 1" SCSI commands, which allow a 32 bit block number field. There was a similar limitation among the oldest of the MicroVAX 3100 series, but a console boot PROM was phased into production and was made available for field retrofits -- this PROM upgrade allows the use of the "Group 1" SCSI commands, and thus larger system disks. There was no similar PROM upgrade for the VAXstation 3100 series. Systems that are affected by this limit: o VAXstation 3100 series, all members. No PROM upgrade is available. o MicroVAX 3100 models 10 and 20. No PROM upgrade is available. o MicroVAX 3100 models 10e and 20e. Only systems with console VMB versions prior to V6.4 are affected. A PROM upgrade for these specific systems is (was once) available. Also see: http://www.whiteice.com/~williamwebb/intro/DOC-i.html Also see FILE5. [Stephen Hoffman] ------------------------------------------------------------ VAX6. replaced by TIME section. ------------------------------------------------------------ VAX7. What are the VMB boot flag values? The following flags are passed (via register R5) to the OpenVMS VAX primary bootstrap image VMB.EXE. These flags control the particular behaviour of the bootstrap: The exact syntax is console-specific, recent VAX consoles tend to use the following: >>> BOOT/R5:flags Bit Meaning --- ------- 0 RPB$V_CONV Conversational boot. At various points in the system boot procedure, the bootstrap code solicits parameter and other input from the console terminal. If the DIAG is also on then the diagnostic supervisor should enter "MENU" mode and prompt user for the devices to test. 1 RPB$V_DEBUG Debug. If this flag is set, VMS maps the code for the XDELTA debugger into the system page tables of the running system. 2 RPB$V_INIBPT Initial breakpoint. If RPB$V_DEBUG is set, VMS executes a BPT instruction immediately after enabling mapping. 3 RPB$V_BBLOCK Secondary boot from the boot block. Secondary bootstrap is a single 512-byte block, whose LBN is specified in R4. 4 RPB$V_DIAG Diagnostic boot. Secondary bootstrap is image called [SYSMAINT]DIAGBOOT.EXE. 5 RPB$V_BOOBPT Bootstrap breakpoint. Stops the primary and secondary bootstraps with a breakpoint instruction before testing memory. 6 RPB$V_HEADER Image header. Takes the transfer address of the secondary bootstrap image from that file's image header. If RPB$V_HEADER is not set, transfers control to the first byte of the secondary boot file. 7 RPB$V_NOTEST Memory test inhibit. Sets a bit in the PFN bit map for each page of memory present. Does not test the memory. 8 RPB$V_SOLICT File name. VMB prompts for the name of a secondary bootstrap file. 9 RPB$V_HALT Halt before transfer. Executes a HALT instruction before transferring control to the secondary bootstrap. 10 RPB$V_NOPFND No PFN deletion (not implemented; intended to tell VMB not to read a file from the boot device that identifies bad or reserved memory pages, so that VMB does not mark these pages as valid in the PFN bitmap). 11 RPB$V_MPM Specifies that multi-port memory is to be used for the total EXEC memory requirement. No local memory is to be used. This is for tightly-coupled multi-processing. If the DIAG is also on, then the diagnostic supervisor enters "AUTOTEST" mode. 12 RPB$V_USEMPM Specifies that multi-port memory should be used in addition to local memory, as though both were one single pool of pages. 13 RPB$V_MEMTEST Specifies that a more extensive algorithm be used when testing main memory for hardware uncorrectable (RDS) errors. 14 RPB$V_FINDMEM Requests use of MA780 memory if MS780 is insufficient for booting. Used for 11/782 installations. <31:28> RPB$V_TOPSYS Specifies the top level directory number for system disks with multiple systems. ------------------------------------------------------------ VAX8. What is the Accuracy of VAX the Time of Year (TOY) Clock? The VAX Time-Of-Year (TOY) clock (used to save the time over a reboot or power failure) is specified as having an accuracy of .0025%. This is a drift of roughly 65 seconds per month. The VAX Interval Time is used to keep the running time, and this has a specified accuracy of .01%. This is a drift of approximately 8.64 seconds per day. Any high-IPL activity can interfere with the IPL 22 or IPL 24 (this depends on the VAX implementation) clock interrupts -- activities such as extensive device driver interrupts or memory errors are known to slow the clock. Also see ALPHA17, TIME6. ------------------------------------------------------------ VAX9. Which serial port is the console on the MicroVAX 3100? Just to keep life interesting, the MicroVAX 3100 has some "interesting" console ports behaviours based on the setting of the BREAK enable switch. When the console is not enabled to respond to BREAK, MMJ-1 is the console port. MMJ-3 will (confusingly) output the results of the selftest in parallel with MMJ-1. When the console is enabled to respond to BREAK, MMJ-3 becomes the console port, and MMJ-1 will (confusingly) output the results of selftest in parallel with MMJ-3. ------------------------------------------------------------ VAX10. How can I set up an alternate console on a VAXstation? Most VAXstation systems have a switch -- often labeled S3 -- that enables one of the serial lines as the system console. Also see ALPHA1, DECW13, and MGMT22. ------------------------------------------------------------ VAX11. What are the VAX processor (CPU) codes? CPU: Platform: ----- --------- KA600 : VAX 4000-50 (aka VAXbrick) KA610 : MicroVAX I, VAXstation I (aka KD32) KA620 : rtVAX (VAXeln) KA630 : MicroVAX II, VAXstation II KA640 : MicroVAX 3300, MicroVAX 3400 KA650 : VAXstation 3200, MicroVAX 3500, MicroVAX 3600, MicroVAX III KA655 : MicroVAX 3800, MicroVAX 3900, MicroVAX III+ KA660 : VAX 4000-200, VAX 4 KA670 : VAX 4000-300 KA675 : VAX 4000-400 KA680 : VAX 4000-500 KA681 : VAX 4000-500A KA690 : VAX 4000-600 KA691 : VAX 4000-605A KA692 : VAX 4000-700A KA693 : VAX 4000-605A KA694 : VAX 4000-705A KA730 : VAX-11/730 KA750 : VAX-11/750 KA780 : VAX-11/780, VAX-11/782 KA785 : VAX-11/785 KA800 : VAXrta KA820 : VAX 8200, VAX 8300 KA825 : VAX 8250, VAX 8350 KA85 : VAX 8500 KA86 : VAX 8600 KA865 : VAX 8650 KA88 : VAX 8800 KA62A : VAX 6000-200 KA62B : VAX 6000-300 KA64A : VAX 6000-400 KA65A : VAX 6000-500 KA66A : VAX 6000-600 KA7AA : VAX 7000-600 KA7AB : VAX 7000-700 KA7AC : VAX 7000-800 ------------------------------------------------------------ SUPP1. Where can I get software and hardware support information? Contact Compaq Customer Support. Services and information, manuals, guides, downloads, and various other information is available at: http://www.compaq.com/support/ Various hardware and system documentation is available at: http://www.digital.com/lists/QB_archive_HD.html http://www.europe.digital.com/info/CUHOME/BACK_ISSUES.HTM http://www.compaq.com/support/techpubs/user_reference_guides/ http://www.adenzel.demon.nl/vaxes/microvax3100/ http://www.adenzel.demon.nl/vaxes/infoserver150/ ------------------------------------------------------------ SUPP2. Where can I get hardware self-maintenance support assistance? The Compaq Assisted Services program is available to customers that wish to maintain their own systems (self-maintenance), but that require some assistance with acquiring hardware diagnostics, hardware manuals, and with hardware swaps and spares: http://www.digital.com/info/DAHOME/ http://www.digital.com/DAS-Catalog/ ------------------------------------------------------------ SUPP3. Why does my system halt when I power-cycle the console terminal? Various VAX and Alpha consoles are designed to process the BREAK signal, treating it as a HALT request. A BREAK is a deliberately-generated serial line framing error. When a serial line device such as a terminal powers up (or sometimes when powering down) it can generate framing errors. These framing errors are indistingushable from a BREAK signal. When a BREAK is received on a serial line console for various VAX systems -- including most VAXstation, MicroVAX, and VAX 4000 series -- it is typically interpreted as a HALT. Alpha systems will also often process a BREAK in a similar fashion, halting the system. There is no uniform or generally-available way to disable this behaviour on every VAX or Alpha system. On some systems, BREAK processing can be disabled in favor of [CTRL/P], or [CTRL/P] is the only way to halt the processor. The most common way to avoid these halts is to disable the serial line console or to simply not power-cycle the console terminal. There is certain important system state information that is displayed only on the console, OpenVMS expects to always have access to the system console. Also see MGMT5. ------------------------------------------------------------ SUPP4. Can I reuse old keyboards, mice and monitors with a PC? Older Compaq keyboards (those with the DIGITAL logo and the RJ modular jacks), older Compaq mice (those with the DIGITAL logo and with the RJ modular jacks, or with a DIN connector with pins in a configuration other than the PC-standard DIN connector pin orientation), and older video monitors (with RGB synch-on-green video signaling) all use signaling formats and/or communications protocols that differ from the PC standards, and are not (easily) interchangable nor (easily) compatible with typical PC peripheral device controllers. LK201, LK401, VSXXX, VR260, VR290, etc., are incompatible with most PC systems. Newer Compaq keyboards (those with with PC-style DIN plugs, and Compaq or DIGITAL logo), newer Compaq mice (with PC-pin DIN plugs, and Compaq or DIGITAL logo), and newer video monitors (multi-synch) are often interchangeable with "industry standard" PC systems, and can often be used with most PC peripheral device controllers. LK461, LK471, PC7XS-CA, VRC16, VRC21, etc., are compatible with most PC systems. Rule of thumb: if the peripheral device component was sold for use with the DEC 2000 (DECpc 150 AXP), an AlphaServer series, an AlphaStation series, or more recent Alpha system, it will probably work with a PC peripheral controller. If the peripheral device component was sold for use with an VT420 or older terminal, most VAX, most VAXstation, and most Alpha systems with names in the format `DEC ', it probably won't work on a PC. Note that the above is a general guideline, and should not be read to indicate that any particular peripheral device will or will not work in any particular configuration, save for those specific configurations the device is explicitly supported in. [Stephen Hoffman] Software Integrators sells a video adapter card called Gemini P1 which will drive many of the older Compaq (DIGITAL-logo) fixed-frequency monitors on a PC system: http://www.si87.com/ The Digital part number 29-32540-01 converts the output from the RGB cable (3 BNC, synch-on-green) that comes with the VAXstation 3100 and VAXstation 4000 series to a female SVGA D connector. This will allow PC Multisync monitors with the needed frequency specifications to be used with the VAXstations. It may work with a VAXstation 2000 series, but I have not tried that combination. [John E. Malmberg] The protocol definition for the old DIGITAL keyboard and mouse interfaces is buried at the back of the QDSS section in the old VAXstation II manual, specifically, in the back of the VCB02 Video Subsystem Technical Manual (EK-104AA-TM). The keyboard wiring and protocol is in appendix B, and occupies circa 44 pages. The mouse is in appendix C, circa 12 pages. Also see SUPP5 ------------------------------------------------------------ SUPP5. Which video monitor works with which graphics controller? To determine the answer to the "will this monitor work with this graphics controller?" question, please first locate the resolution(s) and the frequencies that are possible/supported at both ends of the video cable (on the monitor and the graphics controller, in other words), and then determine if there are any matching settings available. If there are multiple matches, you will need to determine which one is most appropriate for your needs. You will also need to determine if the video monitor or graphics controller requires the 3 BNC signaling with the synchronization signals on the green wire, or the 5 BNC signalling common on many PCs, or other connections such as the DB15 video connector or USB connector used on various systems. If there are no matches, you will likely need to change the hardware at one or both ends of the "video cable". The refresh frequencies for many devices have been posted to comp.os.vms and/or other newsgroups. Search the archives for details. Also see: http://www.repairfaq.org/ http://plop.phys.cwru.edu/repairfaq/REPAIR/F_monfaq.html http://www.mirage-mmc.com/faq/ http://www.geocities.com/SiliconValley/Foothills/4467/fixedsync.html Also see SUPP4. ------------------------------------------------------------ SUPP6. Where can I get information on storage hardware? Information on various Compaq OpenVMS and other disk storage hardware and controllers, and related technical information on SCSI, device jumpers, etc., is available at: http://theref.aquascape.com/ ------------------------------------------------------------ SUPP7. Problem - My LK401 keyboard unexpectedly autorepeats There are several modes of failure: a) Pressing 2 and 3 keys at the same time causes one key to autorepeat when released. Check the hardware revision level printed on the bottom of the keyboard. If the revision level is C01, the keyboard firmware is broken. Call field service to replace the keyboard with any revision level other than C01. b) Pressing certain keys is always broken. Typical sympypoms are: delete always causes a autorepeat, return needs to be pressed twice, etc. This is frequently caused by having keys depressed while the keyboard is being initialized. Pressing ^F2 several times or unplugging and replugging the keyboard frequently fix this problem. There is a patch available to fix this problem [contact the CSC for information - a CSCPAT number will be included here when available. - Ed.] c) A key that was working spontaneously stops working correctly. This may be either (a) or (b) or it may be bad firmware. Ensure that you have the most recent firmware installed on your CPU. An old version of the DEC 3000 firmware had a bug that could cause this symptom. [Fred Kleinsorge] ------------------------------------------------------------ SUPP8. Problem - My LK411 sends the wrong keycodes or some keys are dead Check the firmware revision on the keyboard. Hardware revision B01 introduced an incompatability with the device driver which causes the keyboard to not be recognized correctly. There is a patch available to fix this problem: [AXPDRIV06_061] - the fix is also included in OpenVMS V6.2. The rev A01 keyboard, and the LK450 should work without problems. [Fred Kleinsorge] [inazu_k] ------------------------------------------------------------ SCSI1. Are the 2X-KZPCA-AA and SN-KZPCA-AA LVD Ultra2 SCSI? Both of these controllers are Ultra2 low-voltage differential (LVD) SCSI controllers. ------------------------------------------------------------ WIRES1. Looking for connector wiring pinouts? DECconnect DEC-423 MMJ pinout: 1: Data Terminal Ready (DTR) 2: Transmit (TXD) 3: Transmit Ground (TXD-) 4: Receive Ground (RXD-) 5: Receive (RXD) 6: Data Set Ready (DSR) +------------------+ | 1 2 3 4 5 6 | +------------+ ++ +____+ The PC-compatible DB9 connector pinout follows: 1: Data Carrier Detect (DCD) 2: Received Data 3: Transmit Data 4: Data Terminal Ready (DTR) 5: Ground 6: Data Set Ready (DSR) 7: Request To Send (RTS) 8: Clear To Send 9: floating The MicroVAX DB9 console connector pinout predates the PC-style DB9 pinout, and uses a then-common (older) standard pinout, and uses the following EIA-232-standard signals: 1: Protective Ground 2: Transmited Data 3: Received Data 4: Request To Send (RTS) 5: Data Terminal Ready (DTR) 6: Data Set Ready (DSR) 7: Signal Ground 8: Shorted to pin 9 on MicroVAX and VAXstation 2000... 9: ...series systems, otherwise left floating. The BC16E-nn (where -nn indicates the cable length) cable key impliicitly "flips over" (crosses-over) the signal wires, so all DECconnect MMJ connectors are wired the same. // ---- ---- | |---------------------------------------| | ---- ---- \\ The BC16-E-nn cross-over wiring looks like this: Terminal Host MMJ MMJ DTR 1 --->-------------->----------------->--- 6 DSR TXD 2 --->-------------->----------------->--- 5 RXD 3 ---------------------------------------- 4 4 ---------------------------------------- 3 RXD 5 ---<--------------<-----------------<--- 2 TXD DSR 6 ---<--------------<-----------------<--- 1 DTR Also see: http://www.partner.compaq.com:9003/public/cheat_sheets/cables/padapters.html http://www.airborn.com.au/rs232.html For adapters and connectors, see MISC4. [Stephen Hoffman] [Mike Thompson] ------------------------------------------------------------ WIRES2. What connectors and wiring adapters are available? The H8571-B converts the (non-2000-series) MicroVAX DB9 to MMJ DECconnect. The MicroVAX 2000 and VAXstation 2000 requires a BCC08 cable (which has the 8-9 short) and the H8571-D for use with DECconnect. More recent Compaq (Compaq or DIGITAL logo) systems will use either the DECconnect MMJ wiring or (on all recent system designs) the PC-compatible DB9 pinout. DECconnect MMJ adapters: Part: Converts BC16E MMJ male to fit into: H8575-A EIA232 25 pin female (common) H8575-B EIA232 9 pin male (MicroVAX II console) H8571-D EIA232 25 pin male (modem-wired) H8571-J PC/AT 9 pin male (PC serial port) H8572-0 0BC16E MMJ male (MMJ extender) BC16E-** MMJ cable, available in various lengths Numerous additional adapters and cables are available from the _OPEN DECconnect Building Wiring Components and Applications Catalog_, as well as descriptions of the above-listed parts. The H8571-A and H8575-A are MMJ to DB25 (female) and are wired as follows: Also see: http://www.partner.digital.com:9003/public/cheat_sheets/cables/padapters.html http://www.networks.digital.com.au/dr/npgc/opdec-mn.html Jameco offers a USB-A to PS/2 Mini DIN 6 Adapter (as part 168751), for those folks wishing to (try to) use PS/2 Keyboards via USB-A connections. For wiring and pinouts, see MISC4. [Stephen Hoffman] [Eric Dittman] ------------------------------------------------------------ WIRES3. What is flow control and how does it work? XON/XOFF is one kind of flow control. In ASCII, XON is the [CTRL/Q] character, and XOFF is the [CTRL/S]. XON/XOFF flow control is typically associated with asynchronous serial line communications. XON/XOFF is an in-band flow control, meaning that the flow control is mixed in with the data. CTS/RTS is another type of flow control, and is sometimes called hardware flow control. Out-of-band means that seperate lines/pins from the data lines (pins) are used to carry the CTS/RTS signals. Both kinds of flow control are triggered when a threshold is reached in the incoming buffer. The flow control is suppose to reach the transmitter in time to have it stop transmitting before the receiver buffer is full and data is lost. Later, after a sufficient amount of the receiver's buffer is freed up, the resume flow control signal is sent to get the transmitter going again. DECnet Phase IV on OpenVMS VAX supports the use of asynchronous serial communications as a network line. The communication devices (eg. modems, and drivers) *must not* be configured for XON/XOFF flow control. The incidence of these (unexpected) in-band characters will corrupt data packets. Further, the serial line device drivers might normally remove the XON and XOFF characters from the stream for terminal applications, but DECnet configures the driver to pass *all* characters through and requires that all characters be permitted. (The communication devices must pass through not only the XON and XOFF characters, they must pass *all* characters including the 8-bit characters. If data compression is happening, it must reproduce the source stream exactly. No addition or elimination of null characters, and full data transparency. An Ethernet network is rather different than an asynchronous serial line. Ethernet specifies the control of data flow on a shared segment using CSMA/CD (Carrier Sense Multiple Access, with Collision Detect) An Ethernet station that is ready to transmit listens for a clear channel (Carrier Sense). When the channel is clear, the station begins to transmit by asserting a carrier and encoding the packet appropriately. The station concurrently listens to its own signal, to permit the station to detect if another station began to transmit at the same time -- this is called collision detection. (The collision corrupts the signal in a way that can reliably be detected.) Upon detecting the collision, both stations will stop transmitting, and will back off and try again a little later. (You can see a log of this activity in the DECnet NCP network counters.) DECnet provides its own flow control, above and beyond the flow control of the physical layer (if any). The end nodes handshake at the beginning to establish a transmit window size -- and a transmitter will only send that much data before stopping and waiting for an acknowledgement. The acknowledgement is only sent when the receiver has confirmed the packet is valid. (A well-configured DECnet generally avoids triggering any underlying (out-of-band) flow control mechanism.) [David Rabahy] [End of Part 5/5] --------------------------- pure personal opinion --------------------------- Hoff (Stephen) Hoffman OpenVMS Engineering hoffman#xdelta.zko.dec.com