The Apollo ground stations had phase-lock loop receivers that could compensate for doppler. Doppler measurements were used as part of the range and range-rate system that was used to determine the spacecraft's position and velocity.
Now that it has been released, what 64-bit compilers are available for the operating system? The last time I looked, Microsoft was planning to use an ugly data model (LLP64) where only "long long" variables and pointers would be 64-bits. To me, that's a chicken-shit decision, broken code should be fixed or rewritten, not accommodated by crippling the compiler.
1996 Act required that broadcasters' agree to surrender one of their licenses as a condition of receiving a second DTV license. ( 336(c))
FCC set 2006 as the target date for return of the analog license on which broadcasters currently operate. Fifth Report and Order, 99. It pledged, however, to monitor deployment of DTV and to modify the surrender deadline if necessary. ( 100)
The Balanced Budget Act specified that no analog broadcast license may be renewed beyond December 31, 2006. (143 Cong. Rec. H6032-H6033, adding new section 309(j)(14)(A) to the Communications Act). At the same time, Congress directed the FCC to extend that deadline in any television market:
if any ABC, NBC, CBS, or Fox affiliate in that market is not broadcasting a DTV signal, assuming that the FCC finds that the station has exercised "due diligence" in trying to deploy DTV;
if digital-to-analog converter technology is not generally available in the market; or
if 15 percent or more of the households in the market do not subscribe to a multichannel provider (e.g., cable, MMDS, DBS) that retransmits at least one digital programming service from each DTV station in that market and those households do not have a digital television set or digital-to-analog converter.
I believe ATSC was developed before DVB-T. While there are some technical considerations, much of it is politics and economics. If the USA developed a matter transporter that operated at 50 THz, Europe would design a competing transporter that operated at 51 THz. Japan and China often do similar things to protect their own manufacturers and markets.
...or have access to the local digital channels through cable or satellite service. The FCC doesn't care how you get the channels, just that you get them.
In most places, there's no place to move them to. The FCC has a set of complex rules that determine the geographic spacing of stations on the same and nearby channels. This prevents interference between analog television stations. Just because a channel is unused doesn't mean that it is available for a new television station.
The savings in spectrum is derived from the relaxation of the rules concerning channel spacing and geographic separation that were necessary to prevent analog stations from interfering with each other. The channels aren't smaller, but the unused space between active channels has been reduced.
One of the nice features of ATSC is the support for multiple SD program streams. The local PBS stations take advantage of this to broadcast three or four separate programs during daytime hours. They can simultaneously broadcast a kids program, a documentary and a college telecourse.
Another nice feature is the electronic program guide that isn't cluttered up with ads.
I recently bought a refurbished ATSC set-top box (Samsung SIR-T451) for $160. New, it costs about $240. That's all I needed to watch digital TV on my standard NTSC television set. The STB down-converts everything to 480i for compatibility with NTSC television sets. If I had an HD monitor, I could set the output to 480p, 720p or 1080i.
I live in an area with poor to mediocre analog television reception, lots of noise and ghosts. There's a very noticeable improvement in picture and sound quality when watching the digital signals from the local television stations. It isn't perfect, they are glitches and dropouts when the signal fades, but it is much more watchable than the analog version. I'm using a cheap indoor UHF antenna.
I upgraded to digital television with a total expenditure of $190, $160 for a STB and $30 for an antenna. That doesn't seem unreasonable to me.
Tape works great if you are willing to make the investment in high-quality hardware, backup software that actually works, a well-designed process, testing, maintenance, and people. Unfortunately, that is rare. Most low-end tape drives are crap. You need multiple drives for reliability and interoperability. They need regular maintenance. Can the vendor support the drives with spare parts, repair and overhaul services, replacement drives, for the long term? Where are the tapes stored? How are they organized and tracked? How often do you simulate failures or disasters, and verify that the process actually works?
The PDP-11 had a beautiful instruction set. Even though R6 and R7 had special uses, they could also be treated as general purpose registers. You could index off the program counter for position-independent code and data. All of the addressing modes worked with all of the registers.
The 8086 was still, at its heart, an accumulator oriented machine, even though it made some efforts at generalizing the register pairs (AX, BX, CX, DX).
Because systems with 4 GB or more of RAM are going to be commonplace in the not-too-distant future. A 64-bit operating system is needed to make efficient use of that much memory. You may not need that much memory, but it will eventually become standard. Many Windows PCs are already being sold with 512 MB of RAM as the base configuration.
When they say virtual memory, I think they actually mean virtual address space, the maximum address space for a process. NT and its descendants have a 4 GB address space, split into 2 GB for the user and 2 GB for the system, just like the VAX.
I didn't think that the 8086 had any GPRs. The instruction set had so many limitations and special cases, which made life miserable for anyone trying to write a good code generator for a compiler.
It also radiates substantial amounts of electromagnetic interference (EMI). That's why the FCC has regulations that require computers to be tested and certified for EMI before they are offered for sale in the USA.
There has been a great deal of automation. That's one of the reasons that the Saturn V was cancelled. It took an army of engineers and technicians to prepare and launch the thing.
That just makes things worse. A cosmic ray hits an atom of lead and produces a shower of less energetic particles, which still have enough energy to cause damage and flip bits.
One important point that the author missed was determinism. Many of these computers are used in hard real-time applications. If the tasks don't meet their deadlines, the system has failed. This requires predictable timing. That means cache is a liability, as are many of the advanced features of modern processors. You need to be able to sit down with a program listing and count how many CPU cycles it takes to execute a segment of code. If you have a 10 ms time slot to do a task, you have to be able to prove that the code can run in less than 10 ms. If you poll a set of sensors every 100 ms, you want the timing to be identical every time the code runs, to eliminate timing jitter in the measurements.
The controller for the SSME (Space Shuttle Main Engine) uses a pair of 68000 processors. It is a very critical system. If something starts to go wrong with the engine, it has to detect the problem and shut the engine down before it progresses to a catastrophic failure. It uses two redundant processors for reliability. Each engine has its own controller.
Old microprocessors like the 80386 and the 68000 were the last commercial processors before cache, pipelines and other trickery made timing analysis difficult or impossible. Some people have used DSPs for controllers because they still offer predictable timing.
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The Apollo ground stations had phase-lock loop receivers that could compensate for doppler. Doppler measurements were used as part of the range and range-rate system that was used to determine the spacecraft's position and velocity.
I'd like to see some of these programmers try to compile their code on a word-addressed machine like a Cray, where most arithmetic types are 64-bits.
Now that it has been released, what 64-bit compilers are available for the operating system? The last time I looked, Microsoft was planning to use an ugly data model (LLP64) where only "long long" variables and pointers would be 64-bits. To me, that's a chicken-shit decision, broken code should be fixed or rewritten, not accommodated by crippling the compiler.
Is it necessary for you to put your prejudices and neuroses on public display? It isn't flattering.
You might want to take a moment to remember Billy Dale, his fellow employees, and other innocent victims of Democratic purges.
From http://www.ntia.doc.gov/pubintadvcom/octmtg/tatalk .htm:
I believe ATSC was developed before DVB-T. While there are some technical considerations, much of it is politics and economics. If the USA developed a matter transporter that operated at 50 THz, Europe would design a competing transporter that operated at 51 THz. Japan and China often do similar things to protect their own manufacturers and markets.
...or have access to the local digital channels through cable or satellite service. The FCC doesn't care how you get the channels, just that you get them.
In most places, there's no place to move them to. The FCC has a set of complex rules that determine the geographic spacing of stations on the same and nearby channels. This prevents interference between analog television stations. Just because a channel is unused doesn't mean that it is available for a new television station.
The savings in spectrum is derived from the relaxation of the rules concerning channel spacing and geographic separation that were necessary to prevent analog stations from interfering with each other. The channels aren't smaller, but the unused space between active channels has been reduced.
Another nice feature is the electronic program guide that isn't cluttered up with ads.
The data bandwidth is 19 Mbps per 6 MHz channel.
I live in an area with poor to mediocre analog television reception, lots of noise and ghosts. There's a very noticeable improvement in picture and sound quality when watching the digital signals from the local television stations. It isn't perfect, they are glitches and dropouts when the signal fades, but it is much more watchable than the analog version. I'm using a cheap indoor UHF antenna.
I upgraded to digital television with a total expenditure of $190, $160 for a STB and $30 for an antenna. That doesn't seem unreasonable to me.
Tape works great if you are willing to make the investment in high-quality hardware, backup software that actually works, a well-designed process, testing, maintenance, and people. Unfortunately, that is rare. Most low-end tape drives are crap. You need multiple drives for reliability and interoperability. They need regular maintenance. Can the vendor support the drives with spare parts, repair and overhaul services, replacement drives, for the long term? Where are the tapes stored? How are they organized and tracked? How often do you simulate failures or disasters, and verify that the process actually works?
The 8086 was still, at its heart, an accumulator oriented machine, even though it made some efforts at generalizing the register pairs (AX, BX, CX, DX).
Because systems with 4 GB or more of RAM are going to be commonplace in the not-too-distant future. A 64-bit operating system is needed to make efficient use of that much memory. You may not need that much memory, but it will eventually become standard. Many Windows PCs are already being sold with 512 MB of RAM as the base configuration.
When they say virtual memory, I think they actually mean virtual address space, the maximum address space for a process. NT and its descendants have a 4 GB address space, split into 2 GB for the user and 2 GB for the system, just like the VAX.
I didn't think that the 8086 had any GPRs. The instruction set had so many limitations and special cases, which made life miserable for anyone trying to write a good code generator for a compiler.
The Alpha was 64-bit, the Alpha version of NT was mostly 32-bit due to the architectural limitations of NT.
I've seen people do similar things, and worse, in real life. If you want to be weird, you're going to have to try harder :-).
It also radiates substantial amounts of electromagnetic interference (EMI). That's why the FCC has regulations that require computers to be tested and certified for EMI before they are offered for sale in the USA.
See Computers in Spaceflight: The NASA Experience by James E. Tomayko.
There has been a great deal of automation. That's one of the reasons that the Saturn V was cancelled. It took an army of engineers and technicians to prepare and launch the thing.
That just makes things worse. A cosmic ray hits an atom of lead and produces a shower of less energetic particles, which still have enough energy to cause damage and flip bits.
The controller for the SSME (Space Shuttle Main Engine) uses a pair of 68000 processors. It is a very critical system. If something starts to go wrong with the engine, it has to detect the problem and shut the engine down before it progresses to a catastrophic failure. It uses two redundant processors for reliability. Each engine has its own controller.
Old microprocessors like the 80386 and the 68000 were the last commercial processors before cache, pipelines and other trickery made timing analysis difficult or impossible. Some people have used DSPs for controllers because they still offer predictable timing.