Posts by Nigel 11
1554 posts • joined Wednesday 10th June 2009 11:28 GMT
Page:
Energy multiplier
Missed points?
You might consider the possibility of an energy multiplier, using one unit of electricity to get very many units of propulsion. It's called a rotor sail. Yes, you do need some wind, though with screw propulsion as a backup you'd never be completely becalmed. (The first use of steam on mostly-sailships was to escape from dead calm conditions).
Also the power needed to propel a ship rises as a high power of its velocity. Travel slower? Optimum velocity is an economic function of cargo and fuel costs. As for engine efficiency curve, that's an internal combustion problem. Electric motors can work efficiently over a wide range of speeds and power outputs.
A totally solar boat could do a LOT better!
This is a very poor design of solar boat. A test-bed for marine deployment of solar panels at best. Be a bit more ambitious!
The right way to go would surely be a rotor-sail ship with the rotors solar-powered. You'd be propelled by the wind whenever there was any, switch to direct propellor drive if becalmed. Rotor-sails use the Bernoulli effect to generate as much a 20 times more propulsive force than a sail of the same cross-sectional area as the rotors (which are vertical spinning cylinders). The amount of energy needed to make them rotate is small. They also need little manpower to operate them compared to sails, kite-sails, etc.
Also note that in a boat, crude lead-acid batteries should suffice to store solar energy. Weight isn't much of a problem for a boat. Indeed, many designs of boat require a considerable weight of ballast to stabilize them.
Sail plus solar has another advantage. Becalmed normally implies sunny, or at worst light overcast: a high-pressure system. Heavy cloud cover normally implies wind.
Big kernel lock has gone
This won't mean much to many, but recently the Big Kernel Lock has finally been removed. It's been a very long time going, so maybe that justifies going to 3.0
The write-lock switch, yet again.
The answer for all such issues, is to make the functionality work only if something mechanical has been done to the hardware. The classic is the write-lock button on an old exchangeable-platter disk drive. These days, any hardware that is user-flashable should have a firmware write enable switch (shipped OFF), and anything with a built-in password should have a built-in-password-enable switch (ditto shipped OFF).
Best, in my view, if the switch requires taking the cover off the equipment. But even more important, that these switches exist in the first place.
Netbook = Tablet - TouchScreen + Keyboard
Two things. Firstly, a netbook has a keyboard. For some modes of usage, prodding a tablet screen doesn't cut the mustard. For use on the move, up a ladder, etc. a separate wireless keyboard and mouse doesn't work either.
Also as far as the hardware is concerned, most of it is identical between a netbook and a tablet. The difference is keyboard vs touch screen. Is a touch screen cheaper than an ordinary screen plus a keyboard? I see no evidence of this in current prices ... rather the reverse, unless tablet manufacturers are profiteering off the hype.
The netbook format (physical, not necessarily Windows-compatible) will be around forever, or at least until there is a better way to input text than a keyboard. I'm not so sure about the tablet, once smartphones cost £100 or less.
Name ...
Cholomondeleigh?
Slartibartfast?
Excreted?
Some vitamin excesses are excreted or metabolised, some aren't. The ones that aren't can build up to dangerously toxic levels. I think I've read of people dying of chronic massive Vitamin D overdosing. Vitamin A is supplemented as beta-carotene rather than the vitamin, because the body turns carotene into vitamin A as needed, but can't get rid of a surplus of the actual vitamin.
The B vitamins (in Marmite) are excreted. In fact your body can't maintain a stockpile, so Marmite on toast every day is likely a good thing (but watch your salt intake). Tastes nice too!
Danes should be able to buy Marmite by mail order from another EU country. It would be against EU rules to block such imports (as well as totally impractical).
The Danes are being inconsistent. Vitamin C is also known by its E-number. It's commonly added to a huge range of foods as an anti-oxidant preservative (in quite small amounts compared to eating an Orange, let alone a Kiwi fruit, but even so, it is an added vitamin suppplement! )
Posted in Steve Ballmer window-dresses Windows 8
I hate all GUI redesigners.
If only the new user interface for Windows 7 *had been* just a different colour scheme!
Why can't anyone (even the Gnome folks on LInux) understand that not all users see a changed user interface as an improvement. Especially not if it is forced on us in one enormous downgrade with no route back up (XP to Vista or 7). Now Gnome have decided me-too, although at least on Linux there will be the option to keep Gnome 2 while upgrading the OS, for as long as someone deems Gnome 2 worth maintaining.
Why, for example, did anyone at MS think keeping most of the same control panel applets but renaming them and moving them around so that you can't find them any more using your XP experience, would be regarded as anything other than a confounded nuisance? Ditto Ofice 2003 to 2007.
Every time someone at MS changes the GUI, a billion people have to spend time re-learning what they already knew well. Every time, because they are distracted by the unfamiliar, some of them will make mistakes with the actual work they are trying to accomplish with their computer. Multiply an hour of wasted time and a day or two of frustration (and occasional consequential heart attacks) by a billion or so Windows users, and that's what the inflated egos of graphics designers and marketeers cost us. Fuck 'em all. I hate them.
Cool name
the cool name predates Skynet and Cylon - it was given to a purposeless buy eye-catching structure at the festival of Britain in 1951. This beast's fuselage is much the same shape.
http://en.wikipedia.org/wiki/Skylon_%28tower%29
$$$ cost
You quite assuredly would want the best compression you could get, if you were paying the bandwidth bill for a website that transmitted billions of images per day
Like Google.
More interesting is the green angle. Are compressed images unconditionally better because they eat less electricity in all the network routers? Or are they worse because they need extra CPU cycles to create them in the first instance? How many retransmissions equals one compression in CO2 emissions? (Sorry, no answers).
Escape tracking
You can escape tracking with any browser - just run it in a virtual machine that you blow away after each session. VMware player is free (-beer) as is any Linux-based browser application (containing Firefox, Chrome, Opera, ...). If it's IE you are after, MS probably expects you to pay for a second copy of Windows even if it's running inside your first copy.
What's hard is if you want to save state between sessions, but only state you approve of, and not the state that the rest of the world inflicts on you.
Try Scientific Linux?
If you want free beer and don't want to wait for Centos to solve its problems, then the answer is Scientific Linux, another RHEL clone. It's maintained for use by the particle physics communities at Cern and Fermilab, so it won't be going away soon, and SL 6.0 came out about 3 months after RLEL6.0 did (the usual timescale).
It's not quite the same as Centos, in that they do not maintain total bug-for-bug compatibility with RHEL, and do make a few tweaks. It's close enough for anything I've ever heard of where free-beer is acceptable. There's nothing specifically scientific about it other than the name, and a number of extra packages (not in RHEL) that don't install by default.
It's a bit premature to write off Centos ("reports of my death are somewhat exaggerated"). Red Hat made a number of distro-build utilities closed-source with RHEL6, so Centos have to develop their own build system. Progress is reportedly being made. I'd hope that once Centos 6.0 is out, they'll be able to catch up on the minor releases.
@Bear Features - probably true
I'm no Mac fanboi, but your statement is as true for a Mac as it is true for Linux. There's a big difference between a virus, and plain ordinary malware / crapware.
A virus spreads itself without any interaction with the computer's user. On a properly-designed operating system this is impossible, modulo any bugs. Provided such bugs are fixed promptly as soon as they are discovered, viruses are rare to nonexistent on that system (Unix, Linux, OSX). Some versions of Windows are broken by design rather than by mistake, and Microsoft is renowned for doing nothing about known bugs until some months / years later when a virus starts exploiting them.
Malware is the equivalent of giving the user a bottle labelled "Drink me". An idiot or child will do just that, without asking any questions, and whatever happens next is his own fault (or the fault of whoever gave him administrator access to that computer - his parent or school, for example).
On a properly-designed operating system it is possible, indeed normal, to use the system without having the ability to install anything. On a multi-user system, only the administrators can do installs, and you are as safe as your admins are competent. On a sensibly-configured single-user linux, its sensible single user normally runs unprivileged, and nothing gets installed without the user doing rather more than just clicking "OK" by mistake. IMO, Anything that makes software installing easier than logging in as root or invoking su, is a mistake. Humans suffer from their conditioned reflexes taking over simple repeated tasks. Dangerous tasks should never be made simple enough for the conscious brain to escape from the loop.
UAC Unix-like?
Unix-like is surely a requirement to log in as or su root in order to install the download. Mere users don't know how to do that or haven't been authorized to do that.
On Linux there are some desktops where package installation has been "made easier". This, in my opinion, is a big mistake. Drinking potential poison should not be made easier, it should be made harder. Being able to do so by clicking "yup" is a big mistake, on any system where it's possible.
Not quite that simple
If the planet had rather more water than the Earth, it would be ocean over most of it (maybe with islands, or not). Anyway, ocean circulation might be able to maintain a habitable temperature, and not just in the twilight zone. Sure, some of the surface might be at 100C and some of the other side frozen, but the ocean depths might well be at 4C just as on Earth, because water is denser at 4C than at hotter or colder temperatures.
That's stil quite Earthlike. It's also possible to imagine a planet with many tens or hundreds of kilometers of water depth. I don't think we know enough to speculate what might or might not be possible in such ocean depths, any more than whether life can exist deep in a gas-giant's atmosphere. For all we know, there may be life within Jupiter, and a hot Jupiter might be an even better place to look.
Maybe the answer to the Fermi paradox is that all the aliens "know" that there's no point looking for life on low-gravity slightly damp balls of rock?
Indeed...
The obvious things:
Stimulant -> raised blood pressure -> increased heart attacks, strokes?
Dark roast -> carcinogenic organic chemicals created -> digestive system cancer risk?
These are guesses. A long-term study of heavy coffee drinkers against a control group is needed, before coffee can be recommended for warding off prostate cancer!
Posted in Pint-sized 3D printer produced
Jewellery revolution
This might revolutionize the jewellery business, if they can print in wax or a acceptable plastic alternative for "lost wax" casting in gold or silver. (You need something that can be burned without toxic fumes or any solid residues).
3D graphic designing is a lot easier than sculpting tiny details in wax, and some geometries would be possible that are all but impossible to sculpt from a solid lump.
Emulator?
It's not beyond the realms of possibility to run x86 code in an emulator / interpreter on an ARM system. Sure, performance would be seriously lower than natively, but for some classes of apps that may just be a matter of 10ms per user-interaction rather than 1ms. Provided Windows was done right, all system calls would be in native mode, and it ought to be possible to call some shared-library code in native mode as well.
Posted in Third mighty WD 'data tub' launched
What??
"Now these really would be big fat data tubs as EMC calls them, but best used for desktop systems rather than in RAIDed storage arrays, where the RAID rebuild time would be diabolically long."
That's utter BS!
You use RAID if you want to be sure that when a drive fails, you still have your data both safe and on-line. If you have 20Tb of such data, then a 5- or 6-drive RAID of 5Tb drives would be ideal. The only alternative is a larger number of smaller drives, also RAIDed.
Personally I'd call for RAID-6 not RAID-5, because the rebuild time will indeed be long, and the chance of another drive error during that rebuild time is therefore higher - perhaps 10x what it would be for 500Gb drives.
Apart from that, just let the system get on with it. Using Linux software RAID, access by users to the data on the array is prioritized over rebuilding, so performance isn't noticeably poor during a rebuild, and if the rebuild takes several days, so be it. (That's a RAID-6 rebuild so you can survive losing another drive during that window ... I might have trouble sleeping if it were RAID-5, imagining that the first drive failure might signal a comon-mode fault with the others).
With the alternative, using (say) 50 or 60 500Gb drives, you'll be replacing them maybe 10x more frequently, so the total time per annum in rebuild may well be much the same, and the human time spent drive-swapping 10x greater. True, with more spindles you may get more performance ... but in the applications I look after, performance isn't an issue. Our researchers just need many Tb of data on-line and safer than relying on single drives not to fail.
Sin to extract cash ...?
I don't think so, as long as you take the money in good faith and genuinely care about pets. You're offering someone peace of mind, which is a much better product offering than, say, Windows Vista and a pre-installed crapware bundle on a PC with 0.5Gb RAM. In the unlikely event of the Rapture during the pet's lifetime (or yours if shorter), with both yourself and the insured pets being left behind on a survivable earth, you'd use best efforts to look after the pet(s).
It's a perfectly ethical insurance policy. Unless you get a lawyer to write it, and he puts in the usual disclaimers about force majeure and acts of God. Hmmm, must find out, where and what did Dante envisage for lawyers?
World's end
The reason there are many pubs, and even places, called the World's End. All the unrepentant sinners gathered there on the promised last day, to enjoy their last opportunity at enjoyment for, er, all eternity thereafter. When the day passed uneventally, they re-named the pub.
The original typo
GOD ... DOG ... ?!
Echoes of Digital?
Seems like the Digital (DEC) story all over again. Market-leading high-tech company loses its way, suffers infighting verging on civil war, gets infiltrated by the worst sort of top-level managers, is sold out to loser(s) / competitor(s) that chiefly want a customer base, and to kill off all the great technology that wasn't invented by them.
With Digital there was the added spice of Kenneth Lay (later of Enron infamy) on the board. I've always wondered whether there was an active conspiracy within the company's board, to destroy the company. We'll probably never know.
And now Nokia treads the same path to oblivion. What a shame.
I'll be hanging on to my fairly ancient Nokia candy-bar phone that I kept as a spare. Like certain DEC microcomputers, I expect it to last for a decent approximation of forever. It was all downhill from there.
Posted in BOFH: Every silver lining has a cloud
TRue BoFH territory
"the inch of water from the burst water main that had already claimed their floor-mounted UPS units..."
I wonder, did the on-call bod have enough of a clue to make absolutely sure that the *uninterruptible* power supply had indeed managed to interrupt itself in this circumstance?
Splish. Splash. Kzeeert, as the ripples reach the UPS "on" button height and convince the thing to make one last heroic effort at uninterruptibility.
Spain
Strange, I was in Spain recently and the driving didn't seem any worse than the UK.
Posted in BOFH: Every silver lining has a cloud
Yes, never.
It's a bad idea for your systems to be anywhere that might get submerged in what might euphemistically be called water under the influence of nothing more than gravity.
There's a BOfH to be written in which a competitor's subterranean datacentre gets cross-connected with a six-foot main sewer, at the same time that all of the blast-proof security doors mysteriously slam shut. Or something like that.
Posted in Official: phones sting bees
Obvious explanations for city bee success
Less insecticide exposure, a more natural habitat.
Urban parks are not heavily sprayed with insecticides, unlike crop fields. I suspect that many gardens and parks are "green", not sprayed at all.
More natural? Yes, many parks have large areas of natural meadow and wooodland, and even the carefully managed flower borders are more natural than the multiple square-mile monocultures that farmers create. Cities are also full of man-made nooks and crannies that bees can nest in, though that's perhaps more relevant to bumble-bees than honeybees.
Also, honeybees have been bred by beekeepers for many millennia. I wonder how inbred and weakened the species might be by now? Do wild honeybees still exist? (apart from the African ones ... crossbreeding domesticated bees with those was not a great success for humans, though the bees might think differently).
Posted in Official: phones sting bees
Inverse-squares law
The strength of EM radiation falls of as the square of the distance from the source. Therefore a mobile at 10cm is 100 times stronger than a mobile at 1m and 100 million times stronger than a mobile at 1km.
Cell towers operate continuously and at somewhat higher power than a single mobile, but for human phone users, even humans living adjacent to a cell-tower, it's the phone next to their head that's creating the greatest level of exposure. As for bees, the obvious study is of hives next to a mobile base-station tower, 50m distant, and 500m distant. I'd guess that the bees will be OK adjacent, but even if every cell-tower has a small radius of bee-confusion around it, that's unlikely to threaten the species.
The basis for my guess. If mobile EM radiation upset bees that much, there would be no bees at all in big city centres where cell density is close to saturation point. A visit to any park shows that's not the case.
Posted in Reg ed rattles the Red-Headed League
Completely non-racist technical comment
The gene for red hair is more common amongst Celts than other peoples. It's recessive, masked if one also has the genes for black hair. It might have been unique to Celts, many millennia ago, but since then it's been spread around quite a bit.
Flame bait for racists: outbreeding is better for one's children than inbreeding.
Posted in Crucial M4 256GB Sata 3 SSD
Wrong!
"Short of a major CPU upgrade, an SSD is the best performance addition you can really go for"
That's comparing chalk and cheese. There are many workloads (those involving intensive access to many smallish files) where a faster CPU will buy you very little, and an SSD will result in a spectacular gain. Booting an operating system tends to be one of these.
Odd...
Odd, that no-one is keen on "Look to Windward" or "Against a Dark Background".
"Look to Windward" has a relatively straightforward plot to film, and a Mind that mere humans can easily empathize with. Perhaps a bit gloomy, but some great movies are. I thought this might be the last Culture novel when I first read it - had the feel of an author closing the door on his creation.
"Against a Dark Background" isn't part of the Culture series, so carries less baggage. Again, could make a great film.
I really hate Skype
Skype is the ultimate security-by-obscurity product.
I don't know what it does inside, and I can't pin any blame on it except by correlation, but statistically in my experience, it's the PCs whose users have installed Skype that go down with malware infestations, and the ones that haven't that don't.
One good thing MS are going to do ...
... is support ARM for Windows 8. Which will create a market for PC-format ARM boards with all the canonical PC interfaces. Which will mean that at last, low-power always-on LInux boxes won't be tied to obscure overpriced hardware, or graphics-deprived hardware like Pogo/Guru plugs.
As for tablets - no keyboard, fundamental flaw. I'd rather have a notebook-format device. At present there isn't even any cost saving for not having a keyboard.
USB current limit and extra power
I can confirm that USB ports shut down and generate a software warning if something tries to take too much current. On my PC, anyway.
If you need more than the USB current limit but less than twice as much, you can do what the vendors of some USB disk drives do. Supply a special USB cable with two host connectors, one for power + data and the second for extra power.
In the case of something containing a battery it should always be possible to charge off USB when the device is off, even if it would overload the USB with the device on. If you were really smart you'd have two batteries, with the device running off one while the other charges, with a controller switching the batteries around every few minutes. That way even if the power going out was in excess of the power going in, at least USB wouldn't overload, and you'd extend the runtime, though not to infinity.
Unlikely?
"Or, for that matter, Intel could license the ARM architecture and start buiding its own ARM variants in its own fabs, using its 22nm Tri-Gate process"
I'd have thought, more like a dead cert, than unlikely.
If Intel has the best process technology for low-power devices, ARM without question has a better CPU architecture for low-power devices like Smartphones. Put them together and what do you get? The best possible Smartphone CPU, that can either double battery runtime, or allow for a large cut in the weight of the phone without any loss of runtime.
If Intel suffers from the "not invented here" syndrome, Smartphone manufacturers will have to choose between i86 architecture running on the best Silicon, or ARM running on less good silicon. It won't be so long before TSMC or some other chip foundry catches up with Intel enough to put ARM back at the front of the pack. Best for Intel if it's Intel that makes the best mobile device chips.
Kiddie-porn. MALE kiddie-porn.
Whether true or not, the more folks believe it, the better.
It's a mistranslation
A more learned punchline would be Allah telling bin Laden that "houris" was a mis-translation between Syriac and Arabic, and then giving him his 72 sultanas (sweet dried grapes)
Oddly, sultana / sultanah is almost the same mistake in English!
An error
"Tape's cost/GB stored blows disk away". Oh no it doesn't!
Prices just Googled: LTO5 cartridges about £50 (1.6Tb). 1Tb SATA disks about £33. Cost/Tbyte about the same. And then there's the cost of a very expensive tape drive to factor in. Disk just needs a hot-swap enclosure and a few caddies, or a raw-drive docking station.
Of course it's comparing different sorts of fruit. Tape wins for offline off-site storage, because a tape cassette is mechanically rather more robust than a SATA disk. On the other hand, Rsync or similar algorithms across a network to a remote disk mirror is far more accessible for things like recovering accidentally deleted or corrupted files, or doing post-mortems after TS hits TF.
I know someone who'd have wanted to buy one of those
Ever tried to buy a Ukrainian keyboard in the UK?
He carefully painted the tops of all the letter keys black. Then he equally carefully relabelled them in Ukrainian.
Someone should sell a blank keyboard with stick-on labelling for every known keyboard variant in the world. Also Klingon and Elvish.
Not an IT company?
More a disinformation technology company?
Vibration
I've heard it said that one head actuator seeking inside an HDA would create so much vibration as to prevent any other heads from being stable enough to read or write. If you couldn't do seek and read/write concurrently, there wouldn't be very much point in multiple heads.
Reportedly, this can even be a problem between disk drives in a badly-designed multi-drive cage: if all drives are engaged in seek-intensive activity, the vibration mechanically coupled between them can degrade each other's performance. Or so the manufacturers of heavy-guage server towers with rubber drive suspension bushes claim. OTOH it might work on the same basis that wearing a paper bag over your head in the UK keeps the elephants away.
@Graham Wilson
You do have quite a few namesakes out there. Care to post your address as well? I'll guess not.
I do post under a unique registered name, which any computer-savvy person might hack through to my true name. I don't volunteer my surname directly because I have few if any namesakes out in the real world.
Proof?
Proof is hard to come by, but there are a lot of former colonies to study.
I can't help comparing Vietnam with Zimbabwe. Vietnam was first colonised, then carpet-bombed by a super-power. Despite this (and a subsequent detour into communism) it's become a halfway decent country to live in. At least by comparison with Zimbabwe, which escaped the carpet-bombing. Then there's South Africa, which shares a very similar history with Zimbabwe, up until its first democratic election. Or Liberia, which never was a colony, and turned itself into hell anyway (or rather, a few of its people did so, with the rest powerless).
Looks to me like the influence of the former colonial power fades pretty quickly, compared to the influence of the politicians or megalomaniacs running the show afterwards.
Seek time worse?
That depends on your usage pattern. If you are reading huge sequential files stored without significant fragmentation, then the 3-platter drive may have to do a one-cylinder seek 5/3 times as often as the five-platter one. A one-cylinder (minimum) seek is much faster than a random seek. It could also be optimised, if the start of each cylinder is rotated with respect to the previous one by an amount of rotation with a latency just slightly bigger than the one-cylinder seek time.
If your typical file is smaller than one three-platter cylinder, both drives will be pretty much identical.
While thinking about performance, isn't this technology crying out for use in a small-platter drive spinning at 15000 rpm or faster? With twice the competition's areal density, they could make an ultra-fast drive twice as capacious. The last gasp of the sub-Terabyte hard disk, before SSDs take over?
Anime?
I'm sure most of them could be filmed, even filmed well, if one counts Anime as film.
Also judging by Smeagol in the film of LoTR, special effects these days is quite capable of realising any sort of alien life-form. It's our extreme familiarity with human beings that makes computer-generated people look slightly wrong. Give it another decade or two ....
A Fire upon the deep
True, far too much to make into one movie. Would work as a series (but how to afford the special effects in something made for TV?) Anime?
Sad, because it has something I haven't found elsewhere in literature (except possibly, Lord of the Rings). A sense of what it's like to be caught up in vast events ot only utterly beyond one's control but beyone one's comprehension, armed with little more than hope that one might be able to do something rather than nothing.
(Also the really cool idea that interstellar FTL bandwidth might be measured in mere bits per second, making the galactic net look a lot like the internet of the early 90s! )
Filming Canticle
"A Canticle for Liebowicz" could make a great movie, but would almost certainly be made into a truly dreadful travesty of the book. It's chances would be somewhat better if it were made into a 2-hour drama or 3-episode series by an independent TV company or by the BBC (please? ). Unlike most, it could manage with a very small special effects budget. Spend the money on good actors instead.
Why probable travesty? Because most directors would not put their prejudices aside and let the characters speak for themselves. In a book the author can let you know where he stands without warping his characters. In a film, that can't be done.
BTW, it could also make an excellent stage play, unlike just about any of the others. Even better chance of getting it right in that format?
Polycyclic Aromatic Hydrocarbons are mostly bad
True, a benzene ring with a substitution isn't carcinogenic in the same way as benzene. However, most of the polycyclics are evil carcinogens, with the notable exception of Naphthalene (C10H8, two rings), otherwise known as mothballs.
Hurdle depends on the physics
It won't be nearly such a big hurdle if energy costs keep rising, and the amount of processing you can do on an ARM system per watt-hour remains many times the same for an i86_64 system.
Of course, adoption of ARM has to be made reasonably practical. ARM boards have to become available as commodity products at a comparable price to an Intel one (say £60 for ARM CPU + motherboard competitive with Atom CPU + board of similar performance). They have to have standard interfaces (SATA, USB, ATX PSU connector, etc). And they have to run mainstream O/Ses. Windows 8 is going there. Linux already is there, but we'll need RHEL for ARM and a more standardised ARM board ecosystem before it takes off.
Stupid taxation rules
It's stupid (utterly, completely pig-headedly stupid) to tax a fuel by volume, or to compare distance-per-volume. Diesel is a denser fuel. One liter contains more carbon (hence more CO2 when burned) and more energy (hence better mpg for cars of similar weight and power).
Fuel should be taxed as energy, so the tax per volume on diesel *should* be considerably higher than on petrol per unit volume. Not equal, definitely not less! This would allow motorists to select the best vehicle for their needs, on a taxation system that doesn't discriminate.
Diesels have a small thermodynamic efficiency advantage because of the higher compression ratio. This is more significant for big engines (HGVs) than for small ones (cars). Therefore for the best use of our crude oil imports, the majority of cars should use petrol. We can't do all-diesel: an oil refinery creates both petrol and diesel and has limited ability to adjust the proportions.
BTW I drive a diesel. The distorted tax system made that make sense. In a sane world I'd have chosen petrol (quieter engine, less pollution, with sane tax a lower running cost, after the expensive fully-synth oil and shorter service intervals that a diesel needs is allowed for).
Also BTW - there's a trade in refined petroleum products across the Atlantic, driven by this same tax anomaly. USA car drivers hate diesels (low winter temperatures may have something to do with it). So we ship surplus petrol to the USA, and they ship their surplus diesel back.
