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Comment: Re:The problem is not switch speed (Score 3, Informative) 183

by lowen (#47306381) Attached to: How Vacuum Tubes, New Technology Might Save Moore's Law

One of the problems with increasing clock speed is gate capacitance and the RC time constant charging curve causing the switching FETs to operate in the linear region, causing power dissipation to go up with clock speed. This is why a decrease in process size has typically yielded a corresponding decrease in power dissipation at a given clock speed.

If you make the capacitance smaller, you can increase the switching speed (capacitance would decrease with the square of the feature size (gate capacitance is dependent upon gate area), wheras resistance would increase linearly, inversely proportional to feature width, assuming the feature depth doesn't change (resistance dependent upon cross-sectional area)).

Another poster has already mentioned asynchronous designs, so I'll pass on that particular nuance.

But clock propagation is a serious issue, and I can see a vacuum transistor improving this considerably.

Now, figuring out how far a wavefront will propagate in some period of time isn't too hard.

Undoped silicon has a relative permittivity of 11.68; the reciprocal of the square root of the relative permittivity is the velocity factor of a particular dielectric; for undoped silicon that's about 30% of c. Silicon dioxide, as used for most of the insulation on the typical MOSFET design, has a relative permittivity of 3.9 and thus a VF of about 51%. On a stripline laid on silicon dioxide (silica glass) the velocity of propagation is about 153 million meters per second, or 153 meters per microsecond or 153 millimeters per nanosecond or 153 microns per picosecond. 153 microns is a bit larger than the cladding on a typical fiber optic strand (most have a cladding diameter of 125 microns; OM1 multimode is 62.5 micron core/125 micron cladding, OM4 is 50 micron core/125 micron cladding, and single-mode is 8 micron core/125 micron cladding, for comparison). That's best case propagation time.

Now, to see how this translates to something of today, at least one of the models of the latest Haswell-DT Core i7 chips has a die size of 177 square millimeters. The chip is not square, and seems to be about a 4:1 rectangle in photos, which would yield about a 6.5 mm by 27.25mm die (yes, I know that gives 177.125 square millimeters; close enough).

Now, if a clock signal needs to go straight across the narrow portion, it will take about 42.5 picoseconds to do so, assuming transmission across silion dioxide alone. Propagation in the long direction would take about 178 picoseconds to do so, with the same assumption. The published top speed of this processor is at the time of this writing about 4.5GHz (I know it's a bit higher, but that's a moving target). This is a 222 picosecond clock period; easily doable in the short dimension, a bit more difficult in the long dimension, and probably already requiring some asynchronous elements and delay compensation. If you limit solely on clock propagation time, and are able to work in a slip of a full clock cycle, the long dimension will give you a limit of a bit over 5.5GHz; the short dimension will similarly give you a limit of 23.5GHz.

That's drastically oversimplified; each gate has it's own propagation delay that must be figured, and there are four cores (which makes it pretty understandable why the chip would have a 4:1 die dimension ratio, no?). A 20% clock delay factor will allow, with care, a good chance for synchronous operation (42.5 is pretty close to 20% of 222), but that's assuming straight clock traces (and they are not just straight across the chip).

Food for thought.

Comment: Re:Are there any old drives around that read these (Score 1) 481

by lowen (#46869971) Attached to: US Nuclear Missile Silos Use Safe, Secure 8" Floppy Disks

I seem to recall from my BIOS writing days with CP/M, that the 8" drives had twice the data rate of the 5" drives. They also spun faster, 360 RPM vs 300 RPM. The 8" IBM format was soft sectored 26 sectors of 128 bytes, and the 5" used 16 sectors of 128 bytes or something like that. too many numbers to remember.

Right, for the 360K double-density 5.25.

Like the 8 inch System/34 format, the 5.25 high-density drive in the PC AT also ran at 360 RPM instead of 300, and had double the data rate of the double-density 5.25 inch drives, yielding exactly the same number of sectors per track, with the only difference being that the 8 inch has 77 tracks and the 5.25 HD drive has 80.

Comment: Re:Now was it ... (Score 2) 481

by lowen (#46868173) Attached to: US Nuclear Missile Silos Use Safe, Secure 8" Floppy Disks

Well, in my experience the good quality double-sided drives are more reliable as they age. The reason being is that a single-sided drive has a rather critical piece of felt as a pressure pad on the top surface, and those pads are notorious for the glue holding them to the head carriage drying out and causing them to fall off.

Double-sided drives, on the other hand, have an actual head on the top surface and those tend to stay put.

Comment: Re:Are there any old drives around that read these (Score 1) 481

by lowen (#46868029) Attached to: US Nuclear Missile Silos Use Safe, Secure 8" Floppy Disks

I've got to see pics of that, as that would be one rare 4P (I have two in my office right now.....). The case after all only allowed two Tandon TM-50 single-sided 5.25 drives to fit.

Now, the Model II had a single internal full-height 8; the 12, the 16, the 16B, and the 6000 had two internal 'slimline' 8's.

And 8's were the most common for the various CP/M boxen. Side-by-side 8's fit quite nicely in a 19 inch rackmount chassis, such as several boxen by Altos.

Then there were the RX01 and RX02 drives for PDP 11's.

Comment: Re:Floppy drives? (Score 2) 481

by lowen (#46867949) Attached to: US Nuclear Missile Silos Use Safe, Secure 8" Floppy Disks


I know this is opening things up for lots of bad jokes..... but, it really boils down to whether the cookie's lubricant is still effective at allowing the cookie to spin to the correct RPM, +/- the FDC's tolerance. And that is dependent upon the storage conditions (mostly humidity) and the media quality. Being in a military application, this media is likely the most expensive made, if not the highest quality.

Yes, the actual magnetic media is called a 'cookie.' And the word 'cookie' is a bit more difficult to twist into a bad pun.....

If the dry lube used in the oxide coating on the cookie has become ineffective, then there will be a rather distinct screeching sound as oxide (and your data) flakes away. There are techniques to overcome this with bad media; however, back when 8 inch media was common it was also far higher quality that the cheap 5.25 media of the 80's was, and those 5.25 diskettes are the ones that have given my data recovery attempts the most difficulty.

Comment: Re:Are there any old drives around that read these (Score 5, Informative) 481

by lowen (#46867805) Attached to: US Nuclear Missile Silos Use Safe, Secure 8" Floppy Disks

Yes, there are. I have one, and a Catweasel controller that can read and write basically any format on it.

The 8 inch standard format is very similar to the 1.2MB 5.25 inch format. Actually, it's the other way around, as when IBM built the PC AT and the high-density drives for it they apparently intentionally made the formats nearly identical. They're so close that computers that use 8 inch diskettes can typically be modified to run with 1.2MB HD 5.25 drives and media with only a new controller to drive cable and new drive power supply (8 inch drives typically take either AC mains power to run the spindle or 24VDC, and 5.25 drives take 12VDC to run the spindle). See for some tech info on how to do this with one of the first multiuser 'personal' computers, the Radio Shack TRS-80 Model 16 (and descendents the 16B and the 6000). Also see for the 'proper' adapter board.

8 inch diskettes are famously reliable with good quality media, and the bits aren't packed so densely that an EMP event will wipe them out, as long as they're in a faraday cage with sufficient attenuation and power handling capacity.

Current production high-density PC FDC's can easily handle the 8 inch drive with the proper adapter cable, but the number of supported formats is small. More flexible is the USB interfaced Kryoflux, and the PCI Catweasel MK3 and MK4 (the Kryoflux is currently in production and available for purchase; the Catweasels have been out of production for a while and are a bit difficult to obtain last I checked; I bought my MK4 from, but they appear to only have the Amiga-specific MK2's in stock.

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