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^ original poster of that was not internet savvy enough to blank out their name. Sarah Linton is possibly soon to be unemployed. HIPPA is not to be fucked with.
There was a time, long ago, when it was common to add hard drives to PCs by pluggin a card containing both the hard drive and the controller into one of the system's expansion slots.
Then, we became enlightened, and drive controllers began to be integrated into the motherboard, eliminating the next for bulky and expensive expansion cards.
I picked up a used LSI "Warp Drive" a little while ago (~$150 IIRC). Its the better part of a decade old, a mere 800GB, but its as fast as a lot of these new NVMe drives. Its basically x4 200GB SSDs on a single pci-e card. Together in raid 0 it feels like it lives up to the name. I can only imagine how mind blowing they would have been a few years back.
Isnt a modem defined by doing an analog-digital translation? So a cable modem is not really a modem?
A modem is a modulator/demodulator. It's a layer 1 device (physical layer) that encodes information on a carrier wave by modulating it and decodes information in the opposite direction.
A "cable modem" is a layer 2 (link layer) device if it's acting as a bridge and a layer 3 device (network layer) if it's acting as router. (arguably layer 4 if it's doing NAT, or even layer 5 if it's doing VPN). It may contain one or more modems, but they are just components. Calling it a "cable modem" is a bit like calling a car a "road light". Yes, it goes on the road and it's usually got at least one light in it, but that's sort of missing the point.
Also, in the case of a "cable modem" the physical layer interfaces are usually ethernet, DOCSIS, and possibly wifi. The component that imposes digital signals onto an analog carrier wave for these protocols could be considered to be a "modem", but is generally referred to as a "phy" instead. The FIOS router is optical, and I'm not actually sure what the encoding scheme is for the optical side of things there. It might just be flashing the light on/off, and if so then it's not modulating a carrier wave at all.
Isnt a modem defined by doing an analog-digital translation? So a cable modem is not really a modem?
Originally Posted by codrus
Also, in the case of a "cable modem" the physical layer interfaces are usually ethernet, DOCSIS, and possibly wifi. The component that imposes digital signals onto an analog carrier wave for these protocols could be considered to be a "modem", but is generally referred to as a "phy" instead.
On the public side, a cable modem is a modem in the same sense that a POTS modem is. Both are modulating an analog carrier to encode digital data. The only meaningful difference is that with a POTS modem the carrier is down at audible frequencies, whereas with a cable modem it's up in the RF range, typically several hundred Mhz. Both units work in exactly the same manner, one is just a lot faster than the other.
Originally Posted by codrus
The FIOS router is optical, and I'm not actually sure what the encoding scheme is for the optical side of things there. It might just be flashing the light on/off, and if so then it's not modulating a carrier wave at all.
That is correct. A FiOS connection is truly digital, with no carrier* to modulate.
* = if you wanted to be really pedantic, you could argue that light is a carrier, but it's not being modulated in either amplitude or frequency.
Wanna really twist your nipple? Read up about how Laserdisc works. Like a CD or a DVD, the disc contains only two states: pit and land. And yet, despite using a binary medium, it's a 100% analog** system. The width and spacing of the pits and lands correspond directly to a clipping point in the original composite analog carrier, and are directly translated back out into the carrier with no digital processing during playback. It's a completely analog implementation of PWM:
** = later variants supported PCM-encoded information such as digital audio, but these were run through a process which overlaid them onto the analog carrier, similarly to how the "Hi-Fi" system worked in the latter years of VHS. The process by which the carrier was encoded and decoded remained fully analog throughout the entire lifespan of the format.
On the public side, a cable modem is a modem in the same sense that a POTS modem is. Both are modulating an analog carrier to encode digital data. The only meaningful difference is that with a POTS modem the carrier is down at audible frequencies, whereas with a cable modem it's up in the RF range, typically several hundred Mhz. Both units work in exactly the same manner, one is just a lot faster than the other.
This is true as far as it goes -- it just doesn't go far enough. A true "cable modem" would be a point-to-point device that you plugged into a high-speed serial port. It would send data between two defined endpoints in a serial stream with no framing, and if you wanted to use it for internet connectivity then you would need to run PPP or some similar protocol over it. A modem has no clue what a packet is, it runs in terms of bits/bytes.
The "cable modems" that actually exist contain a lot more logic than that. They are, at the very least, remote ethernet bridges, where they bridge ethernet frames across a DOCSIS network using the source and destination mac addresses in order to decide which packets go where. Most of them are routers, having their own IP addresses, making packet forwarding decisions based upon the IP addresses in the packet, and usually supporting network and port address translation features in order to make multiple devices in your house appear to be a single globally routable IP address.
This is true as far as it goes -- it just doesn't go far enough. A true "cable modem" would be a point-to-point device that you plugged into a high-speed serial port.
Fair enough. A "cable modem" contains a modem, as well as a router, a network-address-translator, a DHCP server, and a bunch of other modern ****.
But, by the same token, a 1980's vintage POTS modem also contains a UART, a microcontroller to interpret escape codes (eg, the Hayes command set), a synthesizer to generate DTMF tones, and so on.
Technology evolves. Concepts remain the same.
Also, you posted in the pictures thread without a picture. And as I'm in a bit of a transitional stage in my life right now, pony:
Fair enough. A "cable modem" contains a modem, as well as a router, a network-address-translator, a DHCP server, and a bunch of other modern ****.
But, by the same token, a 1980's vintage POTS modem also contains a UART, a microcontroller to interpret escape codes (eg, the Hayes command set), a synthesizer to generate DTMF tones, and so on.
Sure, but a modulation and demodulation is a modem's primary and highest-level purpose, whereas it is not in a "cable modem". Any car with a built in cell phone or bluetooth system has a modem in it as well, but you don't it a "road modem", do you?
As for photos, here's one. Captioned "wrong tool for the job":
A Miata is actually more useful for holding groceries than an FD.
Wanna really twist your nipple? Read up about how Laserdisc works...
Good explanation. I was always fascinated about the dichotomy of analogue and digital inherent to the LD format. In its day, it was truly a fabulous medium.
I still have a couple of large boxes in my basement containing my collection of very expensive LaserDiscs (in the '90s, they typically cost between $60 and $90 each, with some special editions being in the hundreds of dollars). Besides the Collector's Editions of Toy Story, 7even, Aliens and the like, I also have the original cuts of Star Wars Episodes IV-VI (you know, where Han shot first and there was no CGI Jabba The Hut).
I also have the below AC3- RF demodulator, which allowed me to enjoy the full 5.1 DD soundtrack, when available:
From Wikipedia:
Extracting Dolby Digital from a LaserDisc required a player equipped with a special "AC-3 RF" output and an external demodulator in addition to an AC-3 decoder. The demodulator was necessary to convert the 2.88 MHz modulated AC-3 information on the disc into a 384 kbit/s signal that the decoder could handle.
Sure, but a modulation and demodulation is a modem's primary and highest-level purpose, whereas it is not in a "cable modem". Any car with a built in cell phone or bluetooth system has a modem in it as well, but you don't it a "road modem", do you?
A car's primary function is to move people and objects over physical space, using a network of roads.
A modem's primary function is to move digital data over analog carriers, using a network of wires (and, increasingly, electromagnetic radiation in free space.)
These devices may also provide ancillary functions, such as:
Air conditioning (cars)
Ring detection and auto-answer (80s modems)
DHCP (00s modems)
AM/FM/CD/Sirius-XM audio reproduction (cars)
Escape-code processing (80s modems)
Network address translation (00s modems)
Geolocation / navigation (cars)
Echo-cancellation and line conditioning (80s modems)
Routing (00s modems)
Prostate massage (cars)
Buffering, flow-control, and RS-232 UART (80s modems)
Buffering, flow-control, and USB / Ethernet (00s modems)
None of these ancillary functions differentiate the device in question from its primary task. In the year 2017, a car and a modem are equally likely to contain a bluetooth transceiver (which, to be pedantic, is ALSO a modem. So that'd be a modem inside a modem in the case of the modem, but just a regular modem in the case of the car,) and yet we are still able to intuitively know which one we put the groceries into, and which one plugs into the wall.
(Dammit...)
Originally Posted by codrus
A Miata is actually more useful for holding groceries than an FD.
Haha. Also for holding sofas, lawnmowers, full size residential water heaters, 50cc motorcycles, Ikea furniture, rollaround toolchests, beer fridges, 12 foot ladders, plumbing pipe and electrical conduit, engine stands and engine hoists from Harbor Freight (at the same time, no less- albeit with the pax seat removed), and a whole bunch of other hilarious **** that most of us have managed to pack in there from time to time.
EDIT: Man, I'm getting all kinds of nostalgic here, what with the various returns that Google is providing me in the course of researching this post. Thinking back to the renegade network that we built in college, the BBSes of the same era, the bookstores that we used to hang out in, the Radio Shack in the Promenades Mall in Port Charlotte, FL which disappeared during Hurricane Charley, and so on.
So very nerd...
Last edited by Joe Perez; Jul 8, 2017 at 06:22 AM.
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