wiring - Are Cat5e fully compatible with GBabit specification?
2014-07
Rushino
Are Cat5e fully compatible with GBabit specification? What the main difference between Cat6?
Would like a proof if possible.
music2myear
The main different between each version of the Cat specification is the numbers of twists per length of the cable.
Two wires running in parallel will create cross-talk. That is, if a current is running down one of the wires, the parallel wire will generate a current as well directly proportional to the distance between the wires and the current running in the wire. This is how a transformer works.
Twisting the wires interrupts this cross-talk, resulting in a cleaner signal as current running in one wire producese less of a current in the other wires. As signal speeds increase, the importance of cross-talk-free wires becomes more and more important and thus the twisting requirements become more and more stringent.
Cat6 has more dense twisting of the wires so that it produces a cleaner signal on each individual wire and thus will produce fewer errors allowing for higher communication speeds than Cat5e, Cat5, or any lower numbered Cat specification.
Technically, Cat5 can support Gigabit communication, but the primary factors would be the length of the cable involved and the environment the cable is running through. You may only get a Gigabit signal over a few feet of Cat5 or Cat5e while using Cat6 would allow you to send a solid and reliable Gigabit connection over dozens of feet without issue.
UPDATE for OP additional question: You are always playing odds with any situation like this. If you have low quality Cat5e, and/or low quality networking components, and/or your network cords run parallel to power conduit or telephone you'll find you have much, much less than 100m before you'll have difficulty running Gigabit over Cat5e.
Using Cat6, which was desiged for Gigabit, is much less likely to experience significant signal degredation when faced with similar problems.
Because there are so many factors you must take into account, there is simply no way for us to tell you "Cat5e will always allow stable and fast Gigabit connections if the run is less than x feet". And so we play odds. And so I will state that the odds are that, if you're dealing with lines parallelling power conduit or phone, if you're dealing with runs longer than several feet, and if you're dealing with consumer-grade components that will be connecting over these lines, you will not experience a speedy and stable Gigabit connection between all your components. It's possible you will have a perfectly OK connection. I just think there is a signficant likelihood that you won't unless you use Cat6.
However, since you've already run the cable, there's really no sense in tearing it all out unless after you've tested the lines and found whether or not their performance meets your needs.
Questioner
When considering to buy a SSD, how should I interpret the different specifications of the SSD?
Here are some specific things that need to be deciphered:
- Controller (this can affect performance and endurance more than all other factors combined)
- Bus Technology
- Form Factor (Physical Size)
- Capacity
- NAND or NOR technology
- Power Consumption during Read, during Write, when Idle
- Read/Write Burst and Sustained Throughput
All of these things I would like to be explained in more detail and their actual importance in selecting an SSD.
I have a couple of laptops with SSDs - a recent MacBook Air and a 64GB Kingston V100 placed into a Lenovo Thinkpad T60p. Both are fast - the Thinkpad is much faster than previously, with boot times below 30 seconds, and much improved battery life.
Your points:
Controller (this can affect performance and endurance more than all other factors combined)
I don't fully agree - if both the drive and the hard drive controller follows SATA 1.5, SATA 3.0 (aka SATA II) or SATA 6.0 (aka SATA III) standard, they'll probably work together: the performance limits in the standard are UPPER LIMITS: many things can make your performance worse. I have not yet found a source of reliable test results allowing SSD performance comparison across brands, devices and OSes.
Bus Technology
Some SATA II devices claim SATA III compatibility but really just take advantage of SATA III's downward compatibility with SATA II. It's easy to see that only few of the spinning SATA III drives actually push more than 3Gb/sec of data. SSDs have an easier time of it, but I've not seen benchmarks showing any pair of SATA III SSDs + SATA III controllers reliably pushing anywhere near 6 Gb/sec.
Form Factor (Physical Size)
Some devices expect a 9.5mm 2.5in drive; the 7mm 2.5in drives don't fit as well. The Kingston drive fit perfectly into the T60p's 9.5mm slot.
Capacity
This seems linearly correlated to price, as you'd expect. Increasingly, SSDs are over-provisioned, where a 64GB drive actually has 72GB addressable. The excess allows for longer drive life in the face of SSD "bits" write cycles being limited to about 100,000. To compensate, SSD controllers move rather than overwrite changing file sectors, in order to balance the limited lifespan. Some OCZ devices destined for servers are reputedly 25% over-provisioned.
NAND or NOR technology
NAND technology appears to have won: NOR technology either isn't as cost-effective, or it is hidden under more meaningful wrappers, such as wear-levelling, mean-time-between-failure (MTBF), and ever higher rates of over-provisioning
Power Consumption during Read, during Write, when Idle
It is difficult to measure this: as with many parameters for electronic devices, you're trusting the reliability of manufacturer vs. the difficulty of measuring these by reviewers or consumers. Having said that, common SSDs are said to consume ~2W during operation, and 0.5W while idle.
Read/Write Burst and Sustained Throughput
Complex: Some SATA II SSDs can't saturate SATA I's 1.5Mb/sec pipe: others can. And you're taking manufacturer's word for it, despite the fact it's possible to measure, with low precision, at least.
But other issues can obscure the results. For example: TRIM, which must be supported by the OS, the controller and the drive. TRIM is a technique to prevent SSDs from experiencing progressively slower write performance over time. Because SSD sectors are written all at once, if a previously used, partially full sector is to be written to, the drive must read the existing sector, add it to the new data in cache, then write the whole sector, then update the file table, which may require the same read-modify-write cycle. This can take some time.
Recently some reviewers tested whether Macs running Snow Leopard really needed TRIM, which isn't supported by Snow Leopard: the reviewers built some seemingly solid tests, and reported some interesting but reasonable results. But other commenters pointed out the researchers assumed Apple's secure formatting tool worked as promised: overwriting every bit of every sector with zeros, even for un-used file space. It turns out that Apple's tool might not actually do this, and if the zero'd status of the tested SSD isn't reliable, maybe the performance tests of new vs. "dirty" disks wasn't reliable, either.