Second hand laptop - yes or no

afasoas said:
Laptops tend to have fewer cycles per second these days in order to reduce power consumption.
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Kind of right and yet so wrong that it would probably take pages to explain why....
 
arad85 said:
Kind of right and yet so wrong that it would probably take pages to explain why....
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I know this is going off topic, but I'm intrigued as to why I'm wrong.

I recently bought a second hand CPU for a media server. I could have picked between the Sandy Bridge, Ivy Bridge and Haswell versions. In each generation, Intel had reduced Thermal Design Power, clock speed and overall processing power. (Going from Sandy Bridge to Ivy Bridge, Intel had reduced the manufacturing process from 32 to 22 nanometres). The Ivy Bridge version seemed like the best choice for me as the reduced clock speed of the Haswell processor would not have had the grunt I wanted.

Not that Wikipedia is always the best source of information, but it says (paraphrasing):
  • Reducing a processors clock rate reduces power consumption
  • Turning off unused transistors reduces power consumption
  • Smaller transistors reduce power consumption

The dynamic power consumed by a CPU is approximately proportional to the CPU frequency, and to the square of the CPU voltage:[3]

222cbca1910b272872267d4a45928eb5.png

where C is capacitance, f is frequency, and V is voltage.

The article is here:
https://en.wikipedia.org/wiki/CPU_power_dissipation
 
afasoas said:
I know this is going off topic, but I'm intrigued as to why I'm wrong.
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Because it is far too simplistic. So.. it's now Saturday and I have a little time :)

There are two aspects to power consumption for laptops - idling power and power when computing. You get extra battery life by making idling power consumption as low as possible. This is done by hardware on chip which calculates thousands of times a second how fast the clocks should be running on each part of the chip and scales the clocks back. On my Sandy Bridge desktop, the idle speed is 1600MHz. On my Sandy Bridge laptop, it is 800MHz - if the CPU is not clock gated to 0Hz (where nothing is running), each CPU runs at this speed until it needs more power where the clocks ramp higher up to their maximum value. This clock ramping is done on a CPU by CPU basis (so you may have the CPUs on one die running at different speeds). Battery life is generally proportional to how low these clocks go and how often the CPU is scheduled to run. Newer processors do more and better clock scaling so power goes lower, even though the clocks are the same. There is also an effect from the Operating System - my understanding is that Microsoft have done a lot of work here on Windows 8. Apple have always been good at this which is why Macbooks have relatively long battery life. Fundamentally battery life is dominated by the idling power as the clock scaling takes care of only running the chip fast enough for the task in hand - and it does it many thousands of times a second!

Intel CPUs also have something called Turbo Boost whereby the clocks are ramped above the nominal maximum. The amount they can boost by is limited and depends on the number of CPUs active - the fewer that are active, the higher those fewer processors are clocked. Looking at the fastest quad-core i7's in each lineup you have:
  • i7-2700K: 95W TDP, 3.5GHz, 1/2/3/4 turbo (i.e. max speed for 1, 2, 3 and 4 cores flat out is 3.9GHz, 3.8GHz, 3.7GHz and 3.6GHz respectively)
  • i7-3770K: 77W TDP, 3.5GHz, 2/3/4/4 turbo (i.e. max speed for 1, 2, 3 and 4 cores flat out is 3.9GHz, 3.9GHz, 3.8GHz and 3.7GHz respectively)
  • i7-4790K: 88W TDP, 4GHz, 2/3/4/4 turbo (i.e. max speed for 1, 2, 3 and 4 cores flat out is 4.4GHz, 4.4GHz, 4.3GHz and 4.2GHz respectively)

So Sandy->Ivy = less power, slightly faster maximum speed (3.6GHz vs 3.7GHz), whilst Ivy->Haswell gives the same power (77/3.5 * 4 = 88) with higher maximum speed which is what you'd expect - Sandy->Ivy is a process shrink so things should get faster and use less power whilst Ivy->Haswell is a design change but same process (so similar power) but improved design has allowed them to get faster clocks (4.2GHz vs 3.7GHz). You will also notice there are normally a range of processors that are pretty similar but run at different speeds. These will be speed-binned at manufacture and the faster processors sold at a premium.

But this isn't the total story. There is also hardware that is measuring the total power being used. It also checks the total thermal envelope of the processor and if it is reaching the limits, it will also scale clocks back until things get better. This is known as throttling and the CPU automatically does it if needed. Low TDP parts tend to have lower clock speeds to reduce the maximum power dissipation. Why do this? Why not just put a high performance CPU in and let clock scaling take care of things? Yes, you do get reduced maximum performance, but more interesting for laptop designers is reduced thermal stresses on the laptop chassis. If you have a 100W processor in a laptop, not only is the battery life going to be pants when it's running flat out, you have 100+ watts to get rid of from your beautifully designed enclosure and most of it will try going into the owner's lap!

But clocking isn't the only thing that matters.

You may know Intel tinker between related architectures and do significant redesign between pairs of designs (their tick-tock design cycle if you want to google it). You can tell paired designs as they have similar names Sandy Bridge & Ivy Bridge, Haswell & Broadwell etc. The first of these is the major redesign, the second of these is process shrink (which pipecleans the process for the next re-design). Process shrink means smaller die so less power, it should also mean faster clocks, but getting the heat out of the chip is becoming a major problem, so often things are not increased but left pretty much as-is clockwise. To compare clock for clock performance, the measure instructions per cycle (often written IPC) is used. This is effectively a measure of how much work you can get done in single clock cycle. The more work you can get done in one cycle, the fewer cycles you have to expend to do the same amount of work. Between iterations of the same architecture, Intel might do some minor tweaks. I think they modified the number and type of execution units in the CPU between Sandy and Ivy which means that each new generation tends to ramp IPCs. Sandy->Ivy saw an ~10% IPC improvement which translates to ~10% better performance per MHz. Looking at the numbers above, if all 4 cores are 100% loaded (and ignoring hyperthreading) then the i7-2600K performance is effectively 3.6GHz x 4 = 14.4 whilst the Ivy is 3.7GHz x 4 x 1.1 = 16.28. In other words, the Ivy processor, even though it runs at the same nominal clock speed is approximately 13% faster. It's also dissipating 19% less power too. The same type of gains will be made between Ivy and Haswell....

If you have higher IPC, you can get the same amount of work done in a shorter time. Conversely, you can also do that work in the same amount of time but at a lower clock speed which has the added benefit of reducing the maximum power consumption. It is very unlikely to alter the idle power consumption as clock scaling takes care of that. Given laptop design is always a compromise it allows manufacturers to have a still perfomant laptop that uses less power whilst still being cheap enough for consumers to buy.... Bottom line is that the driver on power consumption/battery life is only very loosely related to headline GHz (try defining what f and V are in the equation above given the discussion above and knowing similar processes are ongoing on voltage scaling too).
 
Would I buy a second hand laptop?

Only if there was a significant saving on new. And only if the cooling solution is one that is not prone to getting blocked or sucking in lots of crud.

Invariably laptops get used on yer lap. So you get lots of fibres and dust right next to where all the air to cool the thing gets sucked in. If the machine has a vent that sucks air in from beneath the body, I wouldn't. The sides are better, much better. The rear not so much, although slightly better than underneath.
 
Do you guys think this is worth £400 second hand? It's £899 new from amazon.

HP ENVY 6-1202ea Ultrabook Beats Audio, 3rd generation Intel® CoreTM i7-3517U processor, 8GB RAM, 500GB HDD, Microsoft Windows 8, AMD Radeon HD 8750M (2 GB DDR3 dedicated)

Product Details
  • Amazon Sales Rank: #146774 in Personal Computer
  • Brand: HP
  • Model: D0X06EA
  • Dimensions: .78" h x 14.72" w x 9.95" l, 4.74 pounds
  • CPU: Core i7 1.9 GHz
  • Memory: 8GB
  • Hard Disk: 500GB
  • Processors: 2
  • Display size: 15.6
Features
  • 3rd generation Intel® CoreTM i7-3517U
  • HP ENVY 6 Ultrabook
  • 8GB RAM
  • Wi-Fi, Bluetooth, HD Webcam & Microphone
  • AMD Radeon HD 8750M (2 GB DDR3 dedicated)
 
Looks alright. Nice thing with windows 8 is you can wioe and return to out of box condition with a couple of clicks which is great if you're not technical. I would NEVER use a 2nd hand laptop that wasn't a clean install, it'd be like not washing second hand clothes...!
 
Cheers mate. I'm just trying to get my mate who's very techy to go with me to make sure it's all as it should be.
 
Finally ordered this and will pick it up tomorrow. Hopefully more than adequate for my needs. £399 from Curry's. Model HP Pavilion 15-p189sa 15.6" Laptop.

OVERVIEW
TypeLaptop
Operating systemWindows 8.1
SPECIFICATION
ProcessorIntel® Core™ i5-4288U Processor (2.6 GHz, 3.1 GHz with TurboBoost, 3 MB cache)
RAM8 GB DDR3L
Graphics cardIntel® Iris™
Storage1.5 TB HDD, 5400 rpm
SCREEN
Screen size15.6"
Screen typeLCD
Resolution1366 x 768
TouchscreenNo
Screen featuresLED backlighting
CONNECTIVTY
Wireless802.11 b/g/n
Ethernet10/100 Ethernet
BluetoothBluetooth 4.0
USB- USB 3.0 x 1
- USB 2.0 x 2
Video interface- HDMI x 1
- Miracast
Audio interface3.5 mm jack
MEDIA
Optical driveDVD/RW
Memory card readerSD card reader
SOUND
SoundBeats Audio
SpeakersIntegrated stereo speakers
FEATURES
CameraHP TrueVision webcam
MicrophoneYes
Mouse / trackpadHP ImagePad
KeyboardFull-size island-style keyboard with numeric keypad
Security featuresKensington MicroSaver lock slot
POWER
Battery type4-cell Lithium-ion
Battery lifeUp to 6 hours
GENERAL
ColourSilver & snow white
Box contents- HP Pavilion 15-p189sa 15.6" Laptop
- AC power adapter
- Quick start guide
Dimensions23.9 x 384.5 x 260.2 mm (H x W x D )
Weight2.27 kg
Manufacturer’s guarantee1 year
Software included- Adobe Shockwave Player
- BeatsAudio
- CyberLink Media Suite
- Evernote
- Foxit PhantomPDF Express for HP
- Mahjong
- mysms
- Netflix
- Skype
- Solitaire
- TripAdvisor
- 7-Zip
 
Have fun removing all of the prel-installed applications you dont need! Seriously, good luck.
 
I'll be passing this over to my mate to remove all these things and to install either photo shop or lightroom. Hopefully he'll get it done over the next couple of days.
 
afasoas said:
Have fun removing all of the prel-installed applications you dont need! Seriously, good luck.
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Hi mate,

Can you tell me whether most laptops these days have pre installed rubbish on them or this one in particular?
 
its normal to have preinstalled c***p on laptops as the manufacturers get a kickback from the software companies in the hope that people will actually use their rubbish software lol
 
Okay so regardless of whether I bought this one or another one I'd have the same issues.
 
Yeah pardon my silly comment. removing skunkware and installing updates are two of my pet hates.
 
Not all - Lenovo tend to be free of crapware & any pre-installed apps are genuinely useful - or that's how it used to be. The Dell I bought last year (refurb) came with just windows, drivers and a couple of utilities like a basic backup app, and no junk at all (other than the default stuff for social networking in W8).
 
If you are buying a used laptop, be prepared for a tired battery with short life. If you need good battery life then you may need to also budget for a new battery. Beware of non-original batteries as they can sometimes have less capacity than claimed and have been known to cause fires if they overheat.

Also, processor clock speed on its own can be a seriously misleading indicator of performance, the processor generation, number of cores, support for multi-threading & processor cache configuration can have a far greater impact. Processor Clock speed is a measure of how quickly the cpu waits for data. What you need is bandwidth when accessing data and instructions.

If you don't have room for a desktop, have you room for a decent sized monitor? There are a number of very small PCs available that will mount on the back of a monitor using industry standard VESA mounting points.
 
ancient_mariner said:
The Dell I bought last year (refurb) came with just windows, drivers and a couple of utilities like a basic backup app, and no junk at all (other than the default stuff for social networking in W8).
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yup, dell seem to have binned off all of the junk. at least their business models have but we still wipe them for our vol licence install.
 
neil_g said:
yup, dell seem to have binned off all of the junk. at least their business models have but we still wipe them for our vol licence install.
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Same as this, my Precision M4800 came with no bloat at all, still wiped it to use our WDS and then wiped again shortly after to run Windows 10

Acer and HP are terrible for it though, and I swear I'd never buy another HP pavilion or envy series again!!
 
Not much point buying second hand unless your looking for a particular model or a high spec unit.
Basic reasonable laptops are quite cheap, try ebuyer.

warranty and batterys that last :-)
 
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