Cheaper ?
           How to not go broke, fixing old relic PC's           

Why spend hard earned cash on dead PC's, when the sea is full of live fish, in fact PCs in the USA are in GLUT status now. (too many fish)
Most old PCs parts are very hard to find, 10 years or older, and many times, the parts only on found used, on auction sites... and many are bad or worse than yours, and some are at scalping prices.. avoid this...
Nothing smacks more of that truth than old Dram DMM DDR memory sticks, many of the old ones are not made now.
If you have an  old silly gutless and funky i5 intel processor, omg, what pain the MMC in it is LAME .   see pain below in my last coments sections. 
Example 2, my screens dead and the new one is over $100 , dang. Why spend $100 to fix a $5 used and broken monitor .
My examples, off what is best to have best usage, cost of ownership in the future, (good) and support... to continue.

Walmart screens, cheap, near $60 or even less some days.
If you laptop screen blows up, and it never leaves home , the above is cheap fix.

Walmart,  PC refurbs , near new for $77 or less some days, and with Windows 10 , if you dont like 10 add to it, O&Oshutup10 (Free) and $3.74  START 10, and now it works just  like W7 but 10x better.
I'm telling you  there is nothing wrong with W10, at all.  (using the $3.74 cent fix above and O&O total security.) and free windows DEFENDER !

GOODWILL® stores,  Laptops.

GOODWILL® stores,  PC's

I walk in to GW and , read the bottom COA tag W7 or above, and walk out for low cash.  The tag is worth $100 , ever buy W7 your self?, so the PC is free. dang.

Comments:  ( this is only to demonstrate how hard it is to buy old memory, that is no longer made ,leaving piles of used bad memory sticks left and pain sorting that...)
DRAM dynamic RAM, or DDR memory sticks. (limits)  All comments here assume user has windows 64bit running or the limit is 4GB, (less actually) (and a matching 64bit processor)
Specifications, limits,etc:
Speed,  you can mostly run faster., sticks , seening as how the CPU is actually running as fast as it can  now, no where near you better sticks speed limits. (newer sticks tend to have a higher speed rating (progress and die shinks)
The biggest limits can be the limit of the memory controller,  the i5 has this MMC inside the processor DIE. (with strict limits)  The intel data sheet on page one shows all those limits in both modes, single and dual channel modes.
There are much worse examples of MMC, NVIDIA nForce  Memory Controller (MCP)  most PC's made the CPU runs the memory, but not 600i series or700i series Nforce. 610i  run DDR2, at 2GB max per slot and 4GB total. 2007
News flash: nVidia ,hides the old , nForce chips here, toggle up "legacy" to get the old chip drivers.
Know  that the iNtel  datasheet limits are 10 years old now and newer memories (chips) can allow better density per stick.  (the stuctural and logic rules apply but bus loading actual can change in time and get better)
Denisty rules,
  • Number of sticks sides allowed, some i5s do not allow,  2 sided stick.  there are bus capacitances limits is way.
  • Max chip density. per chip and per stick.
  • If the density is too high the bus capacitance too high total per bit line then the MMC may not be above to driver that line to VIH proper levels and fail.   The means the actual DRAM chip desides of this works or not)
  • This is why the sticks are certified, to make sure they actually work at full speed and not overload the bus.
Memory limits,  per slot , some have  1 GB limit (others 4 and 8) the i5 in DUAL channel mode does 16GB ,with 2 slots but the memory needs to be certified to work on HP mobo. !!!
A per Mobo memory limits some are 2, 4, 8 or more GB but is a hard limit. Read you manual for your PC or mobo. The old i5 has  8GB or 16 limit, it can be less due to each maker of PC, restrictions
Voltage, there are different voltage allowed,  some sticks run all voltages "dual",  or just go slower, with the wrong voltage or fail.  The stick maker is clear on this ask them.
The best choice is to match voltage,  so the speed is max. Stick matches mobo rule.
Number of pins. (pay attention also to the , slot notch location,  this can tell you what volages is uses too. hint hint?)
Form factor DDR1,2,3.

DDR3 is the top memory used now, most popular. (the charts here are priceless)  If your PC does not use DMR3 or higher , I'd trash it.  (unless running very expensive old software that only runs in XP)!

version 1.  5-9-2017 (all this is Opinion, I get paid by no one in the PC businesses. (this is not spam, nor are you tracked or exploited in any way ever by me)