SSD = no need for more ram

LyonParis

macrumors newbie
Original poster
Dec 5, 2011
5
0
I've read on a lot of SSD tests that these disks could "substitute" to RAM.
As they have a latency time in micro-seconds (while HDD have it in milliseconds) they can expand RAM need with a widely acceptable performance loss ?

What do you think of that ?
Did you observe significant performance gain by adding more RAM memory with an SSD disk ?
(if you confirm I could save some money to buy me a better SSD).
 

maflynn

Moderator
Staff member
May 3, 2009
66,675
33,532
Boston
No, you're mistaken.

RAM is used by applications, while executing. Disk or SSD storage used to hold data.

----------

SSDs improve only disk or IO bound operations, more ram can possibly increase the performance by reducing the amount of swap outs to disk (or SSDs) that is its able to keep more memory pages in RAM instead of sending to the disk which is slower then RAM.
 

Weaselboy

Moderator
Staff member
Jan 23, 2005
30,328
10,079
California
I've read on a lot of SSD tests that these disks could "substitute" to RAM.
As they have a latency time in micro-seconds (while HDD have it in milliseconds) they can expand RAM need with a widely acceptable performance loss ?

What do you think of that ?
Did you observe significant performance gain by adding more RAM memory with an SSD disk ?
(if you confirm I could save some money to buy me a better SSD).
I think what you are referring to is the fact that if you are short of RAM and this causes page in/out to the drive, these page in/out would be much faster on a SSD than a HDD. So if you have a machine that is short of RAM it would be much less noticeable on a SSD equipped machine.
 

thundersteele

macrumors 68030
Oct 19, 2011
2,984
7
Switzerland
It's true. When I run out of RAM with a HDD, the applications whose data gets swapped out to the HDD get incredibly slow and beachball a lot. With a SSD under the same conditions, the performance loss is hardly noticeable, at least for me.

If you regularly run out of RAM, I would still upgrade it:

- swapping adds read/write cycles to your SSD, which will make it wear out faster (maybe negligible, I don't know)
- SSD storage is expensive, you don't want to reserve too much of it for a huge swap file
- there still is some performance loss
 

RealEvil

macrumors 6502
Aug 5, 2007
322
10
I can definitely vouch for an SSD improving Paging performance but it still doesn't compete with actual RAM.
If I max out my Mac Mini with VMs to the point where it has to page a LOT, eventually OSX will die (within 20 mins the machine will lock up). Thats with a M4 256GB.
 

VMMan

macrumors 6502a
Mar 29, 2009
766
238
If I had to choose between the following:

1. MacBook Pro with 4 GB RAM + SSD vs 8 GB RAM + HDD

==> I would easily choose the 4 GB RAM + SSD.


2. MacBook Pro with 1 GB RAM + SSD vs 16 GB RAM + HDD

==> I would choose the 16 GB RAM + HDD



If you have anything near a "decent" amount of RAM, then an SSD is the way to go.

If you're seriously deficient in RAM, then get more of the RAM.

2x4GB DDR3 RAM is $20-35 nowadays anyways, and 2x8GB DDR3 is about $200...
 

thundersteele

macrumors 68030
Oct 19, 2011
2,984
7
Switzerland
8 GB RAM is sufficient for most users. That's about $40-$50.

A SSD might make a machine that's low on RAM feel less limited by it's lack of RAM. Still, there is no reason to not upgrade to 8 GB... if you could afford the $2k+ for a MBP with SSD, the RAM upgrade shouldn't be a problem.
 
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