Go Back   AnandTech Forums > Hardware and Technology > Highly Technical

Forums
· Hardware and Technology
· CPUs and Overclocking
· Motherboards
· Video Cards and Graphics
· Memory and Storage
· Power Supplies
· Cases & Cooling
· SFF, Notebooks, Pre-Built/Barebones PCs
· Networking
· Peripherals
· General Hardware
· Highly Technical
· Computer Help
· Home Theater PCs
· Consumer Electronics
· Digital and Video Cameras
· Mobile Devices & Gadgets
· Audio/Video & Home Theater
· Software
· Software for Windows
· All Things Apple
· *nix Software
· Operating Systems
· Programming
· PC Gaming
· Console Gaming
· Distributed Computing
· Security
· Social
· Off Topic
· Politics and News
· Discussion Club
· Love and Relationships
· The Garage
· Health and Fitness
· Merchandise and Shopping
· For Sale/Trade
· Hot Deals with Free Stuff/Contests
· Black Friday 2014
· Forum Issues
· Technical Forum Issues
· Personal Forum Issues
· Suggestion Box
· Moderator Resources
· Moderator Discussions
   

Reply
 
Thread Tools
Old 03-07-2006, 11:17 AM   #1
StrangerGuy
Diamond Member
 
StrangerGuy's Avatar
 
Join Date: May 2004
Posts: 7,118
Default Why memory capacities are always in powers of two?

See title.
__________________
My crappy PC: Stock 4790K + Asus H81i-Plus mITX, Crucial 16GB VLP DDR3-1600, HIS HD7950 Boost, 256GB Evo 840, 3TB Seagate, Seasonic G 650W, Dell U2311H, Promedia 2.1
Worthless spare parts: 2500K @ 4.3GHz / G1610 + Biostar TP67B+, 8GB DDR3-1333, GTX460 1GB / HD5850, 1TB Samsung F3, Antec Neo Eco 450W
StrangerGuy is offline   Reply With Quote
Old 03-07-2006, 11:34 AM   #2
Soccerman06
Diamond Member
 
Soccerman06's Avatar
 
Join Date: Jul 2004
Posts: 5,718
Default Why memory capacities are always in powers of two?

2^x
__________________
puppy1
puppy2
puppy3
Steam: soccerman05
Soccerman06 is offline   Reply With Quote
Old 03-07-2006, 12:42 PM   #3
SamurAchzar
Platinum Member
 
SamurAchzar's Avatar
 
Join Date: Feb 2006
Posts: 2,422
Default Why memory capacities are always in powers of two?

Probably due to addressing conecerns - as the addressing is done using binary coding (which means there are X address lines coming into the memory, each can be either ON or OFF), the address range is always a power of 2.



__________________
Get busy living, or get busy dying
SamurAchzar is offline   Reply With Quote
Old 03-07-2006, 12:48 PM   #4
TuxDave
Lifer
 
TuxDave's Avatar
 
Join Date: Oct 2002
Posts: 10,441
Default Why memory capacities are always in powers of two?

Not really sure why exactly. Maybe it has to do with the addresses being encoded in binary and putting as many cells as you can address so that you have a fully utilized decoder in the memory. I don't think there's a technical restriction on why it HAS to be a power of two.
__________________
post count = post count + 0.999.....
(\__/)
(='.'=)This is Bunny. Copy and paste bunny into your
(")_(")signature to help him gain world domination.
TuxDave is offline   Reply With Quote
Old 03-07-2006, 01:39 PM   #5
BrownTown
Diamond Member
 
Join Date: Dec 2005
Posts: 5,315
Default Why memory capacities are always in powers of two?

Tehre are several reasons why sizes go up in powers of 2. First off the memory is adressed in binary, so in order to get larger memmories you need to ad another adress bit, which allows you to double the size of the memmory. Obviously it isnt nescecarry to do so, but it just makes more sense. Also, computer geeks always want things to be in multiples of 2. Even if there was no reason at all for memmory to double it probably would. Kinda like why process sizes get half the size each generation, there is nothing saying you have to do it that way, yet it seems everyone goes from 180>130>90>65>45>32>22nm, the onyl reason is that each time it gets half as big.
__________________
Logical Fallacies: http://www.nizkor.org/features/fallacies/

ALOT of people on this board need to consider these before they post...
BrownTown is offline   Reply With Quote
Old 03-07-2006, 04:40 PM   #6
Peter
Elite Member
 
Join Date: Oct 1999
Posts: 9,640
Default Why memory capacities are always in powers of two?

RAM chips are organized in rows and columns, addressed by binary values. Making a bigger chip means adding a row or column address line - and that doubles the size of the chip.
Peter is offline   Reply With Quote
Old 03-07-2006, 04:57 PM   #7
Braznor
Diamond Member
 
Braznor's Avatar
 
Join Date: Oct 2005
Location: Banana Republic
Posts: 3,403
Default Why memory capacities are always in powers of two?

Not always, certain computer manufacturers used to sell memory in odd sizes like 48 MB or so just to force the consumer to upgrade it from them alone
__________________
Quote:
A touch of greatness destroys a man. That which allows him to remain great is only the sense of irony fate lets him find in his own legends.

---- Frank Herbert, Dune.
Braznor is online now   Reply With Quote
Old 03-07-2006, 05:03 PM   #8
Varun
Golden Member
 
Join Date: Aug 2002
Posts: 1,161
Default Why memory capacities are always in powers of two?

Everything in a computer is in powers of 2, since the base unit is a bit with 2 values. The Row/Column addressing posts are correct. You add one bit you double the addressing.
Varun is offline   Reply With Quote
Old 03-07-2006, 05:15 PM   #9
Peter
Elite Member
 
Join Date: Oct 1999
Posts: 9,640
Default Why memory capacities are always in powers of two?

Quote:
Originally posted by: Braznor
Not always, certain computer manufacturers used to sell memory in odd sizes like 48 MB or so just to force the consumer to upgrade it from them alone
You can always have an "odd" total, in this case from 32- and 16-MB memory ranks. The individual RAM chip still has a capacity that is exactly a power of two.
Peter is offline   Reply With Quote
Old 03-07-2006, 08:34 PM   #10
Braznor
Diamond Member
 
Braznor's Avatar
 
Join Date: Oct 2005
Location: Banana Republic
Posts: 3,403
Default Why memory capacities are always in powers of two?

Quote:
Originally posted by: Peter
Quote:
Originally posted by: Braznor
Not always, certain computer manufacturers used to sell memory in odd sizes like 48 MB or so just to force the consumer to upgrade it from them alone
You can always have an "odd" total, in this case from 32- and 16-MB memory ranks. The individual RAM chip still has a capacity that is exactly a power of two.
Thats a given assumption.
__________________
Quote:
A touch of greatness destroys a man. That which allows him to remain great is only the sense of irony fate lets him find in his own legends.

---- Frank Herbert, Dune.
Braznor is online now   Reply With Quote
Old 03-07-2006, 09:28 PM   #11
CTho9305
Elite Member
 
Join Date: Jul 2000
Posts: 9,214
Default Why memory capacities are always in powers of two?

In a banked memory, you'd want to use the upper bits of the address to select the bank, and the lower bits of the address to select an entry from the bank. If your bank size is not a power of two, however, this simple scheme would have problems. Consider a 48 byte bank size - you need 6 bits to address the 48 bytes, but if you have 2 banks, addresses 0110000 through 1000000 would need to somehow be mapped onto the second bank, and you can't just wire up the lower 6 address bits straight to each bank any more. This applies to actual data arrays within chips as well.
__________________
*Not speaking for any company
CTho9305 is offline   Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 04:28 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.