Why is my laptop limited to 2Gb total memory?

October 17, 2007 6:56 AM

Why is my laptop limited to 2Gb total memory, according to the specs? It has 2 PC2-5300 DDR2 memory slots, and the manufacturer sells a 2Gb card for it (in addition to 1Gb cards). Maybe a dumb question, but why can't it take two 2Gb cards? It's a Toshiba Satellite L45-S7423.
posted by DarkForest to computers & internet (10 comments total)

If the motherboard isnt designed to take 4 gigs, it cannot. They save money by only putting in a memory controller that can handle 2 gigs. This is pretty typical in laptop motherboards.
posted by damn dirty ape at 7:06 AM on October 17, 2007

Well, I'd have gladly paid a dollar extra to get the better memory controller, if the option had been available. Thanks. I was hoping it would just be a documentation error, or one of those artificial price-point crippling things that could be easily defeated.
posted by DarkForest at 7:19 AM on October 17, 2007

damn dirty ape is correct; just to expound on what he said, though, you might want to take a look at the WP articles for Physical address and Memory controller. (The first article is pretty technically dense.)

Basically, the memory controller is responsible for actually taking bytes of data and stuffing them into the RAM. If it's only designed to work with 2GB, it can't deal with any more. The limit is probably because of the size of the physical addresses that it can work with.

In most Intel-based systems, the memory controller is part of the Northbridge, so it's impossible to replace without swapping the motherboard. In a few AMD systems it's integrated into the processor, but I don't think that includes any laptops.
posted by Kadin2048 at 7:39 AM on October 17, 2007

Crucial thinks it's capped at 2gb, as well. From Intel's spec sheet for the Mobile 965 (part 1.1.2)(That's the 'North bridge' of your laptop, I believe.):

• One SO-DIMM connector per channel
• 256-mb, 512-mb and 1Gb memory technologies supported
• Maximum memory supported: 4GB

...The hardware apparently is capable of supporting twice that, but only if you can plug it in as four 1gb modules. Since you don't have the plugs, or probably the space for them, it's probably not happening.
posted by Orb2069 at 7:40 AM on October 17, 2007

Thanks. I guess I was fooled by the Toshiba 2Gb offering for the laptop. Maybe it was really a 2x1Gb kit.
posted by DarkForest at 8:10 AM on October 17, 2007

I thought this often happened when the specs were drawn up before the availability of higher capacity DIMMs. I swear I've encountered this before and there has been no trouble putting in larger DIMMs down the road. They weren't certified for use with the board at the time of its production, because they weren't available. Maybe I'm completely wrong, though...
posted by daveleck at 10:57 AM on October 17, 2007

As another example of what I'm trying to say: I have several devices that take removable media cards. The owners manual says they take up to 2GB cards. Well, lo and behold, as 4GB and 8GB cards hit the market (at later dates), they also magically worked. Is it not the same scenario for this laptop?
posted by daveleck at 10:59 AM on October 17, 2007

That's a different situation. That card reader hardware and driver were made when 4gig or 8gig cards did not exist. The manufacterer can only test 2gig cards. It turns out that the 4gig or 8 gig cards work also. They limit liability by being precise.

Well, 2gig ram modules are well known to intel. Like someone wrote above the controller only wants 1gig or less per slot. Thats not because intel couldnt get its hands on a 2gig chip, but because of how the memory architecture is designed. I imagine it wont hurt to try, but you better get it from a place with a liberal return policy.
posted by damn dirty ape at 11:47 AM on October 17, 2007

Thanks all! 2x1Gb kit purchased. I'll live with it till I can afford a better laptop. Anyone want to buy the two 512Mb DDR2 cards I'm replacing? Mods: edit this out if it breaks the rules.
posted by DarkForest at 12:44 PM on October 17, 2007

Dan's Data has this to say about memory.
posted by M Edward at 5:14 PM on October 17, 2007