I have a Toshiba Satellite A15-S157 laptop with 512mb of ram and 1 gig capacity. I want to add a 512mb stick, but I dont know what kind would be compatible and what company would work with my existing ram best. Thanks.

The best place I found was www.crucial.com - just plug in your motherboard or computer's specs and it will tell you what memory type you need. You could also check your owner's manual.

According to the specs on your computer I found on the net, you should be using DDR266/PC2100. Go to Newegg.Com . They have good deals and are great if you need help. Just go to the laptop memory category and select PC2100. Just remember yo MoBo maxes out at 1gb of Ram. Hope this helps.

I would replace both sticks at the same time with the exact same model/serial or lot number. Don't have 2 different kinds in there please! It may cause you problems.

You can also go to www.tigerdirect.com. They have a memory configurer on there that works well. You just put in what kind of computer you have, model #, stuff like that(all from drop down menus) and it will show you what they got that will work.

Again, it may be smart to replace both sticks at the same time with the same type.

Have a good day.