I have an old Acer Aspire T180 desktop. The specs are as follows: AMD Athlon 64 3800+ 2.4GHz 1GB DDR2 SDRAM 160GB DVD-Writer (DVD±R/±RW) Gigabit Ethernet 17" Active Matrix TFT Color LCD Windows Vista Home Basic Mini-tower AST180-UA381B According to the information in the computer's documentation the computer comes with 1 GB of RAM. It has two DDR2 SDRAM sticks. I used to have Windows Vista installed. Then I removed it and install Windows 7, and now I have since removed Windows 7 and installed Windows XP. According to Windows XP with both RAM sticks in the computer has 768 MB. Isn't this supposed to be 1 GB of RAM or 1024 MB of RAM? Is the amount of RAM installed only partly used by the Operating System? Is there's something I'm missing? If I remove either one of the RAM sticks I'm left with 448 MB of RAM. These numbers don't seem to add up. If each of the RAM sticks contains at least 448 MB of RAM shouldn't they (both being in) provide 896 MB of RAM. Even then, isn't that less than a GB of RAM? I'm not too experienced in hardware so I thought this would be the best place to ask. As a follow up question, is the RAM I have enough to run/multitask with Windows XP efficiently? I plan to do a lot of computing with the system (although not gaming), should I invest in more RAM?