Pushing the limits of a PC's memory has its own limits

Q: In your column two weeks ago, you said Windows ReadyBoost allowed a PC to supplement its RAM (random access memory) with as much as 256 gigabytes of high-speed memory from attached flash memory devices. But when I tried it on my Windows 7 PC, I could use only 4 gigabytes of storage on a 32-gigabyte camera memory card. Why is that?

Susan Stombaugh, South Bend, Ind.

A: The Web page to which I referred readers (tinyurl.com/ns5bcmc) explained this, but I should have made it clearer. Windows ReadyBoost can combine the memory from up to eight PC flash drives or camera memory cards to provide as much as 256 gigabytes of additional memory (a maximum of 32 gigabytes per device).

But ReadyBoost can't always provide that much. The person whose question I answered had the 64-bit version of Windows. A PC must have 64-bit Windows for ReadyBoost to access the maximum 256 gigabytes of flash memory.

I'm guessing that your PC uses a 32-bit version of Windows 7 (to check, go to Control Panel and click "System"). Due to memory limitations in 32-bit Windows, ReadyBoost can use only 4 gigabytes of storage on each flash device (or as much as 32 gigabytes of total memory if you used eight flash devices at once).

Why does your PC have this storage limit? All stored information has a "data address" that enables the PC to find and retrieve it. In 32-bit Windows, these addresses are 32 bits long. (A bit is a basic unit of information.) In 64-bit Windows, the addresses are twice as long.

The longer the storage address is, the more different ways there are to combine the bits into addresses, and the more possible addresses there are. As a result, 64-bit Windows has enough address combinations to handle 32 gigabytes of memory per flash device, but 32-bit Windows runs out of address combinations at about 4 gigabytes per device.

Q: My husband and I have four Gmail accounts, but we use only three of them. Recently, e-mail sent from one of the three main accounts was delivered to recipients as if it had been sent from our unused Gmail account. As a result, the e-mail recipients are replying to the unused account.

There is nothing in the Gmail account setup or preferences to link these two e-mail accounts. Why is this happening, and how can we stop it?

Laura Hamilton, Minneapolis

A: Other users of Google's Gmail have voiced similar complaints, but no solution has emerged. As a result, I think it's a software error that Google has to fix. You can report it to Google via Gmail: Click the gear wheel icon at the top right, click "help" and select "send feedback."