# Computer CPU and memory question

**URL:** <https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123>\
**Category:** Factual Questions\
**Created:** [June 13, 2005, 7:09pm UTC](https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123 "2005-06-13T19:09:18Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![TurdFerguson](https://avatars.discourse-cdn.com/v4/letter/t/e9a140/32.png) [@TurdFerguson](https://boards.straightdope.com/u/TurdFerguson)\
**Post date:** [June 13, 2005, 7:09pm UTC](https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123/1 "2005-06-13T19:09:18Z")

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I have a Socket A CPU that has uses 266 MHz FSB and PC2100 memory. The [motherboard](http://www.giga-byte.com/MotherBoard/Products/Products_Spec_GA-7S748-L.htm) supports a CPUs that use 333 and 400 MHz FSB and PC2700 and PC3200 memory.

If I upgraded the CPU to a 400 MHz FSB processor would I also have to upgrade the memory?

Would the new CPU be compatible with the old memory?

(And now the dumb question that I probably know the answer) Should I upgrade the memory as well to take advantage of the faster processor?

More specifics: I’m upgrading from an AthlonXP 1600+ (266 MHz FSB) to an AthlonXP 3000+ (400 MHz FSB).

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**Author:** ![Jman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jman/32/4416_2.png) [@Jman](https://boards.straightdope.com/u/Jman)\
**Post date:** [June 13, 2005, 7:18pm UTC](https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123/2 "2005-06-13T19:18:26Z")

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The motherboard should work fine at the slower RAM speeds, but the problem is, your CPU will run slower too. That’s if you’re running 1:1 memory divider. If your motherboard supports running the RAM at a division of the front side bus speed (some can, some can’t…don’t know if yours can), you should be able to run the new processor with the slower RAM and still run the CPU at stock speeds (4/5 divider on PC2700 and 2/3 on PC3200).

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**Author:** ![Hirka\_T\_Bawa](https://avatars.discourse-cdn.com/v4/letter/h/db5fbb/32.png) [@Hirka\_T\_Bawa](https://boards.straightdope.com/u/Hirka_T_Bawa)\
**Post date:** [June 13, 2005, 7:19pm UTC](https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123/3 "2005-06-13T19:19:55Z")

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You don’t need to upgrade the RAM, the new CPU will be able to use your current RAM. However, it will be a bottleneck in your system, in order to get full use of the CPU I would recommend upgrading to PC3200 (DDR400) RAM.

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**Author:** ![D\_Odds](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/d_odds/32/2882_2.png) [@D\_Odds](https://boards.straightdope.com/u/D_Odds)\
**Post date:** [June 13, 2005, 7:33pm UTC](https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123/4 "2005-06-13T19:33:47Z")

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Technically, **Jman** and **Hirka T’Bawa** are correct. It will be a _bottleneck_.

That said, you will probably see significant gains from the new processor without upgrading memory. If you then upgraded memory, you would be unlikely to notice the difference for most common tasks.

Change the CPU. If you are unhappy with your new speed, then look into increasing the memory. Just don’t expect anywhere near the same speed boost.

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**Author:** ![TurdFerguson](https://avatars.discourse-cdn.com/v4/letter/t/e9a140/32.png) [@TurdFerguson](https://boards.straightdope.com/u/TurdFerguson)\
**Post date:** [June 13, 2005, 8:57pm UTC](https://boards.straightdope.com/t/computer-cpu-and-memory-question/308123/5 "2005-06-13T20:57:19Z")

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Thanks to all for the info

Turd