Re: Amount of RAM L1 cache on a processor will support
I don't know how to answer the question you asked, but there is
something you need to consider. Assuming you have an Athlon of the
Thunderbird core or later, you have:
128K of L1 cache
256K of L2 cache
Most CPU's use an inclusive cache mechanism. What this means is that all
data stored in the L1 cache is also mirrored in L2. This makes it easier
to do a fetch; when data is fetched into cache, it is placed into L2.
When a smaller subset is requested, it goes from L2 into L1, leaving a
copy in L2.
With the Thunderbird core, AMD switched over to using an exclusive cache
mechanism. I.E., the data in L1 is NOT mirrored in L2. Thus, you have
384K of usable cache, and the differentiation of L1 and L2 is just for
speed. Things get swapped between L1 and L2 as needed, but you really
have 384K of cache to work with. That gives you more cacheable mem than
you would with an inclusive system.
Now, with a mere 512MB of RAM on a very modern system, you should be
fine. Most modern systems can handle > 1GB without having caching
problems. There are some speed issues to worry about, however; Most
larger DIMMs are slower than smaller DIMMs. For instance, most 512MB
DIMMs are registered, which is slower than unbuffered. Most 512MB DIMMs
have a CAS latency of 3 (CAS = Column Access Strobe), while many smaller
DIMMs are rated at CAS 2. There are also signal integrigty issues with
having 3 or more double-sided DIMMs on the same Mobo (case in point, the
nForce chipset goes into "SuperStability Mode" if there is a
double-sided DIMM in the third slot, which turns down performance a
great deal to keep from becoming unstable.)
I'm sorry if this answer was more than you bargained for, but I'm known
among friends for not being able to give simple answers :)
--Aaron
David Teague wrote:
>
> If you put more RAM in a computer system than the caching system
> will suppport, the system will run more slowly than it would with
> less RAM. IF I understand correctly, the amount of RAM depends on
> the amount of tag RAM.
>
> I have 512 MB on my Abit MoBo with a 1GHz Athlon.
>
> How do I determine how much RAM the L1 cache in a 1GHz Athlon will
> support?
>
> --David
> David Teague, dbt@cs.wcu.edu
> Debian GNU/Linux Because software support is free, timely,
> useful, technically accurate, and friendly.
> (I hope this is all of the above.)
>
> --
> To UNSUBSCRIBE, email to debian-user-request@lists.debian.org
> with a subject of "unsubscribe". Trouble? Contact listmaster@lists.debian.org
Reply to: