I am thinking about trying a cpu upgrade on my D800. It currently has a Pentium M at 1.60 ghz. What the best upgrade chip that will work? Thanks in advance.

The fastest Pentium 3 that will work in your board is a Intel Pentium III 1GHz chip. Here is a link to the specs:
http://www.cpu-world.com/CPUs/Pentium-III/Intel-Pentium%20III%201000%20-%20RB80526PY001256%20%28BX80526F1000256%29.html

You could also get a Intel Celeron 1.1 GHz but it only has half the level 2 cache size so it's actually a bit slower than the Pentium III 1GHz chip.
Here's a link to celeron specs:
http://www.cpu-world.com/CPUs/Celeron/Intel-Celeron%201100%20-%20RB80526RY005128%20%28BX80526F1100128%29.html

A Pentium 4 2.0 Ghz with Willamette core, code numbers SL5TL or SL5UH

Yes, it will work just fine, as you can see for yourself - on the mb's link is the third processor from the second group (Prescott).

If new processor supports your old motherboard then you will upgrade system with your old motherboard.

If its not supported to new mother board then you have to buy new motherboard to upgrade your system.

Thanks.
Happy to help you.

You did not post what operating system you have. There are a lot of things that can cause a computer to run slow. RAM is big issue More so than the CPU. The series of CPU that you have is upgradeable by 4 models but the gains are modest. There is also an issue of availability of the processor because that model is 12 years old. Another issue that you need to look into is the programs that are running when the system starts.

CPU If Central Processing Unit stops functioning your system is dead. If you think your CPU is too slow you can look into upgrading to a faster CPU, but it has to match with your chip-set and would have to be installed by someone that understands computer architecture. mysleuth

Your motherboard supports 2 different fsb's.
look these up @ cpu-world
you can use:
Intel Pentium 4 processor (478-pin)
- 533MHz system data bus - supports up to 2.8 GHz
- 400MHz system data bus - supports up to 2.4 GHz

Intel Celeron processor
- 400MHz system data bus - supports up to 2.0 GHz CPU speed
and here are the suppoted cpus:
Intel Celeron RK80531RC029128 BX80531P170G128 1.7 GHz 17 x 400 MHz, Willamette Any A RK80531RC033128 BX80531P180G128 1.8 GHz 18 x 400 MHz, Willamette Any A RK80531RC037128 BX80531P190G128 1.9 GHz 19 x 400 MHz, Willamette Any A RK80532RC041128 BX80532RC2000B 2.0 GHz 20 x 400 MHz, Northwood A 1.525V not supported RK80532RC045128 BX80532RC2100B 2.1 GHz 21 x 400 MHz, Northwood A 1.525V not supported Intel Pentium 4 RK80532PC021512 1.5 GHz 15 x 400 MHz, Northwood Any A RK80532PC025512 BX80532PC1600D 1.6 GHz 16 x 400 MHz, Northwood Any A RK80532PC029512 1.7 GHz 17 x 400 MHz, Northwood Any A RK80532PC033512 BX80532PC1800D 1.8 GHz 18 x 400 MHz, Northwood Any A RK80532PC037512 1.9 GHz 19 x 400 MHz, Northwood Any A RK80532PC041512 BX80532PC2000D 2.0 GHz 20 x 400 MHz, Northwood A 1.525V not supported 2.1 GHz 21 x 400 MHz, Northwood A 1.525V not supported RK80532PC049512 BX80532PC2200D 2.2 GHz 22 x 400 MHz, Northwood A 1.525V not supported RK80532PE051512 BX80532PE2266D 2.26 GHz 19 x 533 MHz, Northwood A 1.525V not supported RK80532PE056512 BX80532PE2400D 2.4 GHz 18 x 533 MHz, Northwood A 1.525V not supported RK80532PC056512 BX80532PC2400D 2.4 GHz 24 x 400 MHz, Northwood A 1.525V not supported RK80532PC060512 BX80532PC2500D 2.5 GHz 25 x 400 MHz, Northwood A 1.525V not supported RK80532PE061512 BX80532PE2533D 2.53 GHz 19 x 533 MHz, Northwood A 1.525V not supported RK80532PC064512 BX80532PC2600D 2.6 GHz 26 x 400 MHz, Northwood A 1.525V not supported RK80532PE067512 BX80532PE2667D 2.66 GHz 20 x 533 MHz, Northwood A 1.525V not supported RK80532PE072512 BX80532PE2800D 2.8 GHz 21 x 533 MHz, Northwood A 1.525V not supported

I told you my opinion, If I was in your shoes I won't upgrade the CPU.Professionals do not do works against Factory specifications, and I fixcomputers for living.
Acer says Pentium dual is not supported on Acer 4315, I can only tell you not to do such an upgrade.
Itwould be the same as if you ask me if you can mount a Jaguar engine ona Mini, yes, for sure there is the way to mount it, but the car won'twork as it is supposed to, and risk to blow at first corner.
If you really want to replace your CPU consider the following.
Acersays pentium 2 dual core is not supported on 4315, if you do ityourself you risk to damage the computer. Do not do the CPU upgrade ifthis is your only laptop, or if you care of this laptop, chance ofdamaging laptop are high. This kind of upgrades are done more as anexperiment.
I know Core 2 Duo T5300 1.73 Ghz had been installedsuccessfully on Aspire 4315, Acer says not to install any core duo, Iknow for sure Pentium duo T5200 1.6 Ghz works on Aspire 4315 with noneed for replacing cooling system.
Both chipset are difficult to find, best place to find them is Ebay.

Check this link for an extensive report on this matter:

check also: Is it worth upgrading the CPU on Acer Laptops?

Maximum you may go upto 2.4 GHZ. [p4]. Not dula core etc.

Best Regards
Rafique

According to this review, you can upgrade as far as a 2 GHz P4-M at least; http://www.pcmag.com/article2/0,1895,669029,00.asp Other than that, i have been unable to find the details of your motherboard - if you can post the make and model (should be printed on it somewhere) then I would hope to find a more complete list of compatible and incompatible processors. Gateway themselves no longer offer online info or support for this model, but the motherboard details should enable me to find out what you need to know. Waiting for your post :)