I would start by looking up the laptop model's spec sheets. They often say "up to P3 x00 Mhz" or some such. If you list the specific model here, I bet we could figure it out collectively.

I think this is the laptop: http://www.toshiba-europe.com/computers/produ … techspecs_7.htm
Here is a video I found of someone upgrading cpu of bit slower one to 800Mhz P3: https://www.youtube.com/watch?v=BSUKj06LLuw&t=503s
There are faster P3 cpus on ebay though, but do they work?

Here's one that's at 900Mhz. Given the 100Mhz FSB, this may be about as fast as you get. I'm not sure they ever made a 1Ghz mobile P3?
https://www.cnet.com/products/toshiba-satelli … d-series/specs/

edit: Ha! I spoke too soon. https://www.amazon.com/Toshiba-Satellite-Lapt … m/dp/B00005NCFH

They are selling new ones on ebay: https://www.ebay.com/itm/Intel-P3-Mobile-Proc … ew/232441450724
Main thing is that do all of the 4600 models have the same motherboard? I know the 1Ghz version had bigger screen and more 2nd level cache on motherboard.

After looking into those 1Ghz cpus on ebay. It seems there is 2 models. One of them is SL53S and one of them is SL5TF. What is the difference?

Baoran wrote:

After looking into those 1Ghz cpus on ebay. It seems there is 2 models. One of them is SL53S and one of them is SL5TF. What is the difference?

Comparing them on cpu-world.com, the only difference I can see is the SL53S has a slightly higher max temp rating (100 vs 92 C). If the prices are cheap for you, I'd just buy the 1Ghz SL53S and try it. If it works, great. If not, the low price made it worth the risk.

When it comes to retro gaming, would upgrading the cpu matter or is the laptop limited by its slow graphics chip?
When I got the laptop, it came with windows xp even though it was probably originally meant for win98. It has 384Mb of ram currently and it seems to only have a cd drive even if in the specs it says it comes with a dvd drive. It has Trident blade xp graphics chip and 16Mb of video ram.
Also hard drive probably has been upgraded too because it has 80Gb hard drive.

I tried 3dmark99, 3dmark2000 and 3dmark 2001se
3dmark99 installation failed. (perhaps because it has winxp)
3dmark2001se crashed during second test during default test with error related to textures.
3dmark2000 passed all default 1024x768 resolution tests with score of 1571

Laptop is in really good condition and really quiet.

The only way to answer that question is to check CPU usage during gaming. If you're stuck at 100% when things start to slow down, you're CPU limited. If you are well below that, you are GPU (if you can call a Blade XP that) limited.

Edit:
Hang on... is that a dedicated Trident Blade XP chip, or does this laptop have an ALi CyberAladdin-T chipset with integrated BladeXP and UMA? In the latter case you're probably bottlenecking on memory bandwidth...

CPU-Z says it has i815EM chipset and 82801BA southbridge.

I've upgraded a few laptop CPU's P4 or later but would think the same rules apply.
Get CPU's that can be returned. In theory researching the laptop and also the chipset will give you an idea of the fastest CPU, clueless1 is anything but this and given good info already
BUT
the reality is sometimes the laptop will run with a much faster CPU as whoever never updated the spec sheets or it may go the other way and not run at all due to lack of BIOS updates, motherboard revisions or maybe even was done intentionally as the cooling isn't upto the task for hotter CPU's

I've retuned a few CPU's just be honest and say it doesn't work with your system and I've never had anyone refuse retuning the item for a refund.

You didn't say but if you haven't max out the RAM, especially if your trying to run WinXP on a P3, It'll love you for it.

You could also try replacing the HDD, laptops usually have slow RPM drives to save on battery, probably not a concern anymore.

You could also try Win2k rather then XP to squeeze more speed out of it. P3 was right at the crossover so makes a fast 2k system or a slow XP system.

The system has 384Mb ram and the max is 2x256mb. Not sure how much of a speed upgrade it would be to change the 128Mb dimm to 256Mb one to get full 512Mb. I might install win98se there because the graphics chip might be too slow for any later games.

I bought Pentium III 1Ghz SL5TF one and it seems to be working fine. It was ebay listing that was also from Finland, so it made it much cheaper than other listings. I have been running prime95 for some time and temperature is not going above 70C, so I think it will be ok even with that 92C limit.

Thank you for the help.

I am bit of a collector when it comes to older laptops for retro gaming and it is rarely a bad idea to upgrade the cpu especially when the cost is so low unless the machine you want to upgrade is a real pain in the ass to service but usually most older laptops are fairly reasonable to get into. I've lost count as I got so many laptops.

Good to hear that this worked out.
But as a comment for other laptops in general, I want to mention that Mobile P3s support "SpeedStep", while Celerons of that time did not. This can potentially cause a problem when trying to upgrade a Celeron laptop to a P3.
I remember looking into an upgrade like this for a Thinkpad, and found that the Celeron version of it's motherboard was widely reported not to properly support a P3. The Celeron motherboard would never toggle the full speed of a P3 CPU, and so the Mobile P3 would be stuck running permanently at it's down-throttled power saving clock speed.

Updating the BIOS is scary on laptops, but it can help to allow faster or later stepping CPUs. On a similar Thinkpad (with a full P3 motherboard in it), I was able to use a faster, later stepping CPU than was ever advertised but only after the BIOS was updated. The release notes for the BIOS did not mention this, but the update was definitely in there.