Ram Size locked at 256mb on Toshiba satellite 2805 laptop

Currently I am using a Toshiba satellite 2805 S503 laptop which is based on the Intel 815 Chipset Family. The motherboard is compatible with both CL2 and CL3 ram. Currently it has a onboard 256mb RAM and it seems it is locked out. In order to get more onboard RAM I have to buy higher end laptops. If I try to put more RAM over it, the laptop throws error message indicating as incompatible RAM. The specs document says chipset supports is 512 maximum but why don’t take 512. Is there any way to get 512MB RAM work along with the onboard 256MB RAM? Should I need to mod the BIOS to enable this?

As far as I know that this motherboard only supports up to 256MB memory modules in each slot maximum. So I think that you can add up to total of 768MB. But the problem is even if you add the 768MB memory, it will recognize 512MB. I don’t what would be the reason for it but I assume that it is either due the limitation of BIOS or the memory controller of the CPU. Even if the motherboard supports 768MB memory, the memory controller will not able to detect more than what it supports. To make it correct, there should be BIOS update and I don’t have any idea about that. The memory controller specs are as follows:

• DRAM Type : SDRAM
• DRAM Size : 384 MBytes
• DRAM Frequency : 132.6 MHz
• FSB-DRAM : 1:1
• CAS# Latency : 3.0 clocks
• RAS# to CAS# : 3 clocks
• RAS# Precharge : 3 clocks
• Cycle Time (TRAS) : 7 clocks
• Bank Cycle Time (TRC) : 9 clocks
• # of memory modules : 2
• Module 0 : SDRAM PC133 - 256 MBytes
• Module 1 : SDRAM PC133 - 128 MBytes

This is a very old laptop with very old chipset and I don’t think that nowadays anyone will be using this model. You will get complete information about the chipset on Intel website. The chipset surely has a support of Total 512mb RAM but if you install another 256MB module on the mainboard, the memory controller will not able to address the lines connected to it and it will be risky in some situations. So you should not get a 512MB module. The internal addressing of the motherboard circuitry is limited. You should get lower actually.

In earlier days, the 815 chipset from Intel was one of the best chipset due to its various features and the support of PC133 memory as well as PC100 memory. The Intel PC133 specification denotes, memory must support called 2-2-2 timing (also known as CAS-2 (column address strobe) or CL-2 timing). The number indicates the clock cycles which needs to be completes. They are actually for the functions. PC133 memory takes three cycles/functions and termed as PC133 3-3-3, CAS-3, or CL-3 memory. There is a backward compatibility where you can use the faster PC133 CL-2 in slower CL-3 variety but not reversible.

The memory controller present in Intel 815 chipset is very interesting than the past models. There controller comes with a support of two different memory frequencies (100MHz or 133MHz). The best thing is, if you use 66MHz FSB Celeron processor, the memory bus will be 100MHz. So this chipset has a slight edge over BX chipset. But the problem is 133MHz memory bus frequency is only compatible with 133MHz FSB. One more limitation is the memory controller supports 3 banks of SDRAM but only when PC100 SDRAM is used. But you can use only 2 banks of SDRAM with PC133 SDRAM used. So you can only install 2 double-sided DIMMs at 133MHz. If you put more than that, the chipset will automatically revert back memory bus setting to 100MHz