I have a 
Sony Vaio PCG-K23 which came preinstalled with 2 x 256MB 
Infineon HYS64D32020GDL-7-B PC2100 SO-DIMMs. I recently purchased 2 x 512MB 
Patriot Memory PSD512333S PC2700 SO-DIMMs hoping to replace the Infineon SO-DIMMs and bring it up to the maximum capability of 1GB. I realise that the PC2700 parts will only run at PC2100 speeds so don't worry about that. However when I install the 2 x 512MB parts the laptop (BIOS and Windows) still only reports 512MB.
Lavalys Everest reports the following BIOS details:
	Code:
	[ BIOS ]
    BIOS Properties:
      Vendor                                            Phoenix Technologies LTD
      Version                                           R0110X1
      Release Date                                      05/19/2004
      Size                                              512 KB
      Boot Devices                                      Floppy Disk, Hard Disk, CD-ROM
      Capabilities                                      Flash BIOS, Shadow BIOS, Selectable Boot, EDD, BBS, Smart Battery
      Supported Standards                               DMI, ACPI, ESCD, PnP
      Expansion Capabilities                            PCI, AGP, PCMCIA, USB
 and unfortunately I can't find any BIOS update available from Sony. I've tried 
eSupport but they don't say in advance of purchase what BIOS update you are buying for your $30.
I installed one of each SO-DIMMs just to collect the details on them for comparison and Everest gives the following:
	Code:
	    SPD Memory Modules:
      DIMM1: PDP Systems                                512 MB PC2700 DDR SDRAM  (2.5-3-3-7 @ 166 MHz)  (2.0-3-3-6 @ 133 MHz)
      DIMM2: Infineon 64D32020GDL7B                     256 MB PC2100 DDR SDRAM  (2.5-3-3-7 @ 142 MHz)  (2.0-3-3-6 @ 133 MHz)
 and
	Code:
	  [ DIMM1: PDP Systems (512 MB PC2700 DDR SDRAM) ]
    Memory Module Properties:
      Module Name                                       PDP Systems
      Serial Number                                     None
      Module Size                                       512 MB (1 rank, 4 banks)
      Module Type                                       Unbuffered
      Memory Type                                       DDR SDRAM
      Memory Speed                                      PC2700 (166 MHz)
      Module Width                                      64 bit
      Module Voltage                                    SSTL 2.5
      Error Detection Method                            None
      Refresh Rate                                      Reduced (7.8 us), Self-Refresh
    Memory Timings:
      @ 166 MHz                                         2.5-3-3-7  (CL-RCD-RP-RAS)
      @ 133 MHz                                         2.0-3-3-6  (CL-RCD-RP-RAS)
    Memory Module Features:
      Early RAS# Precharge                              Not Supported
      Auto-Precharge                                    Not Supported
      Precharge All                                     Not Supported
      Write1/Read Burst                                 Not Supported
      Buffered Address/Control Inputs                   Not Supported
      Registered Address/Control Inputs                 Not Supported
      On-Card PLL (Clock)                               Not Supported
      Buffered DQMB Inputs                              Not Supported
      Registered DQMB Inputs                            Not Supported
      Differential Clock Input                          Supported
      Redundant Row Address                             Not Supported
  [ DIMM2: Infineon 64D32020GDL7B ]
    Memory Module Properties:
      Module Name                                       Infineon 64D32020GDL7B
      Serial Number                                     010C5B16h 
      Manufacture Date                                  Week 32 / 2004
      Module Size                                       256 MB (2 ranks, 4 banks)
      Module Type                                       Unbuffered
      Memory Type                                       DDR SDRAM
      Memory Speed                                      PC2100 (133 MHz)
      Module Width                                      64 bit
      Module Voltage                                    SSTL 2.5
      Error Detection Method                            None
      Refresh Rate                                      Reduced (7.8 us), Self-Refresh
    Memory Timings:
      @ 142 MHz                                         2.5-3-3-7  (CL-RCD-RP-RAS)
      @ 133 MHz                                         2.0-3-3-6  (CL-RCD-RP-RAS)
    Memory Module Features:
      Early RAS# Precharge                              Supported
      Auto-Precharge                                    Not Supported
      Precharge All                                     Not Supported
      Write1/Read Burst                                 Not Supported
      Buffered Address/Control Inputs                   Not Supported
      Registered Address/Control Inputs                 Not Supported
      On-Card PLL (Clock)                               Not Supported
      Buffered DQMB Inputs                              Not Supported
      Registered DQMB Inputs                            Not Supported
      Differential Clock Input                          Supported
      Redundant Row Address                             Not Supported
    Memory Module Manufacturer:
      Company Name                                      Infineon Technologies AG
      Product Information                               ...
 and the following about the North Bridge:
	Code:
	  [ North Bridge: ATI Mobility Radeon 7000 IGP ]
    North Bridge Properties:
      North Bridge                                      ATI Mobility Radeon 7000 IGP
    Memory Timings:
      CAS Latency (CL)                                  2T
      RAS To CAS Delay (tRCD)                           3T
      RAS Precharge (tRP)                               3T
    Memory Slots:
      DRAM Slot #1                                      256 MB  (DDR SDRAM)
      DRAM Slot #2                                      256 MB  (DDR SDRAM)
 Does anybody know what the problem here might be with the laptop not recognising the full capacity of the 512MB parts? Could it be
- The Patriot parts are simply not compatible?
 - The BIOS needs an upgrade (if so - where would be a good place to get this since I can't get it from Sony)?
 - The Infineon 2 ranks, 4 banks versus the Patriot 1 rank, 4 banks details above are significant?
 - The North Bridge/memory controller is limited even though the Sony specs on the laptop claim that up to 1GB of RAM (2 x 512MB) is possible?
 - Something else?
 
If anybody needs further technical information feel free to ask and I'll post it. Thanks in advance for any assistance that anybody here can provide on this query.