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Adept I

Bristol Ridge and 16GB DIMMs?

1) Does Bristol Ridge support 16GB DIMMs?

Lenovo claims the A475 supports a 2 x 16GB memory config, suggesting it does. It'd be nice to confirm with a second data point.

2) If so, would you expect every Bristol Ridge system to work with 16GB DIMMs?

HP claims the EliteBook 755 G4 max memory is only 8GB x 2. IIUC there's no logic between the integrated memory controller and the DIMMs, only PCB traces. So if the limit is truly 8GB per socket, the OEM must have artificially limited the upgrade potential in the BIOS. Am I thinking about the technical side of this correctly?

ps. I know it's 2021 and nobody cares about this old chip. But humor me  :^D

3 Replies

Found this HP Support site that shows the Specs for the Elitebook 755 G4. Not sure if this is your exact HP Laptop model but it seems to be for all of those models:

HP EliteBook 755 G4 Notebook PC - Specifications

Screenshot 2021-04-30 164028.png

HP probably uses the same motherboard for all EliteBook 755 G4 laptops so all use the same RAM Memory specs. What the processor supports in RAM depends on the Motherboard being used.

All APUs Processor uses System Ram for its vRAM. Most laptops has a Maximum of up to 2GB of System RAM to be used exclusively as the Integrated Graphics vRAM.  In BIOS you can decrease or increase the vRAM of the Integrated Graphics. But depends if the BIOS supports this feature or not.


Thanks. Yes that's the model. I'm just wondering if HP is likely to be understating the max RAM. There might not be any way to know, short of taking a gamble on it.

OEMs understate memory capacity all the time. I'm playing Spotify right now on an old Dell laptop that's spec'd for 2GB max RAM and yet it has 4GB installed which it recognizes. OEMs don't always understand the difference between "max config we sell as new" and "max config down the road".

My question relates to that gamble: if I understand the technical side of this, the only way the OEM could stop 16GB DIMMs from working is by removing support for them from firmware -- as otherwise the machine could support them perfectly well -- the Bristol Ridge chips must have this support since the Lenovo A475 can do it -- and there's zero bridges (north, south, or otherwise) between the APU and the DIMM.


Bristol Ridge Processors can support far more than 16GB of RAM Memory.  What limits the RAM support is the Motherboard or OS itself.

For instance a x32 Windows  can support a maximum of 4 GB of RAM Memory.

So HP is saying that your Laptop Motherboard can support a Maximum of 16GB for your specific Laptop model. I don't believe that HP is understating the Maximum amount of RAM that can be installed.

Generally if you were to install, as an example, 2 x 16GB RAM modules, BIOS on the motherboard would only recognize 16GBs of RAM installed and ignore the other 16GB of RAM that is also installed.

That is the way the motherboard was engineered to only recognize a certain amount of RAM.

You might want to read this Wikipedia article about RAM Memory to show you how much RAM a x64 BIT Processor can support:

The maximum random access memory (RAM) installed in any computer system is limited by hardware, software and economic factors. The hardware may have a limited number of address bus bits, limited by the processor package or design of the system. Some of the address space may be shared between RAM, peripherals, and read-only memory. In the case of a microcontroller with no external RAM, the size of the RAM array is limited by the size of the integrated circuit die. In a packaged system, only enough RAM may be provided for the system's required functions, with no provision for addition of memory after manufacture.

Software limitations to usable physical RAM may be present. An operating system may only be designed to allocate a certain amount of memory, with upper address bits reserved to indicate designations such as I/O or supervisor mode or other security information. Or the operating system may rely on internal data structures with fixed limits for addressable memory.

For mass-market personal computers, there may be no financial advantage to a manufacturer in providing more memory sockets, address lines, or other hardware than necessary to run mass-market software. When memory devices were relatively expensive compared with the processor, often the RAM delivered with the system was much less than the address capacity of the hardware, because of cost.

Sometimes RAM limits can be overcome using special techniques. Bank switching allows blocks of RAM memory to be switched into the processor's address space when required, under program control. Operating systems routinely manage running programs using virtual memory, where individual program operate as if they have access to a large memory space that is being simulated by swapping memory areas with disk storage.

64 bit computing

Modern 64-bit processors such as designs from ARM, Intel or AMD are typically limited to supporting fewer than 64 bits for RAM addresses. They commonly implement from 40 to 52 physical address bits[1][2][3][4] (supporting from 1 TB to 4 PB of RAM). Like previous architectures described here, some of these are designed to support higher limits of RAM addressing as technology improves. In both Intel64 and AMD64, the 52-bit physical address limit is defined in the architecture specifications (4 PB).