RAM+secrets+of

RAM secrets of

Would you like a speed boost by tinkering with your PC’s memory settings?

It is possible, once you’ve learned a few RAM basics…

Are you getting the best possible performance out of your PC?

Tuning the memory settings in your BIOS can deliver impressive results, but of course it helps if you have someone to decipher what they all mean.

You need a basic understanding of just how RAM really works.

At its RAM’s heart, is a memory chip

It consists of a grid of tiny capacitors, each one capable of holding an electrical charge.

If a particular capacitor has a charge, then it represents a binary one; if it doesn’t, then it represents a zero.

That’s simple isn’t it ?

Your PC uses this mechanism to write particular information to memory, and then read it back later.

Of course, it is not all straight forward because for example.

A capacitor’s charge state can be flipped through interference, particularly by cosmic rays.

This doesn’t happen often, but is one reason why vital systems tend to use special ECC (error‐correcting code) RAM.

This contains additional capacitors to help detect and fix these errors, which could otherwise cause serious problems.

Another RAM complication is based around the chip’s capacitors, which lose charge fast

As a result, the chip must read the contents of each capacitor and then write them back, a process known as refresh.

The refresh rate is the speed at which this happens, which could be as frequently as once every 64 milliseconds.

This raises another question: if the chip is reading or writing a capacitor as part of a refresh, then how can it simultaneously be fetching or saving data for your PC?

The simple answer is that it can’t.

The refresh process has to have priority over regular memory reads or writes, which means that you and your CPU are forced to wait.

However, knowing how refreshing, and memory access work is the most important part.

Rows and columns

When your PC wants to read an item from memory, the RAM controller circuitry starts by calculating its row in the grid.

This information is sent to the hardware and then the controller sets the Row

Address Strobe (RAS) pin, which tells the chip to read the address.

Now the controller calculates the column within that row that holds your data bit, and sends that address to the chip.

This time it sets the Column Address Strobe pin, instructing the chip to read that column within the currently selected row.

That is just what it does, and after a pause (CAS Latency Time) returns the results to your PC.

There’s one more delay while your memory gets ready to go again – the pre‐charge interval – then it’s ready for the next read or write.

The innocents amongst us see this process as unnecessarily complicated, but it’s important to bear in mind that more reads and writes are to consecutive capacitors, and so typically you’ll have the row selected once, then many different columns read in succession.

It has to be accepted that overall, this scheme offers good performance without making the controller circuitry too complicated.

BIOS settings

In real life this all translates to five common RAM settings that are likely to be found somewhere in your BIOS set‐up program.

Command rate ‐ is the delay (in clock cycles) between when chip select is asserted (i.e. the RAM is selected) and commands (i.e. Activate Row) can be issued to the RAM. Typical values are 1T (one clock cycle) and 2T (two clock cycles).

CAS (Column Address Strobe or Column Address Select) ‐ is the number of clock cycles (or Ticks, denoted with T) between the issuance of the READ command and when the data arrives at the data bus. Memory can be visualized as a table of cell locations and the CAS delay is invoked every time the column changes, which is more often than row changing.

tRP (RAS Precharge Delay) ‐ is the speed or length of time that it takes DRAM to terminate one row access and start another. In simpler terms, it means switching memory banks.

tRCD (RAS (Row Access Strobe) to CAS delay) ‐ As it says itʹs the time between RAS and CAS access, ie. the delay between when a memory bank is activated to when a read/write command is sent to that bank. Picture an Excel spreadsheet with a number across the top and along the left side. They numbers down the left side represent the Rows and the numbers across the top represent the Columns. The time it would take you, for example, to move down to Row 20 and across to Column 20 is RAS to CAS.

tRAS (Active to Precharge or Active Precharge Delay) ‐ controls the length of the delay between the activation and precharge commands ‐‐‐‐ basically how long after activation can the access cycle be started again. This influences row activation time which is taken into account when memory has hit the last column in a specific row, or when an entirely different memory location is requested

Adjusting all these delays except tRAS should speed up your memory

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__**Note :‐**__

If your RAM isn’t of high‐enough quality to work at an improved rate, then your PC will crash or lock up.

By all means play, but don’t do serious work on your system until you know that it’s stable.

As a precaution, locate the ‘clear CMOS RAM’ switch on your motherboard, so that you can restore the default memory settings if your new ones prevent it from booting.