What DDR1 means
DDR is an acronym for double data rate RAM (DDR1) which translates to the capacity to perform two reads or two write task for every clock cycle. Due to its high speed, it was widely adopted and everyone abandoned the single data rate RAM types. It was the second generation of synchronous DRAM.
One of the basic features you will find in the double data rate (DDR1) ram is that it uses very precise time control so that the data transfer rate approaches twice that used by the single data rate RAM. This is achieved since the DDR1 (or otherwise known as (DDR SDRAM) is able to transfer that data on both the falling and the rising edges of the clock pulse.
You will find that it is not the speed that improved only but also the signal integrity requirement problems were also solved.
It will interest you to find that there are three types of DDR SDRAM. The difference was in both the number of pins as well as the n the clock speed. The three types of the DDR1 are;
DDR-266 which as 266 pins and memory clock speed of 133MHz
DDR-333 which as 333 pins and memory clock speed of 166MHz and
DDR-400 which has 400 and memory clock speed of 200 MHz.
This memory type performed read operation using two commands, the activate command and then a read command. Though this type of RAM some latency which was not an issue when it was first introduced into the market. This RAM type was capable of providing a read or a write from up to 8 memory locations at rate of two memory location per cycle. It is right to say you can read four memory locations in two consecutive clock cycles.
Memory arrays and bank
The double data rate (DDR1) memory RAM has several memory bank. This is why your PC is able to access RAM in an interleaved manner. The high number if banks is the reason for the increase in the memory bandwidth.
Today, tech giant companies has already introduced other double data rate generation RAMs. The DDR2 SDRAM has a speed almost double of the DDR1.